Muthana Sartawi, MD

ABSTRACT

The subvastus (SV) approach is a well-known muscle- and tendon-sparing approach for total knee arthroplasty (TKA), which has been shown in some studies to provide better outcomes in the visual analog pain score (VAS), knee range of motion (ROM), straight-leg raise, as well as faster rehabilitation, compared with the standard medial parapatellar (MP) approach. We previously described a new knee replacement technique known as the modified intervastus (MIV) approach. The MIV approach is a muscle- and tendon-sparing approach that is extensile and simple to perform. It may be used in the majority of complex primary cases and revisions. Here we describe the surgical technique for performing the MIV approach and provide functional outcome measures. A total of 127 patients (mean age, 66.75 years) underwent TKA using the MIV approach with 1-year follow-up. Clinical outcomes were assessed by recording both a VAS and knee ROM preoperatively, and again at several postoperative time points when the length of time required to ambulate independently (without assistive devices) was also measured. The VAS decreased significantly from the preoperative period (3.69 ± 2.22) to postoperative day 1 (3.17 ± 1.97) (P < .05). Although knee ROM decreased 1 week after surgery, the ROM increased by 6 weeks after surgery compared with the preoperative ROM, and the trend continued over the 1-year follow-up. One-third (33%) of patients were able to walk independently (without assistive devices) at 2 weeks and 78% at 8 weeks. The MIV approach to the knee is a muscle- and tendon-sparing approach that offers advantages over the SV approach and may be used for complex primary and revision total knee cases.

Continue to: Total knee arthroplasty... 

Total knee arthroplasty (TKA) is one of the most common orthopedic surgical procedures, with more than 600,000 TKAs performed annually in the United States, and by 2030 the number is expected to reach 3.48 million per year.¹Several approaches have been described for total TKA, and the medial parapatellar (MP) approach to the knee is considered the workhorse of total knee replacements. It is an extensile approach that is easy to perform but may delay active knee extension and straight-leg raise after surgery.²  Alternative approaches such as the subvastus (SV) and midvastus approaches to the knee (Figure 1A) typically allow a more rapid straight-leg raise but may be more challenging to perform and time-consuming in morbidly obese patients, muscular patients, and patients with severe deformities.³

The intervastus approach (Figure 1A) described by Jojima⁴ and others utilizes the interval between the quadriceps tendon and vastus medialis. Although it is a simple approach to perform that is extensile, it is not considered tendon-sparing since the vastus medialis inserts onto the medial aspect of the quadriceps tendon (Figure 2).⁵  Therefore, dissecting through this interval, without elevation of the vastus medialis (Figure 3A), damages the quadriceps tendon, and strangulation of the muscle occurs with repair of the arthrotomy site (Figure 3B).  This situation is even more likely in patients with a low-lying vastus medialis.⁶

The modified intervastus (MIV) approach described previously,⁷ may be used in the majority of patients undergoing TKA. The advantages of this approach include its extensile nature, similarities to an MP approach, and preservation of both the extensor mechanism and the vastus medialis, leading to a more rapid return to active knee extension than is traditionally observed.^2,7 The approach is simple to perform, easy to close, and is compatible with more extensile approaches such as a quadriceps snip if required in revision scenarios.⁷ However, functional outcomes of the MIV approach have not been quantified. It is unknown whether these outcomes will offer any advantages compared with the SV approach. Therefore, the objective of this study was to measure functional outcomes of the MIV approach and to compare the results with those previously published for the SV approach. We hypothesized that using the MIV approach for TKA surgery would lead to early straight-leg raise and increase in knee range of motion (ROM) postoperatively.

SURGICAL TECHNIQUE

The MIV approach preserves the quadriceps tendon and vastus medialis.⁷ After exposure of the vastus medialis muscle, the interval between the quadriceps tendon and vastus medialis is identified (Figure 4).  The fascia overlying the lateral edge of the vastus medialis is incised where it meets the quadriceps tendon (Figure 5).  The muscle is then bluntly elevated off the underlying capsule just enough to allow for a capsular repair later (Figure 6).  An arthrotomy is then performed from cephalad to caudal (Figure 7).  This interval may be extended proximally between the vastus intermedius and vastus medialis to expose the distal femur if needed. The closure is performed by repairing the capsule with absorbable suture (Figure 8A), and the vastus medialis fascia is repaired back to the medial edge of the quadriceps tendon, restoring the anatomy (Figure 8B).

Continue to: PATIENTS AND METHODS...

 

 

PATIENTS AND METHODS

A retrospective review of functional outcomes after TKA using the MIV approach was conducted; the study was approved by the University of Illinois Institutional Review Board. A total of 127 patients of mean age 66.75 years (range, 48–86 years) with primary osteoarthritis of the knee who were indicated for a total knee replacement with 1-year follow-up were included. The patient demographics are shown in Table 1.  All patients underwent TKA using the MIV approach described above by 2 experienced orthopedic surgeons at the same institution. Patients received spinal anesthesia and a periarticular pain block intraoperatively. A measured resection technique was used by 1 surgeon, and a gap-balancing technique by the other. Surgeon 1 used the Persona PS cemented knee system (Zimmer Biomet, and Surgeon 2 used the Sigma PS cemented knee system (Depuy). Patellar resurfacing was done in all cases. Patellar tracking was checked intraoperatively using the ‘no-touch’ technique, and the need for a lateral release was noted. Drains were removed on postoperative day 1. Oral opioids were given as needed. Intravenous antibiotics were continued for 24 hours. Oral anticoagulants were used for thromboembolism prophylaxis for 3 weeks. Patients were mobilized on the day of surgery with full weight-bearing under the supervision of an experienced physical therapist. Static and dynamic quadriceps exercises were started on the same day of surgery along with active knee ROM exercises. Pain score, extensor lag, ROM, walking ability, and complications were recorded in all patients.

Table 1. Patient Demographics

Total no. of patients		127
Gender	Male	44
	Female	83
Age (years)	Mean ± Standard deviation	66.75 ± 9.12
	Range	48 – 86
Weight (lb)	Mean ± Standard deviation	218.38 ± 54.47
	Range	125 – 364
BMI (kg/m2)	Mean ± Standard deviation	34.10 ± 7.22
	Range	21.1 – 62.5

The visual analog score (VAS) was obtained preoperatively and recorded on postoperative day 1. Patient walking distance with assistance was measured on the day of surgery, after surgery, and on the day of hospital discharge. Patients were assessed preoperatively and postoperatively at 1 week, 2 weeks, 6 weeks, 3 months, 6 months, and 1 year for knee ROM. A one-way ANOVA was conducted to compare the preoperative and postoperative day 1 VAS with significance set at P < .05 (OriginPro 2015, OriginLab Corporation). Differences in knee ROM between preoperative and postoperative follow-up periods (1 week, 2 weeks, 6 weeks, 3 months, 6 months, and 1 year) were identified using a 1-way ANOVA with a post hoc Tukey test. Significance was set at P < .05.

RESULTS

All patients were able to fully straight-leg raise and demonstrate functional knee ROM by postoperative day 1. The patella tracked centrally in all patients, and none required a lateral retinacular release. The majority of patients were discharged in the first 48 hours after surgery on oral narcotics. None required IV narcotics during their hospital stay or a blood transfusion. Two cases were complicated by severe knee skin blistering postoperatively due to a reaction to an adhesive dressing; one was complicated by skin necrosis leading to a flap reconstruction that became infected, requiring a 2-stage revision. A separate case had an acute postoperative infection that required irrigation and debridement with polyethylene exchange. After a 12-week course of antibiotics, the infection was eradicated. All patients reported a high satisfaction rate during their acute postoperative phase.

Postoperatively, all patients were able to walk on the day of surgery either independently or with some assistance. On the day of surgery, 10% of patients were able to walk >200 feet, and this increased to 65% of patients able to walk >200 feet on the day of discharge (compare Figure 9A and Figure 9B).  Within 2 weeks of surgery, 30% of patients could walk independently (without assistive devices), and this number increased to 78% by 8 weeks after surgery (Figure 10).

Pain assessed using the VAS was lower on postoperative day 1 (3.17 ± 1.97) than the preoperative score (3.69 ± 2.22, P< .05). Overall, knee ROM significantly increased during the follow-up after surgery. Initially, the ROM decreased 1 week after surgery (90.82 ± 10.28) compared with preoperative ROM (101.04 ± 19.48, P < .001) (Figure 10).  At 2 weeks after surgery, knee ROM returned to the preoperative value (100.70 ± 13.36). By 6 weeks after surgery, knee ROM was 17° greater than the preoperative ROM (118.45 ± 11.89, P < .001). Knee ROM remained stable at 3- and 6-month assessments, and showed further improvement by 1 year (126.62 ± 9.81, P < .001) compared with the preoperative state (Figure 10). The net improvement in knee ROM was 25° of increased knee flexion by 1 year.

Continue to: DISCUSSION...

