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Factors affecting range of flexion after total knee arthroplasty
J Orthop Sci (2001) 6:248–252
Factors affecting range of flexion after total knee arthroplasty Haruo Kawamura and Robert B. Bourne Adult Reconstructive Surgery, London Health Sciences Centre, University Campus, 339 Windermere Road, London, Ontario, N6A 5A5, Canada
Abstract Many factors affect postoperative range of flexion after total knee arthroplasty (TKA). The purpose of this study was to identify the most important factors that affect range of knee flexion after TKA. Sixty-five patients (73 knees) were treated with Genesis II knee replacements. Minimum follow-up was 2 years. Patient demographics (sex, age, body mass index, previous surgery, component type, patella resurfacing, preoperative Knee Society score preoperative range of motion) and radiographic measurements (preoperative tibiofemoral varus/valgus angle, height of the joint line, length of the patellar tendon, shift and tilt angle of the patella) were analyzed statistically. Among these factors, preoperative range of flexion, positively, and preoperative varus/valgus tibiofemoral angle, negatively, affected postoperative range of flexion. The tilt angle of the patella and the tilt angle of the patellar button approached statistical significance in revealing a negative relation with postoperative range of flexion. TKAs in which the patella was not resurfaced tended to lose range of flexion, whereas TKAs in which the patella was resurfaced tended to have no loss of flexion, although the number of TKAs in which the patella was not resurfaced was small. In conclusion, preoperative range of flexion and preoperative varus/valgus tibiofemoral angle affected postoperative range of flexion. The tilt angle of the patella and tilt angle of the patellar button may be factors that affect postoperative range of flexion. Key words Total knee arthroplasty · Flexion · Range of motion · Patella
Introduction Postoperative knee flexion after total knee arthroplasty (TKA) is important and correlates closely with patient satisfaction and functional level.1,4,5,8,11 Many factors Offprint requests to: R.B. Bourne Received: September 28, 2000 / Accepted: January 9, 2001
affect postoperative range of flexion after TKA. Up to now, preoperative flexion,1,8,9,11,12 tibiofemoral varus/ valgus angle,12 diagnosis,8,12 age of the patient,12 body weight,9 preoperative knee score,1 surgical closure,6 and implant design5,10 have been listed as significant factors. Patellar tilt and shift, as well as whether or not the patella was resurfaced, have been considered to be important factors that could affect range of flexion after TKA, although these factors have not yet been proved. The purpose of this study was to identify the important factors that affect range of knee flexion after TKA.
Patients and methods Sixty-five patients (73 knees) were treated with Genesis II total knee replacements (Smith & Nephew, Memphis, TN, USA). All patients were followed for at least 2 years after the operation. The mean age of the 65 patients (37 men and 28 women) at the time of the surgery was 66 years (range, 48 to 88 years). There were 34 right knees and 39 left knees. The preoperative diagnosis was osteoarthritis in 68 knees, rheumatoid arthritis in 2, psoriatic arthritis in 2, and posttraumatic arthritis in 1. Thirty-eight patients had previous surgeries; 10 had a high tibial osteotomy, 25 had a knee arthroscopy, and 13 had a menisectomy. The mean body mass index (BMI) at the time of the surgery was 31.9 (range, 17.9 to 50.7). All operative procedures were performed by or under the direct supervision of the same surgeon (R.B.B.), using a medial parapatellar surgical approach. All components were inserted with cement. Cruciate retaining (CR) components were used for 48 knees and cruciate substituting (CS) components were used for 25 knees. The patella was not resurfaced if a patient had no patellofemoral symptoms preoperatively, minimal signs of patellofemoral arthritis on preoperative radiographs, and an intraoperative finding of mild degeneration of
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the patellar articular cartilage. Using these criteria, the patella was not resurfaced in 7 knees. For the remaining 66 knees, the patella was resurfaced with an allpolyethylene biconvex patellar button. The patellar button was placed in a medialized position, just lateral to the odd facet. When tracking of the patella was examined, a “no thumbs” technique was used, holding the hindfoot in internal rotation. As a result, a release of the lateral patellar retinaculum was performed in 5 (7%) knees. Surgical wound closure was done in knee extension, taking care to accurately re-align the extensor mechanism. One day after the surgery, the patients were encouraged to start range-of-motion exercises and to bear weight on the operated leg. The patients were assessed postoperatively at 6 weeks, 3 months, 6 months, and 1 year, and annually thereafter. At each visit, the Knee Society knee score was determined.
