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Fact or Fiction: Is Orthopedic Follow-Up Worse for Patients Who Sustain Penetrating Trauma?
There is a paucity of literature on how mechanism of injury may be associated with patient retention. Failure to attend outpatient clinics is a form of noncompliance and a major obstacle to safe, effective, and efficient healthcare delivery. Noncompliance may lead to increased patient morbidity and carries substantial financial implications for the healthcare system.1,2 In addition to these direct patient and healthcare issues, loss of patient follow-up or the belief of potential loss of follow-up of penetrating trauma patients may also significantly affect research studies. These patients often may be excluded from studies, even if they might otherwise meet inclusion criteria, because of concerns that they are unlikely to follow-up after leaving hospital. Is this myth or fact? To validate or to disprove this selection bias, we conducted a study in which we retrospectively evaluated long bone fractures caused by either penetrating or blunt trauma.
Methods
After obtaining Institutional Review Board approval for this study, we used the trauma database of an American College of Surgeons–verified level I trauma center in a major Midwest metropolitan area to compile a list of all cases of long bone fractures caused by penetrating trauma between 2006 and 2009 (N = 132). Gunshot wounds were the mechanism of injury for the penetrating trauma. We also compiled a list of control cases—long bone fractures caused by blunt trauma in patients demographically matched to the penetrating group patients on sex, race, and age (N = 104) (Table). 
We retrospectively performed chart reviews to obtain patient follow-up data 3, 6, 9, and 12 months after injury from penetrating or blunt trauma. Patients scheduled to return on an as-needed basis were considered to have completed follow-up. The 2 groups were also statistically compared with respect to sex, race, age, surgical fixation, and history of tobacco, alcohol, or drug use.
SAS/STAT Version 8 (SAS Institute) was used to test the equality of survival functions (patient retention) for the penetrating and blunt trauma patient groups. A similar comparison was made for the categories of sex, race, and age. Pearson χ2 test was used to compare the 12-month survival rates of the 2 treatment groups across sex and race. Binary logistic regression was used to compare the 12-month survival rates of the 2 treatment groups removing the effect of age. A comparison of the frequency distributions of the 2 treatment groups with respect to alcohol use, tobacco use, drug use, and surgical intervention was also performed. Power analysis showed power of more than 90% in detecting at least a 20% difference in the follow-up rates between the penetrating and blunt trauma groups based on our sample size.
Results
There was no statistically significant difference (P = .736) between the penetrating and blunt trauma patients in terms of follow-up within 1 year after injury. At 1 year, 103 (78%) of the 132 penetrating trauma patients and 83 (80%) of the 104 blunt trauma patients were lost to follow-up (Figure). 
Discussion
Trauma outcomes historically have been difficult to determine because of lack of patient follow-up. In a simulation series, Zelle and colleagues3 found that the turning point from significant to nonsignificant varied from 15% to 75% loss of follow-up, thus compromising the validity of a study. They and others have emphasized the importance of establishing research protocols to minimize follow-up loss and eliminate reporting bias, ensure randomization, and report accurate outcomes.3-7
Very few have tried to investigate factors associated with failure to follow up after trauma.1,2,4 Leukhardt and colleagues4 evaluated the medical services that trauma patients follow up with most often. Orthopedic surgery had the largest portion of follow-up visits (37%), followed by the trauma surgery clinic and the emergency department (19% each). The authors also found that penetrating trauma patients were more likely to follow up, though more than 90% of the authors’ patients had blunt trauma. Although our study did not support their finding, it does call into question the commonly held belief that penetrating trauma patients are less likely to follow up, as our study found no difference in follow-up between penetrating and blunt trauma patients.
One of the most interesting findings in this retrospective study is that almost 80% of patients were lost to follow-up regardless of mechanism of injury. Most prospective studies try to reduce loss to follow-up to below 10%. This difference may be attributable to having a dedicated research team and the resources required to ensure follow-up of research patients to improve follow-up beyond baseline values. At our institution, 13 prospective studies (most multicenter) are currently enrolling patients, and the worst loss to follow-up has been 30%. The majority of the studies have loss to follow-up of 15% or less. This low rate represents a significant difference from the 80% “baseline” clinical loss to follow-up for the blunt and penetrating trauma patients treated at our institution, based on the findings of this study. We have been improving follow-up by having dedicated research coordinators call patients to remind them of their appointments (all clinic patients who are not research patients receive a recorded reminder); by having the hospital agree that research patients can be seen without charge (by the facility or the physician), which helps defray costs to the patient; and by excluding patients the principal investigator thinks are unlikely to follow up. Patients unlikely to follow up are routinely excluded by all centers that enroll in prospective studies. Although it is difficult to quantitate, this factor may play a large role in reducing loss to follow-up. Penetrating trauma patients historically routinely biased investigators to exclude them from studies, regardless of whether being considered unlikely to follow-up was an exclusion criterion. Our study results suggest this bias may not be valid.
