Arthroplasty/Joint Replacement

Significantly fewer men received evaluation for osteoporosis following a distal radial fracture, with rates of evaluation unacceptably low according to published guidelines, according to a study published November 5 in Journal of Bone & Joint Surgery.

Treating men for bone fractures, but not the underlying cause, places them at a greater risk for future bone breaks and related complications,” said study investigator Tamara Rozental, MD, Associate Professor of Orthopaedic Surgery, Harvard Medical School in Boston, Massachusetts.

In this study, researchers reviewed the medical records of 95 men and 344 women older than 50, who were treated for a wrist fracture at a single institution between 2007 and 2012. Data collected included age, mechanism of injury, fracture severity, associated comorbidities, and type of treatment. Fractures were classified according to the AO Foundation and Orthopaedic Trauma Association (AO/OTA) classification system. Comorbidities were estimated with use of the Charlson comorbidity index (CCI), providing a weighted score to predict short and long-term outcomes, taking into account the number and severity of predefined comorbid conditions. The WHO online Fracture Risk Assessment Tool (FRAX) was used to estimate the 10-year risk of major osteoporotic fractures in men.

Patient injuries were assessed to determine whether or not they were screened for osteoporosis before their injury and/or if they received a dual-energy x-ray absorptiometry scan and osteoporosis treatment within six months following their wrist fracture.

Fewer men than women underwent bone mass density testing prior to their fracture. Following the wrist fracture, the number of men undergoing osteoporosis assessment continued to be lower, 184 (53%) of women versus 17 (18%) of men.

Study findings also indicate:

• Twenty-one percent of men compared with 55% of women initiated treatment with calcium and vitamin D supplements within six months of injury, and 3% of men versus 22% of women started taking bisphosphonates.

• Using the World Health Organization (WHO) online Fracture Risk Assessment Tool (FRAX), 50% of men who obtained a bone density test were deemed at risk for a second major osteoporotic fracture in the next decade.

• Male sex, less severe fracture patterns and high-energy mechanism of injury were independent predictors of failure to initiate treatment with calcium and vitamin D.

• Overall, the men had less severe fractures than women with 20% of the men and 40% of the women in the study having a “Type-C” fracture.

“The results of this study lead us to suggest that men over the age of 50 with fractures of the distal radius should undergo bone density testing and evaluation with the FRAX algorithm to better identify those at high risk for future fracture and those who would benefit from further treatment,” said Dr. Rozental.

Significantly fewer men received evaluation for osteoporosis following a distal radial fracture, with rates of evaluation unacceptably low according to published guidelines, according to a study published November 5 in Journal of Bone & Joint Surgery.

Treating men for bone fractures, but not the underlying cause, places them at a greater risk for future bone breaks and related complications,” said study investigator Tamara Rozental, MD, Associate Professor of Orthopaedic Surgery, Harvard Medical School in Boston, Massachusetts.

In this study, researchers reviewed the medical records of 95 men and 344 women older than 50, who were treated for a wrist fracture at a single institution between 2007 and 2012. Data collected included age, mechanism of injury, fracture severity, associated comorbidities, and type of treatment. Fractures were classified according to the AO Foundation and Orthopaedic Trauma Association (AO/OTA) classification system. Comorbidities were estimated with use of the Charlson comorbidity index (CCI), providing a weighted score to predict short and long-term outcomes, taking into account the number and severity of predefined comorbid conditions. The WHO online Fracture Risk Assessment Tool (FRAX) was used to estimate the 10-year risk of major osteoporotic fractures in men.

Patient injuries were assessed to determine whether or not they were screened for osteoporosis before their injury and/or if they received a dual-energy x-ray absorptiometry scan and osteoporosis treatment within six months following their wrist fracture.

Fewer men than women underwent bone mass density testing prior to their fracture. Following the wrist fracture, the number of men undergoing osteoporosis assessment continued to be lower, 184 (53%) of women versus 17 (18%) of men.

Study findings also indicate:

• Twenty-one percent of men compared with 55% of women initiated treatment with calcium and vitamin D supplements within six months of injury, and 3% of men versus 22% of women started taking bisphosphonates.

• Using the World Health Organization (WHO) online Fracture Risk Assessment Tool (FRAX), 50% of men who obtained a bone density test were deemed at risk for a second major osteoporotic fracture in the next decade.

• Male sex, less severe fracture patterns and high-energy mechanism of injury were independent predictors of failure to initiate treatment with calcium and vitamin D.

• Overall, the men had less severe fractures than women with 20% of the men and 40% of the women in the study having a “Type-C” fracture.

“The results of this study lead us to suggest that men over the age of 50 with fractures of the distal radius should undergo bone density testing and evaluation with the FRAX algorithm to better identify those at high risk for future fracture and those who would benefit from further treatment,” said Dr. Rozental.

Significantly fewer men received evaluation for osteoporosis following a distal radial fracture, with rates of evaluation unacceptably low according to published guidelines, according to a study published November 5 in Journal of Bone & Joint Surgery.

Treating men for bone fractures, but not the underlying cause, places them at a greater risk for future bone breaks and related complications,” said study investigator Tamara Rozental, MD, Associate Professor of Orthopaedic Surgery, Harvard Medical School in Boston, Massachusetts.

In this study, researchers reviewed the medical records of 95 men and 344 women older than 50, who were treated for a wrist fracture at a single institution between 2007 and 2012. Data collected included age, mechanism of injury, fracture severity, associated comorbidities, and type of treatment. Fractures were classified according to the AO Foundation and Orthopaedic Trauma Association (AO/OTA) classification system. Comorbidities were estimated with use of the Charlson comorbidity index (CCI), providing a weighted score to predict short and long-term outcomes, taking into account the number and severity of predefined comorbid conditions. The WHO online Fracture Risk Assessment Tool (FRAX) was used to estimate the 10-year risk of major osteoporotic fractures in men.

Patient injuries were assessed to determine whether or not they were screened for osteoporosis before their injury and/or if they received a dual-energy x-ray absorptiometry scan and osteoporosis treatment within six months following their wrist fracture.

Fewer men than women underwent bone mass density testing prior to their fracture. Following the wrist fracture, the number of men undergoing osteoporosis assessment continued to be lower, 184 (53%) of women versus 17 (18%) of men.

Study findings also indicate:

• Twenty-one percent of men compared with 55% of women initiated treatment with calcium and vitamin D supplements within six months of injury, and 3% of men versus 22% of women started taking bisphosphonates.

• Using the World Health Organization (WHO) online Fracture Risk Assessment Tool (FRAX), 50% of men who obtained a bone density test were deemed at risk for a second major osteoporotic fracture in the next decade.

• Male sex, less severe fracture patterns and high-energy mechanism of injury were independent predictors of failure to initiate treatment with calcium and vitamin D.

• Overall, the men had less severe fractures than women with 20% of the men and 40% of the women in the study having a “Type-C” fracture.

“The results of this study lead us to suggest that men over the age of 50 with fractures of the distal radius should undergo bone density testing and evaluation with the FRAX algorithm to better identify those at high risk for future fracture and those who would benefit from further treatment,” said Dr. Rozental.

BOSTON—Innovimmune Biotherapeutics Holding, LLC (Brooklyn, New York) presented data demonstrating successful treatment of rheumatoid arthritis in a murine collagen-induced arthritis (CIA) model with its proprietary oral small molecule Retinoic acid receptor-related Orphan Receptor gamma t (RORγt) modulators from their INV-17 portfolio. The results were presented at the 2014 Annual Meeting of the American College of Rheumatology.

In the CIA study, an INV-17 RORγt modulator lead compound was administered orally for 28 days in a therapeutic regimen following rheumatoid arthritis disease induction. The data demonstrate that mice treated with INV-17 achieved statistically significant reduction in cumulative arthritis score as the primary study end point, in contrast to a vehicle (placebo) group.

Significant improvement in clinical disease scores in the INV-17 group began on day 13, with maximal therapeutic effects observed on day 16 through day 26 and through the end of the study.

“This is a remarkable finding in that a novel therapeutic approach targeting pathogenic T helper 17 (T_^H17) cells through RORγt modulation provides superior preclinical treatment efficacy in rheumatoid arthritis. These results, which demonstrate successful rheumatoid arthritis disease amelioration in the absence of toxicity, may provide a novel oral disease-modifying antirheumatic drug treatment strategy with an oral INV-17 drug for rheumatoid arthritis and other TH17-mediated autoimmune diseases,” said Ellen M. Ginzler, MD, MPH, Distinguished Teaching Professor of Medicine and Chief, Division of Rheumatology, SUNY Downstate Medical Center in Brooklyn, New York.

BOSTON—Innovimmune Biotherapeutics Holding, LLC (Brooklyn, New York) presented data demonstrating successful treatment of rheumatoid arthritis in a murine collagen-induced arthritis (CIA) model with its proprietary oral small molecule Retinoic acid receptor-related Orphan Receptor gamma t (RORγt) modulators from their INV-17 portfolio. The results were presented at the 2014 Annual Meeting of the American College of Rheumatology.

In the CIA study, an INV-17 RORγt modulator lead compound was administered orally for 28 days in a therapeutic regimen following rheumatoid arthritis disease induction. The data demonstrate that mice treated with INV-17 achieved statistically significant reduction in cumulative arthritis score as the primary study end point, in contrast to a vehicle (placebo) group.

Significant improvement in clinical disease scores in the INV-17 group began on day 13, with maximal therapeutic effects observed on day 16 through day 26 and through the end of the study.

“This is a remarkable finding in that a novel therapeutic approach targeting pathogenic T helper 17 (T_^H17) cells through RORγt modulation provides superior preclinical treatment efficacy in rheumatoid arthritis. These results, which demonstrate successful rheumatoid arthritis disease amelioration in the absence of toxicity, may provide a novel oral disease-modifying antirheumatic drug treatment strategy with an oral INV-17 drug for rheumatoid arthritis and other TH17-mediated autoimmune diseases,” said Ellen M. Ginzler, MD, MPH, Distinguished Teaching Professor of Medicine and Chief, Division of Rheumatology, SUNY Downstate Medical Center in Brooklyn, New York.

BOSTON—Innovimmune Biotherapeutics Holding, LLC (Brooklyn, New York) presented data demonstrating successful treatment of rheumatoid arthritis in a murine collagen-induced arthritis (CIA) model with its proprietary oral small molecule Retinoic acid receptor-related Orphan Receptor gamma t (RORγt) modulators from their INV-17 portfolio. The results were presented at the 2014 Annual Meeting of the American College of Rheumatology.

In the CIA study, an INV-17 RORγt modulator lead compound was administered orally for 28 days in a therapeutic regimen following rheumatoid arthritis disease induction. The data demonstrate that mice treated with INV-17 achieved statistically significant reduction in cumulative arthritis score as the primary study end point, in contrast to a vehicle (placebo) group.

Significant improvement in clinical disease scores in the INV-17 group began on day 13, with maximal therapeutic effects observed on day 16 through day 26 and through the end of the study.

“This is a remarkable finding in that a novel therapeutic approach targeting pathogenic T helper 17 (T_^H17) cells through RORγt modulation provides superior preclinical treatment efficacy in rheumatoid arthritis. These results, which demonstrate successful rheumatoid arthritis disease amelioration in the absence of toxicity, may provide a novel oral disease-modifying antirheumatic drug treatment strategy with an oral INV-17 drug for rheumatoid arthritis and other TH17-mediated autoimmune diseases,” said Ellen M. Ginzler, MD, MPH, Distinguished Teaching Professor of Medicine and Chief, Division of Rheumatology, SUNY Downstate Medical Center in Brooklyn, New York.

DALLAS—Results of an independent, physician-initiated study designed to evaluate the difference in postsurgical pain and opioid consumption between patients who received Exparel (bupivacaine liposome injectable suspension) versus a multi-drug analgesic cocktail for pain management following total knee arthroplasty (TKA) were presented at the 24th Annual Meeting of the American Association of Hip and Knee Surgeons. Researchers found that patients treated with Exparel reported significantly lower patient-perceived pain scores and morphine sulfate equivalence consumption, and reported higher satisfaction with pain control and overall experience compared with patients who received the multi-drug analgesic cocktail.

“A majority of patients who undergo total knee arthroplasty report dissatisfaction with overall pain control and side effects associated with narcotic medications, so there is clearly a need for a more effective and better-tolerated pain management option,” said Mark A. Snyder, MD, Director of the Orthopaedic Center of Excellence at Good Samaritan Hospital in Cincinnati.

In the double-blind, randomized clinical study, 70 patients who underwent a TKA were randomly assigned to receive either a periarticular injection with Exparel or a multi-drug analgesic cocktail for postsurgical analgesia.

Findings showed that compared with patients who received the multi-drug analgesic cocktail, patients who received EXPAREL reported:

• Significantly lower pain levels on post-op days one and two.

• Higher satisfaction in pain control and overall experience.

• Significantly fewer adverse events.

• Significantly lower total morphine equivalency consumption in the postanesthesia care unit (PACU) and by post-op day two.

“Our study found that Exparel not only provided effective pain control, but also reduced opioid load and improved the patient’s overall experience. In addition, we found that Exparel eliminated the incidence of post-operative falls, a serious patient safety risk resulting from muscle weakness associated with nerve blocks and prolonged indwelling pain catheters, and confusion or disorientation caused by opioids,” stated Dr. Snyder.

Exparel is marketed by Pacira Pharmaceuticals Inc, in Parsippany, New Jersey.

DALLAS—Results of an independent, physician-initiated study designed to evaluate the difference in postsurgical pain and opioid consumption between patients who received Exparel (bupivacaine liposome injectable suspension) versus a multi-drug analgesic cocktail for pain management following total knee arthroplasty (TKA) were presented at the 24th Annual Meeting of the American Association of Hip and Knee Surgeons. Researchers found that patients treated with Exparel reported significantly lower patient-perceived pain scores and morphine sulfate equivalence consumption, and reported higher satisfaction with pain control and overall experience compared with patients who received the multi-drug analgesic cocktail.

“A majority of patients who undergo total knee arthroplasty report dissatisfaction with overall pain control and side effects associated with narcotic medications, so there is clearly a need for a more effective and better-tolerated pain management option,” said Mark A. Snyder, MD, Director of the Orthopaedic Center of Excellence at Good Samaritan Hospital in Cincinnati.

In the double-blind, randomized clinical study, 70 patients who underwent a TKA were randomly assigned to receive either a periarticular injection with Exparel or a multi-drug analgesic cocktail for postsurgical analgesia.

Findings showed that compared with patients who received the multi-drug analgesic cocktail, patients who received EXPAREL reported:

• Significantly lower pain levels on post-op days one and two.

• Higher satisfaction in pain control and overall experience.

• Significantly fewer adverse events.

• Significantly lower total morphine equivalency consumption in the postanesthesia care unit (PACU) and by post-op day two.

“Our study found that Exparel not only provided effective pain control, but also reduced opioid load and improved the patient’s overall experience. In addition, we found that Exparel eliminated the incidence of post-operative falls, a serious patient safety risk resulting from muscle weakness associated with nerve blocks and prolonged indwelling pain catheters, and confusion or disorientation caused by opioids,” stated Dr. Snyder.

Exparel is marketed by Pacira Pharmaceuticals Inc, in Parsippany, New Jersey.

DALLAS—Results of an independent, physician-initiated study designed to evaluate the difference in postsurgical pain and opioid consumption between patients who received Exparel (bupivacaine liposome injectable suspension) versus a multi-drug analgesic cocktail for pain management following total knee arthroplasty (TKA) were presented at the 24th Annual Meeting of the American Association of Hip and Knee Surgeons. Researchers found that patients treated with Exparel reported significantly lower patient-perceived pain scores and morphine sulfate equivalence consumption, and reported higher satisfaction with pain control and overall experience compared with patients who received the multi-drug analgesic cocktail.

“A majority of patients who undergo total knee arthroplasty report dissatisfaction with overall pain control and side effects associated with narcotic medications, so there is clearly a need for a more effective and better-tolerated pain management option,” said Mark A. Snyder, MD, Director of the Orthopaedic Center of Excellence at Good Samaritan Hospital in Cincinnati.

In the double-blind, randomized clinical study, 70 patients who underwent a TKA were randomly assigned to receive either a periarticular injection with Exparel or a multi-drug analgesic cocktail for postsurgical analgesia.

Findings showed that compared with patients who received the multi-drug analgesic cocktail, patients who received EXPAREL reported:

• Significantly lower pain levels on post-op days one and two.

• Higher satisfaction in pain control and overall experience.

• Significantly fewer adverse events.

• Significantly lower total morphine equivalency consumption in the postanesthesia care unit (PACU) and by post-op day two.

“Our study found that Exparel not only provided effective pain control, but also reduced opioid load and improved the patient’s overall experience. In addition, we found that Exparel eliminated the incidence of post-operative falls, a serious patient safety risk resulting from muscle weakness associated with nerve blocks and prolonged indwelling pain catheters, and confusion or disorientation caused by opioids,” stated Dr. Snyder.

Exparel is marketed by Pacira Pharmaceuticals Inc, in Parsippany, New Jersey.

Experiments in mice with a bone disorder similar to osteoporosis after menopause show that an overlooked group of cells are likely crucial to the process of bone loss caused by the disorder, according to a study published online ahead of print October 5 in Nature Medicine. The finding, researchers say, not only raises the research profile of the cells, called preosteoclasts, but also explains the success and activity of an experimental osteoporosis drug currently in phase III clinical trials.