Fig. 1. Radiographic measurements in the skyline view of A tilt angle of the patella and B tilt angle of the patellar button
Radiographic measurements Standing anteroposterior (AP) and lateral radiographs, as well as a 45° skyline view of the patella, were obtained preoperatively, and postoperatively at each visit. All radiographs were taken with a standardized beam distance and knee position. Using standing AP views, we determined pre- and postoperative tibiofemoral varus/valgus angles (anatomic axis of the knee). Height of the joint line on the AP and lateral views were determined as the distance from the tip of the fibular styloid process to the joint line. The amount of joint line elevation was calculated by subtracting the preoperative height of the joint line from the postoperative height of the joint line. Change in length of the patellar tendon (PT) was calculated by subtracting the preoperative PT length from the postoperative PT length. Shift and tilt angle of the patella on the skyline views were measured using the modified method described by Gomes et al.7 Shift of the patella was determined as the distance from the center of the trochlear groove to the center of the patella, pre- and postoperatively. The tilt angle of the patella was defined as the angle between a line from the anterior limits of the femoral condyles and the equatorial line of the patella. The tilt angle of the patellar button was defined as the angle between a line from the anterior limits of the femoral condyles and a line drawn through the wire marker of the patellar button (Fig. 1). Tilt angle of the patella and the patellar button were measured only for postoperative radiographs. Any discrepancy between the tilt angle of the patella and the tilt angle of the patellar button was calculated. Statistical analysis Patient demographics included sex, age, BMI, previous surgeries (high tibial osteotomy, menisectomy, and
arthroscopy), component type (Genesis II CR or CS), preoperative Knee Society scores, and preoperative range of motion (extension, flexion, and flexion arc). Radiographic measurements included preoperative tibiofemoral varus/valgus angle, the amount of joint line elevation, shift of the patella, tilt angle of the patella, and tilt angle of the patellar button. Patient demographics and radiographic measurements were analyzed to identify the factors that affected postoperative range of flexion. Upon completion of data collection, summary statistics were compiled so as to allow description of the study population and the validity of the underlying statistical assumptions. Comparisons were performed using SPSS 9.0 (SPSS, Chicago, ILL, USA). Categorical variables were analyzed using the χ2 test or Fisher’s exact test where appropriate. Student’s two-tailed ttests were used to compare continuous variables. Finally, logistic regression was used to determine the factors affecting postoperative range of flexion.