Our study evaluated the role of mechanism of injury, penetrating or blunt trauma, and the respective orthopedic follow-up. There was no statistically significant difference in the 1-year follow-up rate based on the mechanism of injury. Our study was conducted with a well-matched control group that eliminated potential confounding variables, such as sex, race, age, tobacco use, and alcohol use. Although the prevalence of drug use was higher in the penetrating trauma group, patient retention seemed not to be affected by it. Surprisingly, patient loss to follow-up was extremely high (almost 80%) for both the penetrating and blunt trauma patient groups at the 1-year mark. Our findings call into question the commonly accepted theory that patients with penetrating injuries are less likely to follow up, at least in an academic level I trauma center population. We suggest that the commonly held belief that penetrating trauma patients are less likely to follow up may not be valid and that, when prospective studies are designed, it may not be appropriate to exclude penetrating trauma patients on this basis alone.
The primary limitation of this study is that it was performed at a single institution. Eighty-five percent of blunt trauma patients and 93% of penetrating trauma patients live in the county that is predominantly served by our institution, and electronic medical records from all major hospitals in the metropolitan area are linked, suggesting that the large majority of patients lost to follow-up do not seek further medical care, at least not from local facilities in our metropolitan area. A prospective multicenter study is being designed to help us gain a better understanding of the variables that affect musculoskeletal trauma patient follow-up and learn interventional strategies that can be used to improve patient retention.
Dr. Turner is an Orthopedic Surgeon, Rockwood Clinic, Spokane, Washington. Dr. Turner was a resident at the time the article was written. Dr. Hiatt is an Anesthesia Resident, University of Louisville Department of Anesthesiology and Perioperative Medicine, Louisville, Kentucky. Dr. Mullis is Chief of the Orthopaedic Trauma Service, Eskenazi Health, and Professor & Program Director, Indiana University School of Medicine Department of Orthopaedics, Indianapolis, Indiana.
Acknowledgments: This study was first reported in a poster presentation at the annual meeting of the Orthopaedic Trauma Association, October 2013, Phoenix, Arizona.
The authors gratefully acknowledge and thank Jyoti Sarkar, PhD, for his assistance with statistical analysis and manuscript preparation.
Am J Orthop. 2016;45(6):E331-E334. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.
1. Sciberras N, Gregori A, Holt G. The ethical and practical challenges of patient noncompliance in orthopaedic surgery. J Bone Joint Surg Am. 2013;95(9):e61.
2. Sharma H, Crane E, Syme B, Foxworthy M. Non-compliance in orthopaedic surgery and its ethical challenges. Orthop Trauma. 2007;21(4):310-313.
3. Zelle BA, Bhandari M, Sanchez AI, Probst C, Pape HC. Loss of follow-up in orthopaedic trauma: is 80% follow-up still acceptable? J Orthop Trauma. 2013;27(3):177-181.
4. Leukhardt WH, Golob JF, McCoy AM, Fadlalla AM, Malangoni MA, Claridge JA. Follow-up disparities after trauma: a real problem for outcomes research. Am J Surg. 2010;199(3):348-352.
5. Shumaker SA, Dugan E, Bowen DJ. Enhancing adherence in randomized controlled clinical trials. Control Clin Trials. 2000;21(5 suppl):226S-232S.
6. Smith JS, Watts HG. Methods for locating missing patients for the purpose of long-term clinical studies. J Bone Joint Surg Am. 1998;80(3):431-438.
7. Sprague S, Leece P, Bhandari M, Tornetta P 3rd, Schemitsch E, Swiontkowski MF; S.P.R.I.N.T. Investigators. Limiting loss to follow-up in a multicenter randomized trial in orthopedic surgery. Control Clin Trials. 2003;24(6):719-725.