“We didn’t know that the drug affects preosteoclasts, nor did we understand how important preosteoclasts are in maintaining healthy bones,” says Xu Cao, PhD, the Lee H. Riley Jr., MD, Professor of Orthopaedic Surgery at Johns Hopkins University in Baltimore. “Now drug companies hoping to reverse osteoporosis can look for even more drugs that make use of and target these interesting cells.”

Dr. Cao and colleagues grew two cell types separately in the laboratory and collected the liquid around them to test for proteins released by the cells. They found that preosteoclasts, but not mature osteoclasts, secrete platelet-derived growth factor-BB (PDGF-BB). When the preosteoclasts of mice were prevented from making PDGF-BB, the mice had weak bones.

When the mice were given L-235, the animal form of odanacatib, the numbers of their preosteoclasts and osteoclasts increased, and they secreted more PDGF-BB. The increased PDGF-BB brought in more cells for making blood vessels and bone, which led to more of the specialized blood vessels and thicker bones.

To see if the drug could help reverse the increased bone resorption and decreased blood vessel formation of postmenopausal osteoporosis, the investigators simulated menopause in female mice by removing their ovaries.

At first, the mice had thinner bones and fewer blood vessels, but treatment with the drug increased the concentration of PDGF-BB in the blood, the number of specialized blood vessels both inside and outside of the bones, and the overall thickness and density of the bone.

According to Dr. Cao, in addition to slowing bone resorption by blocking cathepsin K, the drug also appears to slow the maturation of preosteoclasts, lengthening the amount of time they secrete PDGF-BB before becoming osteoclasts. With increased PDGF-BB, more specialized blood vessels are made and more bone-building cells arrive, restoring the balance between bone resorption and bone rebuilding.

Odanacatib is produced by Merck & Co. Inc. (Whitehouse Station, New Jersey) and has already gone through phase III clinical trials with good results, according to Dr. Cao.

“It is unusual to see a single drug that decreases bone resorption and increases bone rebuilding at the same time,” Dr. Cao said.

Experiments in mice with a bone disorder similar to osteoporosis after menopause show that an overlooked group of cells are likely crucial to the process of bone loss caused by the disorder, according to a study published online ahead of print October 5 in Nature Medicine. The finding, researchers say, not only raises the research profile of the cells, called preosteoclasts, but also explains the success and activity of an experimental osteoporosis drug currently in phase III clinical trials.

“We didn’t know that the drug affects preosteoclasts, nor did we understand how important preosteoclasts are in maintaining healthy bones,” says Xu Cao, PhD, the Lee H. Riley Jr., MD, Professor of Orthopaedic Surgery at Johns Hopkins University in Baltimore. “Now drug companies hoping to reverse osteoporosis can look for even more drugs that make use of and target these interesting cells.”

Dr. Cao and colleagues grew two cell types separately in the laboratory and collected the liquid around them to test for proteins released by the cells. They found that preosteoclasts, but not mature osteoclasts, secrete platelet-derived growth factor-BB (PDGF-BB). When the preosteoclasts of mice were prevented from making PDGF-BB, the mice had weak bones.

When the mice were given L-235, the animal form of odanacatib, the numbers of their preosteoclasts and osteoclasts increased, and they secreted more PDGF-BB. The increased PDGF-BB brought in more cells for making blood vessels and bone, which led to more of the specialized blood vessels and thicker bones.

To see if the drug could help reverse the increased bone resorption and decreased blood vessel formation of postmenopausal osteoporosis, the investigators simulated menopause in female mice by removing their ovaries.

At first, the mice had thinner bones and fewer blood vessels, but treatment with the drug increased the concentration of PDGF-BB in the blood, the number of specialized blood vessels both inside and outside of the bones, and the overall thickness and density of the bone.

According to Dr. Cao, in addition to slowing bone resorption by blocking cathepsin K, the drug also appears to slow the maturation of preosteoclasts, lengthening the amount of time they secrete PDGF-BB before becoming osteoclasts. With increased PDGF-BB, more specialized blood vessels are made and more bone-building cells arrive, restoring the balance between bone resorption and bone rebuilding.

Odanacatib is produced by Merck & Co. Inc. (Whitehouse Station, New Jersey) and has already gone through phase III clinical trials with good results, according to Dr. Cao.

“It is unusual to see a single drug that decreases bone resorption and increases bone rebuilding at the same time,” Dr. Cao said.

Experiments in mice with a bone disorder similar to osteoporosis after menopause show that an overlooked group of cells are likely crucial to the process of bone loss caused by the disorder, according to a study published online ahead of print October 5 in Nature Medicine. The finding, researchers say, not only raises the research profile of the cells, called preosteoclasts, but also explains the success and activity of an experimental osteoporosis drug currently in phase III clinical trials.

“We didn’t know that the drug affects preosteoclasts, nor did we understand how important preosteoclasts are in maintaining healthy bones,” says Xu Cao, PhD, the Lee H. Riley Jr., MD, Professor of Orthopaedic Surgery at Johns Hopkins University in Baltimore. “Now drug companies hoping to reverse osteoporosis can look for even more drugs that make use of and target these interesting cells.”

Dr. Cao and colleagues grew two cell types separately in the laboratory and collected the liquid around them to test for proteins released by the cells. They found that preosteoclasts, but not mature osteoclasts, secrete platelet-derived growth factor-BB (PDGF-BB). When the preosteoclasts of mice were prevented from making PDGF-BB, the mice had weak bones.

When the mice were given L-235, the animal form of odanacatib, the numbers of their preosteoclasts and osteoclasts increased, and they secreted more PDGF-BB. The increased PDGF-BB brought in more cells for making blood vessels and bone, which led to more of the specialized blood vessels and thicker bones.

To see if the drug could help reverse the increased bone resorption and decreased blood vessel formation of postmenopausal osteoporosis, the investigators simulated menopause in female mice by removing their ovaries.

At first, the mice had thinner bones and fewer blood vessels, but treatment with the drug increased the concentration of PDGF-BB in the blood, the number of specialized blood vessels both inside and outside of the bones, and the overall thickness and density of the bone.

According to Dr. Cao, in addition to slowing bone resorption by blocking cathepsin K, the drug also appears to slow the maturation of preosteoclasts, lengthening the amount of time they secrete PDGF-BB before becoming osteoclasts. With increased PDGF-BB, more specialized blood vessels are made and more bone-building cells arrive, restoring the balance between bone resorption and bone rebuilding.

Odanacatib is produced by Merck & Co. Inc. (Whitehouse Station, New Jersey) and has already gone through phase III clinical trials with good results, according to Dr. Cao.

“It is unusual to see a single drug that decreases bone resorption and increases bone rebuilding at the same time,” Dr. Cao said.

Young baseball pitchers who throw more than 100 pitches per week are at risk for a newly identified overuse injury that can impede normal shoulder development and lead to additional problems, including rotator cuff tears, according to a study published online ahead of print October 14 in Radiology.

The injury, termed acromial apophysiolysis by the researchers, is characterized by incomplete fusion and tenderness at the acromion. The acromion, which forms the bone at the top of the shoulder, typically develops from four individual bones into one bone during the teenage years.

“We kept seeing this injury over and over again in young athletes who come to the hospital at the end of the baseball season with shoulder pain and edema at the acromion on MRI, but no other imaging findings,” said Johannes B. Roedl, MD, a radiologist in the Musculoskeletal Division at Thomas Jefferson University Hospital in Philadelphia.

Dr. Roedl and a team of researchers conducted a retrospective study of 2,372 consecutive patients between the ages of 15 and 25, who underwent magnetic resonance imaging (MRI) for shoulder pain between 1998 and 2012. The majority of the patients, which included both males and females, were baseball pitchers.

Patients with edema at the acromial apophyses and no other abnormalities on MRI were included in the study group. Association of acromial edema with incomplete fusion , pitching, and clinical findings was determined in the study group and in an age- and sex-matched control group. Association with the development of an os acromial and rotator cuff tears later in life was assessed with follow-up imaging after age 25.

Edema at the acromial apophyses was found in 2.6% (61 of 2,372) and was associated with incomplete fusion of the acromial apophyses and superior shoulder tenderness.

A pitch count of more than 100 pitches per week was a substantial risk factor for developing acromial apophysiolysis (odds ratio 6.5). Among the patients with this overuse injury, 40% threw more than 100 pitches per week, compared to 8% in the control group.

All 61 injured patients took a three-month rest from pitching. One patient underwent surgery while the remaining 60 patients were treated conservatively with non-steroidal pain medication. Follow-up imaging conducted a minimum of two years later after the patients turned 25 were available for 29 of the 61 injured patients and for 23 of the 61 controls. Follow-up imaging revealed that 25 of the 29 patients (86%) with the overuse injury showed incomplete fusion of the acromion, compared to only one of the 23 (4%) controls.

Twenty-one of the 29 patients with the overuse injury continued pitching after the rest period, and all 21 showed incomplete bone fusion at the acromion. Rotator cuff tears were significantly more common among this group than in the control group (68% versus 29%, respectively). The severity of the rotator cuff tears was also higher in the overuse injury group compared with the control group.

“More and more kids are entering sports earlier in life and are overtraining,” said Dr. Roedl. “Baseball players who pitch too much are at risk of developing a stress response and overuse injury to the acromion. It is important to limit stress to the growing bones to allow them to develop normally.”

Young baseball pitchers who throw more than 100 pitches per week are at risk for a newly identified overuse injury that can impede normal shoulder development and lead to additional problems, including rotator cuff tears, according to a study published online ahead of print October 14 in Radiology.

The injury, termed acromial apophysiolysis by the researchers, is characterized by incomplete fusion and tenderness at the acromion. The acromion, which forms the bone at the top of the shoulder, typically develops from four individual bones into one bone during the teenage years.

“We kept seeing this injury over and over again in young athletes who come to the hospital at the end of the baseball season with shoulder pain and edema at the acromion on MRI, but no other imaging findings,” said Johannes B. Roedl, MD, a radiologist in the Musculoskeletal Division at Thomas Jefferson University Hospital in Philadelphia.

Dr. Roedl and a team of researchers conducted a retrospective study of 2,372 consecutive patients between the ages of 15 and 25, who underwent magnetic resonance imaging (MRI) for shoulder pain between 1998 and 2012. The majority of the patients, which included both males and females, were baseball pitchers.

Patients with edema at the acromial apophyses and no other abnormalities on MRI were included in the study group. Association of acromial edema with incomplete fusion , pitching, and clinical findings was determined in the study group and in an age- and sex-matched control group. Association with the development of an os acromial and rotator cuff tears later in life was assessed with follow-up imaging after age 25.

Edema at the acromial apophyses was found in 2.6% (61 of 2,372) and was associated with incomplete fusion of the acromial apophyses and superior shoulder tenderness.

A pitch count of more than 100 pitches per week was a substantial risk factor for developing acromial apophysiolysis (odds ratio 6.5). Among the patients with this overuse injury, 40% threw more than 100 pitches per week, compared to 8% in the control group.

All 61 injured patients took a three-month rest from pitching. One patient underwent surgery while the remaining 60 patients were treated conservatively with non-steroidal pain medication. Follow-up imaging conducted a minimum of two years later after the patients turned 25 were available for 29 of the 61 injured patients and for 23 of the 61 controls. Follow-up imaging revealed that 25 of the 29 patients (86%) with the overuse injury showed incomplete fusion of the acromion, compared to only one of the 23 (4%) controls.

Twenty-one of the 29 patients with the overuse injury continued pitching after the rest period, and all 21 showed incomplete bone fusion at the acromion. Rotator cuff tears were significantly more common among this group than in the control group (68% versus 29%, respectively). The severity of the rotator cuff tears was also higher in the overuse injury group compared with the control group.

“More and more kids are entering sports earlier in life and are overtraining,” said Dr. Roedl. “Baseball players who pitch too much are at risk of developing a stress response and overuse injury to the acromion. It is important to limit stress to the growing bones to allow them to develop normally.”

Young baseball pitchers who throw more than 100 pitches per week are at risk for a newly identified overuse injury that can impede normal shoulder development and lead to additional problems, including rotator cuff tears, according to a study published online ahead of print October 14 in Radiology.

The injury, termed acromial apophysiolysis by the researchers, is characterized by incomplete fusion and tenderness at the acromion. The acromion, which forms the bone at the top of the shoulder, typically develops from four individual bones into one bone during the teenage years.

“We kept seeing this injury over and over again in young athletes who come to the hospital at the end of the baseball season with shoulder pain and edema at the acromion on MRI, but no other imaging findings,” said Johannes B. Roedl, MD, a radiologist in the Musculoskeletal Division at Thomas Jefferson University Hospital in Philadelphia.

Dr. Roedl and a team of researchers conducted a retrospective study of 2,372 consecutive patients between the ages of 15 and 25, who underwent magnetic resonance imaging (MRI) for shoulder pain between 1998 and 2012. The majority of the patients, which included both males and females, were baseball pitchers.

Patients with edema at the acromial apophyses and no other abnormalities on MRI were included in the study group. Association of acromial edema with incomplete fusion , pitching, and clinical findings was determined in the study group and in an age- and sex-matched control group. Association with the development of an os acromial and rotator cuff tears later in life was assessed with follow-up imaging after age 25.

Edema at the acromial apophyses was found in 2.6% (61 of 2,372) and was associated with incomplete fusion of the acromial apophyses and superior shoulder tenderness.

A pitch count of more than 100 pitches per week was a substantial risk factor for developing acromial apophysiolysis (odds ratio 6.5). Among the patients with this overuse injury, 40% threw more than 100 pitches per week, compared to 8% in the control group.

All 61 injured patients took a three-month rest from pitching. One patient underwent surgery while the remaining 60 patients were treated conservatively with non-steroidal pain medication. Follow-up imaging conducted a minimum of two years later after the patients turned 25 were available for 29 of the 61 injured patients and for 23 of the 61 controls. Follow-up imaging revealed that 25 of the 29 patients (86%) with the overuse injury showed incomplete fusion of the acromion, compared to only one of the 23 (4%) controls.

Twenty-one of the 29 patients with the overuse injury continued pitching after the rest period, and all 21 showed incomplete bone fusion at the acromion. Rotator cuff tears were significantly more common among this group than in the control group (68% versus 29%, respectively). The severity of the rotator cuff tears was also higher in the overuse injury group compared with the control group.

“More and more kids are entering sports earlier in life and are overtraining,” said Dr. Roedl. “Baseball players who pitch too much are at risk of developing a stress response and overuse injury to the acromion. It is important to limit stress to the growing bones to allow them to develop normally.”

Patellar height may be important in determining function after total knee arthroplasty (TKA). By altering patellofemoral joint mechanics, patella baja may cause several functional issues after TKA.^1-8 Patella baja leads to decreased range of motion (ROM) affecting both extension and flexion.^5,8,9 Deep flexion can be restricted in TKA patients with patella baja because of tracking limitations associated with an inferiorly displaced patella. As the knee is brought into flexion, the patella can impinge on the anterior aspect of the tibial polyethylene or the tibial tray—presenting a true block to flexion and potentially altering wear.^1,10

Another functional issue with patella baja is loss of strength in the extensor mechanism. The patella serves as a fulcrum for the extensor muscles of the knee. When positioned properly and functioning properly, the patella increases the extensor forces generated. When the patella is positioned in baja, the knee generates decreased extensor mechanism force.^6,7 This can result in a lag, with the patient being unable to fully extend the knee. Extension-dependent activities are impaired. Patients with weak extensor function can experience poor function with stair climbing, rising from a chair, and exiting an automobile. The improper function and scarring of the patella can result in increased anterior knee pain and worse functional outcome scores after TKAs.^3,9

An abnormally positioned patella can either result from or lead to increased scarring in the knee.^9,11 Patellar height is often measured with the Insall-Salvati ratio (ISR), which is the patella tendon length (measurement of the tendon from the tibial tubercle to the inferior pole of the patella) divided by the patellar length (longest measured dimension of the patella) (Figure 1).¹² Patella baja is defined as an ISR of less than 0.8. Other indices that reference off the tibial plateau (Blackburne-Peel ratio, Canton-Deschamps ratio) reflect an elevation of the joint line, or pseudobaja, and are unreliable for analysis of patella baja after TKA.¹³

Postoperative patella baja has been reported in 10% to 34% of primary TKAs.^4,7 Inferior positioning of the patella and scarring can cause intraoperative difficulty with exposure and may complicate outcomes.^9,13 The exposure scar is often larger in TKA revisions for infection compared with primary TKAs.

We conducted a study to compare the incidence of patella baja in noninfected and infected TKA revisions. We hypothesized that, compared with noninfected knees, infected knees treated with nonarticulating spacers would have a higher incidence of patella baja both before and after surgery secondary to more inflammation, immobilization, and related scarring.

Materials and Methods

We conducted a retrospective case–cohort study of 148 consecutive TKA revisions. All TKA revisions were performed between 2003 and 2009 using a mobile-bearing revision system from a single manufacturer. All surgeries were done at a single institution by the 2 senior surgeons. The surgical approach was a standard medial parapatellar approach without patellar eversion. Our institutional review board approved the study and waived the requirement for informed consent, as this was a retrospective study of existing medical records that posed no more than minimal risk to patients.

To properly evaluate patellar height, orthopedic specialty–trained radiologic technicians obtained preoperative and postoperative weight-bearing radiographs using a standardized lateral radiograph in clinic. Two blinded investigators measured ISR radiographically both before surgery (preexplant for septic revisions) and at latest follow-up (postreplant for septic revisions). Patients with inadequate films and/or patellectomies were excluded, along with patients who had less than 6 months of postoperative follow-up.