Results Range of motion Preoperative values for range of extension, flexion, and flexion arc were 6 6 5°, 113 6 11°, and 107 6 15°, respectively. Postoperative values for range of extension, flexion, and flexion arc were 1 6 3°, 110 6 12°, and 109 6 13°, respectively. Decrease in the flexion contracture was significant (P , 0.01), but the decrease in the range of flexion and the increase in range of flexion were not significant (P 5 0.06 and 0.33, respectively). Although no significant difference was found between the pre- and postoperative range of flexion for the 66 TKAs in which the patella was resurfaced (112° and 111°, respectively; P 5 0.32), a significant difference was found between the pre- and postoperative range of flexion for the 7 TKAs in which the patella was not resurfaced (120° and 104°, respectively; P 5 0.03). Four of the 7 knees in which the patella was not resurfaced lost range of motion by more than 20° (maximum, 30°). In contrast, only 5 of the 66 knees in which the patella
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Table 1. Factors included in the statistical analysis Factors Patient demographics Age Sex BMI Previous HTO Previous arthroscopy Previous menisectomy Preoperative extension Preoperative flexion Preoperative flexion arc Preoperative knee score Component type Radiographic measurements Preoperative tibiofemoral varus/valgus angle Joint line elevation (AP) Joint line elevation (lateral) Shift of the patella Tilt angle of the patella Tilt angle of the patellar button
Pearson correlation
Significance (P value)
20.186 0.071 0.034 0.112 20.008 20.157 20.232 0.330 0.322 0.139 0.065
0.057 0.274 0.387 0.174 0.473 0.092 0.024 0.002 0.003 0.121 0.294
20.254 20.030 0.056 20.013 20.210 20.231
0.015 0.808 0.642 0.457 0.075 0.053
BMI, Body mass index; HTO, high tibial osteotomy; AP, anteroposterior
was resurfaced lost range of motion by more than 20° (maximum, 25°). No difference was found between CR and CS TKAs in terms of postoperative range of flexion (110° and 112°, respectively). Radiographic measurements Tibiofemoral varus/valgus angle. The average preand postoperative tibiofemoral varus/valgus angles were 178° (range, 153°–192°) and 175° (range, 169°– 181°), respectively. The difference was significant (P 5 0.02). Amount of joint line elevation. The height of the joint line on the AP radiographs was 13.9 6 5.8 mm preoperatively and 17.5 6 4.6 mm postoperatively. The height of the joint line on the lateral view was 15.4 6 5.4 mm preoperatively and 17.8 6 4.6 mm postoperatively. These differences were significant (P , 0.01). The differences between the pre- and postoperative joint lines; namely, the amounts of joint line elevation on the AP and lateral views, were 3.5 and 2.4 mm, respectively. Length of the patellar tendon. The length of the patellar tendon was 47.3 6 6.1 mm preoperatively and 47.7 6 7.0 mm postoperatively. No difference was found between the pre- and postoperative lengths of the patellar tendon (P 5 0.27). Shift of the patella. The preoperative shift of the patella was 5.2 mm lateral to the center of the trochlear
groove (range, 5 mm medial to 25 mm lateral). The postoperative shift of the patella was 0.6 mm lateral to the center of the trochlear groove (range, 6 mm medial to 9 mm lateral). The postoperative shift of the patella was significantly smaller than the preoperative shift of the patella (P , 0.01). Tilt angle of the patella and tilt angle of the patellar button. The tilt angle of the patella ranged from 5° medially to 33° laterally (average, 6° laterally). The tilt angle of the patellar button ranged from 11° medially to 21° laterally (average, 1° laterally). The difference between the tilt angle of the patella and that of the patellar button was 5.2° on average. Statistical analysis First, we analyzed patient demographics and radiographic measurements to model variables associated with postoperative range of flexion for all patients. Of the variables, preoperative extension (r 5 20.232; P 5 0.024), preoperative flexion (r 5 0.330; P 5 0.002), preoperative flexion arc (r 5 0.322; P 5 0.003), and preoperative tibiofemoral varus/valgus angle (r 5 20.254; P 5 0.015) were related to postoperative flexion (Table 1). Using logistic regression analysis, we found that preoperative flexion (P 5 0.005) and preoperative tibiofemoral varus/valgus angle (P 5 0.033) were significant factors. Second, we examined loss of flexion, comparing preand postoperative flexion. The loss of flexion for TKAs in which the patella was not resurfaced (16.4 6 15.7°)
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was significantly greater than that for TKAs in which the patella was resurfaced (1.5 6 12.0°) (P 5 0.003). Third, we again analyzed patient factors and radiographic measurements to model variables associated with postoperative range of flexion for only the 66 TKAs in which the patella was resurfaced. Again, preoperative flexion showed significant correlation with postoperative flexion (r 5 0.457; P , 0.01). The tilt angle of the patella (r 5 20.210; P 5 0.075) and the tilt angle of the patellar button (r 5 20.231; P 5 0.053) showed interesting statistical trends with postoperative knee flexion.
