Assessment of influences of posterior rotation of the tibial condyles on the Insall-Salvati ratio.

The positional relationship between patellar and femoral articular surfaces may vary according to the degree of posterior rotation of the tibial condyle, which may influence the patellar configuration. We hypothesized that the configuration of the patella has a rhomboid transformation similar to that of the tibial condyle. This cohort study included 313 patients with knee pain who underwent lateral-view knee digital radiography. The length of the long axis, short axis of the patella, and patellar tendon length of the patellofemoral joint were measured. The patella axis ratio (length of long/short axis) as patellar configuration and Insall-Salvati ratio were calculated. Correlations between the configuration of the tibial condyle and the three length parameters and the Insall-Salvati ratio were assessed. Posterior rotation and the rhomboid transformation of the tibial condyle were positively correlated with the length of the long axis of the patella and negatively correlated with the Insall-Salvati ratio. The more the tibial articular surface shifted posteriorly due to posterior rotation and rhomboid transformation of the tibial condyle, the longer the long axis of the patella was, and the smaller the Insall-Salvati ratio was. The long axis of the patella became longer due to rhomboid transformation, similar to the tibial condyle.

Component gap control during posterior-stabilised total knee arthroplasty using the posterior condylar pre-cut technique.

PURPOSE: Adjusting the gap lengths to ensure equal lengths in both extension and flexion during total knee arthroplasty (TKA) is important for achieving successful outcomes. We designed a new pre-cut trial component (PCT) for posterior-stabilised (PS) TKA and aimed to determine whether the pre-cut technique is useful for component gap (CG) control in PS TKA. METHODS: A total of 70 knees were included. The PS PCT for PS TKA is composed of a 9-mm-thick distal part and 5-mm-thick posterior part with a cam structure. First, the distal femur and proximal tibia were cut to create an extension gap. Next, a 4-mm pre-cut was made from the posterior femoral condylar line; then, the PS PCT was attached, and the CGs were checked and compared at 0° and 90° knee flexion. Final CGs with the trial femoral components were compared with gaps in PS PCT at 0° and 90° knee flexion. RESULTS: CGs using PS PCTs were 10.2 mm at 0° and 13.6 mm at 90° knee flexion. According to the release of the posterior capsule at intercondylar notch and the adjustment of the cutting level of posterior femoral condyle, the final CG on knee extension was 11.3 mm; it did not significantly differ from CGs with PS PCT. The final CG at 90° knee flexion was 12.7 mm; it did not significantly differ from the estimated gap (12.4 mm) in PS PCT after flexion gap control. CONCLUSION: CG control using PS PCT is a useful technique during PS TKA. LEVEL OF EVIDENCE: Level IV: Case series.

The posterior tibial slope is mainly created by the posterior rotation of the tibial condyles.

PURPOSE: Constitutional varus in the coronal plane is formed based on the Hueter-Volkmann's law. The varus deformity occurs at the proximal metaphysis of the tibia and the tibial condyle rotates medially. In the sagittal plane, we hypothesized that the posterior slope angle of the tibial articular surface may also occur at the proximal metaphysis and the tibial condyle rotates posteriorly. The purpose of this study was to verify the hypothesis. METHODS: A total of 208 patients who underwent TKA had lateral view proximal tibia digital radiograph on which seven parameters were analyzed. The posterior slope angle of the tibial articular surface relative to the anterior wall of the tibial condyle and that relative to the anterior cortex of the tibial shaft were assessed. Correlation between the position of the tibial condyle and the posterior slope angle of the articular surface were assessed. RESULTS: The proximal tibial condyle itself did not have a posterior slope in the 86.5% of the participants. Posterior rotation of the tibial condyle created posterior slope of the tibial articular surface relative to the anterior cortex of the tibial shaft. The more tibial condyle was posteriorly rotated, the more the tibial articular surface shifted posteriorly. CONCLUSION: Study findings showed that the posterior tibial slope occurs at the proximal metaphysis of the tibia, and the tibial condyle rotates posteriorly. The posterior tibial slope involves the posterior shift of the tibial articular surface. The posterior tibial slope is mainly created by the posterior rotation of the tibial condyle.

Proximal tibia vara involves the medial shift of the tibial articular surface.