 

 

DISCUSSION

TKA is a successful procedure that restores knee function with pain relief in osteoarthritis patients. The SV approach for TKA has better outcomes in terms of the VAS, ROM, straight-leg raise with faster rehabilitation compared with the standard MP approach;^8–12 however, it can be challenging and time-consuming when used in morbidly obese and muscular patients.³ The SV approach can also increase the risk of complications such as patellar tendon avulsion or medial collateral injury because of the difficulty in exposure specifically for knees with limited ROM.¹³ Here we introduce the MIV approach as an alternative to the SV approach, overcoming most of these difficulties.

With the prevalence of morbid obesity and the market demand for minimally invasive techniques, we believe the MIV approach represents a good approach for surgeons since it is easy to perform, does not require specialized instrumentation, and is a reproducible approach even on the most complex deformities. The minimal time added to ensure blunt elevation of the vastus medialis muscle and an anatomic repair of the underlying knee capsule and vastus medialis fascia to the medial edge of the quadriceps tendon allows restoration of the anatomy and a robust double-layered watertight seal closure with no strangulation of soft tissues. We believe this reproducible muscle- and tendon-sparing approach that allows gentle, soft tissue handling even in the most complex primary total knee cases may lead to less soft tissue swelling, and therefore, less postoperative pain resulting in an accelerated recovery.

The pain level in this group of patients was reduced after the MIV approach as indicated by the VAS. The VAS was significantly decreased on postoperative day 1 compared with the VAS recorded preoperatively (P < .05), indicating patients felt less pain on the day after surgery. The average VAS on postoperative day 1 from other studies for SV approach ranged from 2.1 to 5,^9,12,14–19 whereas our MIV approach value was 3.17. Periarticular blocks were available for this study group, and no peripheral nerve blocks were used. Some studies of the SV approach mention the use of peripheral nerve blocks, while others did not describe the method used for treatment or control of postoperative pain. The decreased reported pain levels and the observed increased knee ROM seen in the MIV and SV approach study groups might be attributable to the treatment of postoperative pain.

Patient ambulation also increased from the day of surgery to the day of discharge for the MIV approach. Only 10% of patients were able to walk with assistance >200 feet on the day of surgery; however, this percentage increased to 65% on the discharge day showing an excellent recovery of walking ability within 2 days of surgery. Mehta and colleagues²⁰reported that 95% of patients undergoing subvastus/midvastus approaches could walk >10 blocks at 6 months follow-up. For the MIV approach, 78% of patients were able to walk independently within 8 weeks of surgery.

Continue to: The MIV approach shows improvement...

 

 

The MIV approach shows improvement in functional outcomes in terms of knee ROM from preoperative to postoperative. Although knee ROM decreased significantly at postoperative week 1, which is most likely because of a peak in postoperative pain and swelling; the ROM started to increase significantly at postoperative week 6. After 1 year, the knee ROM increased by 25% compared with preoperative ROM for the MIV approach. We found the average knee ROM at postoperative 3 months using the MIV approach to be 120.4°. Knee ROM at postoperative 3 months using the SV approach reported by other studies ranged from 87.1° to 120°.^19,21–23 Similarly, after 1 year, the average ROM by MIV approach was 126.62°, whereas average knee ROM from other studies using the SV approach was 114.1°.^2,10,19,21 Achieving a knee ROM of 120° allows patients to return to their baseline function and perform activities of daily living without limitation. With the prevalence of knee osteoarthritis in the younger population, the need for increased knee ROM post-TKA becomes more important so patients can return to work and function at their baseline.

In addition to being both a muscle- and tendon-sparing approach, other advantages of the MIV approach are that it is simple to perform and gives similar exposure to the MP approach even in difficult primary cases. It is also as extensile as the medial parapatellar approach, and it can be converted to a quadriceps snip if required. There is also minimal, if any, muscle retraction preventing muscle injury that may be seen with some other muscle-sparing approaches to the knee, especially in more difficult primary total knee cases. Another advantage to this approach, as opposed to the other approaches to the knee described here, is that it allows a double-layered closure, decreasing the possibility of arthrotomy dehiscence. Because of this double-layered closure, there is no muscle strangulation with repair of the arthrotomy site as seen in some other approaches to the knee, and both vascularity and innervation to the vastus medialis are preserved.

One limitation of this study is that it is a retrospective analysis. Future studies of the consequences of using this approach need to include quantitative assessment of muscle function using electromyography or dynamometer measurements, utilization of any number of validated knee score systems to measure functional outcomes, and incorporation of a randomized controlled trial.

In summary, the new MIV approach is easy to perform and is compatible with more extensile approaches such as a quadriceps snip, if required in revision scenarios. The MIV approach preserves the extensor mechanism, vascularity, and innervation to the vastus medialis. Our study documents both safety and good clinical outcomes using the MIV approach in TKA. Therefore, the MIV approach may be used in the majority of patients undergoing TKA.

ABSTRACT

The subvastus (SV) approach is a well-known muscle- and tendon-sparing approach for total knee arthroplasty (TKA), which has been shown in some studies to provide better outcomes in the visual analog pain score (VAS), knee range of motion (ROM), straight-leg raise, as well as faster rehabilitation, compared with the standard medial parapatellar (MP) approach. We previously described a new knee replacement technique known as the modified intervastus (MIV) approach. The MIV approach is a muscle- and tendon-sparing approach that is extensile and simple to perform. It may be used in the majority of complex primary cases and revisions. Here we describe the surgical technique for performing the MIV approach and provide functional outcome measures. A total of 127 patients (mean age, 66.75 years) underwent TKA using the MIV approach with 1-year follow-up. Clinical outcomes were assessed by recording both a VAS and knee ROM preoperatively, and again at several postoperative time points when the length of time required to ambulate independently (without assistive devices) was also measured. The VAS decreased significantly from the preoperative period (3.69 ± 2.22) to postoperative day 1 (3.17 ± 1.97) (P < .05). Although knee ROM decreased 1 week after surgery, the ROM increased by 6 weeks after surgery compared with the preoperative ROM, and the trend continued over the 1-year follow-up. One-third (33%) of patients were able to walk independently (without assistive devices) at 2 weeks and 78% at 8 weeks. The MIV approach to the knee is a muscle- and tendon-sparing approach that offers advantages over the SV approach and may be used for complex primary and revision total knee cases.

Continue to: Total knee arthroplasty... 

Total knee arthroplasty (TKA) is one of the most common orthopedic surgical procedures, with more than 600,000 TKAs performed annually in the United States, and by 2030 the number is expected to reach 3.48 million per year.¹Several approaches have been described for total TKA, and the medial parapatellar (MP) approach to the knee is considered the workhorse of total knee replacements. It is an extensile approach that is easy to perform but may delay active knee extension and straight-leg raise after surgery.²  Alternative approaches such as the subvastus (SV) and midvastus approaches to the knee (Figure 1A) typically allow a more rapid straight-leg raise but may be more challenging to perform and time-consuming in morbidly obese patients, muscular patients, and patients with severe deformities.³

The intervastus approach (Figure 1A) described by Jojima⁴ and others utilizes the interval between the quadriceps tendon and vastus medialis. Although it is a simple approach to perform that is extensile, it is not considered tendon-sparing since the vastus medialis inserts onto the medial aspect of the quadriceps tendon (Figure 2).⁵  Therefore, dissecting through this interval, without elevation of the vastus medialis (Figure 3A), damages the quadriceps tendon, and strangulation of the muscle occurs with repair of the arthrotomy site (Figure 3B).  This situation is even more likely in patients with a low-lying vastus medialis.⁶

The modified intervastus (MIV) approach described previously,⁷ may be used in the majority of patients undergoing TKA. The advantages of this approach include its extensile nature, similarities to an MP approach, and preservation of both the extensor mechanism and the vastus medialis, leading to a more rapid return to active knee extension than is traditionally observed.^2,7 The approach is simple to perform, easy to close, and is compatible with more extensile approaches such as a quadriceps snip if required in revision scenarios.⁷ However, functional outcomes of the MIV approach have not been quantified. It is unknown whether these outcomes will offer any advantages compared with the SV approach. Therefore, the objective of this study was to measure functional outcomes of the MIV approach and to compare the results with those previously published for the SV approach. We hypothesized that using the MIV approach for TKA surgery would lead to early straight-leg raise and increase in knee range of motion (ROM) postoperatively.

SURGICAL TECHNIQUE

The MIV approach preserves the quadriceps tendon and vastus medialis.⁷ After exposure of the vastus medialis muscle, the interval between the quadriceps tendon and vastus medialis is identified (Figure 4).  The fascia overlying the lateral edge of the vastus medialis is incised where it meets the quadriceps tendon (Figure 5).  The muscle is then bluntly elevated off the underlying capsule just enough to allow for a capsular repair later (Figure 6).  An arthrotomy is then performed from cephalad to caudal (Figure 7).  This interval may be extended proximally between the vastus intermedius and vastus medialis to expose the distal femur if needed. The closure is performed by repairing the capsule with absorbable suture (Figure 8A), and the vastus medialis fascia is repaired back to the medial edge of the quadriceps tendon, restoring the anatomy (Figure 8B).