suggested that a combination of a medialized position of the patellar button and deepening of the patellar groove of the femoral component provided the most anatomically correct position and the most normal tilting of the patella. Chew et al.4 investigated the differences in patellar tracking and knee kinematics among three different total knee designs. Using whole cadaveric lower extremities, they found that all three prosthetic designs showed a significant degree of lateral tilting when compared with the intact knee. Bindelglass et al.2 found no difference in postoperative flexion between centrally tracking knees (103.3°) and poorly tracking knees (102.6°). Our study has suggested that patellar tracking is important in terms of flexion after TKA. This study has implied that the postoperative tilt angles of the patella and the patellar button may be factors that affect postoperative range of flexion. Ideally, the postoperative tilt angle of the patella should be less than 5°. Careful positioning of the patellar button and soft-tissue balancing about the patella seem to be beneficial in maximizing flexion after TKA. This study has also demonstrated that contemporary knee replacement instrumentation tended to elevate the joint line by 2.4 mm (lateral radiograph) to 3.5 mm (AP radiograph). The adverse effect of this joint line elevation after TKA, in terms of knee kinematics and knee flexion, remains to be investigated. Certainly this study suggests that modifications in instrumentation to distalize the joint line by 2 to 3 mm might be in order. In conclusion, the preoperative range of flexion and the preoperative tibiofemoral varus/valgus angles were the factors that affected postoperative range of flexion. The tilt angles of the patella and the patellar button may also be factors that affect the postoperative range of flexion.
Discussion The results of our study confirm those of previous studies, demonstrating that the preoperative range of flexion affects the postoperative range of flexion, and that patients with a high range of motion preoperatively tended to lose motion, whereas patients with poor preoperative motion tended to gain motion, and patients in the midrange tended to stay in the mid range.1,8,9,11,12 Although preoperative flexion significantly influences postoperative flexion, the correlation between preoperative and postoperative range of flexion was not high (r 5 0.330). The preoperative tibiofemoral varus/valgus angle negatively affected the postoperative range of flexion. This negative correlation suggested that patients who had varus deformity preoperatively tended to have less range of flexion than patients who had no deformity or valgus deformity preoperatively. Using a regression tree analysis, Schurman et al.12 also identified tibiofemoral varus/valgus angle as one of the preoperative factors that affect postoperative flexion. To resurface or not to resurface the patella is a controversial problem with TKAs. Many studies suggested that the results of TKA without patellar resurfacing were as good as those with patellar resurfacing.3 Harvey et al.8 found nothing to support routine patellar replacement in terms of improved flexion. Although we found no difference in postoperative range of flexion between TKAs in which the patella was resurfaced and those in which the patella was not resurfaced, we found significant loss of flexion for TKAs in which the patella was not resurfaced, in comparison with TKAs with a resurfaced patella. However, because the number of TKAs without patellar resurfacing was small, no definitive conclusion was drawn from this study as to whether or not the patella should be resurfaced. Although patellar tracking, patellar tilt, and patellar button placement are considered to be critical factors in TKA, no study has suggested a direct relation between these factors and postoperative flexion. Yoshii et al.13
References 1. Anouchi YS, McShane M, Kelly F Jr, et al. Range of motion in total knee replacement. Clin Orthop 1996;331:87–92. 2. Bindelglass DF, Cohen JL, Dorr LD. Patellar tilt and subluxation in total knee arthroplasty. Clin Orthop 1993;286:103–9. 3. Bourne RB, Rorabeck CH, Vaz M, et al. Resurfacing versus not resurfacing the patella during total knee replacement. Clin Orthop 1995;321:156–61. 4. Chew JTH, Stewart NJ, Hanssen AD, et al. Differences in patellar tracking and knee kinematics among three different total knee designs. Clin Orthop 1997;345:87–98. 5. Dennis DA, Komistek RD, Stiehl JB, et al. Range of motion after total knee arthroplasty: the effect of implant design and weightbearing conditions. J Arthroplasty 1998;13:748–52. 6. Emerson RH Jr, Ayers C, Head WC, et al. Surgical closing in primary total knee arthroplasties. Clin Orthop 1996;331:74–80. 7. Gomes LSM, Bechtold JE, Gustilo RB. Patellar prosthesis positioning in total knee arthroplasty. Clin Orthop 1988;236:72–81. 8. Harvey IA, Barry K, Kirby SPJ, et al. Factors affecting the range of movement of total knee arthroplasty. J Bone Joint Surg Br 1993;75:950–5.