PURPOSE: According to the concept of the constitutional varus, the tibial articular surface (TAS) has varus inclination. On the other hand, it has been reported that proximal tibia vara involved medial shift of the TAS. However, it has not been assessed whether varus inclination of the TAS has a correlation with the medial shift. We investigated whether varus inclination of the TAS has a correlation with the medial shift. If there is a correlation between two parameters, the influence of the medial shift of the TAS on the value of the hip-knee-ankle (HKA) angle and the femorotibial angle should be considered. METHODS: A total of 112 patients who underwent total knee arthroplasty had anteroposterior view tibia digital radiograph on which five parameters were analyzed. Varus angle of the TAS, the distance between the mechanical axis and the anatomical axis on the articular surface, and the width of the articular surface were measured. RESULTS: The more the proximal tibia had varus deformity, the more the TAS shift medially would be. Therefore, the mechanical axis does not match the anatomical axis. Because the HKA angle was assessed based on the concept that the mechanical and anatomical axes match on the tibia, this angle may not express the true alignment of the lower extremity in knees with proximal tibia vara. CONCLUSION: In varus knees, the proximal tibia has a medial shift of the TAS that may influence the value of the HKA angle.

Suppression of joint destruction with subcutaneous tocilizumab for Japanese patients with rheumatoid arthritis in clinical practice.

Objectives: To investigate the efficacy of suppressing joint destruction with subcutaneous tocilizumab (TCZ-SC) for Japanese rheumatoid arthritis (RA) patients in the real-world clinical setting.Methods: This 1-year prospective, multicenter study included 110 RA patients in whom TCZ-SC was newly initiated. Primary endpoint was the change from baseline in vdH-modified total Sharp score (mTSS) at week 52. Structural remission was defined as yearly mTSS of 0.5 or less. Disease activity was evaluated using the disease activity score (DAS28-ESR) and clinical disease activity index (CDAI).Results: At baseline, the patients' mean age was 58.6 years, and the mean disease duration was 10.6 years. The proportion of patients who were naïve for biologics was 44.5%, and 64.5% concomitantly received methotrexate. The yearly mTSS showed significant improvement from 9.41 before TCZ-SC initiation to -0.15 after 52 weeks. The structural remission rate was 76.1%. After 52 weeks, the DAS28-ESR and CDAI remission rates were 52% and 21%, respectively. Although the previous usage of biologics and baseline disease activity significantly affected the clinical remission, no factors with significant effects on structural remission were identified.Conclusion: These findings support the efficacy of TCZ-SC in suppressing disease activity as well as joint destruction over a 1-year period.

Comparative evaluation of posterior cruciate ligament in total knee arthroplasty.

INTRODUCTION: It has been realized that for osteoarthritis (OA) knee with varus deformity, posterior cruciate ligament (PCL) release resulted in the increase of the flexion gap without significant effect on the extension gap. While the effect of release on gap angle is still obscure. On the other hand, gap distance and varus angle measured under different distraction forces suggest different patterns. OBJECTIVES: In the current study, mechanical gap balance in displacement and angular alternation of extension and flexion gaps will be evaluated, with PCL fully retained or resected under different distracting forces in varus knees. METHODS: Fifty cases with medial OA undergoing posterior-stabilized (PS) total knee arthroplasty (TKA) were included in the study. PCL of all the cases were identified intact before resection. After distal femoral and proximal tibial cuts were initially performed and anterior cruciate ligament was excised, joint gap angle and distance in full extension and at 90° flexion were obtained by means of a tensioning device with 10, 20 and 30 inch-pounds (in-lbf) of distraction force. The gap angle and distance were measured three times at each step. After the excision of PCL, the same measurement was performed. RESULTS: Both the distance and the varus angles of the knee gap enlarged accordingly with the augment of distraction forces at both extension and flexion with or without PCL resection. As to the gap distance, it remained the same after PCL resection at extension; while at flexion, the gap distance significantly ( p < 0.001) enlarged - 1.2, 1.6 and 1.9 mm - under 10, 20 and 30 in-lbf, respectively, after PCL resection. As to the varus angles, it significantly ( p < .050) decreased 0.6°, 0.3° and 0.4° at extension; while at flexion, the varus angles decreased 0° (not significant), 0.6° ( p < 0.050) and 1.1° ( p < 0.001) with 10, 20 and 30 in-lbf, respectively, after PCL resection. CONCLUSION: Our study indicated that the sacrifice of PCL will decrease the varus deformity at both extension and flexion, but with the exception under low distraction force at flexion. A proper distraction tension is of great importance in gap balancing during TKA. Sufficient attention of varus differences should be paid to the gap balance technique when choosing from different techniques, PCL-retained TKA or PCL-sacrificed TKA, as well as and an appropriate distract tension during measurement.