There is a paucity of literature on how mechanism of injury may be associated with patient retention. Failure to attend outpatient clinics is a form of noncompliance and a major obstacle to safe, effective, and efficient healthcare delivery. Noncompliance may lead to increased patient morbidity and carries substantial financial implications for the healthcare system.1,2 In addition to these direct patient and healthcare issues, loss of patient follow-up or the belief of potential loss of follow-up of penetrating trauma patients may also significantly affect research studies. These patients often may be excluded from studies, even if they might otherwise meet inclusion criteria, because of concerns that they are unlikely to follow-up after leaving hospital. Is this myth or fact? To validate or to disprove this selection bias, we conducted a study in which we retrospectively evaluated long bone fractures caused by either penetrating or blunt trauma.
Methods
After obtaining Institutional Review Board approval for this study, we used the trauma database of an American College of Surgeons–verified level I trauma center in a major Midwest metropolitan area to compile a list of all cases of long bone fractures caused by penetrating trauma between 2006 and 2009 (N = 132). Gunshot wounds were the mechanism of injury for the penetrating trauma. We also compiled a list of control cases—long bone fractures caused by blunt trauma in patients demographically matched to the penetrating group patients on sex, race, and age (N = 104) (Table).
We retrospectively performed chart reviews to obtain patient follow-up data 3, 6, 9, and 12 months after injury from penetrating or blunt trauma. Patients scheduled to return on an as-needed basis were considered to have completed follow-up. The 2 groups were also statistically compared with respect to sex, race, age, surgical fixation, and history of tobacco, alcohol, or drug use.
SAS/STAT Version 8 (SAS Institute) was used to test the equality of survival functions (patient retention) for the penetrating and blunt trauma patient groups. A similar comparison was made for the categories of sex, race, and age. Pearson χ2 test was used to compare the 12-month survival rates of the 2 treatment groups across sex and race. Binary logistic regression was used to compare the 12-month survival rates of the 2 treatment groups removing the effect of age. A comparison of the frequency distributions of the 2 treatment groups with respect to alcohol use, tobacco use, drug use, and surgical intervention was also performed. Power analysis showed power of more than 90% in detecting at least a 20% difference in the follow-up rates between the penetrating and blunt trauma groups based on our sample size.
Results
There was no statistically significant difference (P = .736) between the penetrating and blunt trauma patients in terms of follow-up within 1 year after injury. At 1 year, 103 (78%) of the 132 penetrating trauma patients and 83 (80%) of the 104 blunt trauma patients were lost to follow-up (Figure).
Discussion
Trauma outcomes historically have been difficult to determine because of lack of patient follow-up. In a simulation series, Zelle and colleagues3 found that the turning point from significant to nonsignificant varied from 15% to 75% loss of follow-up, thus compromising the validity of a study. They and others have emphasized the importance of establishing research protocols to minimize follow-up loss and eliminate reporting bias, ensure randomization, and report accurate outcomes.3-7
Very few have tried to investigate factors associated with failure to follow up after trauma.1,2,4 Leukhardt and colleagues4 evaluated the medical services that trauma patients follow up with most often. Orthopedic surgery had the largest portion of follow-up visits (37%), followed by the trauma surgery clinic and the emergency department (19% each). The authors also found that penetrating trauma patients were more likely to follow up, though more than 90% of the authors’ patients had blunt trauma. Although our study did not support their finding, it does call into question the commonly held belief that penetrating trauma patients are less likely to follow up, as our study found no difference in follow-up between penetrating and blunt trauma patients.
One of the most interesting findings in this retrospective study is that almost 80% of patients were lost to follow-up regardless of mechanism of injury. Most prospective studies try to reduce loss to follow-up to below 10%. This difference may be attributable to having a dedicated research team and the resources required to ensure follow-up of research patients to improve follow-up beyond baseline values. At our institution, 13 prospective studies (most multicenter) are currently enrolling patients, and the worst loss to follow-up has been 30%. The majority of the studies have loss to follow-up of 15% or less. This low rate represents a significant difference from the 80% “baseline” clinical loss to follow-up for the blunt and penetrating trauma patients treated at our institution, based on the findings of this study. We have been improving follow-up by having dedicated research coordinators call patients to remind them of their appointments (all clinic patients who are not research patients receive a recorded reminder); by having the hospital agree that research patients can be seen without charge (by the facility or the physician), which helps defray costs to the patient; and by excluding patients the principal investigator thinks are unlikely to follow up. Patients unlikely to follow up are routinely excluded by all centers that enroll in prospective studies. Although it is difficult to quantitate, this factor may play a large role in reducing loss to follow-up. Penetrating trauma patients historically routinely biased investigators to exclude them from studies, regardless of whether being considered unlikely to follow-up was an exclusion criterion. Our study results suggest this bias may not be valid.