Continue to: PATIENTS AND METHODS...

 

 

PATIENTS AND METHODS

A retrospective review of functional outcomes after TKA using the MIV approach was conducted; the study was approved by the University of Illinois Institutional Review Board. A total of 127 patients of mean age 66.75 years (range, 48–86 years) with primary osteoarthritis of the knee who were indicated for a total knee replacement with 1-year follow-up were included. The patient demographics are shown in Table 1.  All patients underwent TKA using the MIV approach described above by 2 experienced orthopedic surgeons at the same institution. Patients received spinal anesthesia and a periarticular pain block intraoperatively. A measured resection technique was used by 1 surgeon, and a gap-balancing technique by the other. Surgeon 1 used the Persona PS cemented knee system (Zimmer Biomet, and Surgeon 2 used the Sigma PS cemented knee system (Depuy). Patellar resurfacing was done in all cases. Patellar tracking was checked intraoperatively using the ‘no-touch’ technique, and the need for a lateral release was noted. Drains were removed on postoperative day 1. Oral opioids were given as needed. Intravenous antibiotics were continued for 24 hours. Oral anticoagulants were used for thromboembolism prophylaxis for 3 weeks. Patients were mobilized on the day of surgery with full weight-bearing under the supervision of an experienced physical therapist. Static and dynamic quadriceps exercises were started on the same day of surgery along with active knee ROM exercises. Pain score, extensor lag, ROM, walking ability, and complications were recorded in all patients.

Table 1. Patient Demographics

Total no. of patients		127
Gender	Male	44
	Female	83
Age (years)	Mean ± Standard deviation	66.75 ± 9.12
	Range	48 – 86
Weight (lb)	Mean ± Standard deviation	218.38 ± 54.47
	Range	125 – 364
BMI (kg/m2)	Mean ± Standard deviation	34.10 ± 7.22
	Range	21.1 – 62.5

The visual analog score (VAS) was obtained preoperatively and recorded on postoperative day 1. Patient walking distance with assistance was measured on the day of surgery, after surgery, and on the day of hospital discharge. Patients were assessed preoperatively and postoperatively at 1 week, 2 weeks, 6 weeks, 3 months, 6 months, and 1 year for knee ROM. A one-way ANOVA was conducted to compare the preoperative and postoperative day 1 VAS with significance set at P < .05 (OriginPro 2015, OriginLab Corporation). Differences in knee ROM between preoperative and postoperative follow-up periods (1 week, 2 weeks, 6 weeks, 3 months, 6 months, and 1 year) were identified using a 1-way ANOVA with a post hoc Tukey test. Significance was set at P < .05.

RESULTS

All patients were able to fully straight-leg raise and demonstrate functional knee ROM by postoperative day 1. The patella tracked centrally in all patients, and none required a lateral retinacular release. The majority of patients were discharged in the first 48 hours after surgery on oral narcotics. None required IV narcotics during their hospital stay or a blood transfusion. Two cases were complicated by severe knee skin blistering postoperatively due to a reaction to an adhesive dressing; one was complicated by skin necrosis leading to a flap reconstruction that became infected, requiring a 2-stage revision. A separate case had an acute postoperative infection that required irrigation and debridement with polyethylene exchange. After a 12-week course of antibiotics, the infection was eradicated. All patients reported a high satisfaction rate during their acute postoperative phase.

Postoperatively, all patients were able to walk on the day of surgery either independently or with some assistance. On the day of surgery, 10% of patients were able to walk >200 feet, and this increased to 65% of patients able to walk >200 feet on the day of discharge (compare Figure 9A and Figure 9B).  Within 2 weeks of surgery, 30% of patients could walk independently (without assistive devices), and this number increased to 78% by 8 weeks after surgery (Figure 10).

Pain assessed using the VAS was lower on postoperative day 1 (3.17 ± 1.97) than the preoperative score (3.69 ± 2.22, P< .05). Overall, knee ROM significantly increased during the follow-up after surgery. Initially, the ROM decreased 1 week after surgery (90.82 ± 10.28) compared with preoperative ROM (101.04 ± 19.48, P < .001) (Figure 10).  At 2 weeks after surgery, knee ROM returned to the preoperative value (100.70 ± 13.36). By 6 weeks after surgery, knee ROM was 17° greater than the preoperative ROM (118.45 ± 11.89, P < .001). Knee ROM remained stable at 3- and 6-month assessments, and showed further improvement by 1 year (126.62 ± 9.81, P < .001) compared with the preoperative state (Figure 10). The net improvement in knee ROM was 25° of increased knee flexion by 1 year.

Continue to: DISCUSSION...

 

 

DISCUSSION

TKA is a successful procedure that restores knee function with pain relief in osteoarthritis patients. The SV approach for TKA has better outcomes in terms of the VAS, ROM, straight-leg raise with faster rehabilitation compared with the standard MP approach;^8–12 however, it can be challenging and time-consuming when used in morbidly obese and muscular patients.³ The SV approach can also increase the risk of complications such as patellar tendon avulsion or medial collateral injury because of the difficulty in exposure specifically for knees with limited ROM.¹³ Here we introduce the MIV approach as an alternative to the SV approach, overcoming most of these difficulties.

With the prevalence of morbid obesity and the market demand for minimally invasive techniques, we believe the MIV approach represents a good approach for surgeons since it is easy to perform, does not require specialized instrumentation, and is a reproducible approach even on the most complex deformities. The minimal time added to ensure blunt elevation of the vastus medialis muscle and an anatomic repair of the underlying knee capsule and vastus medialis fascia to the medial edge of the quadriceps tendon allows restoration of the anatomy and a robust double-layered watertight seal closure with no strangulation of soft tissues. We believe this reproducible muscle- and tendon-sparing approach that allows gentle, soft tissue handling even in the most complex primary total knee cases may lead to less soft tissue swelling, and therefore, less postoperative pain resulting in an accelerated recovery.

The pain level in this group of patients was reduced after the MIV approach as indicated by the VAS. The VAS was significantly decreased on postoperative day 1 compared with the VAS recorded preoperatively (P < .05), indicating patients felt less pain on the day after surgery. The average VAS on postoperative day 1 from other studies for SV approach ranged from 2.1 to 5,^9,12,14–19 whereas our MIV approach value was 3.17. Periarticular blocks were available for this study group, and no peripheral nerve blocks were used. Some studies of the SV approach mention the use of peripheral nerve blocks, while others did not describe the method used for treatment or control of postoperative pain. The decreased reported pain levels and the observed increased knee ROM seen in the MIV and SV approach study groups might be attributable to the treatment of postoperative pain.

Patient ambulation also increased from the day of surgery to the day of discharge for the MIV approach. Only 10% of patients were able to walk with assistance >200 feet on the day of surgery; however, this percentage increased to 65% on the discharge day showing an excellent recovery of walking ability within 2 days of surgery. Mehta and colleagues²⁰reported that 95% of patients undergoing subvastus/midvastus approaches could walk >10 blocks at 6 months follow-up. For the MIV approach, 78% of patients were able to walk independently within 8 weeks of surgery.

Continue to: The MIV approach shows improvement...

 

 

The MIV approach shows improvement in functional outcomes in terms of knee ROM from preoperative to postoperative. Although knee ROM decreased significantly at postoperative week 1, which is most likely because of a peak in postoperative pain and swelling; the ROM started to increase significantly at postoperative week 6. After 1 year, the knee ROM increased by 25% compared with preoperative ROM for the MIV approach. We found the average knee ROM at postoperative 3 months using the MIV approach to be 120.4°. Knee ROM at postoperative 3 months using the SV approach reported by other studies ranged from 87.1° to 120°.^19,21–23 Similarly, after 1 year, the average ROM by MIV approach was 126.62°, whereas average knee ROM from other studies using the SV approach was 114.1°.^2,10,19,21 Achieving a knee ROM of 120° allows patients to return to their baseline function and perform activities of daily living without limitation. With the prevalence of knee osteoarthritis in the younger population, the need for increased knee ROM post-TKA becomes more important so patients can return to work and function at their baseline.

In addition to being both a muscle- and tendon-sparing approach, other advantages of the MIV approach are that it is simple to perform and gives similar exposure to the MP approach even in difficult primary cases. It is also as extensile as the medial parapatellar approach, and it can be converted to a quadriceps snip if required. There is also minimal, if any, muscle retraction preventing muscle injury that may be seen with some other muscle-sparing approaches to the knee, especially in more difficult primary total knee cases. Another advantage to this approach, as opposed to the other approaches to the knee described here, is that it allows a double-layered closure, decreasing the possibility of arthrotomy dehiscence. Because of this double-layered closure, there is no muscle strangulation with repair of the arthrotomy site as seen in some other approaches to the knee, and both vascularity and innervation to the vastus medialis are preserved.