Efficacy and safety of olokizumab in Asian patients with moderate-to-severe rheumatoid arthritis, previously exposed to anti-TNF therapy: Results from a randomized phase II trial.

OBJECTIVES: This phase II, dose-ranging, double-blind, placebo-controlled, randomized study (NCT01463059) evaluated efficacy and safety of olokizumab (OKZ), a humanized anti-interleukin 6 monoclonal antibody, in Asian patients with moderately-to-severely active rheumatoid arthritis (RA) who had previously failed anti-TNF therapy. METHODS: Patients were randomized to one of six treatment arms: placebo or OKZ (60 mg/120 mg/240 mg every four weeks [Q4W]; or 60 mg/120 mg every two weeks [Q2W]); stratified by country and number of prior anti-TNFs. Primary efficacy variable was Week 12 change from baseline (CFB) in DAS28 CRP for 4-week cumulative dose groups of OKZ and placebo; secondary efficacy variables were Week 12 ACR20/ACR50/ACR70 response rates. Patients continued MTX treatment from baseline, without additional csDMARDs. RESULTS: Of 119 randomized patients, 88.2% completed the study. Greater improvements in DAS28(CRP) mean CFB at Week 12 were observed in all OKZ 4-week cumulative dose groups (60 mg/120 mg/240 mg) versus placebo (p < 0.0001). Week 12 ACR20/ACR50 response rates were higher in all OKZ cumulative dose groups versus PBO (p < 0.05). Incidences of adverse events were similar across OKZ 4-week cumulative dose groups (76.9-84.4%) and placebo (82.8%) with no deaths. CONCLUSIONS: OKZ demonstrated improvements in efficacy variables versus placebo in Asian patients with moderately-to-severely active RA who had previously failed anti-TNF therapy. The safety profile was as expected for this class of drug.

Dynamic finite element analysis of mobile bearing type knee prosthesis under deep flexional motion.

The primary objective of this study is to distinguish between mobile bearing and fixed bearing posterior stabilized knee prostheses in the mechanics performance using the finite element simulation. Quantifying the relative mechanics attributes and survivorship between the mobile bearing and the fixed bearing prosthesis remains in investigation among researchers. In the present study, 3-dimensional computational model of a clinically used mobile bearing PS type knee prosthesis was utilized to develop a finite element and dynamic simulation model. Combination of displacement and force driven knee motion was adapted to simulate a flexion motion from 0° to 135° with neutral, 10°, and 20° internal tibial rotation to represent deep knee bending. Introduction of the secondary moving articulation in the mobile bearing knee prosthesis has been found to maintain relatively low shear stress during deep knee motion with tibial rotation.

The effect of malrotation of tibial component of total knee arthroplasty on tibial insert during high flexion using a finite element analysis.

One of the most common errors of total knee arthroplasty procedure is a malrotation of tibial component. The stress on tibial insert is closely related to polyethylene failure. The objective of this study is to analyze the effect of malrotation of tibial component for the stress on tibial insert during high flexion using a finite element analysis. We used Stryker NRG PS for analysis. Three different initial conditions of tibial component including normal, 15° internal malrotation, and 15° external malrotation were analyzed. The tibial insert made from ultra-high-molecular-weight polyethylene was assumed to be elastic-plastic while femoral and tibial metal components were assumed to be rigid. Four nonlinear springs attached to tibial component represented soft tissues around the knee. Vertical load was applied to femoral component which rotated from 0° to 135° while horizontal load along the anterior posterior axis was applied to tibial component during flexion. Maximum equivalent stresses on the surface were analyzed. Internal malrotation caused the highest stress which arose up to 160% of normal position. External malrotation also caused higher stress. Implanting prosthesis in correct position is important for reducing the risk of abnormal wear and failure.

Remission in patients with active rheumatoid arthritis by tocilizumab treatment in routine clinical practice: results from 3 years of prospectively registered data.