Our study evaluated the role of mechanism of injury, penetrating or blunt trauma, and the respective orthopedic follow-up. There was no statistically significant difference in the 1-year follow-up rate based on the mechanism of injury. Our study was conducted with a well-matched control group that eliminated potential confounding variables, such as sex, race, age, tobacco use, and alcohol use. Although the prevalence of drug use was higher in the penetrating trauma group, patient retention seemed not to be affected by it. Surprisingly, patient loss to follow-up was extremely high (almost 80%) for both the penetrating and blunt trauma patient groups at the 1-year mark. Our findings call into question the commonly accepted theory that patients with penetrating injuries are less likely to follow up, at least in an academic level I trauma center population. We suggest that the commonly held belief that penetrating trauma patients are less likely to follow up may not be valid and that, when prospective studies are designed, it may not be appropriate to exclude penetrating trauma patients on this basis alone.
The primary limitation of this study is that it was performed at a single institution. Eighty-five percent of blunt trauma patients and 93% of penetrating trauma patients live in the county that is predominantly served by our institution, and electronic medical records from all major hospitals in the metropolitan area are linked, suggesting that the large majority of patients lost to follow-up do not seek further medical care, at least not from local facilities in our metropolitan area. A prospective multicenter study is being designed to help us gain a better understanding of the variables that affect musculoskeletal trauma patient follow-up and learn interventional strategies that can be used to improve patient retention.
Dr. Turner is an Orthopedic Surgeon, Rockwood Clinic, Spokane, Washington. Dr. Turner was a resident at the time the article was written. Dr. Hiatt is an Anesthesia Resident, University of Louisville Department of Anesthesiology and Perioperative Medicine, Louisville, Kentucky. Dr. Mullis is Chief of the Orthopaedic Trauma Service, Eskenazi Health, and Professor & Program Director, Indiana University School of Medicine Department of Orthopaedics, Indianapolis, Indiana.
Acknowledgments: This study was first reported in a poster presentation at the annual meeting of the Orthopaedic Trauma Association, October 2013, Phoenix, Arizona.
The authors gratefully acknowledge and thank Jyoti Sarkar, PhD, for his assistance with statistical analysis and manuscript preparation.
Am J Orthop. 2016;45(6):E331-E334. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.
There is a paucity of literature on how mechanism of injury may be associated with patient retention. Failure to attend outpatient clinics is a form of noncompliance and a major obstacle to safe, effective, and efficient healthcare delivery. Noncompliance may lead to increased patient morbidity and carries substantial financial implications for the healthcare system.1,2 In addition to these direct patient and healthcare issues, loss of patient follow-up or the belief of potential loss of follow-up of penetrating trauma patients may also significantly affect research studies. These patients often may be excluded from studies, even if they might otherwise meet inclusion criteria, because of concerns that they are unlikely to follow-up after leaving hospital. Is this myth or fact? To validate or to disprove this selection bias, we conducted a study in which we retrospectively evaluated long bone fractures caused by either penetrating or blunt trauma.
Methods
After obtaining Institutional Review Board approval for this study, we used the trauma database of an American College of Surgeons–verified level I trauma center in a major Midwest metropolitan area to compile a list of all cases of long bone fractures caused by penetrating trauma between 2006 and 2009 (N = 132). Gunshot wounds were the mechanism of injury for the penetrating trauma. We also compiled a list of control cases—long bone fractures caused by blunt trauma in patients demographically matched to the penetrating group patients on sex, race, and age (N = 104) (Table).
We retrospectively performed chart reviews to obtain patient follow-up data 3, 6, 9, and 12 months after injury from penetrating or blunt trauma. Patients scheduled to return on an as-needed basis were considered to have completed follow-up. The 2 groups were also statistically compared with respect to sex, race, age, surgical fixation, and history of tobacco, alcohol, or drug use.