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9. Lizaur A, Marco L, Cebrian R. Preoperative factors influencing the range of movement after total knee arthroplasty for severe osteoarthritis. J Bone Joint Surg Br 1997;79:626–9. 10. Maloney WJ, Schurman DJ. The effects of implant design on range of motion after total knee arthroplasty. Total condylar versus posterior stabilized total condylar designs. Clin Orthop 1992;278:147–52. 11. Parsley BS, Engh GA, Dwyer KA. Preoperative flexion. Does it influence postoperative flexion after posterior-cruciate-
retaining total knee arthroplasty? Clin Orthop 1992;275:204– 10. 12. Schurman DJ, Matityahu A, Goodman SB, et al. Prediction of postoperative knee flexion in Insall-Burstein II total knee arthroplasty. Clin Orthop 1998;353:175–84. 13. Yoshii I, Whiteside LA, Anouchi YS. The effect of patellar button placement and femoral component design on patellar tracking in total knee arthroplasty. Clin Orthop 1992;275:211– 9.
Factors affecting range of flexion after total knee arthroplasty Haruo Kawamura and Robert B. Bourne Adult Reconstructive Surgery, London Health Sciences Centre, University Campus, 339 Windermere Road, London, Ontario, N6A 5A5, Canada
Abstract Many factors affect postoperative range of flexion after total knee arthroplasty (TKA). The purpose of this study was to identify the most important factors that affect range of knee flexion after TKA. Sixty-five patients (73 knees) were treated with Genesis II knee replacements. Minimum follow-up was 2 years. Patient demographics (sex, age, body mass index, previous surgery, component type, patella resurfacing, preoperative Knee Society score preoperative range of motion) and radiographic measurements (preoperative tibiofemoral varus/valgus angle, height of the joint line, length of the patellar tendon, shift and tilt angle of the patella) were analyzed statistically. Among these factors, preoperative range of flexion, positively, and preoperative varus/valgus tibiofemoral angle, negatively, affected postoperative range of flexion. The tilt angle of the patella and the tilt angle of the patellar button approached statistical significance in revealing a negative relation with postoperative range of flexion. TKAs in which the patella was not resurfaced tended to lose range of flexion, whereas TKAs in which the patella was resurfaced tended to have no loss of flexion, although the number of TKAs in which the patella was not resurfaced was small. In conclusion, preoperative range of flexion and preoperative varus/valgus tibiofemoral angle affected postoperative range of flexion. The tilt angle of the patella and tilt angle of the patellar button may be factors that affect postoperative range of flexion. Key words Total knee arthroplasty · Flexion · Range of motion · Patella
Introduction Postoperative knee flexion after total knee arthroplasty (TKA) is important and correlates closely with patient satisfaction and functional level.1,4,5,8,11 Many factors Offprint requests to: R.B. Bourne Received: September 28, 2000 / Accepted: January 9, 2001
affect postoperative range of flexion after TKA. Up to now, preoperative flexion,1,8,9,11,12 tibiofemoral varus/ valgus angle,12 diagnosis,8,12 age of the patient,12 body weight,9 preoperative knee score,1 surgical closure,6 and implant design5,10 have been listed as significant factors. Patellar tilt and shift, as well as whether or not the patella was resurfaced, have been considered to be important factors that could affect range of flexion after TKA, although these factors have not yet been proved. The purpose of this study was to identify the important factors that affect range of knee flexion after TKA.