One limitation of this study is that it is a retrospective analysis. Future studies of the consequences of using this approach need to include quantitative assessment of muscle function using electromyography or dynamometer measurements, utilization of any number of validated knee score systems to measure functional outcomes, and incorporation of a randomized controlled trial.

In summary, the new MIV approach is easy to perform and is compatible with more extensile approaches such as a quadriceps snip, if required in revision scenarios. The MIV approach preserves the extensor mechanism, vascularity, and innervation to the vastus medialis. Our study documents both safety and good clinical outcomes using the MIV approach in TKA. Therefore, the MIV approach may be used in the majority of patients undergoing TKA.

ABSTRACT

The subvastus (SV) approach is a well-known muscle- and tendon-sparing approach for total knee arthroplasty (TKA), which has been shown in some studies to provide better outcomes in the visual analog pain score (VAS), knee range of motion (ROM), straight-leg raise, as well as faster rehabilitation, compared with the standard medial parapatellar (MP) approach. We previously described a new knee replacement technique known as the modified intervastus (MIV) approach. The MIV approach is a muscle- and tendon-sparing approach that is extensile and simple to perform. It may be used in the majority of complex primary cases and revisions. Here we describe the surgical technique for performing the MIV approach and provide functional outcome measures. A total of 127 patients (mean age, 66.75 years) underwent TKA using the MIV approach with 1-year follow-up. Clinical outcomes were assessed by recording both a VAS and knee ROM preoperatively, and again at several postoperative time points when the length of time required to ambulate independently (without assistive devices) was also measured. The VAS decreased significantly from the preoperative period (3.69 ± 2.22) to postoperative day 1 (3.17 ± 1.97) (P < .05). Although knee ROM decreased 1 week after surgery, the ROM increased by 6 weeks after surgery compared with the preoperative ROM, and the trend continued over the 1-year follow-up. One-third (33%) of patients were able to walk independently (without assistive devices) at 2 weeks and 78% at 8 weeks. The MIV approach to the knee is a muscle- and tendon-sparing approach that offers advantages over the SV approach and may be used for complex primary and revision total knee cases.

Continue to: Total knee arthroplasty... 

Total knee arthroplasty (TKA) is one of the most common orthopedic surgical procedures, with more than 600,000 TKAs performed annually in the United States, and by 2030 the number is expected to reach 3.48 million per year.¹Several approaches have been described for total TKA, and the medial parapatellar (MP) approach to the knee is considered the workhorse of total knee replacements. It is an extensile approach that is easy to perform but may delay active knee extension and straight-leg raise after surgery.²  Alternative approaches such as the subvastus (SV) and midvastus approaches to the knee (Figure 1A) typically allow a more rapid straight-leg raise but may be more challenging to perform and time-consuming in morbidly obese patients, muscular patients, and patients with severe deformities.³

The intervastus approach (Figure 1A) described by Jojima⁴ and others utilizes the interval between the quadriceps tendon and vastus medialis. Although it is a simple approach to perform that is extensile, it is not considered tendon-sparing since the vastus medialis inserts onto the medial aspect of the quadriceps tendon (Figure 2).⁵  Therefore, dissecting through this interval, without elevation of the vastus medialis (Figure 3A), damages the quadriceps tendon, and strangulation of the muscle occurs with repair of the arthrotomy site (Figure 3B).  This situation is even more likely in patients with a low-lying vastus medialis.⁶

The modified intervastus (MIV) approach described previously,⁷ may be used in the majority of patients undergoing TKA. The advantages of this approach include its extensile nature, similarities to an MP approach, and preservation of both the extensor mechanism and the vastus medialis, leading to a more rapid return to active knee extension than is traditionally observed.^2,7 The approach is simple to perform, easy to close, and is compatible with more extensile approaches such as a quadriceps snip if required in revision scenarios.⁷ However, functional outcomes of the MIV approach have not been quantified. It is unknown whether these outcomes will offer any advantages compared with the SV approach. Therefore, the objective of this study was to measure functional outcomes of the MIV approach and to compare the results with those previously published for the SV approach. We hypothesized that using the MIV approach for TKA surgery would lead to early straight-leg raise and increase in knee range of motion (ROM) postoperatively.

SURGICAL TECHNIQUE

The MIV approach preserves the quadriceps tendon and vastus medialis.⁷ After exposure of the vastus medialis muscle, the interval between the quadriceps tendon and vastus medialis is identified (Figure 4).  The fascia overlying the lateral edge of the vastus medialis is incised where it meets the quadriceps tendon (Figure 5).  The muscle is then bluntly elevated off the underlying capsule just enough to allow for a capsular repair later (Figure 6).  An arthrotomy is then performed from cephalad to caudal (Figure 7).  This interval may be extended proximally between the vastus intermedius and vastus medialis to expose the distal femur if needed. The closure is performed by repairing the capsule with absorbable suture (Figure 8A), and the vastus medialis fascia is repaired back to the medial edge of the quadriceps tendon, restoring the anatomy (Figure 8B).

Continue to: PATIENTS AND METHODS...

 

 

PATIENTS AND METHODS

A retrospective review of functional outcomes after TKA using the MIV approach was conducted; the study was approved by the University of Illinois Institutional Review Board. A total of 127 patients of mean age 66.75 years (range, 48–86 years) with primary osteoarthritis of the knee who were indicated for a total knee replacement with 1-year follow-up were included. The patient demographics are shown in Table 1.  All patients underwent TKA using the MIV approach described above by 2 experienced orthopedic surgeons at the same institution. Patients received spinal anesthesia and a periarticular pain block intraoperatively. A measured resection technique was used by 1 surgeon, and a gap-balancing technique by the other. Surgeon 1 used the Persona PS cemented knee system (Zimmer Biomet, and Surgeon 2 used the Sigma PS cemented knee system (Depuy). Patellar resurfacing was done in all cases. Patellar tracking was checked intraoperatively using the ‘no-touch’ technique, and the need for a lateral release was noted. Drains were removed on postoperative day 1. Oral opioids were given as needed. Intravenous antibiotics were continued for 24 hours. Oral anticoagulants were used for thromboembolism prophylaxis for 3 weeks. Patients were mobilized on the day of surgery with full weight-bearing under the supervision of an experienced physical therapist. Static and dynamic quadriceps exercises were started on the same day of surgery along with active knee ROM exercises. Pain score, extensor lag, ROM, walking ability, and complications were recorded in all patients.

Table 1. Patient Demographics

Total no. of patients		127
Gender	Male	44
	Female	83
Age (years)	Mean ± Standard deviation	66.75 ± 9.12
	Range	48 – 86
Weight (lb)	Mean ± Standard deviation	218.38 ± 54.47
	Range	125 – 364
BMI (kg/m2)	Mean ± Standard deviation	34.10 ± 7.22
	Range	21.1 – 62.5

The visual analog score (VAS) was obtained preoperatively and recorded on postoperative day 1. Patient walking distance with assistance was measured on the day of surgery, after surgery, and on the day of hospital discharge. Patients were assessed preoperatively and postoperatively at 1 week, 2 weeks, 6 weeks, 3 months, 6 months, and 1 year for knee ROM. A one-way ANOVA was conducted to compare the preoperative and postoperative day 1 VAS with significance set at P < .05 (OriginPro 2015, OriginLab Corporation). Differences in knee ROM between preoperative and postoperative follow-up periods (1 week, 2 weeks, 6 weeks, 3 months, 6 months, and 1 year) were identified using a 1-way ANOVA with a post hoc Tukey test. Significance was set at P < .05.

RESULTS

All patients were able to fully straight-leg raise and demonstrate functional knee ROM by postoperative day 1. The patella tracked centrally in all patients, and none required a lateral retinacular release. The majority of patients were discharged in the first 48 hours after surgery on oral narcotics. None required IV narcotics during their hospital stay or a blood transfusion. Two cases were complicated by severe knee skin blistering postoperatively due to a reaction to an adhesive dressing; one was complicated by skin necrosis leading to a flap reconstruction that became infected, requiring a 2-stage revision. A separate case had an acute postoperative infection that required irrigation and debridement with polyethylene exchange. After a 12-week course of antibiotics, the infection was eradicated. All patients reported a high satisfaction rate during their acute postoperative phase.

Postoperatively, all patients were able to walk on the day of surgery either independently or with some assistance. On the day of surgery, 10% of patients were able to walk >200 feet, and this increased to 65% of patients able to walk >200 feet on the day of discharge (compare Figure 9A and Figure 9B).  Within 2 weeks of surgery, 30% of patients could walk independently (without assistive devices), and this number increased to 78% by 8 weeks after surgery (Figure 10).

Pain assessed using the VAS was lower on postoperative day 1 (3.17 ± 1.97) than the preoperative score (3.69 ± 2.22, P< .05). Overall, knee ROM significantly increased during the follow-up after surgery. Initially, the ROM decreased 1 week after surgery (90.82 ± 10.28) compared with preoperative ROM (101.04 ± 19.48, P < .001) (Figure 10).  At 2 weeks after surgery, knee ROM returned to the preoperative value (100.70 ± 13.36). By 6 weeks after surgery, knee ROM was 17° greater than the preoperative ROM (118.45 ± 11.89, P < .001). Knee ROM remained stable at 3- and 6-month assessments, and showed further improvement by 1 year (126.62 ± 9.81, P < .001) compared with the preoperative state (Figure 10). The net improvement in knee ROM was 25° of increased knee flexion by 1 year.