SAS/STAT Version 8 (SAS Institute) was used to test the equality of survival functions (patient retention) for the penetrating and blunt trauma patient groups. A similar comparison was made for the categories of sex, race, and age. Pearson χ2 test was used to compare the 12-month survival rates of the 2 treatment groups across sex and race. Binary logistic regression was used to compare the 12-month survival rates of the 2 treatment groups removing the effect of age. A comparison of the frequency distributions of the 2 treatment groups with respect to alcohol use, tobacco use, drug use, and surgical intervention was also performed. Power analysis showed power of more than 90% in detecting at least a 20% difference in the follow-up rates between the penetrating and blunt trauma groups based on our sample size.
Results
There was no statistically significant difference (P = .736) between the penetrating and blunt trauma patients in terms of follow-up within 1 year after injury. At 1 year, 103 (78%) of the 132 penetrating trauma patients and 83 (80%) of the 104 blunt trauma patients were lost to follow-up (Figure).
Discussion
Trauma outcomes historically have been difficult to determine because of lack of patient follow-up. In a simulation series, Zelle and colleagues3 found that the turning point from significant to nonsignificant varied from 15% to 75% loss of follow-up, thus compromising the validity of a study. They and others have emphasized the importance of establishing research protocols to minimize follow-up loss and eliminate reporting bias, ensure randomization, and report accurate outcomes.3-7
Very few have tried to investigate factors associated with failure to follow up after trauma.1,2,4 Leukhardt and colleagues4 evaluated the medical services that trauma patients follow up with most often. Orthopedic surgery had the largest portion of follow-up visits (37%), followed by the trauma surgery clinic and the emergency department (19% each). The authors also found that penetrating trauma patients were more likely to follow up, though more than 90% of the authors’ patients had blunt trauma. Although our study did not support their finding, it does call into question the commonly held belief that penetrating trauma patients are less likely to follow up, as our study found no difference in follow-up between penetrating and blunt trauma patients.
One of the most interesting findings in this retrospective study is that almost 80% of patients were lost to follow-up regardless of mechanism of injury. Most prospective studies try to reduce loss to follow-up to below 10%. This difference may be attributable to having a dedicated research team and the resources required to ensure follow-up of research patients to improve follow-up beyond baseline values. At our institution, 13 prospective studies (most multicenter) are currently enrolling patients, and the worst loss to follow-up has been 30%. The majority of the studies have loss to follow-up of 15% or less. This low rate represents a significant difference from the 80% “baseline” clinical loss to follow-up for the blunt and penetrating trauma patients treated at our institution, based on the findings of this study. We have been improving follow-up by having dedicated research coordinators call patients to remind them of their appointments (all clinic patients who are not research patients receive a recorded reminder); by having the hospital agree that research patients can be seen without charge (by the facility or the physician), which helps defray costs to the patient; and by excluding patients the principal investigator thinks are unlikely to follow up. Patients unlikely to follow up are routinely excluded by all centers that enroll in prospective studies. Although it is difficult to quantitate, this factor may play a large role in reducing loss to follow-up. Penetrating trauma patients historically routinely biased investigators to exclude them from studies, regardless of whether being considered unlikely to follow-up was an exclusion criterion. Our study results suggest this bias may not be valid.
Our study evaluated the role of mechanism of injury, penetrating or blunt trauma, and the respective orthopedic follow-up. There was no statistically significant difference in the 1-year follow-up rate based on the mechanism of injury. Our study was conducted with a well-matched control group that eliminated potential confounding variables, such as sex, race, age, tobacco use, and alcohol use. Although the prevalence of drug use was higher in the penetrating trauma group, patient retention seemed not to be affected by it. Surprisingly, patient loss to follow-up was extremely high (almost 80%) for both the penetrating and blunt trauma patient groups at the 1-year mark. Our findings call into question the commonly accepted theory that patients with penetrating injuries are less likely to follow up, at least in an academic level I trauma center population. We suggest that the commonly held belief that penetrating trauma patients are less likely to follow up may not be valid and that, when prospective studies are designed, it may not be appropriate to exclude penetrating trauma patients on this basis alone.