Ninety-one patients (101 TKAs) met the study inclusion criteria. Two groups of cases were compared: aseptic revisions (n = 67) and septic revisions (n = 34). Reasons for aseptic revisions included implant loosening (24/67, 35.8%), instability (12/67, 17.9%), pain (12/67, 17.9%), lysis (5/67, 7.5%), stiffness (3/67, 4.5%), and malrotation (2/67, 3.0%). Infection was determined by Musculoskeletal Infection Society criteria, as documented by positive aspirations and/or intraoperative tissue cultures taken at prosthesis explantation, elevated white blood cell count in the aspirate, elevated percentage of polymorphonuclear (PMN) cells in the aspirate, gross purulence, presence of chronic draining sinus, or histologic analysis revealing acute inflammation with more than 5 PMN cells per high power field.^14,15

All infected TKAs were treated with 2-stage revisions. The standard of care at our institution through this series was to use a nonarticulating spacer for the treatment of infection. Weight-bearing status varied by extent of bone damage. Six weeks of culture-specific intravenous antibiotics were administered with assistance from an infectious disease consultant. Reimplantation was performed when clinical and laboratory criteria for resolution of infection were met—specifically, when erythrocyte sedimentation rate was less than 30 mm/h, C-reactive protein level was less than 10 mg/L, and aspirates were culture-negative. Mean (range) follow-up was 33.9 (6.2-75.7) months for aseptic revisions and 32.3 (7.5-94.2) months for septic revisions. Radiographic follow-up was performed at each visit, with weight-bearing anteroposterior and posteroanterior views, along with a lateral knee radiograph. At final follow-up, ROM was recorded by the senior attending evaluating the patient.

Categorical variables were statistically analyzed with χ² tests, and continuous variables were analyzed with Student t test, analysis of variance, and univariate analysis of covariance (ANCOVA). Statistical significance was set at P < .05. Intrarater reliability was measured with the intraclass correlation coefficient (ICC). All statistical analysis was performed with Predictive Analytics SoftWare Statistics Version 20.0 (SPSS, Chicago, Illinois).

Results

Ninety-one consecutive patients (43 men, 48 women) were included in this study. Mean (SD) age was 66.4 (10.1) years. Mean (SD) preoperative ISR in septic and aseptic cases was 0.94 (0.25) for men and 1.02 (0.23) for women (P = .10). Mean postoperative ISR in septic and aseptic cases was 0.84 (0.27) for men and 0.99 (0.23) for women (P = .004). There was a sex difference between septic and aseptic revisions. There were 22 men and 36 women in the aseptic group and 21 men and 12 women in the septic group (P = .01). Men were more likely than women to have septic revisions and patella baja. Table 1 compares the patient demographics of the 2 patient populations. Mean (SD) number of surgeries, including irrigation and débridement procedures before reimplantation, was larger for septic revisions, 2.9 (0.9), than for aseptic revisions, 1.4 (0.8) (P < .001).

Infection was the most common reason for revision and accounted for 33.7% (34/101) of all revisions. Noninfectious indications, in declining order of frequency, included loosening (23.8%, 24/101), instability (11.9%, 12/101), pain (11.9%, 12/101), osteolysis (5.0%, 5/101), polyethylene wear (5.0%, 5/101), failed unicompartmental knee (4.0%, 4/101), stiffness (3.0%, 3/101), and patellar problems (2.0%, 2/101) (Table 2). ISR decreased significantly only in infected revisions. It is important to note that there was not a high incidence of stiffness or patellofemoral failure in revision patients before surgery.

Mean (SD) ISR did not differ between groups before surgery, 1.00 (0.25) for aseptic and 0.96 (0.22) for septic (P = .49), but differed significantly after surgery, 0.99 (0.23) for aseptic and 0.77 (0.24) for septic (P < .001) (Figure 2). The univariate ANCOVA also demonstrated a postoperative difference between groups when taking the preoperative ratio into account: 0.99 (0.23) for aseptic and 0.78 (0.24) for septic (P = .005) (Table 3). Before surgery, 22.4% and 23.9% of the aseptic and septic groups, respectively, had patella baja (P = .58). After surgery, 17.6% and 58.8% of the aseptic and septic groups had patella baja (P = .001) (Table 4). The ICC for preoperative ISR was 0.94, and the ICC for postoperative ISR was 0.96, which indicates excellent agreement of measurements between the 2 blinded investigators.

ROM differed between septic and aseptic groups owing to the difference in postoperative flexion. Mean (SD) postoperative extension was 2.2° (5.4°) for the aseptic group and 5.1° (9.8°) for the septic group—not significantly different (P = .13). Mean (SD) postoperative flexion was 110.2° (18.8°) for the aseptic group and 97.2° (29.4°) for the septic group—significantly different (P = .02). The groups differed significantly (P = .02) in mean (SD) ROM: 108.0° (20.7°) for aseptic and 92.2° (34.6°) for septic (Table 1). ROM was also significantly associated with patella baja (P = .04), as patients with ISR of less than 0.8 had mean (SD) postoperative ROM of 95.1° (31.6°), and patients without patella baja had mean (SD) postoperative ROM of 106.8° (23.6°).

For the septic group, mean (SD) time between first and second stages was 13.0 (8.3) weeks (range, 1-44.3 weeks). Mean (SD) timing of spacer placement was not statistically significantly different (P = .90) between patients who had patella baja, 12.9 (8.8) weeks, and patients who did not have patella baja, 13.2 (7.8) weeks.

Discussion    

This study demonstrated that TKAs done for septic reasons resulted in a higher incidence of patella baja and decreased ROM. Incidence of patella baja was higher both before and after revision in septic TKAs than in aseptic TKAs, proving the hypothesis under study. Prerevision incidence was not significantly different, but there was a trend that could not be ignored. This may suggest that there is already an ongoing process in the infected knee that contributes to patella baja; the precise etiology remains unclear and is likely multifactorial. For example, scar formation may be increased in patients with chronic infection, predisposing to patella baja. This assertion is indirectly supported by a recent study from our institution revealing longer average surgical time in septic versus aseptic knee revisions; the difference was thought to reflect increased scar-tissue formation.¹⁶ That study also found that patients who underwent septic revisions had significantly more surgical procedures than patients who underwent aseptic revisions. Repetitive surgeries—specifically, repetitive arthrotomies during irrigation and débridement before reimplantation—lead to increased scar formation, which may contribute to preoperative and postoperative patella baja. This may be reflected in the findings that ROM was decreased in patients in the septic group versus patients in the aseptic group and that ROM was decreased in patients with patella baja. In addition, our study found that male patients were more likely to undergo TKA revision for septic reasons and to develop postoperative patella baja. This finding contrasts with that of a study⁵ that compared preoperative and postoperative ISR in primary TKA and found that women were more likely than men to have patella baja. Although women are more likely to undergo TKA revision,¹⁷ men may be more susceptible to infection and subsequent patella baja.

The higher postoperative rate of patella baja in the septic group became statistically significant even when preoperative incidence was considered. This may have been caused by infection-related scarring and by prolonged immobilization of septic knees with use of nonarticulating antibiotic spacers. By keeping these knees immobile with a nonarticulating spacer for a prolonged period in the healing phase of the infection, scar tissue may mature and form over the time between stages. A comparable example may be high tibial osteotomies, in which a high incidence of patella baja has been partly attributed to prolonged casting.¹¹ Future work comparing the results of articulating and nonarticulating spacers will help to determine if immobilization contributes to patella baja in infected TKAs.

There are several limitations to our study. Patient outcome questionnaires were not used, and they would have allowed for the assessment of physical outcomes and emotional satisfaction by comparing outcomes between patients with and without patella baja and comparing septic and aseptic TKAs. In addition, there was no standard method for quantifying difficulty of revision, which would have enabled us to compare difficulty of revision in patients with patella baja.

Conclusion

This study identified a high rate of patella baja and decreased ROM in TKA revisions, particularly infected revisions treated with a nonarticulating spacer. It is important to determine if there are functional consequences. Further investigation is needed regarding the cause, prevention, and management of this potentially debilitating outcome after revision TKA.

Patellar height may be important in determining function after total knee arthroplasty (TKA). By altering patellofemoral joint mechanics, patella baja may cause several functional issues after TKA.^1-8 Patella baja leads to decreased range of motion (ROM) affecting both extension and flexion.^5,8,9 Deep flexion can be restricted in TKA patients with patella baja because of tracking limitations associated with an inferiorly displaced patella. As the knee is brought into flexion, the patella can impinge on the anterior aspect of the tibial polyethylene or the tibial tray—presenting a true block to flexion and potentially altering wear.^1,10

Another functional issue with patella baja is loss of strength in the extensor mechanism. The patella serves as a fulcrum for the extensor muscles of the knee. When positioned properly and functioning properly, the patella increases the extensor forces generated. When the patella is positioned in baja, the knee generates decreased extensor mechanism force.^6,7 This can result in a lag, with the patient being unable to fully extend the knee. Extension-dependent activities are impaired. Patients with weak extensor function can experience poor function with stair climbing, rising from a chair, and exiting an automobile. The improper function and scarring of the patella can result in increased anterior knee pain and worse functional outcome scores after TKAs.^3,9

An abnormally positioned patella can either result from or lead to increased scarring in the knee.^9,11 Patellar height is often measured with the Insall-Salvati ratio (ISR), which is the patella tendon length (measurement of the tendon from the tibial tubercle to the inferior pole of the patella) divided by the patellar length (longest measured dimension of the patella) (Figure 1).¹² Patella baja is defined as an ISR of less than 0.8. Other indices that reference off the tibial plateau (Blackburne-Peel ratio, Canton-Deschamps ratio) reflect an elevation of the joint line, or pseudobaja, and are unreliable for analysis of patella baja after TKA.¹³

Postoperative patella baja has been reported in 10% to 34% of primary TKAs.^4,7 Inferior positioning of the patella and scarring can cause intraoperative difficulty with exposure and may complicate outcomes.^9,13 The exposure scar is often larger in TKA revisions for infection compared with primary TKAs.

We conducted a study to compare the incidence of patella baja in noninfected and infected TKA revisions. We hypothesized that, compared with noninfected knees, infected knees treated with nonarticulating spacers would have a higher incidence of patella baja both before and after surgery secondary to more inflammation, immobilization, and related scarring.

Materials and Methods

We conducted a retrospective case–cohort study of 148 consecutive TKA revisions. All TKA revisions were performed between 2003 and 2009 using a mobile-bearing revision system from a single manufacturer. All surgeries were done at a single institution by the 2 senior surgeons. The surgical approach was a standard medial parapatellar approach without patellar eversion. Our institutional review board approved the study and waived the requirement for informed consent, as this was a retrospective study of existing medical records that posed no more than minimal risk to patients.

To properly evaluate patellar height, orthopedic specialty–trained radiologic technicians obtained preoperative and postoperative weight-bearing radiographs using a standardized lateral radiograph in clinic. Two blinded investigators measured ISR radiographically both before surgery (preexplant for septic revisions) and at latest follow-up (postreplant for septic revisions). Patients with inadequate films and/or patellectomies were excluded, along with patients who had less than 6 months of postoperative follow-up.

Ninety-one patients (101 TKAs) met the study inclusion criteria. Two groups of cases were compared: aseptic revisions (n = 67) and septic revisions (n = 34). Reasons for aseptic revisions included implant loosening (24/67, 35.8%), instability (12/67, 17.9%), pain (12/67, 17.9%), lysis (5/67, 7.5%), stiffness (3/67, 4.5%), and malrotation (2/67, 3.0%). Infection was determined by Musculoskeletal Infection Society criteria, as documented by positive aspirations and/or intraoperative tissue cultures taken at prosthesis explantation, elevated white blood cell count in the aspirate, elevated percentage of polymorphonuclear (PMN) cells in the aspirate, gross purulence, presence of chronic draining sinus, or histologic analysis revealing acute inflammation with more than 5 PMN cells per high power field.^14,15

All infected TKAs were treated with 2-stage revisions. The standard of care at our institution through this series was to use a nonarticulating spacer for the treatment of infection. Weight-bearing status varied by extent of bone damage. Six weeks of culture-specific intravenous antibiotics were administered with assistance from an infectious disease consultant. Reimplantation was performed when clinical and laboratory criteria for resolution of infection were met—specifically, when erythrocyte sedimentation rate was less than 30 mm/h, C-reactive protein level was less than 10 mg/L, and aspirates were culture-negative. Mean (range) follow-up was 33.9 (6.2-75.7) months for aseptic revisions and 32.3 (7.5-94.2) months for septic revisions. Radiographic follow-up was performed at each visit, with weight-bearing anteroposterior and posteroanterior views, along with a lateral knee radiograph. At final follow-up, ROM was recorded by the senior attending evaluating the patient.

Categorical variables were statistically analyzed with χ² tests, and continuous variables were analyzed with Student t test, analysis of variance, and univariate analysis of covariance (ANCOVA). Statistical significance was set at P < .05. Intrarater reliability was measured with the intraclass correlation coefficient (ICC). All statistical analysis was performed with Predictive Analytics SoftWare Statistics Version 20.0 (SPSS, Chicago, Illinois).

Results

Ninety-one consecutive patients (43 men, 48 women) were included in this study. Mean (SD) age was 66.4 (10.1) years. Mean (SD) preoperative ISR in septic and aseptic cases was 0.94 (0.25) for men and 1.02 (0.23) for women (P = .10). Mean postoperative ISR in septic and aseptic cases was 0.84 (0.27) for men and 0.99 (0.23) for women (P = .004). There was a sex difference between septic and aseptic revisions. There were 22 men and 36 women in the aseptic group and 21 men and 12 women in the septic group (P = .01). Men were more likely than women to have septic revisions and patella baja. Table 1 compares the patient demographics of the 2 patient populations. Mean (SD) number of surgeries, including irrigation and débridement procedures before reimplantation, was larger for septic revisions, 2.9 (0.9), than for aseptic revisions, 1.4 (0.8) (P < .001).

Infection was the most common reason for revision and accounted for 33.7% (34/101) of all revisions. Noninfectious indications, in declining order of frequency, included loosening (23.8%, 24/101), instability (11.9%, 12/101), pain (11.9%, 12/101), osteolysis (5.0%, 5/101), polyethylene wear (5.0%, 5/101), failed unicompartmental knee (4.0%, 4/101), stiffness (3.0%, 3/101), and patellar problems (2.0%, 2/101) (Table 2). ISR decreased significantly only in infected revisions. It is important to note that there was not a high incidence of stiffness or patellofemoral failure in revision patients before surgery.

Mean (SD) ISR did not differ between groups before surgery, 1.00 (0.25) for aseptic and 0.96 (0.22) for septic (P = .49), but differed significantly after surgery, 0.99 (0.23) for aseptic and 0.77 (0.24) for septic (P < .001) (Figure 2). The univariate ANCOVA also demonstrated a postoperative difference between groups when taking the preoperative ratio into account: 0.99 (0.23) for aseptic and 0.78 (0.24) for septic (P = .005) (Table 3). Before surgery, 22.4% and 23.9% of the aseptic and septic groups, respectively, had patella baja (P = .58). After surgery, 17.6% and 58.8% of the aseptic and septic groups had patella baja (P = .001) (Table 4). The ICC for preoperative ISR was 0.94, and the ICC for postoperative ISR was 0.96, which indicates excellent agreement of measurements between the 2 blinded investigators.

ROM differed between septic and aseptic groups owing to the difference in postoperative flexion. Mean (SD) postoperative extension was 2.2° (5.4°) for the aseptic group and 5.1° (9.8°) for the septic group—not significantly different (P = .13). Mean (SD) postoperative flexion was 110.2° (18.8°) for the aseptic group and 97.2° (29.4°) for the septic group—significantly different (P = .02). The groups differed significantly (P = .02) in mean (SD) ROM: 108.0° (20.7°) for aseptic and 92.2° (34.6°) for septic (Table 1). ROM was also significantly associated with patella baja (P = .04), as patients with ISR of less than 0.8 had mean (SD) postoperative ROM of 95.1° (31.6°), and patients without patella baja had mean (SD) postoperative ROM of 106.8° (23.6°).

For the septic group, mean (SD) time between first and second stages was 13.0 (8.3) weeks (range, 1-44.3 weeks). Mean (SD) timing of spacer placement was not statistically significantly different (P = .90) between patients who had patella baja, 12.9 (8.8) weeks, and patients who did not have patella baja, 13.2 (7.8) weeks.

Discussion    

This study demonstrated that TKAs done for septic reasons resulted in a higher incidence of patella baja and decreased ROM. Incidence of patella baja was higher both before and after revision in septic TKAs than in aseptic TKAs, proving the hypothesis under study. Prerevision incidence was not significantly different, but there was a trend that could not be ignored. This may suggest that there is already an ongoing process in the infected knee that contributes to patella baja; the precise etiology remains unclear and is likely multifactorial. For example, scar formation may be increased in patients with chronic infection, predisposing to patella baja. This assertion is indirectly supported by a recent study from our institution revealing longer average surgical time in septic versus aseptic knee revisions; the difference was thought to reflect increased scar-tissue formation.¹⁶ That study also found that patients who underwent septic revisions had significantly more surgical procedures than patients who underwent aseptic revisions. Repetitive surgeries—specifically, repetitive arthrotomies during irrigation and débridement before reimplantation—lead to increased scar formation, which may contribute to preoperative and postoperative patella baja. This may be reflected in the findings that ROM was decreased in patients in the septic group versus patients in the aseptic group and that ROM was decreased in patients with patella baja. In addition, our study found that male patients were more likely to undergo TKA revision for septic reasons and to develop postoperative patella baja. This finding contrasts with that of a study⁵ that compared preoperative and postoperative ISR in primary TKA and found that women were more likely than men to have patella baja. Although women are more likely to undergo TKA revision,¹⁷ men may be more susceptible to infection and subsequent patella baja.