Continue to: DISCUSSION...

 

 

DISCUSSION

TKA is a successful procedure that restores knee function with pain relief in osteoarthritis patients. The SV approach for TKA has better outcomes in terms of the VAS, ROM, straight-leg raise with faster rehabilitation compared with the standard MP approach;^8–12 however, it can be challenging and time-consuming when used in morbidly obese and muscular patients.³ The SV approach can also increase the risk of complications such as patellar tendon avulsion or medial collateral injury because of the difficulty in exposure specifically for knees with limited ROM.¹³ Here we introduce the MIV approach as an alternative to the SV approach, overcoming most of these difficulties.

With the prevalence of morbid obesity and the market demand for minimally invasive techniques, we believe the MIV approach represents a good approach for surgeons since it is easy to perform, does not require specialized instrumentation, and is a reproducible approach even on the most complex deformities. The minimal time added to ensure blunt elevation of the vastus medialis muscle and an anatomic repair of the underlying knee capsule and vastus medialis fascia to the medial edge of the quadriceps tendon allows restoration of the anatomy and a robust double-layered watertight seal closure with no strangulation of soft tissues. We believe this reproducible muscle- and tendon-sparing approach that allows gentle, soft tissue handling even in the most complex primary total knee cases may lead to less soft tissue swelling, and therefore, less postoperative pain resulting in an accelerated recovery.

The pain level in this group of patients was reduced after the MIV approach as indicated by the VAS. The VAS was significantly decreased on postoperative day 1 compared with the VAS recorded preoperatively (P < .05), indicating patients felt less pain on the day after surgery. The average VAS on postoperative day 1 from other studies for SV approach ranged from 2.1 to 5,^9,12,14–19 whereas our MIV approach value was 3.17. Periarticular blocks were available for this study group, and no peripheral nerve blocks were used. Some studies of the SV approach mention the use of peripheral nerve blocks, while others did not describe the method used for treatment or control of postoperative pain. The decreased reported pain levels and the observed increased knee ROM seen in the MIV and SV approach study groups might be attributable to the treatment of postoperative pain.

Patient ambulation also increased from the day of surgery to the day of discharge for the MIV approach. Only 10% of patients were able to walk with assistance >200 feet on the day of surgery; however, this percentage increased to 65% on the discharge day showing an excellent recovery of walking ability within 2 days of surgery. Mehta and colleagues²⁰reported that 95% of patients undergoing subvastus/midvastus approaches could walk >10 blocks at 6 months follow-up. For the MIV approach, 78% of patients were able to walk independently within 8 weeks of surgery.

Continue to: The MIV approach shows improvement...

 

 

The MIV approach shows improvement in functional outcomes in terms of knee ROM from preoperative to postoperative. Although knee ROM decreased significantly at postoperative week 1, which is most likely because of a peak in postoperative pain and swelling; the ROM started to increase significantly at postoperative week 6. After 1 year, the knee ROM increased by 25% compared with preoperative ROM for the MIV approach. We found the average knee ROM at postoperative 3 months using the MIV approach to be 120.4°. Knee ROM at postoperative 3 months using the SV approach reported by other studies ranged from 87.1° to 120°.^19,21–23 Similarly, after 1 year, the average ROM by MIV approach was 126.62°, whereas average knee ROM from other studies using the SV approach was 114.1°.^2,10,19,21 Achieving a knee ROM of 120° allows patients to return to their baseline function and perform activities of daily living without limitation. With the prevalence of knee osteoarthritis in the younger population, the need for increased knee ROM post-TKA becomes more important so patients can return to work and function at their baseline.

In addition to being both a muscle- and tendon-sparing approach, other advantages of the MIV approach are that it is simple to perform and gives similar exposure to the MP approach even in difficult primary cases. It is also as extensile as the medial parapatellar approach, and it can be converted to a quadriceps snip if required. There is also minimal, if any, muscle retraction preventing muscle injury that may be seen with some other muscle-sparing approaches to the knee, especially in more difficult primary total knee cases. Another advantage to this approach, as opposed to the other approaches to the knee described here, is that it allows a double-layered closure, decreasing the possibility of arthrotomy dehiscence. Because of this double-layered closure, there is no muscle strangulation with repair of the arthrotomy site as seen in some other approaches to the knee, and both vascularity and innervation to the vastus medialis are preserved.

One limitation of this study is that it is a retrospective analysis. Future studies of the consequences of using this approach need to include quantitative assessment of muscle function using electromyography or dynamometer measurements, utilization of any number of validated knee score systems to measure functional outcomes, and incorporation of a randomized controlled trial.

In summary, the new MIV approach is easy to perform and is compatible with more extensile approaches such as a quadriceps snip, if required in revision scenarios. The MIV approach preserves the extensor mechanism, vascularity, and innervation to the vastus medialis. Our study documents both safety and good clinical outcomes using the MIV approach in TKA. Therefore, the MIV approach may be used in the majority of patients undergoing TKA.

ABSTRACT

This work is a retrospective cohort study evaluating patients who had undergone third-generation cemented total knee arthroplasty (TKA) with prostheses (NexGen, Zimmer Biomet) utilizing posterior-stabilized (PS) and cruciate-retaining (CR) designs at a single center at their 15-year follow-up.

The purpose of this study is to determine the functional knee scores, reoperations, and long-term survivorship for patients with the NexGen Zimmer Biomet Knee system at the 15-year follow-up. In total, 99 patients who had undergone primary TKA were followed for 15 years.

At the 15-year follow-up, survivorship in both study groups was similar: 98% for PS TKAs and 100% for CR TKAs. The 2 groups also showed similar functionality: 80% of the PS implants and 89% of the CR implants were associated with no or mild pain (P = .40). Reoperation rates were 2% for the PS group and 0% for the CR group (P = .38). No differences in any of the outcomes analyzed were observed between patients who had CR TKA and those who had undergone PS TKA.

Our study found no significant differences in functional outcomes between PS and CR NexGen knee implants. Patients treated by both methods showed excellent longevity and survivorship at the 15-year follow-up.

Continue to: Total knee arthroplasty...

Total knee arthroplasty (TKA) is an orthopedic procedure with increasing demand.¹ Over the past 2 decades, a surge in TKA implants has been observed. Of the available prosthetic designs, only a few implants with long-term follow-up have been reported.^2-9 The NexGen TKA system (Zimmer Biomet) has been shown to have excellent clinical and radiographic results at an intermediate follow-up term of 8 years.¹⁰ This system is a third-generation prosthetic design that was developed to improve problems seen with its predecessors, such as the Miller-Galante II system (Zimmer Biomet), the Insall-Burstein II system (Zimmer Biomet), and the Constrained Condylar Knee (Zimmer Biomet), which were mainly for patellar maltracking.^11-17 The NexGen TKA system is a fixed-bearing system designed to include an anatomic femoral trochlea with the option of cruciate-retaining (CR), posterior-stabilized (PS), or more constrained implants. This study evaluates the long-term success of the CR and PS NexGen TKA systems. Outcomes measured include functional knee scores and reoperation rates at the 15-year follow-up. Based on the measured outcomes, potential differences between the PS and CR implants from this system are cited.

MATERIAL AND METHODS

Between July 1995 and July 1997, 334 consecutive primary TKAs were performed on 287 patients at our institution. In total, 167 patients (186 knees) underwent posterior CR TKAs with the NexGen CR prosthesis (Zimmer Biomet), and 120 patients (148 knees) underwent PS TKAs using the NexGen Legacy PS prosthesis (Zimmer Biomet). This retrospective double cohort study was reviewed and approved by our Institutional Review Board. At the 15-year postoperative follow-up, 99 patients were available (Figure 1).

The CR and PS implants were used with similar frequencies by the surgeons who performed the procedures. Patients were not randomized into either the PS- or CR-implant teams; the final decision on implant selection was left to the operating surgeon’s discretion. However, in addition to standard indications for TKA (pain and disability associated with severe arthritic change seen on radiographs and refractory to conservative measures), absolute contraindications to the CR implant included severe combined deformity (flexion contraction >30° combined with a varus or valgus deformity >20°) or posterior cruciate ligament insufficiency (often associated with inflammatory arthritis).

The surgical technique for the CR and PS designs was identical, and included a median parapatellar approach, femoral rotational alignment perpendicular to the transepicondylar axis, measured resection of the flexion and extension gaps, intramedullary femoral alignment, and extramedullary tibial alignment. All components were cemented, and the patella of each patient was resurfaced. All patients received preoperative antibiotics that were continued for 48 hours postoperatively, and 4 weeks of anticoagulation with dose-adjusted warfarin to maintain an international normalized ratio of 1.5 to 2.0.