Patients and methods Sixty-five patients (73 knees) were treated with Genesis II total knee replacements (Smith & Nephew, Memphis, TN, USA). All patients were followed for at least 2 years after the operation. The mean age of the 65 patients (37 men and 28 women) at the time of the surgery was 66 years (range, 48 to 88 years). There were 34 right knees and 39 left knees. The preoperative diagnosis was osteoarthritis in 68 knees, rheumatoid arthritis in 2, psoriatic arthritis in 2, and posttraumatic arthritis in 1. Thirty-eight patients had previous surgeries; 10 had a high tibial osteotomy, 25 had a knee arthroscopy, and 13 had a menisectomy. The mean body mass index (BMI) at the time of the surgery was 31.9 (range, 17.9 to 50.7). All operative procedures were performed by or under the direct supervision of the same surgeon (R.B.B.), using a medial parapatellar surgical approach. All components were inserted with cement. Cruciate retaining (CR) components were used for 48 knees and cruciate substituting (CS) components were used for 25 knees. The patella was not resurfaced if a patient had no patellofemoral symptoms preoperatively, minimal signs of patellofemoral arthritis on preoperative radiographs, and an intraoperative finding of mild degeneration of
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the patellar articular cartilage. Using these criteria, the patella was not resurfaced in 7 knees. For the remaining 66 knees, the patella was resurfaced with an allpolyethylene biconvex patellar button. The patellar button was placed in a medialized position, just lateral to the odd facet. When tracking of the patella was examined, a “no thumbs” technique was used, holding the hindfoot in internal rotation. As a result, a release of the lateral patellar retinaculum was performed in 5 (7%) knees. Surgical wound closure was done in knee extension, taking care to accurately re-align the extensor mechanism. One day after the surgery, the patients were encouraged to start range-of-motion exercises and to bear weight on the operated leg. The patients were assessed postoperatively at 6 weeks, 3 months, 6 months, and 1 year, and annually thereafter. At each visit, the Knee Society knee score was determined.
Fig. 1. Radiographic measurements in the skyline view of A tilt angle of the patella and B tilt angle of the patellar button
Radiographic measurements Standing anteroposterior (AP) and lateral radiographs, as well as a 45° skyline view of the patella, were obtained preoperatively, and postoperatively at each visit. All radiographs were taken with a standardized beam distance and knee position. Using standing AP views, we determined pre- and postoperative tibiofemoral varus/valgus angles (anatomic axis of the knee). Height of the joint line on the AP and lateral views were determined as the distance from the tip of the fibular styloid process to the joint line. The amount of joint line elevation was calculated by subtracting the preoperative height of the joint line from the postoperative height of the joint line. Change in length of the patellar tendon (PT) was calculated by subtracting the preoperative PT length from the postoperative PT length. Shift and tilt angle of the patella on the skyline views were measured using the modified method described by Gomes et al.7 Shift of the patella was determined as the distance from the center of the trochlear groove to the center of the patella, pre- and postoperatively. The tilt angle of the patella was defined as the angle between a line from the anterior limits of the femoral condyles and the equatorial line of the patella. The tilt angle of the patellar button was defined as the angle between a line from the anterior limits of the femoral condyles and a line drawn through the wire marker of the patellar button (Fig. 1). Tilt angle of the patella and the patellar button were measured only for postoperative radiographs. Any discrepancy between the tilt angle of the patella and the tilt angle of the patellar button was calculated. Statistical analysis Patient demographics included sex, age, BMI, previous surgeries (high tibial osteotomy, menisectomy, and
arthroscopy), component type (Genesis II CR or CS), preoperative Knee Society scores, and preoperative range of motion (extension, flexion, and flexion arc). Radiographic measurements included preoperative tibiofemoral varus/valgus angle, the amount of joint line elevation, shift of the patella, tilt angle of the patella, and tilt angle of the patellar button. Patient demographics and radiographic measurements were analyzed to identify the factors that affected postoperative range of flexion. Upon completion of data collection, summary statistics were compiled so as to allow description of the study population and the validity of the underlying statistical assumptions. Comparisons were performed using SPSS 9.0 (SPSS, Chicago, ILL, USA). Categorical variables were analyzed using the χ2 test or Fisher’s exact test where appropriate. Student’s two-tailed ttests were used to compare continuous variables. Finally, logistic regression was used to determine the factors affecting postoperative range of flexion.