The higher postoperative rate of patella baja in the septic group became statistically significant even when preoperative incidence was considered. This may have been caused by infection-related scarring and by prolonged immobilization of septic knees with use of nonarticulating antibiotic spacers. By keeping these knees immobile with a nonarticulating spacer for a prolonged period in the healing phase of the infection, scar tissue may mature and form over the time between stages. A comparable example may be high tibial osteotomies, in which a high incidence of patella baja has been partly attributed to prolonged casting.¹¹ Future work comparing the results of articulating and nonarticulating spacers will help to determine if immobilization contributes to patella baja in infected TKAs.

There are several limitations to our study. Patient outcome questionnaires were not used, and they would have allowed for the assessment of physical outcomes and emotional satisfaction by comparing outcomes between patients with and without patella baja and comparing septic and aseptic TKAs. In addition, there was no standard method for quantifying difficulty of revision, which would have enabled us to compare difficulty of revision in patients with patella baja.

Conclusion

This study identified a high rate of patella baja and decreased ROM in TKA revisions, particularly infected revisions treated with a nonarticulating spacer. It is important to determine if there are functional consequences. Further investigation is needed regarding the cause, prevention, and management of this potentially debilitating outcome after revision TKA.

Patellar height may be important in determining function after total knee arthroplasty (TKA). By altering patellofemoral joint mechanics, patella baja may cause several functional issues after TKA.^1-8 Patella baja leads to decreased range of motion (ROM) affecting both extension and flexion.^5,8,9 Deep flexion can be restricted in TKA patients with patella baja because of tracking limitations associated with an inferiorly displaced patella. As the knee is brought into flexion, the patella can impinge on the anterior aspect of the tibial polyethylene or the tibial tray—presenting a true block to flexion and potentially altering wear.^1,10

Another functional issue with patella baja is loss of strength in the extensor mechanism. The patella serves as a fulcrum for the extensor muscles of the knee. When positioned properly and functioning properly, the patella increases the extensor forces generated. When the patella is positioned in baja, the knee generates decreased extensor mechanism force.^6,7 This can result in a lag, with the patient being unable to fully extend the knee. Extension-dependent activities are impaired. Patients with weak extensor function can experience poor function with stair climbing, rising from a chair, and exiting an automobile. The improper function and scarring of the patella can result in increased anterior knee pain and worse functional outcome scores after TKAs.^3,9

An abnormally positioned patella can either result from or lead to increased scarring in the knee.^9,11 Patellar height is often measured with the Insall-Salvati ratio (ISR), which is the patella tendon length (measurement of the tendon from the tibial tubercle to the inferior pole of the patella) divided by the patellar length (longest measured dimension of the patella) (Figure 1).¹² Patella baja is defined as an ISR of less than 0.8. Other indices that reference off the tibial plateau (Blackburne-Peel ratio, Canton-Deschamps ratio) reflect an elevation of the joint line, or pseudobaja, and are unreliable for analysis of patella baja after TKA.¹³

Postoperative patella baja has been reported in 10% to 34% of primary TKAs.^4,7 Inferior positioning of the patella and scarring can cause intraoperative difficulty with exposure and may complicate outcomes.^9,13 The exposure scar is often larger in TKA revisions for infection compared with primary TKAs.

We conducted a study to compare the incidence of patella baja in noninfected and infected TKA revisions. We hypothesized that, compared with noninfected knees, infected knees treated with nonarticulating spacers would have a higher incidence of patella baja both before and after surgery secondary to more inflammation, immobilization, and related scarring.

Materials and Methods

We conducted a retrospective case–cohort study of 148 consecutive TKA revisions. All TKA revisions were performed between 2003 and 2009 using a mobile-bearing revision system from a single manufacturer. All surgeries were done at a single institution by the 2 senior surgeons. The surgical approach was a standard medial parapatellar approach without patellar eversion. Our institutional review board approved the study and waived the requirement for informed consent, as this was a retrospective study of existing medical records that posed no more than minimal risk to patients.

To properly evaluate patellar height, orthopedic specialty–trained radiologic technicians obtained preoperative and postoperative weight-bearing radiographs using a standardized lateral radiograph in clinic. Two blinded investigators measured ISR radiographically both before surgery (preexplant for septic revisions) and at latest follow-up (postreplant for septic revisions). Patients with inadequate films and/or patellectomies were excluded, along with patients who had less than 6 months of postoperative follow-up.

Ninety-one patients (101 TKAs) met the study inclusion criteria. Two groups of cases were compared: aseptic revisions (n = 67) and septic revisions (n = 34). Reasons for aseptic revisions included implant loosening (24/67, 35.8%), instability (12/67, 17.9%), pain (12/67, 17.9%), lysis (5/67, 7.5%), stiffness (3/67, 4.5%), and malrotation (2/67, 3.0%). Infection was determined by Musculoskeletal Infection Society criteria, as documented by positive aspirations and/or intraoperative tissue cultures taken at prosthesis explantation, elevated white blood cell count in the aspirate, elevated percentage of polymorphonuclear (PMN) cells in the aspirate, gross purulence, presence of chronic draining sinus, or histologic analysis revealing acute inflammation with more than 5 PMN cells per high power field.^14,15

All infected TKAs were treated with 2-stage revisions. The standard of care at our institution through this series was to use a nonarticulating spacer for the treatment of infection. Weight-bearing status varied by extent of bone damage. Six weeks of culture-specific intravenous antibiotics were administered with assistance from an infectious disease consultant. Reimplantation was performed when clinical and laboratory criteria for resolution of infection were met—specifically, when erythrocyte sedimentation rate was less than 30 mm/h, C-reactive protein level was less than 10 mg/L, and aspirates were culture-negative. Mean (range) follow-up was 33.9 (6.2-75.7) months for aseptic revisions and 32.3 (7.5-94.2) months for septic revisions. Radiographic follow-up was performed at each visit, with weight-bearing anteroposterior and posteroanterior views, along with a lateral knee radiograph. At final follow-up, ROM was recorded by the senior attending evaluating the patient.

Categorical variables were statistically analyzed with χ² tests, and continuous variables were analyzed with Student t test, analysis of variance, and univariate analysis of covariance (ANCOVA). Statistical significance was set at P < .05. Intrarater reliability was measured with the intraclass correlation coefficient (ICC). All statistical analysis was performed with Predictive Analytics SoftWare Statistics Version 20.0 (SPSS, Chicago, Illinois).

Results

Ninety-one consecutive patients (43 men, 48 women) were included in this study. Mean (SD) age was 66.4 (10.1) years. Mean (SD) preoperative ISR in septic and aseptic cases was 0.94 (0.25) for men and 1.02 (0.23) for women (P = .10). Mean postoperative ISR in septic and aseptic cases was 0.84 (0.27) for men and 0.99 (0.23) for women (P = .004). There was a sex difference between septic and aseptic revisions. There were 22 men and 36 women in the aseptic group and 21 men and 12 women in the septic group (P = .01). Men were more likely than women to have septic revisions and patella baja. Table 1 compares the patient demographics of the 2 patient populations. Mean (SD) number of surgeries, including irrigation and débridement procedures before reimplantation, was larger for septic revisions, 2.9 (0.9), than for aseptic revisions, 1.4 (0.8) (P < .001).

Infection was the most common reason for revision and accounted for 33.7% (34/101) of all revisions. Noninfectious indications, in declining order of frequency, included loosening (23.8%, 24/101), instability (11.9%, 12/101), pain (11.9%, 12/101), osteolysis (5.0%, 5/101), polyethylene wear (5.0%, 5/101), failed unicompartmental knee (4.0%, 4/101), stiffness (3.0%, 3/101), and patellar problems (2.0%, 2/101) (Table 2). ISR decreased significantly only in infected revisions. It is important to note that there was not a high incidence of stiffness or patellofemoral failure in revision patients before surgery.

Mean (SD) ISR did not differ between groups before surgery, 1.00 (0.25) for aseptic and 0.96 (0.22) for septic (P = .49), but differed significantly after surgery, 0.99 (0.23) for aseptic and 0.77 (0.24) for septic (P < .001) (Figure 2). The univariate ANCOVA also demonstrated a postoperative difference between groups when taking the preoperative ratio into account: 0.99 (0.23) for aseptic and 0.78 (0.24) for septic (P = .005) (Table 3). Before surgery, 22.4% and 23.9% of the aseptic and septic groups, respectively, had patella baja (P = .58). After surgery, 17.6% and 58.8% of the aseptic and septic groups had patella baja (P = .001) (Table 4). The ICC for preoperative ISR was 0.94, and the ICC for postoperative ISR was 0.96, which indicates excellent agreement of measurements between the 2 blinded investigators.

ROM differed between septic and aseptic groups owing to the difference in postoperative flexion. Mean (SD) postoperative extension was 2.2° (5.4°) for the aseptic group and 5.1° (9.8°) for the septic group—not significantly different (P = .13). Mean (SD) postoperative flexion was 110.2° (18.8°) for the aseptic group and 97.2° (29.4°) for the septic group—significantly different (P = .02). The groups differed significantly (P = .02) in mean (SD) ROM: 108.0° (20.7°) for aseptic and 92.2° (34.6°) for septic (Table 1). ROM was also significantly associated with patella baja (P = .04), as patients with ISR of less than 0.8 had mean (SD) postoperative ROM of 95.1° (31.6°), and patients without patella baja had mean (SD) postoperative ROM of 106.8° (23.6°).

For the septic group, mean (SD) time between first and second stages was 13.0 (8.3) weeks (range, 1-44.3 weeks). Mean (SD) timing of spacer placement was not statistically significantly different (P = .90) between patients who had patella baja, 12.9 (8.8) weeks, and patients who did not have patella baja, 13.2 (7.8) weeks.

Discussion    

This study demonstrated that TKAs done for septic reasons resulted in a higher incidence of patella baja and decreased ROM. Incidence of patella baja was higher both before and after revision in septic TKAs than in aseptic TKAs, proving the hypothesis under study. Prerevision incidence was not significantly different, but there was a trend that could not be ignored. This may suggest that there is already an ongoing process in the infected knee that contributes to patella baja; the precise etiology remains unclear and is likely multifactorial. For example, scar formation may be increased in patients with chronic infection, predisposing to patella baja. This assertion is indirectly supported by a recent study from our institution revealing longer average surgical time in septic versus aseptic knee revisions; the difference was thought to reflect increased scar-tissue formation.¹⁶ That study also found that patients who underwent septic revisions had significantly more surgical procedures than patients who underwent aseptic revisions. Repetitive surgeries—specifically, repetitive arthrotomies during irrigation and débridement before reimplantation—lead to increased scar formation, which may contribute to preoperative and postoperative patella baja. This may be reflected in the findings that ROM was decreased in patients in the septic group versus patients in the aseptic group and that ROM was decreased in patients with patella baja. In addition, our study found that male patients were more likely to undergo TKA revision for septic reasons and to develop postoperative patella baja. This finding contrasts with that of a study⁵ that compared preoperative and postoperative ISR in primary TKA and found that women were more likely than men to have patella baja. Although women are more likely to undergo TKA revision,¹⁷ men may be more susceptible to infection and subsequent patella baja.

The higher postoperative rate of patella baja in the septic group became statistically significant even when preoperative incidence was considered. This may have been caused by infection-related scarring and by prolonged immobilization of septic knees with use of nonarticulating antibiotic spacers. By keeping these knees immobile with a nonarticulating spacer for a prolonged period in the healing phase of the infection, scar tissue may mature and form over the time between stages. A comparable example may be high tibial osteotomies, in which a high incidence of patella baja has been partly attributed to prolonged casting.¹¹ Future work comparing the results of articulating and nonarticulating spacers will help to determine if immobilization contributes to patella baja in infected TKAs.

There are several limitations to our study. Patient outcome questionnaires were not used, and they would have allowed for the assessment of physical outcomes and emotional satisfaction by comparing outcomes between patients with and without patella baja and comparing septic and aseptic TKAs. In addition, there was no standard method for quantifying difficulty of revision, which would have enabled us to compare difficulty of revision in patients with patella baja.

Conclusion

This study identified a high rate of patella baja and decreased ROM in TKA revisions, particularly infected revisions treated with a nonarticulating spacer. It is important to determine if there are functional consequences. Further investigation is needed regarding the cause, prevention, and management of this potentially debilitating outcome after revision TKA.

Acromioclavicular (AC) dislocations and displaced fractures of the middle third of the clavicle rarely occur together. Isolated AC joint separation is often treated nonoperatively with internal coracoclavicular (CC) fixation or reconstruction considered for type IV-VI AC dislocations and some type III injuries.¹ Isolated clavicle fractures traditionally have been treated nonoperatively. The current trend is toward internal fixation for displaced and shortened fractures.² There have been only a handful of reports of concomitant AC dislocation and midshaft clavicle fracture.^3-6 Previous treatments have included nonoperative treatment, AC fixation, or internal fixation of the clavicle with ligamentous reconstruction.

We present a previously undescribed technique for internal fixation of this rare shoulder injury. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

While driving an all-terrain vehicle, a healthy 19-year-old right-hand–dominant man hit a bridge and sustained direct impact to his right shoulder. He presented to the emergency department complaining of right shoulder pain and deformity without skin disruption, vascular insufficiency, or neurologic symptoms. Anteroposterior (AP) radiograph showed an oblique, displaced, middle-third clavicle shaft fracture (Figure 1). An associated type IV AC dislocation was confirmed on axillary radiograph (Figure 2) and on an axial cut from a trauma chest computed tomography (CT) scan (Figure 3). The patient was discharged home from the trauma service the next day with a sling for comfort and plans for delayed, elective operative fixation 1 week later.

The patient was placed in a beach-chair position. Through a longitudinal incision extending laterally over the AC joint, the clavicle was exposed for fracture reduction, with care taken to retain soft-tissue attachments. The distal clavicle was buttonholed posteriorly through the trapezius muscle and fascia. The distal fracture fragment was devoid of any remaining CC ligamentous attachment. After satisfactory reduction, a low-profile precontoured clavicle plate (Superior Midshaft Clavicle Plate; Acumed, Hillsboro, Oregon) was placed superiorly; the fracture was compressed through the plate and internally fixed with three 3.5-mm bicortical screws on both sides of the fracture. Approximately 5 mm of the distal clavicle was resected at the AC joint to facilitate adequate AC and CC reduction without disruption of the clavicle fracture. With an adequate CC reduction, a 3.5-mm fully threaded cortical screw was placed through the most distal hole in the clavicle plate, clavicle, and coracoid.

After surgery, the patient was placed into an ARC shoulder immobilizer (Bledsoe, Grand Prairie, Texas) for 6 weeks, removing the immobilizer only for elbow and wrist range of motion (ROM) exercises. Radiographs at 3-month follow-up (Figure 4) showed a healed fracture with no loss of AC or CC reduction. Three months after surgery, another procedure was performed to remove the CC screw. One year after the initial surgery, the patient complained of intermittent soreness over the lateral shoulder but was not limited in his activities and was back to performing manual labor without difficulty. He had full ROM in forward flexion, abduction, internal rotation, and external rotation without weakness, tenderness, or any neurovascular deficit. After CC screw removal, no deformity returned at the shoulder. Radiographs showed a healed fracture with minimal superior subluxation at the AC joint without significant change from the 3-month follow-up (Figure 5).

Discussion

The combined injury pattern of a type IV AC dislocation and a displaced middle-third clavicle shaft fracture is rare. The usual mechanism of injury, as seen in the present case, is a direct blow to the shoulder at the tip of the acromion, though indirect forces from a fall on an outstretched hand are also described.⁷ Disruption of the CC ligaments with AC separation likely dissipates the stress necessary to create a clavicle fracture in most cases,¹ explaining the rarity of this injury. It is imperative to evaluate patients for injury to both the osseous and ligamentous structures.

Previous case reports of concomitant AC separation and midshaft clavicle fracture have described a variety of treatment options, but to date our case represents the only episode in which both the clavicle fracture and the AC joint were treated with open reduction and internal fixation (ORIF). Wurtz and colleagues⁵ reported on a series of 4 patients with AC disruption and middle-third clavicle fracture. Three of the 4 patients had type IV AC separation; all 3 were treated, 2 acutely and 1 chronically, with open reduction of the AC and CC joints; 2 of these patients had CC screw fixation only after reduction, and the third had 2 Steinmann pins placed across the AC joint without CC screw fixation. All hardware was removed after 12 weeks. The fourth patient had a type II AC dislocation and was treated with closed reduction of the clavicle with no intervention for the AC joint. None of the clavicle fractures in this series were treated with internal fixation. All patients had full and pain-free ROM at 1- to 3-year follow-up.

Juhn and Simonian³ reported on a case of type VI separation with greenstick midshaft clavicle fracture in a hockey player seen 7 days after injury. The patient described some tingling in the upper extremity and had shoulder pain on initial presentation but was noted to have minimal displacement of both the AC joint and the midshaft clavicle fracture. Both injuries were treated nonsurgically with good outcome, and the patient returned to full activity (including hockey) within 14 weeks after injury.

Lancourt⁴ described the case of a patient with a type V AC dislocation and a displaced midshaft clavicle fracture. The AC joint was treated with Steinmann pin fixation, and the clavicle fracture was treated nonoperatively. The author cited high complication rates of plate fixation for clavicle fractures as the reason for not performing the additional procedure. The pins were removed 8 weeks after surgery. At 3-year follow-up, the patient had good radiographic and clinical outcome.