Patients were observed postoperatively at the 5- to 8-year and 15-year time points. The 5-year data were previously published in 2005 by Bozic and colleagues.¹⁰ Patients available for follow-up at the 15-year time-point were evaluated using the 100-point Hospital for Special Surgery (HSS) knee scoring system, which assigns up to 30 points for pain, 22 points for function, 18 points for range of motion, and 10 points each for quadricep strength, deformity, and instability. In addition, common medical conditions limiting patient activity were assessed; these included joint replacement; arthritis in another joint, the back, or spine; weakness or fatigue; breathing or heart ailments; and others.

Continue to: At the 15-year follow-up...

At the 15-year follow-up, patients were contacted via telephone to obtain their HSS knee scores. If patients were unavailable/unable to answer the questions asked, knee score information was collected from a first-degree relative or caretaker. Patients that could not be contacted by phone were sent a HSS knee score survey to their last known address. The online Social Security Death Index was queried for confirmation of death. If deceased, a first-degree relative was contacted for confirmation.

Survivorship was evaluated using revision for any reason and revision for aseptic loosening as separate endpoints via the Kaplan-Meier product-limit method, and the CR and PS TKA groups were compared using the log-rank test. The power of the study for detecting differences between the TKA groups was determined to be 80%, based on a moderate hazard ratio of 1.5, using the log-rank test. Differences between PS and CR TKAs were assessed using the Pearson chi-square test for knee pain and functional outcomes, Fisher’s exact test for patient limitations, such as joint replacement, and the non-parametric Mann Whitney U-test for median pain scores (Table 1). Spearman correlations between the patients’ self-reported knee scores (as a percentage of normal) and physician-based knee scores were performed to assess whether self-reported knee scores were significantly correlated with physician-based knee scores. Kaplan-Meier analysis was performed to evaluate time-related freedom from reoperation at 95% confidence intervals. Statistical analysis was conducted using IBM SPSS Statistics (version 21.0, IBM). Two-tailed P < .05 was considered statistically significant.

RESULTS

Of the 287 patients (334 knees) who had primary TKAs, 99 patients (121 knees; 75 CR and 46 PS) were available at the 15-year follow-up. A total of 155 patients (171 knees) died before the 15-year follow-up, and 33 (42 knees) were lost to follow-up (Figure 1). The functional status of the knees of patients who were lost to follow-up or who had died since the previous follow-up data were published is unknown.

Demographic and outcome data for the cohort of 121 TKAs (99 patients) are summarized in Table 2. The median age at surgery was 64 years, and 71% of the cohort was female.

At the 15-year follow-up, survivorship in both groups was similar: 98% for PS TKAs and 100% for CR TKAs. The 2 groups were also similar functionally: 80% of the PS implants and 89% of the CR implants were associated with no or mild pain (P = .40). Approximately half of the patients in both groups (52% PS; 50% CR; P = .88) required walking support (canes or walkers) and nearly half of both groups (46% PS; 48% CR; P = .62) could walk <5 blocks or only short distances in their homes. In addition, 46% of the patients in both groups reported needing arm assistance to functionally rise from a chair (P = .43); 91% of the patients in both groups could also walk up and down stairs (P = .77). No statistical difference in the medical conditions limiting the patients in the 2 groups was found: joint replacement (2% PS; 6% CR; P = .71), arthritis in another joint (43% PS; 45% CR; P = .84), back or spine arthritis (31% PS; 33% CR; P = 1.00), weakness or fatigue (24% PS; 25% CR; P = 1.00), breathing or heart ailments (11% PS; 20% CR; P = .40), and other reasons (27% PS; 25% CR; P = 1.00). In addition, median self-reported knee scores were 95 and 93 points for the PS and CR groups, respectively (P = .55).

Continue to: Patients reported 2 complications...

Patients reported 2 complications since the previous 5- to 8-year follow-up, 1 in each group. The first case underwent a PS TKA that required open reduction internal fixation for a bilateral supracondylar peri-prosthesis femur fracture following a fall, which was subsequently complicated with infection and ultimately led to above-the-knee amputation. In the second case, a CR TKA patient experienced persistent swelling and knee instability. The patient followed up with a local orthopaedist, but to date, no reoperations on the knee have been reported.

Spearman correlations between the patients’ self-reported knee scores (as a percentage of normal) and physician-based knee scores were moderately correlated with physician-based knee scores (r_s = 0.42; P < .001).

Reoperation rates were 2% for PS and 0% for CR (P = .38). Kaplan-Meier analysis was performed to evaluate time-related freedom from reoperation and no significance difference between the PS and CR groups was revealed (log-rank test = 1.40, P = .24, Figure 2).

DISCUSSION

The success of TKA in pain relief and restoration of function has led to increased demands for this surgery.¹ Such demand has enabled the introduction of a new joint replacement prosthesis to the market.¹⁸ Considering the increased incidence of osteoarthritis in the younger population (<55 years of age), critically reviewing the longevity and durability of TKA implant designs is of great importance. Compared with other TKA implant designs, the NexGen Zimmer Biomet Knee system has shown excellent longevity at the 15-year follow-up.^5,6,9,11-15 Our study began with 136 patients, and, after eliminating the deceased, those lost to follow-up, and non-responders, a total of 99 patients were available for the 15-year follow-up. At this time-point, 80% of the PS implants and 89% of the CR implants were associated with no or mild pain. Survivorship at the 15-year follow-up was similar in both groups: 98% for PS TKAs and 100% for CR TKAs. The reoperation rate was low in both groups, and no evidence of aseptic loosening was found. Based on our results, the NexGen Zimmer Biomet Knee system can be concluded to show excellent longevity and functional outcomes at the 15-year follow-up.

Our study includes several limiting factors that were taken into consideration during the analysis of the results. One of the main limitations of this work is that it required a 15-year follow-up of predominantly elderly patients; many of the participants may be expected to be deceased at this time-point. In our study, a total of 7 patients were confirmed to be deceased by a first-degree relative or the Social Security Death Index. In addition, unlike Bozic and colleagues’¹⁰ previous 5-year follow-up study, radiographic imaging data were not collected at the 15-year follow-up. However, given that this study aimed to assess the functional knee scores and reoperation rates of the PS and CR NexGen Zimmer Biomet Knee system, radiographic information did not appear to be necessary.

CONCLUSION

This study found no significant differences in functional outcomes between the PS and CR NexGen knee implants. Patients who received these implants showed excellent longevity and survivorship at their 15-year follow-up.

ABSTRACT

This work is a retrospective cohort study evaluating patients who had undergone third-generation cemented total knee arthroplasty (TKA) with prostheses (NexGen, Zimmer Biomet) utilizing posterior-stabilized (PS) and cruciate-retaining (CR) designs at a single center at their 15-year follow-up.

The purpose of this study is to determine the functional knee scores, reoperations, and long-term survivorship for patients with the NexGen Zimmer Biomet Knee system at the 15-year follow-up. In total, 99 patients who had undergone primary TKA were followed for 15 years.

At the 15-year follow-up, survivorship in both study groups was similar: 98% for PS TKAs and 100% for CR TKAs. The 2 groups also showed similar functionality: 80% of the PS implants and 89% of the CR implants were associated with no or mild pain (P = .40). Reoperation rates were 2% for the PS group and 0% for the CR group (P = .38). No differences in any of the outcomes analyzed were observed between patients who had CR TKA and those who had undergone PS TKA.

Our study found no significant differences in functional outcomes between PS and CR NexGen knee implants. Patients treated by both methods showed excellent longevity and survivorship at the 15-year follow-up.

Continue to: Total knee arthroplasty...

Total knee arthroplasty (TKA) is an orthopedic procedure with increasing demand.¹ Over the past 2 decades, a surge in TKA implants has been observed. Of the available prosthetic designs, only a few implants with long-term follow-up have been reported.^2-9 The NexGen TKA system (Zimmer Biomet) has been shown to have excellent clinical and radiographic results at an intermediate follow-up term of 8 years.¹⁰ This system is a third-generation prosthetic design that was developed to improve problems seen with its predecessors, such as the Miller-Galante II system (Zimmer Biomet), the Insall-Burstein II system (Zimmer Biomet), and the Constrained Condylar Knee (Zimmer Biomet), which were mainly for patellar maltracking.^11-17 The NexGen TKA system is a fixed-bearing system designed to include an anatomic femoral trochlea with the option of cruciate-retaining (CR), posterior-stabilized (PS), or more constrained implants. This study evaluates the long-term success of the CR and PS NexGen TKA systems. Outcomes measured include functional knee scores and reoperation rates at the 15-year follow-up. Based on the measured outcomes, potential differences between the PS and CR implants from this system are cited.