Results Range of motion Preoperative values for range of extension, flexion, and flexion arc were 6 6 5°, 113 6 11°, and 107 6 15°, respectively. Postoperative values for range of extension, flexion, and flexion arc were 1 6 3°, 110 6 12°, and 109 6 13°, respectively. Decrease in the flexion contracture was significant (P , 0.01), but the decrease in the range of flexion and the increase in range of flexion were not significant (P 5 0.06 and 0.33, respectively). Although no significant difference was found between the pre- and postoperative range of flexion for the 66 TKAs in which the patella was resurfaced (112° and 111°, respectively; P 5 0.32), a significant difference was found between the pre- and postoperative range of flexion for the 7 TKAs in which the patella was not resurfaced (120° and 104°, respectively; P 5 0.03). Four of the 7 knees in which the patella was not resurfaced lost range of motion by more than 20° (maximum, 30°). In contrast, only 5 of the 66 knees in which the patella
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Table 1. Factors included in the statistical analysis Factors Patient demographics Age Sex BMI Previous HTO Previous arthroscopy Previous menisectomy Preoperative extension Preoperative flexion Preoperative flexion arc Preoperative knee score Component type Radiographic measurements Preoperative tibiofemoral varus/valgus angle Joint line elevation (AP) Joint line elevation (lateral) Shift of the patella Tilt angle of the patella Tilt angle of the patellar button
Pearson correlation
Significance (P value)
20.186 0.071 0.034 0.112 20.008 20.157 20.232 0.330 0.322 0.139 0.065
0.057 0.274 0.387 0.174 0.473 0.092 0.024 0.002 0.003 0.121 0.294
20.254 20.030 0.056 20.013 20.210 20.231
0.015 0.808 0.642 0.457 0.075 0.053
BMI, Body mass index; HTO, high tibial osteotomy; AP, anteroposterior
was resurfaced lost range of motion by more than 20° (maximum, 25°). No difference was found between CR and CS TKAs in terms of postoperative range of flexion (110° and 112°, respectively). Radiographic measurements Tibiofemoral varus/valgus angle. The average preand postoperative tibiofemoral varus/valgus angles were 178° (range, 153°–192°) and 175° (range, 169°– 181°), respectively. The difference was significant (P 5 0.02). Amount of joint line elevation. The height of the joint line on the AP radiographs was 13.9 6 5.8 mm preoperatively and 17.5 6 4.6 mm postoperatively. The height of the joint line on the lateral view was 15.4 6 5.4 mm preoperatively and 17.8 6 4.6 mm postoperatively. These differences were significant (P , 0.01). The differences between the pre- and postoperative joint lines; namely, the amounts of joint line elevation on the AP and lateral views, were 3.5 and 2.4 mm, respectively. Length of the patellar tendon. The length of the patellar tendon was 47.3 6 6.1 mm preoperatively and 47.7 6 7.0 mm postoperatively. No difference was found between the pre- and postoperative lengths of the patellar tendon (P 5 0.27). Shift of the patella. The preoperative shift of the patella was 5.2 mm lateral to the center of the trochlear
groove (range, 5 mm medial to 25 mm lateral). The postoperative shift of the patella was 0.6 mm lateral to the center of the trochlear groove (range, 6 mm medial to 9 mm lateral). The postoperative shift of the patella was significantly smaller than the preoperative shift of the patella (P , 0.01). Tilt angle of the patella and tilt angle of the patellar button. The tilt angle of the patella ranged from 5° medially to 33° laterally (average, 6° laterally). The tilt angle of the patellar button ranged from 11° medially to 21° laterally (average, 1° laterally). The difference between the tilt angle of the patella and that of the patellar button was 5.2° on average. Statistical analysis First, we analyzed patient demographics and radiographic measurements to model variables associated with postoperative range of flexion for all patients. Of the variables, preoperative extension (r 5 20.232; P 5 0.024), preoperative flexion (r 5 0.330; P 5 0.002), preoperative flexion arc (r 5 0.322; P 5 0.003), and preoperative tibiofemoral varus/valgus angle (r 5 20.254; P 5 0.015) were related to postoperative flexion (Table 1). Using logistic regression analysis, we found that preoperative flexion (P 5 0.005) and preoperative tibiofemoral varus/valgus angle (P 5 0.033) were significant factors. Second, we examined loss of flexion, comparing preand postoperative flexion. The loss of flexion for TKAs in which the patella was not resurfaced (16.4 6 15.7°)
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was significantly greater than that for TKAs in which the patella was resurfaced (1.5 6 12.0°) (P 5 0.003). Third, we again analyzed patient factors and radiographic measurements to model variables associated with postoperative range of flexion for only the 66 TKAs in which the patella was resurfaced. Again, preoperative flexion showed significant correlation with postoperative flexion (r 5 0.457; P , 0.01). The tilt angle of the patella (r 5 20.210; P 5 0.075) and the tilt angle of the patellar button (r 5 20.231; P 5 0.053) showed interesting statistical trends with postoperative knee flexion.