The primary limitation of this study is that it was performed at a single institution. Eighty-five percent of blunt trauma patients and 93% of penetrating trauma patients live in the county that is predominantly served by our institution, and electronic medical records from all major hospitals in the metropolitan area are linked, suggesting that the large majority of patients lost to follow-up do not seek further medical care, at least not from local facilities in our metropolitan area. A prospective multicenter study is being designed to help us gain a better understanding of the variables that affect musculoskeletal trauma patient follow-up and learn interventional strategies that can be used to improve patient retention.
Dr. Turner is an Orthopedic Surgeon, Rockwood Clinic, Spokane, Washington. Dr. Turner was a resident at the time the article was written. Dr. Hiatt is an Anesthesia Resident, University of Louisville Department of Anesthesiology and Perioperative Medicine, Louisville, Kentucky. Dr. Mullis is Chief of the Orthopaedic Trauma Service, Eskenazi Health, and Professor & Program Director, Indiana University School of Medicine Department of Orthopaedics, Indianapolis, Indiana.
Acknowledgments: This study was first reported in a poster presentation at the annual meeting of the Orthopaedic Trauma Association, October 2013, Phoenix, Arizona.
The authors gratefully acknowledge and thank Jyoti Sarkar, PhD, for his assistance with statistical analysis and manuscript preparation.
Am J Orthop. 2016;45(6):E331-E334. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.
1. Sciberras N, Gregori A, Holt G. The ethical and practical challenges of patient noncompliance in orthopaedic surgery. J Bone Joint Surg Am. 2013;95(9):e61.
2. Sharma H, Crane E, Syme B, Foxworthy M. Non-compliance in orthopaedic surgery and its ethical challenges. Orthop Trauma. 2007;21(4):310-313.
3. Zelle BA, Bhandari M, Sanchez AI, Probst C, Pape HC. Loss of follow-up in orthopaedic trauma: is 80% follow-up still acceptable? J Orthop Trauma. 2013;27(3):177-181.
4. Leukhardt WH, Golob JF, McCoy AM, Fadlalla AM, Malangoni MA, Claridge JA. Follow-up disparities after trauma: a real problem for outcomes research. Am J Surg. 2010;199(3):348-352.
5. Shumaker SA, Dugan E, Bowen DJ. Enhancing adherence in randomized controlled clinical trials. Control Clin Trials. 2000;21(5 suppl):226S-232S.
6. Smith JS, Watts HG. Methods for locating missing patients for the purpose of long-term clinical studies. J Bone Joint Surg Am. 1998;80(3):431-438.
7. Sprague S, Leece P, Bhandari M, Tornetta P 3rd, Schemitsch E, Swiontkowski MF; S.P.R.I.N.T. Investigators. Limiting loss to follow-up in a multicenter randomized trial in orthopedic surgery. Control Clin Trials. 2003;24(6):719-725.
1. Sciberras N, Gregori A, Holt G. The ethical and practical challenges of patient noncompliance in orthopaedic surgery. J Bone Joint Surg Am. 2013;95(9):e61.
2. Sharma H, Crane E, Syme B, Foxworthy M. Non-compliance in orthopaedic surgery and its ethical challenges. Orthop Trauma. 2007;21(4):310-313.
3. Zelle BA, Bhandari M, Sanchez AI, Probst C, Pape HC. Loss of follow-up in orthopaedic trauma: is 80% follow-up still acceptable? J Orthop Trauma. 2013;27(3):177-181.
4. Leukhardt WH, Golob JF, McCoy AM, Fadlalla AM, Malangoni MA, Claridge JA. Follow-up disparities after trauma: a real problem for outcomes research. Am J Surg. 2010;199(3):348-352.
5. Shumaker SA, Dugan E, Bowen DJ. Enhancing adherence in randomized controlled clinical trials. Control Clin Trials. 2000;21(5 suppl):226S-232S.
6. Smith JS, Watts HG. Methods for locating missing patients for the purpose of long-term clinical studies. J Bone Joint Surg Am. 1998;80(3):431-438.
7. Sprague S, Leece P, Bhandari M, Tornetta P 3rd, Schemitsch E, Swiontkowski MF; S.P.R.I.N.T. Investigators. Limiting loss to follow-up in a multicenter randomized trial in orthopedic surgery. Control Clin Trials. 2003;24(6):719-725.