MATERIAL AND METHODS

Between July 1995 and July 1997, 334 consecutive primary TKAs were performed on 287 patients at our institution. In total, 167 patients (186 knees) underwent posterior CR TKAs with the NexGen CR prosthesis (Zimmer Biomet), and 120 patients (148 knees) underwent PS TKAs using the NexGen Legacy PS prosthesis (Zimmer Biomet). This retrospective double cohort study was reviewed and approved by our Institutional Review Board. At the 15-year postoperative follow-up, 99 patients were available (Figure 1).

The CR and PS implants were used with similar frequencies by the surgeons who performed the procedures. Patients were not randomized into either the PS- or CR-implant teams; the final decision on implant selection was left to the operating surgeon’s discretion. However, in addition to standard indications for TKA (pain and disability associated with severe arthritic change seen on radiographs and refractory to conservative measures), absolute contraindications to the CR implant included severe combined deformity (flexion contraction >30° combined with a varus or valgus deformity >20°) or posterior cruciate ligament insufficiency (often associated with inflammatory arthritis).

The surgical technique for the CR and PS designs was identical, and included a median parapatellar approach, femoral rotational alignment perpendicular to the transepicondylar axis, measured resection of the flexion and extension gaps, intramedullary femoral alignment, and extramedullary tibial alignment. All components were cemented, and the patella of each patient was resurfaced. All patients received preoperative antibiotics that were continued for 48 hours postoperatively, and 4 weeks of anticoagulation with dose-adjusted warfarin to maintain an international normalized ratio of 1.5 to 2.0.

Patients were observed postoperatively at the 5- to 8-year and 15-year time points. The 5-year data were previously published in 2005 by Bozic and colleagues.¹⁰ Patients available for follow-up at the 15-year time-point were evaluated using the 100-point Hospital for Special Surgery (HSS) knee scoring system, which assigns up to 30 points for pain, 22 points for function, 18 points for range of motion, and 10 points each for quadricep strength, deformity, and instability. In addition, common medical conditions limiting patient activity were assessed; these included joint replacement; arthritis in another joint, the back, or spine; weakness or fatigue; breathing or heart ailments; and others.

Continue to: At the 15-year follow-up...

At the 15-year follow-up, patients were contacted via telephone to obtain their HSS knee scores. If patients were unavailable/unable to answer the questions asked, knee score information was collected from a first-degree relative or caretaker. Patients that could not be contacted by phone were sent a HSS knee score survey to their last known address. The online Social Security Death Index was queried for confirmation of death. If deceased, a first-degree relative was contacted for confirmation.

Survivorship was evaluated using revision for any reason and revision for aseptic loosening as separate endpoints via the Kaplan-Meier product-limit method, and the CR and PS TKA groups were compared using the log-rank test. The power of the study for detecting differences between the TKA groups was determined to be 80%, based on a moderate hazard ratio of 1.5, using the log-rank test. Differences between PS and CR TKAs were assessed using the Pearson chi-square test for knee pain and functional outcomes, Fisher’s exact test for patient limitations, such as joint replacement, and the non-parametric Mann Whitney U-test for median pain scores (Table 1). Spearman correlations between the patients’ self-reported knee scores (as a percentage of normal) and physician-based knee scores were performed to assess whether self-reported knee scores were significantly correlated with physician-based knee scores. Kaplan-Meier analysis was performed to evaluate time-related freedom from reoperation at 95% confidence intervals. Statistical analysis was conducted using IBM SPSS Statistics (version 21.0, IBM). Two-tailed P < .05 was considered statistically significant.

RESULTS

Of the 287 patients (334 knees) who had primary TKAs, 99 patients (121 knees; 75 CR and 46 PS) were available at the 15-year follow-up. A total of 155 patients (171 knees) died before the 15-year follow-up, and 33 (42 knees) were lost to follow-up (Figure 1). The functional status of the knees of patients who were lost to follow-up or who had died since the previous follow-up data were published is unknown.

Demographic and outcome data for the cohort of 121 TKAs (99 patients) are summarized in Table 2. The median age at surgery was 64 years, and 71% of the cohort was female.

At the 15-year follow-up, survivorship in both groups was similar: 98% for PS TKAs and 100% for CR TKAs. The 2 groups were also similar functionally: 80% of the PS implants and 89% of the CR implants were associated with no or mild pain (P = .40). Approximately half of the patients in both groups (52% PS; 50% CR; P = .88) required walking support (canes or walkers) and nearly half of both groups (46% PS; 48% CR; P = .62) could walk <5 blocks or only short distances in their homes. In addition, 46% of the patients in both groups reported needing arm assistance to functionally rise from a chair (P = .43); 91% of the patients in both groups could also walk up and down stairs (P = .77). No statistical difference in the medical conditions limiting the patients in the 2 groups was found: joint replacement (2% PS; 6% CR; P = .71), arthritis in another joint (43% PS; 45% CR; P = .84), back or spine arthritis (31% PS; 33% CR; P = 1.00), weakness or fatigue (24% PS; 25% CR; P = 1.00), breathing or heart ailments (11% PS; 20% CR; P = .40), and other reasons (27% PS; 25% CR; P = 1.00). In addition, median self-reported knee scores were 95 and 93 points for the PS and CR groups, respectively (P = .55).

Continue to: Patients reported 2 complications...

Patients reported 2 complications since the previous 5- to 8-year follow-up, 1 in each group. The first case underwent a PS TKA that required open reduction internal fixation for a bilateral supracondylar peri-prosthesis femur fracture following a fall, which was subsequently complicated with infection and ultimately led to above-the-knee amputation. In the second case, a CR TKA patient experienced persistent swelling and knee instability. The patient followed up with a local orthopaedist, but to date, no reoperations on the knee have been reported.

Spearman correlations between the patients’ self-reported knee scores (as a percentage of normal) and physician-based knee scores were moderately correlated with physician-based knee scores (r_s = 0.42; P < .001).

Reoperation rates were 2% for PS and 0% for CR (P = .38). Kaplan-Meier analysis was performed to evaluate time-related freedom from reoperation and no significance difference between the PS and CR groups was revealed (log-rank test = 1.40, P = .24, Figure 2).

DISCUSSION

The success of TKA in pain relief and restoration of function has led to increased demands for this surgery.¹ Such demand has enabled the introduction of a new joint replacement prosthesis to the market.¹⁸ Considering the increased incidence of osteoarthritis in the younger population (<55 years of age), critically reviewing the longevity and durability of TKA implant designs is of great importance. Compared with other TKA implant designs, the NexGen Zimmer Biomet Knee system has shown excellent longevity at the 15-year follow-up.^5,6,9,11-15 Our study began with 136 patients, and, after eliminating the deceased, those lost to follow-up, and non-responders, a total of 99 patients were available for the 15-year follow-up. At this time-point, 80% of the PS implants and 89% of the CR implants were associated with no or mild pain. Survivorship at the 15-year follow-up was similar in both groups: 98% for PS TKAs and 100% for CR TKAs. The reoperation rate was low in both groups, and no evidence of aseptic loosening was found. Based on our results, the NexGen Zimmer Biomet Knee system can be concluded to show excellent longevity and functional outcomes at the 15-year follow-up.

Our study includes several limiting factors that were taken into consideration during the analysis of the results. One of the main limitations of this work is that it required a 15-year follow-up of predominantly elderly patients; many of the participants may be expected to be deceased at this time-point. In our study, a total of 7 patients were confirmed to be deceased by a first-degree relative or the Social Security Death Index. In addition, unlike Bozic and colleagues’¹⁰ previous 5-year follow-up study, radiographic imaging data were not collected at the 15-year follow-up. However, given that this study aimed to assess the functional knee scores and reoperation rates of the PS and CR NexGen Zimmer Biomet Knee system, radiographic information did not appear to be necessary.

CONCLUSION

This study found no significant differences in functional outcomes between the PS and CR NexGen knee implants. Patients who received these implants showed excellent longevity and survivorship at their 15-year follow-up.

ABSTRACT

This work is a retrospective cohort study evaluating patients who had undergone third-generation cemented total knee arthroplasty (TKA) with prostheses (NexGen, Zimmer Biomet) utilizing posterior-stabilized (PS) and cruciate-retaining (CR) designs at a single center at their 15-year follow-up.

The purpose of this study is to determine the functional knee scores, reoperations, and long-term survivorship for patients with the NexGen Zimmer Biomet Knee system at the 15-year follow-up. In total, 99 patients who had undergone primary TKA were followed for 15 years.

At the 15-year follow-up, survivorship in both study groups was similar: 98% for PS TKAs and 100% for CR TKAs. The 2 groups also showed similar functionality: 80% of the PS implants and 89% of the CR implants were associated with no or mild pain (P = .40). Reoperation rates were 2% for the PS group and 0% for the CR group (P = .38). No differences in any of the outcomes analyzed were observed between patients who had CR TKA and those who had undergone PS TKA.

Our study found no significant differences in functional outcomes between PS and CR NexGen knee implants. Patients treated by both methods showed excellent longevity and survivorship at the 15-year follow-up.

Continue to: Total knee arthroplasty...