Yeh and colleagues⁶ described a patient who sustained a displaced midshaft clavicle fracture and a type IV AC dislocation in a fall from a horse. The patient underwent ORIF of the clavicle fracture with plate fixation. After the procedure, the AC joint was still unstable intraoperatively, and the AC and CC ligaments were reconstructed with semitendinosus allograft. The patient had full and painless ROM at 1-year follow-up.

The present case report serves as a reminder to obtain adequate shoulder radiographs when evaluating “just another clavicle fracture.” The radiographs should include a good axillary view to ensure there is not an associated AC dislocation. Increasingly, some authors have been advocating internal fixation for clavicle fractures, with reports of improved functional outcomes, improved cosmesis, and increased union rates.² Indications for operative fixation include shortening and 100% displacement,⁸ and relative indications include open fractures.¹ Operative fixation is perhaps more important for younger, athletic, and manual-labor populations. The trend in treatment of clavicle fractures toward operative fixation lends itself well to ORIF of the AC and CC joints; hence, a modern treatment for this rarely described combination injury should include internal plate fixation of the clavicle in addition to CC fixation. This additional procedure requires little extra time and energy in an operative scenario already requiring anesthesia, with easy insertion of the CC screw through the clavicle plate. Use of a CC screw obviates any potential risks associated with use of allograft tissue, and there is no anticipated difficulty with screw removal at 12 weeks.

Alternative options for AC stability include CC reconstruction with ligamentous allograft, ligamentous autograft, or suture/tightrope techniques. A noted advantage of these alternative techniques is less need to return to the operating room for the hardware removal that is recommended with CC screw fixation. However, these procedures potentially increase surgical exposure and operating time. In addition, screw fixation minimizes the possibility of donor-site morbidity from autograft transfers and potential complications from allograft tissue.

Hook plate fixation of the AC joint has also been described. In a recent case report of a similar injury pattern, plate fixation of the clavicle with simultaneous hook plate fixation of the AC joint was described.⁹ The patient did well but required removal of hardware of the hook plate and the clavicle plate 1 and 3 years after surgery, respectively. Although screw fixation is biomechanically stronger, debate persists about the clinical importance of this increase in strength.¹ In the setting of plate fixation for the clavicle, these alternative AC fixations would require technique adjustments, including length of grafts and/or sutures, and raise concerns regarding interaction of the metal with the fixation material.

Critical evaluation of our technique revealed a lucency larger than the screw (Figure 5). However, the screw was not clinically loose at removal. This potential complication, in combination with the bent screw (Figure 4) before removal, highlights the concern for screw breakage with this technique, given the increased construct stiffness caused by the added plate.

Conclusion

As in the other reports mentioned, our patient had an excellent clinical and radiographic outcome. It could be inferred that, if fixation for isolated clavicle fractures demonstrates improved function, better outcomes would be seen for higher-energy fractures associated with AC dislocation. Given the current trend toward surgical fixation for certain clavicle fractures, we recommend that clavicle fractures associated with type IV AC dislocation be treated with ORIF of both injuries.

Acromioclavicular (AC) dislocations and displaced fractures of the middle third of the clavicle rarely occur together. Isolated AC joint separation is often treated nonoperatively with internal coracoclavicular (CC) fixation or reconstruction considered for type IV-VI AC dislocations and some type III injuries.¹ Isolated clavicle fractures traditionally have been treated nonoperatively. The current trend is toward internal fixation for displaced and shortened fractures.² There have been only a handful of reports of concomitant AC dislocation and midshaft clavicle fracture.^3-6 Previous treatments have included nonoperative treatment, AC fixation, or internal fixation of the clavicle with ligamentous reconstruction.

We present a previously undescribed technique for internal fixation of this rare shoulder injury. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

While driving an all-terrain vehicle, a healthy 19-year-old right-hand–dominant man hit a bridge and sustained direct impact to his right shoulder. He presented to the emergency department complaining of right shoulder pain and deformity without skin disruption, vascular insufficiency, or neurologic symptoms. Anteroposterior (AP) radiograph showed an oblique, displaced, middle-third clavicle shaft fracture (Figure 1). An associated type IV AC dislocation was confirmed on axillary radiograph (Figure 2) and on an axial cut from a trauma chest computed tomography (CT) scan (Figure 3). The patient was discharged home from the trauma service the next day with a sling for comfort and plans for delayed, elective operative fixation 1 week later.

The patient was placed in a beach-chair position. Through a longitudinal incision extending laterally over the AC joint, the clavicle was exposed for fracture reduction, with care taken to retain soft-tissue attachments. The distal clavicle was buttonholed posteriorly through the trapezius muscle and fascia. The distal fracture fragment was devoid of any remaining CC ligamentous attachment. After satisfactory reduction, a low-profile precontoured clavicle plate (Superior Midshaft Clavicle Plate; Acumed, Hillsboro, Oregon) was placed superiorly; the fracture was compressed through the plate and internally fixed with three 3.5-mm bicortical screws on both sides of the fracture. Approximately 5 mm of the distal clavicle was resected at the AC joint to facilitate adequate AC and CC reduction without disruption of the clavicle fracture. With an adequate CC reduction, a 3.5-mm fully threaded cortical screw was placed through the most distal hole in the clavicle plate, clavicle, and coracoid.

After surgery, the patient was placed into an ARC shoulder immobilizer (Bledsoe, Grand Prairie, Texas) for 6 weeks, removing the immobilizer only for elbow and wrist range of motion (ROM) exercises. Radiographs at 3-month follow-up (Figure 4) showed a healed fracture with no loss of AC or CC reduction. Three months after surgery, another procedure was performed to remove the CC screw. One year after the initial surgery, the patient complained of intermittent soreness over the lateral shoulder but was not limited in his activities and was back to performing manual labor without difficulty. He had full ROM in forward flexion, abduction, internal rotation, and external rotation without weakness, tenderness, or any neurovascular deficit. After CC screw removal, no deformity returned at the shoulder. Radiographs showed a healed fracture with minimal superior subluxation at the AC joint without significant change from the 3-month follow-up (Figure 5).

Discussion

The combined injury pattern of a type IV AC dislocation and a displaced middle-third clavicle shaft fracture is rare. The usual mechanism of injury, as seen in the present case, is a direct blow to the shoulder at the tip of the acromion, though indirect forces from a fall on an outstretched hand are also described.⁷ Disruption of the CC ligaments with AC separation likely dissipates the stress necessary to create a clavicle fracture in most cases,¹ explaining the rarity of this injury. It is imperative to evaluate patients for injury to both the osseous and ligamentous structures.

Previous case reports of concomitant AC separation and midshaft clavicle fracture have described a variety of treatment options, but to date our case represents the only episode in which both the clavicle fracture and the AC joint were treated with open reduction and internal fixation (ORIF). Wurtz and colleagues⁵ reported on a series of 4 patients with AC disruption and middle-third clavicle fracture. Three of the 4 patients had type IV AC separation; all 3 were treated, 2 acutely and 1 chronically, with open reduction of the AC and CC joints; 2 of these patients had CC screw fixation only after reduction, and the third had 2 Steinmann pins placed across the AC joint without CC screw fixation. All hardware was removed after 12 weeks. The fourth patient had a type II AC dislocation and was treated with closed reduction of the clavicle with no intervention for the AC joint. None of the clavicle fractures in this series were treated with internal fixation. All patients had full and pain-free ROM at 1- to 3-year follow-up.

Juhn and Simonian³ reported on a case of type VI separation with greenstick midshaft clavicle fracture in a hockey player seen 7 days after injury. The patient described some tingling in the upper extremity and had shoulder pain on initial presentation but was noted to have minimal displacement of both the AC joint and the midshaft clavicle fracture. Both injuries were treated nonsurgically with good outcome, and the patient returned to full activity (including hockey) within 14 weeks after injury.

Lancourt⁴ described the case of a patient with a type V AC dislocation and a displaced midshaft clavicle fracture. The AC joint was treated with Steinmann pin fixation, and the clavicle fracture was treated nonoperatively. The author cited high complication rates of plate fixation for clavicle fractures as the reason for not performing the additional procedure. The pins were removed 8 weeks after surgery. At 3-year follow-up, the patient had good radiographic and clinical outcome.

Yeh and colleagues⁶ described a patient who sustained a displaced midshaft clavicle fracture and a type IV AC dislocation in a fall from a horse. The patient underwent ORIF of the clavicle fracture with plate fixation. After the procedure, the AC joint was still unstable intraoperatively, and the AC and CC ligaments were reconstructed with semitendinosus allograft. The patient had full and painless ROM at 1-year follow-up.

The present case report serves as a reminder to obtain adequate shoulder radiographs when evaluating “just another clavicle fracture.” The radiographs should include a good axillary view to ensure there is not an associated AC dislocation. Increasingly, some authors have been advocating internal fixation for clavicle fractures, with reports of improved functional outcomes, improved cosmesis, and increased union rates.² Indications for operative fixation include shortening and 100% displacement,⁸ and relative indications include open fractures.¹ Operative fixation is perhaps more important for younger, athletic, and manual-labor populations. The trend in treatment of clavicle fractures toward operative fixation lends itself well to ORIF of the AC and CC joints; hence, a modern treatment for this rarely described combination injury should include internal plate fixation of the clavicle in addition to CC fixation. This additional procedure requires little extra time and energy in an operative scenario already requiring anesthesia, with easy insertion of the CC screw through the clavicle plate. Use of a CC screw obviates any potential risks associated with use of allograft tissue, and there is no anticipated difficulty with screw removal at 12 weeks.

Alternative options for AC stability include CC reconstruction with ligamentous allograft, ligamentous autograft, or suture/tightrope techniques. A noted advantage of these alternative techniques is less need to return to the operating room for the hardware removal that is recommended with CC screw fixation. However, these procedures potentially increase surgical exposure and operating time. In addition, screw fixation minimizes the possibility of donor-site morbidity from autograft transfers and potential complications from allograft tissue.

Hook plate fixation of the AC joint has also been described. In a recent case report of a similar injury pattern, plate fixation of the clavicle with simultaneous hook plate fixation of the AC joint was described.⁹ The patient did well but required removal of hardware of the hook plate and the clavicle plate 1 and 3 years after surgery, respectively. Although screw fixation is biomechanically stronger, debate persists about the clinical importance of this increase in strength.¹ In the setting of plate fixation for the clavicle, these alternative AC fixations would require technique adjustments, including length of grafts and/or sutures, and raise concerns regarding interaction of the metal with the fixation material.

Critical evaluation of our technique revealed a lucency larger than the screw (Figure 5). However, the screw was not clinically loose at removal. This potential complication, in combination with the bent screw (Figure 4) before removal, highlights the concern for screw breakage with this technique, given the increased construct stiffness caused by the added plate.

Conclusion

As in the other reports mentioned, our patient had an excellent clinical and radiographic outcome. It could be inferred that, if fixation for isolated clavicle fractures demonstrates improved function, better outcomes would be seen for higher-energy fractures associated with AC dislocation. Given the current trend toward surgical fixation for certain clavicle fractures, we recommend that clavicle fractures associated with type IV AC dislocation be treated with ORIF of both injuries.

Acromioclavicular (AC) dislocations and displaced fractures of the middle third of the clavicle rarely occur together. Isolated AC joint separation is often treated nonoperatively with internal coracoclavicular (CC) fixation or reconstruction considered for type IV-VI AC dislocations and some type III injuries.¹ Isolated clavicle fractures traditionally have been treated nonoperatively. The current trend is toward internal fixation for displaced and shortened fractures.² There have been only a handful of reports of concomitant AC dislocation and midshaft clavicle fracture.^3-6 Previous treatments have included nonoperative treatment, AC fixation, or internal fixation of the clavicle with ligamentous reconstruction.

We present a previously undescribed technique for internal fixation of this rare shoulder injury. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

While driving an all-terrain vehicle, a healthy 19-year-old right-hand–dominant man hit a bridge and sustained direct impact to his right shoulder. He presented to the emergency department complaining of right shoulder pain and deformity without skin disruption, vascular insufficiency, or neurologic symptoms. Anteroposterior (AP) radiograph showed an oblique, displaced, middle-third clavicle shaft fracture (Figure 1). An associated type IV AC dislocation was confirmed on axillary radiograph (Figure 2) and on an axial cut from a trauma chest computed tomography (CT) scan (Figure 3). The patient was discharged home from the trauma service the next day with a sling for comfort and plans for delayed, elective operative fixation 1 week later.

The patient was placed in a beach-chair position. Through a longitudinal incision extending laterally over the AC joint, the clavicle was exposed for fracture reduction, with care taken to retain soft-tissue attachments. The distal clavicle was buttonholed posteriorly through the trapezius muscle and fascia. The distal fracture fragment was devoid of any remaining CC ligamentous attachment. After satisfactory reduction, a low-profile precontoured clavicle plate (Superior Midshaft Clavicle Plate; Acumed, Hillsboro, Oregon) was placed superiorly; the fracture was compressed through the plate and internally fixed with three 3.5-mm bicortical screws on both sides of the fracture. Approximately 5 mm of the distal clavicle was resected at the AC joint to facilitate adequate AC and CC reduction without disruption of the clavicle fracture. With an adequate CC reduction, a 3.5-mm fully threaded cortical screw was placed through the most distal hole in the clavicle plate, clavicle, and coracoid.

After surgery, the patient was placed into an ARC shoulder immobilizer (Bledsoe, Grand Prairie, Texas) for 6 weeks, removing the immobilizer only for elbow and wrist range of motion (ROM) exercises. Radiographs at 3-month follow-up (Figure 4) showed a healed fracture with no loss of AC or CC reduction. Three months after surgery, another procedure was performed to remove the CC screw. One year after the initial surgery, the patient complained of intermittent soreness over the lateral shoulder but was not limited in his activities and was back to performing manual labor without difficulty. He had full ROM in forward flexion, abduction, internal rotation, and external rotation without weakness, tenderness, or any neurovascular deficit. After CC screw removal, no deformity returned at the shoulder. Radiographs showed a healed fracture with minimal superior subluxation at the AC joint without significant change from the 3-month follow-up (Figure 5).

Discussion

The combined injury pattern of a type IV AC dislocation and a displaced middle-third clavicle shaft fracture is rare. The usual mechanism of injury, as seen in the present case, is a direct blow to the shoulder at the tip of the acromion, though indirect forces from a fall on an outstretched hand are also described.⁷ Disruption of the CC ligaments with AC separation likely dissipates the stress necessary to create a clavicle fracture in most cases,¹ explaining the rarity of this injury. It is imperative to evaluate patients for injury to both the osseous and ligamentous structures.

Previous case reports of concomitant AC separation and midshaft clavicle fracture have described a variety of treatment options, but to date our case represents the only episode in which both the clavicle fracture and the AC joint were treated with open reduction and internal fixation (ORIF). Wurtz and colleagues⁵ reported on a series of 4 patients with AC disruption and middle-third clavicle fracture. Three of the 4 patients had type IV AC separation; all 3 were treated, 2 acutely and 1 chronically, with open reduction of the AC and CC joints; 2 of these patients had CC screw fixation only after reduction, and the third had 2 Steinmann pins placed across the AC joint without CC screw fixation. All hardware was removed after 12 weeks. The fourth patient had a type II AC dislocation and was treated with closed reduction of the clavicle with no intervention for the AC joint. None of the clavicle fractures in this series were treated with internal fixation. All patients had full and pain-free ROM at 1- to 3-year follow-up.

Juhn and Simonian³ reported on a case of type VI separation with greenstick midshaft clavicle fracture in a hockey player seen 7 days after injury. The patient described some tingling in the upper extremity and had shoulder pain on initial presentation but was noted to have minimal displacement of both the AC joint and the midshaft clavicle fracture. Both injuries were treated nonsurgically with good outcome, and the patient returned to full activity (including hockey) within 14 weeks after injury.

Lancourt⁴ described the case of a patient with a type V AC dislocation and a displaced midshaft clavicle fracture. The AC joint was treated with Steinmann pin fixation, and the clavicle fracture was treated nonoperatively. The author cited high complication rates of plate fixation for clavicle fractures as the reason for not performing the additional procedure. The pins were removed 8 weeks after surgery. At 3-year follow-up, the patient had good radiographic and clinical outcome.

Yeh and colleagues⁶ described a patient who sustained a displaced midshaft clavicle fracture and a type IV AC dislocation in a fall from a horse. The patient underwent ORIF of the clavicle fracture with plate fixation. After the procedure, the AC joint was still unstable intraoperatively, and the AC and CC ligaments were reconstructed with semitendinosus allograft. The patient had full and painless ROM at 1-year follow-up.

The present case report serves as a reminder to obtain adequate shoulder radiographs when evaluating “just another clavicle fracture.” The radiographs should include a good axillary view to ensure there is not an associated AC dislocation. Increasingly, some authors have been advocating internal fixation for clavicle fractures, with reports of improved functional outcomes, improved cosmesis, and increased union rates.² Indications for operative fixation include shortening and 100% displacement,⁸ and relative indications include open fractures.¹ Operative fixation is perhaps more important for younger, athletic, and manual-labor populations. The trend in treatment of clavicle fractures toward operative fixation lends itself well to ORIF of the AC and CC joints; hence, a modern treatment for this rarely described combination injury should include internal plate fixation of the clavicle in addition to CC fixation. This additional procedure requires little extra time and energy in an operative scenario already requiring anesthesia, with easy insertion of the CC screw through the clavicle plate. Use of a CC screw obviates any potential risks associated with use of allograft tissue, and there is no anticipated difficulty with screw removal at 12 weeks.