suggested that a combination of a medialized position of the patellar button and deepening of the patellar groove of the femoral component provided the most anatomically correct position and the most normal tilting of the patella. Chew et al.4 investigated the differences in patellar tracking and knee kinematics among three different total knee designs. Using whole cadaveric lower extremities, they found that all three prosthetic designs showed a significant degree of lateral tilting when compared with the intact knee. Bindelglass et al.2 found no difference in postoperative flexion between centrally tracking knees (103.3°) and poorly tracking knees (102.6°). Our study has suggested that patellar tracking is important in terms of flexion after TKA. This study has implied that the postoperative tilt angles of the patella and the patellar button may be factors that affect postoperative range of flexion. Ideally, the postoperative tilt angle of the patella should be less than 5°. Careful positioning of the patellar button and soft-tissue balancing about the patella seem to be beneficial in maximizing flexion after TKA. This study has also demonstrated that contemporary knee replacement instrumentation tended to elevate the joint line by 2.4 mm (lateral radiograph) to 3.5 mm (AP radiograph). The adverse effect of this joint line elevation after TKA, in terms of knee kinematics and knee flexion, remains to be investigated. Certainly this study suggests that modifications in instrumentation to distalize the joint line by 2 to 3 mm might be in order. In conclusion, the preoperative range of flexion and the preoperative tibiofemoral varus/valgus angles were the factors that affected postoperative range of flexion. The tilt angles of the patella and the patellar button may also be factors that affect the postoperative range of flexion.
Discussion The results of our study confirm those of previous studies, demonstrating that the preoperative range of flexion affects the postoperative range of flexion, and that patients with a high range of motion preoperatively tended to lose motion, whereas patients with poor preoperative motion tended to gain motion, and patients in the midrange tended to stay in the mid range.1,8,9,11,12 Although preoperative flexion significantly influences postoperative flexion, the correlation between preoperative and postoperative range of flexion was not high (r 5 0.330). The preoperative tibiofemoral varus/valgus angle negatively affected the postoperative range of flexion. This negative correlation suggested that patients who had varus deformity preoperatively tended to have less range of flexion than patients who had no deformity or valgus deformity preoperatively. Using a regression tree analysis, Schurman et al.12 also identified tibiofemoral varus/valgus angle as one of the preoperative factors that affect postoperative flexion. To resurface or not to resurface the patella is a controversial problem with TKAs. Many studies suggested that the results of TKA without patellar resurfacing were as good as those with patellar resurfacing.3 Harvey et al.8 found nothing to support routine patellar replacement in terms of improved flexion. Although we found no difference in postoperative range of flexion between TKAs in which the patella was resurfaced and those in which the patella was not resurfaced, we found significant loss of flexion for TKAs in which the patella was not resurfaced, in comparison with TKAs with a resurfaced patella. However, because the number of TKAs without patellar resurfacing was small, no definitive conclusion was drawn from this study as to whether or not the patella should be resurfaced. Although patellar tracking, patellar tilt, and patellar button placement are considered to be critical factors in TKA, no study has suggested a direct relation between these factors and postoperative flexion. Yoshii et al.13
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