Total knee arthroplasty (TKA) is an orthopedic procedure with increasing demand.¹ Over the past 2 decades, a surge in TKA implants has been observed. Of the available prosthetic designs, only a few implants with long-term follow-up have been reported.^2-9 The NexGen TKA system (Zimmer Biomet) has been shown to have excellent clinical and radiographic results at an intermediate follow-up term of 8 years.¹⁰ This system is a third-generation prosthetic design that was developed to improve problems seen with its predecessors, such as the Miller-Galante II system (Zimmer Biomet), the Insall-Burstein II system (Zimmer Biomet), and the Constrained Condylar Knee (Zimmer Biomet), which were mainly for patellar maltracking.^11-17 The NexGen TKA system is a fixed-bearing system designed to include an anatomic femoral trochlea with the option of cruciate-retaining (CR), posterior-stabilized (PS), or more constrained implants. This study evaluates the long-term success of the CR and PS NexGen TKA systems. Outcomes measured include functional knee scores and reoperation rates at the 15-year follow-up. Based on the measured outcomes, potential differences between the PS and CR implants from this system are cited.

MATERIAL AND METHODS

Between July 1995 and July 1997, 334 consecutive primary TKAs were performed on 287 patients at our institution. In total, 167 patients (186 knees) underwent posterior CR TKAs with the NexGen CR prosthesis (Zimmer Biomet), and 120 patients (148 knees) underwent PS TKAs using the NexGen Legacy PS prosthesis (Zimmer Biomet). This retrospective double cohort study was reviewed and approved by our Institutional Review Board. At the 15-year postoperative follow-up, 99 patients were available (Figure 1).

The CR and PS implants were used with similar frequencies by the surgeons who performed the procedures. Patients were not randomized into either the PS- or CR-implant teams; the final decision on implant selection was left to the operating surgeon’s discretion. However, in addition to standard indications for TKA (pain and disability associated with severe arthritic change seen on radiographs and refractory to conservative measures), absolute contraindications to the CR implant included severe combined deformity (flexion contraction >30° combined with a varus or valgus deformity >20°) or posterior cruciate ligament insufficiency (often associated with inflammatory arthritis).

The surgical technique for the CR and PS designs was identical, and included a median parapatellar approach, femoral rotational alignment perpendicular to the transepicondylar axis, measured resection of the flexion and extension gaps, intramedullary femoral alignment, and extramedullary tibial alignment. All components were cemented, and the patella of each patient was resurfaced. All patients received preoperative antibiotics that were continued for 48 hours postoperatively, and 4 weeks of anticoagulation with dose-adjusted warfarin to maintain an international normalized ratio of 1.5 to 2.0.

Patients were observed postoperatively at the 5- to 8-year and 15-year time points. The 5-year data were previously published in 2005 by Bozic and colleagues.¹⁰ Patients available for follow-up at the 15-year time-point were evaluated using the 100-point Hospital for Special Surgery (HSS) knee scoring system, which assigns up to 30 points for pain, 22 points for function, 18 points for range of motion, and 10 points each for quadricep strength, deformity, and instability. In addition, common medical conditions limiting patient activity were assessed; these included joint replacement; arthritis in another joint, the back, or spine; weakness or fatigue; breathing or heart ailments; and others.

Continue to: At the 15-year follow-up...

At the 15-year follow-up, patients were contacted via telephone to obtain their HSS knee scores. If patients were unavailable/unable to answer the questions asked, knee score information was collected from a first-degree relative or caretaker. Patients that could not be contacted by phone were sent a HSS knee score survey to their last known address. The online Social Security Death Index was queried for confirmation of death. If deceased, a first-degree relative was contacted for confirmation.

Survivorship was evaluated using revision for any reason and revision for aseptic loosening as separate endpoints via the Kaplan-Meier product-limit method, and the CR and PS TKA groups were compared using the log-rank test. The power of the study for detecting differences between the TKA groups was determined to be 80%, based on a moderate hazard ratio of 1.5, using the log-rank test. Differences between PS and CR TKAs were assessed using the Pearson chi-square test for knee pain and functional outcomes, Fisher’s exact test for patient limitations, such as joint replacement, and the non-parametric Mann Whitney U-test for median pain scores (Table 1). Spearman correlations between the patients’ self-reported knee scores (as a percentage of normal) and physician-based knee scores were performed to assess whether self-reported knee scores were significantly correlated with physician-based knee scores. Kaplan-Meier analysis was performed to evaluate time-related freedom from reoperation at 95% confidence intervals. Statistical analysis was conducted using IBM SPSS Statistics (version 21.0, IBM). Two-tailed P < .05 was considered statistically significant.

RESULTS

Of the 287 patients (334 knees) who had primary TKAs, 99 patients (121 knees; 75 CR and 46 PS) were available at the 15-year follow-up. A total of 155 patients (171 knees) died before the 15-year follow-up, and 33 (42 knees) were lost to follow-up (Figure 1). The functional status of the knees of patients who were lost to follow-up or who had died since the previous follow-up data were published is unknown.

Demographic and outcome data for the cohort of 121 TKAs (99 patients) are summarized in Table 2. The median age at surgery was 64 years, and 71% of the cohort was female.

At the 15-year follow-up, survivorship in both groups was similar: 98% for PS TKAs and 100% for CR TKAs. The 2 groups were also similar functionally: 80% of the PS implants and 89% of the CR implants were associated with no or mild pain (P = .40). Approximately half of the patients in both groups (52% PS; 50% CR; P = .88) required walking support (canes or walkers) and nearly half of both groups (46% PS; 48% CR; P = .62) could walk <5 blocks or only short distances in their homes. In addition, 46% of the patients in both groups reported needing arm assistance to functionally rise from a chair (P = .43); 91% of the patients in both groups could also walk up and down stairs (P = .77). No statistical difference in the medical conditions limiting the patients in the 2 groups was found: joint replacement (2% PS; 6% CR; P = .71), arthritis in another joint (43% PS; 45% CR; P = .84), back or spine arthritis (31% PS; 33% CR; P = 1.00), weakness or fatigue (24% PS; 25% CR; P = 1.00), breathing or heart ailments (11% PS; 20% CR; P = .40), and other reasons (27% PS; 25% CR; P = 1.00). In addition, median self-reported knee scores were 95 and 93 points for the PS and CR groups, respectively (P = .55).

Continue to: Patients reported 2 complications...

Patients reported 2 complications since the previous 5- to 8-year follow-up, 1 in each group. The first case underwent a PS TKA that required open reduction internal fixation for a bilateral supracondylar peri-prosthesis femur fracture following a fall, which was subsequently complicated with infection and ultimately led to above-the-knee amputation. In the second case, a CR TKA patient experienced persistent swelling and knee instability. The patient followed up with a local orthopaedist, but to date, no reoperations on the knee have been reported.

Spearman correlations between the patients’ self-reported knee scores (as a percentage of normal) and physician-based knee scores were moderately correlated with physician-based knee scores (r_s = 0.42; P < .001).

Reoperation rates were 2% for PS and 0% for CR (P = .38). Kaplan-Meier analysis was performed to evaluate time-related freedom from reoperation and no significance difference between the PS and CR groups was revealed (log-rank test = 1.40, P = .24, Figure 2).

DISCUSSION

The success of TKA in pain relief and restoration of function has led to increased demands for this surgery.¹ Such demand has enabled the introduction of a new joint replacement prosthesis to the market.¹⁸ Considering the increased incidence of osteoarthritis in the younger population (<55 years of age), critically reviewing the longevity and durability of TKA implant designs is of great importance. Compared with other TKA implant designs, the NexGen Zimmer Biomet Knee system has shown excellent longevity at the 15-year follow-up.^5,6,9,11-15 Our study began with 136 patients, and, after eliminating the deceased, those lost to follow-up, and non-responders, a total of 99 patients were available for the 15-year follow-up. At this time-point, 80% of the PS implants and 89% of the CR implants were associated with no or mild pain. Survivorship at the 15-year follow-up was similar in both groups: 98% for PS TKAs and 100% for CR TKAs. The reoperation rate was low in both groups, and no evidence of aseptic loosening was found. Based on our results, the NexGen Zimmer Biomet Knee system can be concluded to show excellent longevity and functional outcomes at the 15-year follow-up.

Our study includes several limiting factors that were taken into consideration during the analysis of the results. One of the main limitations of this work is that it required a 15-year follow-up of predominantly elderly patients; many of the participants may be expected to be deceased at this time-point. In our study, a total of 7 patients were confirmed to be deceased by a first-degree relative or the Social Security Death Index. In addition, unlike Bozic and colleagues’¹⁰ previous 5-year follow-up study, radiographic imaging data were not collected at the 15-year follow-up. However, given that this study aimed to assess the functional knee scores and reoperation rates of the PS and CR NexGen Zimmer Biomet Knee system, radiographic information did not appear to be necessary.

CONCLUSION

This study found no significant differences in functional outcomes between the PS and CR NexGen knee implants. Patients who received these implants showed excellent longevity and survivorship at their 15-year follow-up.