Alternative options for AC stability include CC reconstruction with ligamentous allograft, ligamentous autograft, or suture/tightrope techniques. A noted advantage of these alternative techniques is less need to return to the operating room for the hardware removal that is recommended with CC screw fixation. However, these procedures potentially increase surgical exposure and operating time. In addition, screw fixation minimizes the possibility of donor-site morbidity from autograft transfers and potential complications from allograft tissue.

Hook plate fixation of the AC joint has also been described. In a recent case report of a similar injury pattern, plate fixation of the clavicle with simultaneous hook plate fixation of the AC joint was described.⁹ The patient did well but required removal of hardware of the hook plate and the clavicle plate 1 and 3 years after surgery, respectively. Although screw fixation is biomechanically stronger, debate persists about the clinical importance of this increase in strength.¹ In the setting of plate fixation for the clavicle, these alternative AC fixations would require technique adjustments, including length of grafts and/or sutures, and raise concerns regarding interaction of the metal with the fixation material.

Critical evaluation of our technique revealed a lucency larger than the screw (Figure 5). However, the screw was not clinically loose at removal. This potential complication, in combination with the bent screw (Figure 4) before removal, highlights the concern for screw breakage with this technique, given the increased construct stiffness caused by the added plate.

Conclusion

As in the other reports mentioned, our patient had an excellent clinical and radiographic outcome. It could be inferred that, if fixation for isolated clavicle fractures demonstrates improved function, better outcomes would be seen for higher-energy fractures associated with AC dislocation. Given the current trend toward surgical fixation for certain clavicle fractures, we recommend that clavicle fractures associated with type IV AC dislocation be treated with ORIF of both injuries.

A common cause for total hip arthroplasty (THA) revision is joint instability.^1,2 The reported incidence of dislocation in primary THA ranges from 0.4% to 5.8%,^3-5 but this rate increases after revision surgery.^1,3-8 Use of large-diameter femoral heads has been proposed to decrease the risks for instability and to improve impingement-free range of motion (ROM).

The biomechanical rationale for using large-diameter femoral heads is that they must travel farther before subluxation or dislocation occurs (jump distance). Despite these benefits, there were initial concerns that catastrophic failure and high levels of volumetric wear would occur if these heads were used with conventional polyethylene liners. These concerns led to the development of alternative bearing surfaces, particularly metal-on-metal bearings, which offered theoretical benefits of large-diameter articulations that improved stability while purportedly being highly wear-resistant.^9-11 However, concerns about adverse local soft-tissue reactions and high blood concentrations of metal ions tempered the initial enthusiasm for metal bearings.^12-16 Fortunately, highly cross-linked polyethylene and fourth-generation ceramic bearing surfaces, with improved toughness and better wear properties, may allow use of large-diameter heads without the need for metal-on-metal bearings.^17,18

In this article, we review the concepts and principles behind use of large-diameter ceramic or cobalt-chromium femoral heads on polyethylene-bearing surfaces in THA with particular attention to biomechanics, early concerns about polyethylene wear and rim fractures, recent improvements in material properties of polyethylene and ceramic bearings, dislocation rates, and clinical and functional outcomes.

Definitions

For this review, we define large-diameter femoral heads as having diameters of 36 mm or more and conventional or small-diameter femoral heads as having diameters between 22 and 32 mm.

Biomechanics

Head–Neck Ratio, Impingement-Free ROM, and Jump Distance

Several implant design principles have been proposed to reduce the risks for impingement and dislocation. Of these, large femoral head diameters have been extensively studied.^19,20 It is well known that impingement of the femoral neck on the cup edge promotes edge loading and higher wear rates. In addition, impingement increases the tendency of the head to sublux from the acetabulum. One strategy for avoiding this component-to-component impingement is to increase the head–neck ratio (HNR), the ratio of the femoral head to the neck diameter. Biomechanically, increased HNRs lead to delayed contact between the femoral neck and the acetabular liner.^21,22 Therefore, with large femoral heads, which have large HNRs, impingement occurs later and at larger ROMs—compared with small-diameter femoral heads, which have lower HNRs and are more prone to early impingement and subluxation (Figure 1).^23-26

In a cadaveric study of 6 hips, Bartz and colleagues²³ reported a significantly higher preimpingement ROM when the prosthetic head size increased from 22 mm to 28 mm (P < .05). They found a change from prosthetic to osseous impingement when the head size increased from 22 mm to 32 mm. Similar results were observed in a computer simulation model by Cinotti and colleagues,²⁷ who demonstrated that increasing the femoral head size from 28 mm to 38 mm resulted in a 5° improvement in ROM. However, the largest gains were observed when the heads with the smallest diameters were upsized; ROM improved only marginally when femoral head size was further increased from 32 mm to 38 mm. The primary reason for the lack of expected improvement in ROM with head sizes of more than 32 mm is often bone-on-bone impingement. Burroughs and colleagues²⁸ demonstrated that the 38-mm and 44-mm heads virtually eliminated component-to-component impingement except in extremes of external rotation. However, there were no differences in ROM between 38-mm and 44-mm heads because of osseous impingement. In addition, large heads are less likely to sublux or dislocate, as they need to travel farther before reaching the edge of the acetabular cup before dislocation. This is known as the jump distance, and it corresponds to the depth of the acetabular shell, which in turn equates with the radius of the femoral head (Figures 2A, 2B).  For this reason, the larger the femoral head diameter, the farther the jump distance and, correspondingly, the lower the risk for dislocation.²⁹

Elevated liners historically were used to increase the jump distance for dislocation.³⁰ These liners, however, can increase impingement at the extremes of motion.³¹ Some of these problems can be avoided with use of larger heads, which have increased jump distances without additional risks for impingement. Moreover, large heads create a suction effect that provides passive resistance to dislocation.³² With head diameters beyond 38 mm, impingement-free ROM often plateaus. However, the jump distance required for dislocations to occur continues to increase as femoral head diameters increase in size. Thus, patients may experience fewer motion benefits but continue to benefit from overall stability with femoral head sizes increasing beyond 38 mm.

Current evidence suggests there may be substantial benefits toward improved stability from increasing head diameters from 22 mm to 38 mm because of the increase in jump distances and improvements in prosthetic impingement-free ROM. However, there may be little gain in ROM from increasing the head diameters beyond these dimensions because of the potential risks of bony impingement. Nevertheless, there may be some additional benefits toward stability from improvement in jump distances with incremental head sizes
beyond 38 mm.^29,33,34

Finite Element Analysis Studies

Finite element analysis of large-diameter heads in THA has shown that, at optimal cup inclination (45°), most stresses occur on the articular surface of the liner. However, these stresses remain well below the yield strength of the polyethylene liners.²⁹ With increasing abduction angles, the stress concentration increases substantially because of the decreased contact surface area. At these angles, the point of maximum contact moves toward the rim of the polyethylene liner, which can lead to rim fractures or failure of locking mechanisms.^29,35,36

Early Concerns With Large-Diameter Femoral Heads: Wear, Liner Failure, and Fracture of Ceramic Components

Use of small-diameter femoral heads started with the first report by Charnley³⁷ of “low frictional torque arthroplasty.” Charnley initially considered a 41.5-mm femoral head, but he thought it would increase risks for acetabular loosening from high frictional torque generated by the large head, and he switched to a small-diameter (22.5 mm) design. One of the tradeoffs with smaller diameter heads was decreased jump height in addition to increased linear wear.

Large femoral heads used with cemented polyethylene acetabular components historically have been associated with increased rates of volumetric wear but low rates of linear wear, which potentially may increase the risk for osteolysis.^38-40 However, newer highly cross-linked polyethylene liners have shown improved in vitro and in vivo volumetric wear characteristics and potentially lower linear wear rates compared with earlier designs (Table 1).^28,41-43

Another concern about earlier generations of large femoral heads was the risk for catastrophic liner failure on conventional polyethylene. This was originally reported by Berry and colleagues,⁴⁷ who described wear-through and failure in patients with thin (< 5 mm) acetabular cups. However, these concerns have been largely addressed by the development of highly cross-linked polyethylene, which has improved wear characteristics and fatigue resistance.⁴⁸

Recent Improvements in Material Properties of Polyethylene and Ceramic Bearings

The development of highly cross-linked polyethylene and fourth-generation ceramics has renewed interest in large-diameter bearings in THA. These bearing surfaces improve wear, enhance material properties, and have superior oxidation resistance.^42,48-53

We now briefly describe the methods used to improve the material properties of polyethylene and ceramics. Studies have shown that increasing the radiation dose (up to 200 kGy)  increases cross-linking and causes an inverse exponential decrease in polyethylene wear.^28,41,48-51 However, increasing radiation doses also increases production of free radicals, which diminish the material strength of these polyethylenes. The  current generation of highly cross-linked polyethylene liners is produced through a variety of manufacturing strategies to improve cross-linking and reduce wear. These strategies include differential radiation doses (50-100 kGy), techniques (electron beam, radiation), and thermal treatments (melting, annealing). Moreover, to enhance the material properties and reduce the incidence of rim cracking and delamination, authors have proposed using vitamin E supplementation to minimize the amount of subsurface oxidation that occurs as an inevitable consequence of free radical formation during fabrication.^54,55  A terminal sterilization process (eg, gas plasma, ethylene oxide, or gamma sterilization in nitrogen) is needed to make commercial, highly cross-linked polyethylene.^52,53

Fourth-generation ceramics manufactured with nano-sized yttria-stabilized tetragonal zirconia particles in a stable alumina matrix have more fracture toughness and improved wear characteristics.^54,55 In addition, oxide additives (eg, chromium oxide, strontium oxide) improve hardness and dissipate energy by deflecting cracks to prevent their propagation.⁵⁶ Moreover, the smaller grain sizes of fourth-generation ceramic bearings compared with third-generation designs (0.8 µm vs 1-5 µm) cause less disruption of the fluid film layer, which ultimately results in improved wear performance.⁵⁷

Multiple studies have found reduced wear rates with metal and ceramic large heads coupled with highly cross-linked polyethylene-bearings (Table 2).^17,41,50,58 Bragdon and colleagues,⁵⁸ using radiostereometric analysis in 25 patients, found no significant differences in mean head penetration rates between 36-mm and 28-mm cobalt-chromium (Co-Cr) heads articulating with highly cross-linked polyethylene cups at a mean follow-up of 3 years (0.035 mm/y vs 0.046 mm/y; P = .11). Geller and colleagues,⁶⁴ in their study of 42 patients with large-diameter (> 32 mm) Co-Cr femoral heads, found low mean (SD) linear wear rates of 0.06 (0.41) mm/y at a mean follow-up of 3 years. D’Antonio and colleagues,⁶⁵ in a multicenter study, reported low average linear wear (0.015 mm/y) and volumetric wear (12.1 mm³/y) over 5 years using sequentially annealed cross-linked polyethylene. In vitro reports suggest that large-diameter ceramic heads may have lower wear properties than Co-Cr heads do. Galvin and colleagues,⁶⁶ in an in vitro hip simulator study, found that large-diameter ceramic heads on highly cross-linked ultrahigh-molecular-weight polyethylene had 40% reductions in steady-state wear rates compared with Co-Cr heads on highly cross-linked bearings (4.7 vs 8.1 mm³/million cycles; P < 0.01).

Dislocation Rates

Several patient, surgeon, and implant factors affect the rate of dislocations after THA. Multiple implant options utilize the biomechanical advantage that large-diameter heads have in improving stability. Various alternatives include use of constrained tripolar heads, dual-mobility bearings, and conventional large-diameter heads with standard liners.^67-69

Large-Diameter Heads

Despite the biomechanical advantages of large-diameter metal-on-polyethylene bearings, prior studies have questioned use of these bearings because of risks for increased wear and rim failures. However, the improved wear properties of highly cross-linked polyethylene, elaborated earlier, have led to a reappraisal of this option (Table 2).^4,70 Howie and colleagues,⁷¹ in a randomized control trial of 644 patients, also found significantly lower rates of dislocation after primary THA with 36-mm heads compared with 28-mm heads (1.3% vs 5.4%; P = .012); in addition, fewer dislocations occurred with 36-mm heads than with 28-mm heads (4.9% vs 12.2%; P = .27) in a series of 44 patients in revision settings. Similarly, in a study conducted with 39,271 Medicare patients between 1998 and 2007, Malkani and colleagues⁷² found a decrease in the dislocation rate, from 4.21% to 2.14%, with use of large-diameter femoral heads. These results have been confirmed by several other authors.^34,66,73,74 Similar results were observed in 65,992 patients in the Australian National Joint Replacement Registry by Conroy and colleagues,⁷⁵ who reported a significant decrease in the risk for dislocation with large heads (≥ 30 mm) compared with 22-mm heads (relative risk, 1.0 vs 3.1; P ≤ .001).

Few studies have analyzed the role of large-diameter femoral heads in the presence of compromised soft tissues around the hip. Kung and Ries,⁷⁶ evaluating the influence of large-diameter heads in the presence and absence of a deficient abductor mechanism, demonstrated statistically significant reductions in rates of dislocation after 230 revision THAs when the abductor mechanism was intact with use of 36-mm heads compared with 28-mm heads (12.7% vs 0%; P = .015). With abductor deficiency, though, the positive effect of large heads in reducing dislocation rates was substantially reduced and was similar to that of small heads (P = .74).⁷⁶

Large heads considerably improve overall stability and lower dislocation rates in THA. With the development of newer ceramics and highly cross-linked polyethylenes, the wear rates reported in multiple studies appear to be less concerning.

Constrained Tripolar Heads

Tripolar heads have been proposed as treatment options for improving stability in patients with chronic and recurrent instability after THA. The tripolar implant consists of a metal head that snap-fits into a polyethylene liner with a polished Co-Cr backing. This bipolar head articulates with a polyethylene bearing that is press-fitted onto a metal acetabular shell and constrained by a metal ring snapped to the outer polyethylene bearing. The bipolar component behaves as a large-diameter femoral head, and the metal ring provides additional restraint, further improving stability.

Williams and colleagues⁷⁷ performed a systematic review and reported on the outcomes of constrained tripolar liners in 1199 hips at a mean follow-up of 4 years (range, 2-10 years). The mean dislocation rate was 10%, and the mean rate of revision surgery unrelated to instability was 4%. In a study of 43 hips at a mean follow-up of 4 years (range, 2-9 years), Zywiel and colleagues⁷⁸ reported on the clinical and radiographic outcomes of tripolar constrained liners. Their study group had a mean Harris Hip Score (HHS) of 82 points (range, 38-100 points) and overall survival of 91%, with no evidence of radiographic loosening during follow-up. Despite the improvements in stability with constrained tripolar liners, some authors have reported multiple mechanisms of failure with these devices.^79-81 In a study of 43 failed constrained tripolar liners with a mean time to failure of about 2 years, Guyen and colleagues⁷⁹ identified 5 different failure modes (types 1-5) involving all 4 interfaces in these components.

Encouraging outcomes have been reported at midterm follow-up with tripolar constrained liners. However, concerns about failure at the interfaces suggest that use of these components should be restricted to patients with deficient abductor mechanisms or neuromuscular compromise, low-demand elderly patients, and salvage cases of recurrent dislocations.⁷⁹

Dual-Mobility Bearings

For more than 20 years, different dual-mobility bearings have been used for difficult acetabular reconstructive scenarios and prevention of instability.^82,83 Dual-mobility cups provide constructs that snap-fit a small-diameter femoral head within a large polyethylene insert that articulates with a fixed metal shell. This effectively increases the functional head diameter.

Various authors have reported excellent survivorship rates (92%-99%) and low dislocation rates for these bearings at 5- to 10-year follow-up.^82,84-90 Philippot and colleagues,⁸⁶ in a recent study of 438 hips with dual-mobility cups, reported excellent survivorship (96%) and no early or late instability within a 15-year follow-up. Bouchet and colleagues⁶⁹ compared dual-mobility bearings (105 hips) with conventional metal-on-polythene bearings (108 hips) and found significantly (P < .05) lower dislocation rates for the dual-mobility implants at a minimum 1-year follow-up. The French Society of Orthopaedics and Traumatology performed a multicenter analysis of 3473 hips with dual-mobility cups implanted in France between January 1998 and December 2003.⁸⁷ During a mean follow-up of 7 years (range, 5-11 years), there were 15 dislocations (0.43%), 14 of which occurred early, within 3 months of implantation (0.4%). Aseptic implant survivorship was 95% at 10-year follow-up.

Use of these bearings has recently increased in the United States. Short-term and midterm follow-up data show low rates of dislocation and wear. Long-term data are to come.

Clinical and Functional Outcomes of Large-Diameter Femoral Heads

There is a paucity of long-term outcomes data on use of large-diameter heads with highly cross-linked polyethylene bearings. Short-term and midterm clinical results appear to be excellent, with low rates of wear, osteolysis, and aseptic loosening.^{28,41,73,89-92}

Plate and colleagues⁹¹ compared the effects of large-diameter (≥ 36 mm) and small-diameter (26 mm, 28 mm) metal heads on highly cross-linked polyethylene bearings. At a mean follow-up of 5 years (range, 4-8.4 years), the large-head cohort had a mean HHS of 90 points (range, 50-100 points) and no dislocations or radiographic evidence of stem or cup loosening. Similarly, Meftah and colleagues⁹³ reported 100% stem survivorship and excellent clinical outcomes—a mean Western Ontario and McMaster Universities Arthritis Index (WOMAC) score of 30 points—for 72 hips with use of large ceramic heads (≥ 32 mm) on highly cross-linked polyethylene at a mean follow-up of 3 years. Gagala and colleagues⁹⁴ reported excellent clinical and radiographic outcomes in 50 hips (18 ceramic on ceramic, 32 ceramic on polyethylene; 36-mm heads) at a mean follow-up of 3.5 years. Mean HHS was 94 points, and there was no evidence of liner fractures, aseptic loosening, or osteolysis.

In summary, large-diameter femoral heads in THA have become increasingly popular because of improvements in the material properties and wear characteristics of highly cross-linked polyethylene and fourth-generation ceramics. Despite the potential advantages of large heads in preventing dislocations, the basic surgical tenets of placing the acetabular component in appropriate alignment remain firmly established. Implants with functionally large heads (eg, dual-mobility bearings, constrained tripolar liners) may play an important role in patients at high risk for dislocation—particularly elderly patients with poor neuromuscular muscle coordination or deficient abductors, trauma patients, and patients with prior dislocations. Short-term and midterm results are excellent; rates of wear, aseptic loosening, and osteolysis are low. However, long-term outcomes data are needed to support widespread use of large heads in younger and more active patients.

A common cause for total hip arthroplasty (THA) revision is joint instability.^1,2 The reported incidence of dislocation in primary THA ranges from 0.4% to 5.8%,^3-5 but this rate increases after revision surgery.^1,3-8 Use of large-diameter femoral heads has been proposed to decrease the risks for instability and to improve impingement-free range of motion (ROM).

The biomechanical rationale for using large-diameter femoral heads is that they must travel farther before subluxation or dislocation occurs (jump distance). Despite these benefits, there were initial concerns that catastrophic failure and high levels of volumetric wear would occur if these heads were used with conventional polyethylene liners. These concerns led to the development of alternative bearing surfaces, particularly metal-on-metal bearings, which offered theoretical benefits of large-diameter articulations that improved stability while purportedly being highly wear-resistant.^9-11 However, concerns about adverse local soft-tissue reactions and high blood concentrations of metal ions tempered the initial enthusiasm for metal bearings.^12-16 Fortunately, highly cross-linked polyethylene and fourth-generation ceramic bearing surfaces, with improved toughness and better wear properties, may allow use of large-diameter heads without the need for metal-on-metal bearings.^17,18

In this article, we review the concepts and principles behind use of large-diameter ceramic or cobalt-chromium femoral heads on polyethylene-bearing surfaces in THA with particular attention to biomechanics, early concerns about polyethylene wear and rim fractures, recent improvements in material properties of polyethylene and ceramic bearings, dislocation rates, and clinical and functional outcomes.

Definitions

For this review, we define large-diameter femoral heads as having diameters of 36 mm or more and conventional or small-diameter femoral heads as having diameters between 22 and 32 mm.

Biomechanics

Head–Neck Ratio, Impingement-Free ROM, and Jump Distance

Several implant design principles have been proposed to reduce the risks for impingement and dislocation. Of these, large femoral head diameters have been extensively studied.^19,20 It is well known that impingement of the femoral neck on the cup edge promotes edge loading and higher wear rates. In addition, impingement increases the tendency of the head to sublux from the acetabulum. One strategy for avoiding this component-to-component impingement is to increase the head–neck ratio (HNR), the ratio of the femoral head to the neck diameter. Biomechanically, increased HNRs lead to delayed contact between the femoral neck and the acetabular liner.^21,22 Therefore, with large femoral heads, which have large HNRs, impingement occurs later and at larger ROMs—compared with small-diameter femoral heads, which have lower HNRs and are more prone to early impingement and subluxation (Figure 1).^23-26

In a cadaveric study of 6 hips, Bartz and colleagues²³ reported a significantly higher preimpingement ROM when the prosthetic head size increased from 22 mm to 28 mm (P < .05). They found a change from prosthetic to osseous impingement when the head size increased from 22 mm to 32 mm. Similar results were observed in a computer simulation model by Cinotti and colleagues,²⁷ who demonstrated that increasing the femoral head size from 28 mm to 38 mm resulted in a 5° improvement in ROM. However, the largest gains were observed when the heads with the smallest diameters were upsized; ROM improved only marginally when femoral head size was further increased from 32 mm to 38 mm. The primary reason for the lack of expected improvement in ROM with head sizes of more than 32 mm is often bone-on-bone impingement. Burroughs and colleagues²⁸ demonstrated that the 38-mm and 44-mm heads virtually eliminated component-to-component impingement except in extremes of external rotation. However, there were no differences in ROM between 38-mm and 44-mm heads because of osseous impingement. In addition, large heads are less likely to sublux or dislocate, as they need to travel farther before reaching the edge of the acetabular cup before dislocation. This is known as the jump distance, and it corresponds to the depth of the acetabular shell, which in turn equates with the radius of the femoral head (Figures 2A, 2B).  For this reason, the larger the femoral head diameter, the farther the jump distance and, correspondingly, the lower the risk for dislocation.²⁹

Elevated liners historically were used to increase the jump distance for dislocation.³⁰ These liners, however, can increase impingement at the extremes of motion.³¹ Some of these problems can be avoided with use of larger heads, which have increased jump distances without additional risks for impingement. Moreover, large heads create a suction effect that provides passive resistance to dislocation.³² With head diameters beyond 38 mm, impingement-free ROM often plateaus. However, the jump distance required for dislocations to occur continues to increase as femoral head diameters increase in size. Thus, patients may experience fewer motion benefits but continue to benefit from overall stability with femoral head sizes increasing beyond 38 mm.

Current evidence suggests there may be substantial benefits toward improved stability from increasing head diameters from 22 mm to 38 mm because of the increase in jump distances and improvements in prosthetic impingement-free ROM. However, there may be little gain in ROM from increasing the head diameters beyond these dimensions because of the potential risks of bony impingement. Nevertheless, there may be some additional benefits toward stability from improvement in jump distances with incremental head sizes
beyond 38 mm.^29,33,34

Finite Element Analysis Studies

Finite element analysis of large-diameter heads in THA has shown that, at optimal cup inclination (45°), most stresses occur on the articular surface of the liner. However, these stresses remain well below the yield strength of the polyethylene liners.²⁹ With increasing abduction angles, the stress concentration increases substantially because of the decreased contact surface area. At these angles, the point of maximum contact moves toward the rim of the polyethylene liner, which can lead to rim fractures or failure of locking mechanisms.^29,35,36

Early Concerns With Large-Diameter Femoral Heads: Wear, Liner Failure, and Fracture of Ceramic Components

Use of small-diameter femoral heads started with the first report by Charnley³⁷ of “low frictional torque arthroplasty.” Charnley initially considered a 41.5-mm femoral head, but he thought it would increase risks for acetabular loosening from high frictional torque generated by the large head, and he switched to a small-diameter (22.5 mm) design. One of the tradeoffs with smaller diameter heads was decreased jump height in addition to increased linear wear.

Large femoral heads used with cemented polyethylene acetabular components historically have been associated with increased rates of volumetric wear but low rates of linear wear, which potentially may increase the risk for osteolysis.^38-40 However, newer highly cross-linked polyethylene liners have shown improved in vitro and in vivo volumetric wear characteristics and potentially lower linear wear rates compared with earlier designs (Table 1).^28,41-43

Another concern about earlier generations of large femoral heads was the risk for catastrophic liner failure on conventional polyethylene. This was originally reported by Berry and colleagues,⁴⁷ who described wear-through and failure in patients with thin (< 5 mm) acetabular cups. However, these concerns have been largely addressed by the development of highly cross-linked polyethylene, which has improved wear characteristics and fatigue resistance.⁴⁸

Recent Improvements in Material Properties of Polyethylene and Ceramic Bearings

The development of highly cross-linked polyethylene and fourth-generation ceramics has renewed interest in large-diameter bearings in THA. These bearing surfaces improve wear, enhance material properties, and have superior oxidation resistance.^42,48-53

We now briefly describe the methods used to improve the material properties of polyethylene and ceramics. Studies have shown that increasing the radiation dose (up to 200 kGy)  increases cross-linking and causes an inverse exponential decrease in polyethylene wear.^28,41,48-51 However, increasing radiation doses also increases production of free radicals, which diminish the material strength of these polyethylenes. The  current generation of highly cross-linked polyethylene liners is produced through a variety of manufacturing strategies to improve cross-linking and reduce wear. These strategies include differential radiation doses (50-100 kGy), techniques (electron beam, radiation), and thermal treatments (melting, annealing). Moreover, to enhance the material properties and reduce the incidence of rim cracking and delamination, authors have proposed using vitamin E supplementation to minimize the amount of subsurface oxidation that occurs as an inevitable consequence of free radical formation during fabrication.^54,55  A terminal sterilization process (eg, gas plasma, ethylene oxide, or gamma sterilization in nitrogen) is needed to make commercial, highly cross-linked polyethylene.^52,53

Fourth-generation ceramics manufactured with nano-sized yttria-stabilized tetragonal zirconia particles in a stable alumina matrix have more fracture toughness and improved wear characteristics.^54,55 In addition, oxide additives (eg, chromium oxide, strontium oxide) improve hardness and dissipate energy by deflecting cracks to prevent their propagation.⁵⁶ Moreover, the smaller grain sizes of fourth-generation ceramic bearings compared with third-generation designs (0.8 µm vs 1-5 µm) cause less disruption of the fluid film layer, which ultimately results in improved wear performance.⁵⁷

Multiple studies have found reduced wear rates with metal and ceramic large heads coupled with highly cross-linked polyethylene-bearings (Table 2).^17,41,50,58 Bragdon and colleagues,⁵⁸ using radiostereometric analysis in 25 patients, found no significant differences in mean head penetration rates between 36-mm and 28-mm cobalt-chromium (Co-Cr) heads articulating with highly cross-linked polyethylene cups at a mean follow-up of 3 years (0.035 mm/y vs 0.046 mm/y; P = .11). Geller and colleagues,⁶⁴ in their study of 42 patients with large-diameter (> 32 mm) Co-Cr femoral heads, found low mean (SD) linear wear rates of 0.06 (0.41) mm/y at a mean follow-up of 3 years. D’Antonio and colleagues,⁶⁵ in a multicenter study, reported low average linear wear (0.015 mm/y) and volumetric wear (12.1 mm³/y) over 5 years using sequentially annealed cross-linked polyethylene. In vitro reports suggest that large-diameter ceramic heads may have lower wear properties than Co-Cr heads do. Galvin and colleagues,⁶⁶ in an in vitro hip simulator study, found that large-diameter ceramic heads on highly cross-linked ultrahigh-molecular-weight polyethylene had 40% reductions in steady-state wear rates compared with Co-Cr heads on highly cross-linked bearings (4.7 vs 8.1 mm³/million cycles; P < 0.01).

Dislocation Rates

Several patient, surgeon, and implant factors affect the rate of dislocations after THA. Multiple implant options utilize the biomechanical advantage that large-diameter heads have in improving stability. Various alternatives include use of constrained tripolar heads, dual-mobility bearings, and conventional large-diameter heads with standard liners.^67-69

Large-Diameter Heads

Despite the biomechanical advantages of large-diameter metal-on-polyethylene bearings, prior studies have questioned use of these bearings because of risks for increased wear and rim failures. However, the improved wear properties of highly cross-linked polyethylene, elaborated earlier, have led to a reappraisal of this option (Table 2).^4,70 Howie and colleagues,⁷¹ in a randomized control trial of 644 patients, also found significantly lower rates of dislocation after primary THA with 36-mm heads compared with 28-mm heads (1.3% vs 5.4%; P = .012); in addition, fewer dislocations occurred with 36-mm heads than with 28-mm heads (4.9% vs 12.2%; P = .27) in a series of 44 patients in revision settings. Similarly, in a study conducted with 39,271 Medicare patients between 1998 and 2007, Malkani and colleagues⁷² found a decrease in the dislocation rate, from 4.21% to 2.14%, with use of large-diameter femoral heads. These results have been confirmed by several other authors.^34,66,73,74 Similar results were observed in 65,992 patients in the Australian National Joint Replacement Registry by Conroy and colleagues,⁷⁵ who reported a significant decrease in the risk for dislocation with large heads (≥ 30 mm) compared with 22-mm heads (relative risk, 1.0 vs 3.1; P ≤ .001).

Few studies have analyzed the role of large-diameter femoral heads in the presence of compromised soft tissues around the hip. Kung and Ries,⁷⁶ evaluating the influence of large-diameter heads in the presence and absence of a deficient abductor mechanism, demonstrated statistically significant reductions in rates of dislocation after 230 revision THAs when the abductor mechanism was intact with use of 36-mm heads compared with 28-mm heads (12.7% vs 0%; P = .015). With abductor deficiency, though, the positive effect of large heads in reducing dislocation rates was substantially reduced and was similar to that of small heads (P = .74).⁷⁶

Large heads considerably improve overall stability and lower dislocation rates in THA. With the development of newer ceramics and highly cross-linked polyethylenes, the wear rates reported in multiple studies appear to be less concerning.

Constrained Tripolar Heads

Tripolar heads have been proposed as treatment options for improving stability in patients with chronic and recurrent instability after THA. The tripolar implant consists of a metal head that snap-fits into a polyethylene liner with a polished Co-Cr backing. This bipolar head articulates with a polyethylene bearing that is press-fitted onto a metal acetabular shell and constrained by a metal ring snapped to the outer polyethylene bearing. The bipolar component behaves as a large-diameter femoral head, and the metal ring provides additional restraint, further improving stability.

Williams and colleagues⁷⁷ performed a systematic review and reported on the outcomes of constrained tripolar liners in 1199 hips at a mean follow-up of 4 years (range, 2-10 years). The mean dislocation rate was 10%, and the mean rate of revision surgery unrelated to instability was 4%. In a study of 43 hips at a mean follow-up of 4 years (range, 2-9 years), Zywiel and colleagues⁷⁸ reported on the clinical and radiographic outcomes of tripolar constrained liners. Their study group had a mean Harris Hip Score (HHS) of 82 points (range, 38-100 points) and overall survival of 91%, with no evidence of radiographic loosening during follow-up. Despite the improvements in stability with constrained tripolar liners, some authors have reported multiple mechanisms of failure with these devices.^79-81 In a study of 43 failed constrained tripolar liners with a mean time to failure of about 2 years, Guyen and colleagues⁷⁹ identified 5 different failure modes (types 1-5) involving all 4 interfaces in these components.

Encouraging outcomes have been reported at midterm follow-up with tripolar constrained liners. However, concerns about failure at the interfaces suggest that use of these components should be restricted to patients with deficient abductor mechanisms or neuromuscular compromise, low-demand elderly patients, and salvage cases of recurrent dislocations.⁷⁹

Dual-Mobility Bearings

For more than 20 years, different dual-mobility bearings have been used for difficult acetabular reconstructive scenarios and prevention of instability.^82,83 Dual-mobility cups provide constructs that snap-fit a small-diameter femoral head within a large polyethylene insert that articulates with a fixed metal shell. This effectively increases the functional head diameter.

Various authors have reported excellent survivorship rates (92%-99%) and low dislocation rates for these bearings at 5- to 10-year follow-up.^82,84-90 Philippot and colleagues,⁸⁶ in a recent study of 438 hips with dual-mobility cups, reported excellent survivorship (96%) and no early or late instability within a 15-year follow-up. Bouchet and colleagues⁶⁹ compared dual-mobility bearings (105 hips) with conventional metal-on-polythene bearings (108 hips) and found significantly (P < .05) lower dislocation rates for the dual-mobility implants at a minimum 1-year follow-up. The French Society of Orthopaedics and Traumatology performed a multicenter analysis of 3473 hips with dual-mobility cups implanted in France between January 1998 and December 2003.⁸⁷ During a mean follow-up of 7 years (range, 5-11 years), there were 15 dislocations (0.43%), 14 of which occurred early, within 3 months of implantation (0.4%). Aseptic implant survivorship was 95% at 10-year follow-up.

Use of these bearings has recently increased in the United States. Short-term and midterm follow-up data show low rates of dislocation and wear. Long-term data are to come.

Clinical and Functional Outcomes of Large-Diameter Femoral Heads

There is a paucity of long-term outcomes data on use of large-diameter heads with highly cross-linked polyethylene bearings. Short-term and midterm clinical results appear to be excellent, with low rates of wear, osteolysis, and aseptic loosening.^{28,41,73,89-92}

Plate and colleagues⁹¹ compared the effects of large-diameter (≥ 36 mm) and small-diameter (26 mm, 28 mm) metal heads on highly cross-linked polyethylene bearings. At a mean follow-up of 5 years (range, 4-8.4 years), the large-head cohort had a mean HHS of 90 points (range, 50-100 points) and no dislocations or radiographic evidence of stem or cup loosening. Similarly, Meftah and colleagues⁹³ reported 100% stem survivorship and excellent clinical outcomes—a mean Western Ontario and McMaster Universities Arthritis Index (WOMAC) score of 30 points—for 72 hips with use of large ceramic heads (≥ 32 mm) on highly cross-linked polyethylene at a mean follow-up of 3 years. Gagala and colleagues⁹⁴ reported excellent clinical and radiographic outcomes in 50 hips (18 ceramic on ceramic, 32 ceramic on polyethylene; 36-mm heads) at a mean follow-up of 3.5 years. Mean HHS was 94 points, and there was no evidence of liner fractures, aseptic loosening, or osteolysis.

In summary, large-diameter femoral heads in THA have become increasingly popular because of improvements in the material properties and wear characteristics of highly cross-linked polyethylene and fourth-generation ceramics. Despite the potential advantages of large heads in preventing dislocations, the basic surgical tenets of placing the acetabular component in appropriate alignment remain firmly established. Implants with functionally large heads (eg, dual-mobility bearings, constrained tripolar liners) may play an important role in patients at high risk for dislocation—particularly elderly patients with poor neuromuscular muscle coordination or deficient abductors, trauma patients, and patients with prior dislocations. Short-term and midterm results are excellent; rates of wear, aseptic loosening, and osteolysis are low. However, long-term outcomes data are needed to support widespread use of large heads in younger and more active patients.

A common cause for total hip arthroplasty (THA) revision is joint instability.^1,2 The reported incidence of dislocation in primary THA ranges from 0.4% to 5.8%,^3-5 but this rate increases after revision surgery.^1,3-8 Use of large-diameter femoral heads has been proposed to decrease the risks for instability and to improve impingement-free range of motion (ROM).

The biomechanical rationale for using large-diameter femoral heads is that they must travel farther before subluxation or dislocation occurs (jump distance). Despite these benefits, there were initial concerns that catastrophic failure and high levels of volumetric wear would occur if these heads were used with conventional polyethylene liners. These concerns led to the development of alternative bearing surfaces, particularly metal-on-metal bearings, which offered theoretical benefits of large-diameter articulations that improved stability while purportedly being highly wear-resistant.^9-11 However, concerns about adverse local soft-tissue reactions and high blood concentrations of metal ions tempered the initial enthusiasm for metal bearings.^12-16 Fortunately, highly cross-linked polyethylene and fourth-generation ceramic bearing surfaces, with improved toughness and better wear properties, may allow use of large-diameter heads without the need for metal-on-metal bearings.^17,18

In this article, we review the concepts and principles behind use of large-diameter ceramic or cobalt-chromium femoral heads on polyethylene-bearing surfaces in THA with particular attention to biomechanics, early concerns about polyethylene wear and rim fractures, recent improvements in material properties of polyethylene and ceramic bearings, dislocation rates, and clinical and functional outcomes.

Definitions

For this review, we define large-diameter femoral heads as having diameters of 36 mm or more and conventional or small-diameter femoral heads as having diameters between 22 and 32 mm.

Biomechanics

Head–Neck Ratio, Impingement-Free ROM, and Jump Distance

Several implant design principles have been proposed to reduce the risks for impingement and dislocation. Of these, large femoral head diameters have been extensively studied.^19,20 It is well known that impingement of the femoral neck on the cup edge promotes edge loading and higher wear rates. In addition, impingement increases the tendency of the head to sublux from the acetabulum. One strategy for avoiding this component-to-component impingement is to increase the head–neck ratio (HNR), the ratio of the femoral head to the neck diameter. Biomechanically, increased HNRs lead to delayed contact between the femoral neck and the acetabular liner.^21,22 Therefore, with large femoral heads, which have large HNRs, impingement occurs later and at larger ROMs—compared with small-diameter femoral heads, which have lower HNRs and are more prone to early impingement and subluxation (Figure 1).^23-26

In a cadaveric study of 6 hips, Bartz and colleagues²³ reported a significantly higher preimpingement ROM when the prosthetic head size increased from 22 mm to 28 mm (P < .05). They found a change from prosthetic to osseous impingement when the head size increased from 22 mm to 32 mm. Similar results were observed in a computer simulation model by Cinotti and colleagues,²⁷ who demonstrated that increasing the femoral head size from 28 mm to 38 mm resulted in a 5° improvement in ROM. However, the largest gains were observed when the heads with the smallest diameters were upsized; ROM improved only marginally when femoral head size was further increased from 32 mm to 38 mm. The primary reason for the lack of expected improvement in ROM with head sizes of more than 32 mm is often bone-on-bone impingement. Burroughs and colleagues²⁸ demonstrated that the 38-mm and 44-mm heads virtually eliminated component-to-component impingement except in extremes of external rotation. However, there were no differences in ROM between 38-mm and 44-mm heads because of osseous impingement. In addition, large heads are less likely to sublux or dislocate, as they need to travel farther before reaching the edge of the acetabular cup before dislocation. This is known as the jump distance, and it corresponds to the depth of the acetabular shell, which in turn equates with the radius of the femoral head (Figures 2A, 2B).  For this reason, the larger the femoral head diameter, the farther the jump distance and, correspondingly, the lower the risk for dislocation.²⁹

Elevated liners historically were used to increase the jump distance for dislocation.³⁰ These liners, however, can increase impingement at the extremes of motion.³¹ Some of these problems can be avoided with use of larger heads, which have increased jump distances without additional risks for impingement. Moreover, large heads create a suction effect that provides passive resistance to dislocation.³² With head diameters beyond 38 mm, impingement-free ROM often plateaus. However, the jump distance required for dislocations to occur continues to increase as femoral head diameters increase in size. Thus, patients may experience fewer motion benefits but continue to benefit from overall stability with femoral head sizes increasing beyond 38 mm.

Current evidence suggests there may be substantial benefits toward improved stability from increasing head diameters from 22 mm to 38 mm because of the increase in jump distances and improvements in prosthetic impingement-free ROM. However, there may be little gain in ROM from increasing the head diameters beyond these dimensions because of the potential risks of bony impingement. Nevertheless, there may be some additional benefits toward stability from improvement in jump distances with incremental head sizes
beyond 38 mm.^29,33,34

Finite Element Analysis Studies

Finite element analysis of large-diameter heads in THA has shown that, at optimal cup inclination (45°), most stresses occur on the articular surface of the liner. However, these stresses remain well below the yield strength of the polyethylene liners.²⁹ With increasing abduction angles, the stress concentration increases substantially because of the decreased contact surface area. At these angles, the point of maximum contact moves toward the rim of the polyethylene liner, which can lead to rim fractures or failure of locking mechanisms.^29,35,36

Early Concerns With Large-Diameter Femoral Heads: Wear, Liner Failure, and Fracture of Ceramic Components

Use of small-diameter femoral heads started with the first report by Charnley³⁷ of “low frictional torque arthroplasty.” Charnley initially considered a 41.5-mm femoral head, but he thought it would increase risks for acetabular loosening from high frictional torque generated by the large head, and he switched to a small-diameter (22.5 mm) design. One of the tradeoffs with smaller diameter heads was decreased jump height in addition to increased linear wear.

Large femoral heads used with cemented polyethylene acetabular components historically have been associated with increased rates of volumetric wear but low rates of linear wear, which potentially may increase the risk for osteolysis.^38-40 However, newer highly cross-linked polyethylene liners have shown improved in vitro and in vivo volumetric wear characteristics and potentially lower linear wear rates compared with earlier designs (Table 1).^28,41-43

Another concern about earlier generations of large femoral heads was the risk for catastrophic liner failure on conventional polyethylene. This was originally reported by Berry and colleagues,⁴⁷ who described wear-through and failure in patients with thin (< 5 mm) acetabular cups. However, these concerns have been largely addressed by the development of highly cross-linked polyethylene, which has improved wear characteristics and fatigue resistance.⁴⁸

Recent Improvements in Material Properties of Polyethylene and Ceramic Bearings

The development of highly cross-linked polyethylene and fourth-generation ceramics has renewed interest in large-diameter bearings in THA. These bearing surfaces improve wear, enhance material properties, and have superior oxidation resistance.^42,48-53

We now briefly describe the methods used to improve the material properties of polyethylene and ceramics. Studies have shown that increasing the radiation dose (up to 200 kGy)  increases cross-linking and causes an inverse exponential decrease in polyethylene wear.^28,41,48-51 However, increasing radiation doses also increases production of free radicals, which diminish the material strength of these polyethylenes. The  current generation of highly cross-linked polyethylene liners is produced through a variety of manufacturing strategies to improve cross-linking and reduce wear. These strategies include differential radiation doses (50-100 kGy), techniques (electron beam, radiation), and thermal treatments (melting, annealing). Moreover, to enhance the material properties and reduce the incidence of rim cracking and delamination, authors have proposed using vitamin E supplementation to minimize the amount of subsurface oxidation that occurs as an inevitable consequence of free radical formation during fabrication.^54,55  A terminal sterilization process (eg, gas plasma, ethylene oxide, or gamma sterilization in nitrogen) is needed to make commercial, highly cross-linked polyethylene.^52,53

Fourth-generation ceramics manufactured with nano-sized yttria-stabilized tetragonal zirconia particles in a stable alumina matrix have more fracture toughness and improved wear characteristics.^54,55 In addition, oxide additives (eg, chromium oxide, strontium oxide) improve hardness and dissipate energy by deflecting cracks to prevent their propagation.⁵⁶ Moreover, the smaller grain sizes of fourth-generation ceramic bearings compared with third-generation designs (0.8 µm vs 1-5 µm) cause less disruption of the fluid film layer, which ultimately results in improved wear performance.⁵⁷

Multiple studies have found reduced wear rates with metal and ceramic large heads coupled with highly cross-linked polyethylene-bearings (Table 2).^17,41,50,58 Bragdon and colleagues,⁵⁸ using radiostereometric analysis in 25 patients, found no significant differences in mean head penetration rates between 36-mm and 28-mm cobalt-chromium (Co-Cr) heads articulating with highly cross-linked polyethylene cups at a mean follow-up of 3 years (0.035 mm/y vs 0.046 mm/y; P = .11). Geller and colleagues,⁶⁴ in their study of 42 patients with large-diameter (> 32 mm) Co-Cr femoral heads, found low mean (SD) linear wear rates of 0.06 (0.41) mm/y at a mean follow-up of 3 years. D’Antonio and colleagues,⁶⁵ in a multicenter study, reported low average linear wear (0.015 mm/y) and volumetric wear (12.1 mm³/y) over 5 years using sequentially annealed cross-linked polyethylene. In vitro reports suggest that large-diameter ceramic heads may have lower wear properties than Co-Cr heads do. Galvin and colleagues,⁶⁶ in an in vitro hip simulator study, found that large-diameter ceramic heads on highly cross-linked ultrahigh-molecular-weight polyethylene had 40% reductions in steady-state wear rates compared with Co-Cr heads on highly cross-linked bearings (4.7 vs 8.1 mm³/million cycles; P < 0.01).

Dislocation Rates

Several patient, surgeon, and implant factors affect the rate of dislocations after THA. Multiple implant options utilize the biomechanical advantage that large-diameter heads have in improving stability. Various alternatives include use of constrained tripolar heads, dual-mobility bearings, and conventional large-diameter heads with standard liners.^67-69

Large-Diameter Heads

Despite the biomechanical advantages of large-diameter metal-on-polyethylene bearings, prior studies have questioned use of these bearings because of risks for increased wear and rim failures. However, the improved wear properties of highly cross-linked polyethylene, elaborated earlier, have led to a reappraisal of this option (Table 2).^4,70 Howie and colleagues,⁷¹ in a randomized control trial of 644 patients, also found significantly lower rates of dislocation after primary THA with 36-mm heads compared with 28-mm heads (1.3% vs 5.4%; P = .012); in addition, fewer dislocations occurred with 36-mm heads than with 28-mm heads (4.9% vs 12.2%; P = .27) in a series of 44 patients in revision settings. Similarly, in a study conducted with 39,271 Medicare patients between 1998 and 2007, Malkani and colleagues⁷² found a decrease in the dislocation rate, from 4.21% to 2.14%, with use of large-diameter femoral heads. These results have been confirmed by several other authors.^34,66,73,74 Similar results were observed in 65,992 patients in the Australian National Joint Replacement Registry by Conroy and colleagues,⁷⁵ who reported a significant decrease in the risk for dislocation with large heads (≥ 30 mm) compared with 22-mm heads (relative risk, 1.0 vs 3.1; P ≤ .001).

Few studies have analyzed the role of large-diameter femoral heads in the presence of compromised soft tissues around the hip. Kung and Ries,⁷⁶ evaluating the influence of large-diameter heads in the presence and absence of a deficient abductor mechanism, demonstrated statistically significant reductions in rates of dislocation after 230 revision THAs when the abductor mechanism was intact with use of 36-mm heads compared with 28-mm heads (12.7% vs 0%; P = .015). With abductor deficiency, though, the positive effect of large heads in reducing dislocation rates was substantially reduced and was similar to that of small heads (P = .74).⁷⁶

Large heads considerably improve overall stability and lower dislocation rates in THA. With the development of newer ceramics and highly cross-linked polyethylenes, the wear rates reported in multiple studies appear to be less concerning.

Constrained Tripolar Heads

Tripolar heads have been proposed as treatment options for improving stability in patients with chronic and recurrent instability after THA. The tripolar implant consists of a metal head that snap-fits into a polyethylene liner with a polished Co-Cr backing. This bipolar head articulates with a polyethylene bearing that is press-fitted onto a metal acetabular shell and constrained by a metal ring snapped to the outer polyethylene bearing. The bipolar component behaves as a large-diameter femoral head, and the metal ring provides additional restraint, further improving stability.

Williams and colleagues⁷⁷ performed a systematic review and reported on the outcomes of constrained tripolar liners in 1199 hips at a mean follow-up of 4 years (range, 2-10 years). The mean dislocation rate was 10%, and the mean rate of revision surgery unrelated to instability was 4%. In a study of 43 hips at a mean follow-up of 4 years (range, 2-9 years), Zywiel and colleagues⁷⁸ reported on the clinical and radiographic outcomes of tripolar constrained liners. Their study group had a mean Harris Hip Score (HHS) of 82 points (range, 38-100 points) and overall survival of 91%, with no evidence of radiographic loosening during follow-up. Despite the improvements in stability with constrained tripolar liners, some authors have reported multiple mechanisms of failure with these devices.^79-81 In a study of 43 failed constrained tripolar liners with a mean time to failure of about 2 years, Guyen and colleagues⁷⁹ identified 5 different failure modes (types 1-5) involving all 4 interfaces in these components.

Encouraging outcomes have been reported at midterm follow-up with tripolar constrained liners. However, concerns about failure at the interfaces suggest that use of these components should be restricted to patients with deficient abductor mechanisms or neuromuscular compromise, low-demand elderly patients, and salvage cases of recurrent dislocations.⁷⁹

Dual-Mobility Bearings

For more than 20 years, different dual-mobility bearings have been used for difficult acetabular reconstructive scenarios and prevention of instability.^82,83 Dual-mobility cups provide constructs that snap-fit a small-diameter femoral head within a large polyethylene insert that articulates with a fixed metal shell. This effectively increases the functional head diameter.

Various authors have reported excellent survivorship rates (92%-99%) and low dislocation rates for these bearings at 5- to 10-year follow-up.^82,84-90 Philippot and colleagues,⁸⁶ in a recent study of 438 hips with dual-mobility cups, reported excellent survivorship (96%) and no early or late instability within a 15-year follow-up. Bouchet and colleagues⁶⁹ compared dual-mobility bearings (105 hips) with conventional metal-on-polythene bearings (108 hips) and found significantly (P < .05) lower dislocation rates for the dual-mobility implants at a minimum 1-year follow-up. The French Society of Orthopaedics and Traumatology performed a multicenter analysis of 3473 hips with dual-mobility cups implanted in France between January 1998 and December 2003.⁸⁷ During a mean follow-up of 7 years (range, 5-11 years), there were 15 dislocations (0.43%), 14 of which occurred early, within 3 months of implantation (0.4%). Aseptic implant survivorship was 95% at 10-year follow-up.

Use of these bearings has recently increased in the United States. Short-term and midterm follow-up data show low rates of dislocation and wear. Long-term data are to come.

Clinical and Functional Outcomes of Large-Diameter Femoral Heads

There is a paucity of long-term outcomes data on use of large-diameter heads with highly cross-linked polyethylene bearings. Short-term and midterm clinical results appear to be excellent, with low rates of wear, osteolysis, and aseptic loosening.^{28,41,73,89-92}

Plate and colleagues⁹¹ compared the effects of large-diameter (≥ 36 mm) and small-diameter (26 mm, 28 mm) metal heads on highly cross-linked polyethylene bearings. At a mean follow-up of 5 years (range, 4-8.4 years), the large-head cohort had a mean HHS of 90 points (range, 50-100 points) and no dislocations or radiographic evidence of stem or cup loosening. Similarly, Meftah and colleagues⁹³ reported 100% stem survivorship and excellent clinical outcomes—a mean Western Ontario and McMaster Universities Arthritis Index (WOMAC) score of 30 points—for 72 hips with use of large ceramic heads (≥ 32 mm) on highly cross-linked polyethylene at a mean follow-up of 3 years. Gagala and colleagues⁹⁴ reported excellent clinical and radiographic outcomes in 50 hips (18 ceramic on ceramic, 32 ceramic on polyethylene; 36-mm heads) at a mean follow-up of 3.5 years. Mean HHS was 94 points, and there was no evidence of liner fractures, aseptic loosening, or osteolysis.

In summary, large-diameter femoral heads in THA have become increasingly popular because of improvements in the material properties and wear characteristics of highly cross-linked polyethylene and fourth-generation ceramics. Despite the potential advantages of large heads in preventing dislocations, the basic surgical tenets of placing the acetabular component in appropriate alignment remain firmly established. Implants with functionally large heads (eg, dual-mobility bearings, constrained tripolar liners) may play an important role in patients at high risk for dislocation—particularly elderly patients with poor neuromuscular muscle coordination or deficient abductors, trauma patients, and patients with prior dislocations. Short-term and midterm results are excellent; rates of wear, aseptic loosening, and osteolysis are low. However, long-term outcomes data are needed to support widespread use of large heads in younger and more active patients.