OBJECTIVES: This study aimed to evaluate the remission in rheumatoid arthritis (RA) patients treated with tocilizumab (TCZ), based on prospectively registered data in clinical practice. METHODS: We studied 114 consecutive RA patients treated with TCZ for an average of 3.5 years. Remission was evaluated by using the EULAR criteria and the new ACR/EULAR Boolean-based criteria. RESULTS: Among 114 patients (average age 52.2 years; average disease duration 10.6 years), 76 (67 %) had previously received anti-TNF biologics. Mean baseline DAS28-ESR of 5.4 and improved to 2.4 at 36 months. Overall, DAS28-ESR <2.6 was attained by 66.7 %, while ACR/EULAR remission was attained by 35.1 %. ACR/EULAR remission rate was significantly higher in the patients who were biologics-naïve and had good response at the first month. Among 23 patients who completed the treatment for 3 years and had ACR/EULAR remission at 1 year, 15 (65 %) remained in the remission and 16 (70 %) had a DAS28-ESR <2.6 at the final follow-up. The retention rate at 36 months was 68.2 %. CONCLUSIONS: In patients with RA, TCZ is highly effective for both biologics-naïve patients and patients previously exposed to biologics, achieving a high remission rate and drug continuation rate (68.2 %) in clinical practice.

Remission in patients with active rheumatoid arthritis by tocilizumab treatment in routine clinical practice: results from 3 years of prospectively registered data.

OBJECTIVES: This study aimed to evaluate the remission in rheumatoid arthritis (RA) patients treated with tocilizumab (TCZ), based on prospectively registered data in clinical practice. METHODS: We studied 114 consecutive RA patients treated with TCZ for an average of 3.5 years. Remission was evaluated by using the EULAR criteria and the new ACR/EULAR Boolean-based criteria. RESULTS: Among 114 patients (average age 52.2 years; average disease duration 10.6 years), 76 (67 %) had previously received anti-TNF biologics. Mean baseline DAS28-ESR of 5.4 and improved to 2.4 at 36 months. Overall, DAS28-ESR <2.6 was attained by 66.7 %, while ACR/EULAR remission was attained by 35.1 %. ACR/EULAR remission rate was significantly higher in the patients who were biologics-naïve and had good response at the first month. Among 23 patients who completed the treatment for 3 years and had ACR/EULAR remission at 1 year, 15 (65 %) remained in the remission and 16 (70 %) had a DAS28-ESR <2.6 at the final follow-up. The retention rate at 36 months was 68.2 %. CONCLUSIONS: In patients with RA, TCZ is highly effective for both biologics-naïve patients and patients previously exposed to biologics, achieving a high remission rate and drug continuation rate (68.2 %) in clinical practice.

Effect of medial soft-tissue releases during posterior-stabilised total knee arthroplasty.

PURPOSE: To assess the effect of each step of medial soft-tissue releases on the joint gap angle during posterior-stabilised total knee arthroplasty (TKA). METHODS: 82 women and 9 men (mean age, 72 years) with medial osteoarthritic knees underwent 100 posterior-stabilised TKAs, in which release of superficial fibres of the medial collateral ligament (MCL) were required using the gap control technique. The order of releases was the superficial MCL, the pes anserinus, and then the semi-membranosus. The superficial MCL was released selectively. The effect of each step of medial soft-tissue releases in full extension and in 90º flexion was compared. RESULTS: After all medial soft-tissue releases, the mean joint gap angles decreased from 8.7º to 3.8º varus in flexion and from 4.4º to 1.4º varus in extension. The total effect of medial soft-tissue releases was significantly larger in flexion than in extension (4.9º±3.2º vs. 3.0º±2.0º, p<0.0001), except for the release of posterior fibres of the superficial MCL. The effect of release of the semi-membranosus in flexion was largest. CONCLUSION: The release effect was significantly greater in flexion than in extension during posterior-stabilised TKA; the joint gap technique may be more reliable in medial osteoarthritic knees with moderate and severe varus instability.

Clinical evaluation of tocilizumab for patients with active rheumatoid arthritis refractory to anti-TNF biologics: tocilizumab in combination with methotrexate.

We retrospectively observed the clinical efficacy and safety of tocilizumab (TCZ) in 74 patients with rheumatoid arthritis (RA) at 13 hospitals, without any restrictions on disease duration or stage, treatment history, and other influencing factors. TCZ was infused by the approved method, and disease activity was evaluated every 4 weeks until week 24 using a joint disease activity score (DAS28). Remission and treatment response were categorised using European League Against Rheumatism (EULAR) definitions. We also analysed the impact of previous treatment with other biologics and of concomitant methotrexate (MTX) therapy on the efficacy of TCZ. At week 24, the DAS28 had improved from 5.5 to 2.7 and the EULAR remission rate was 55.2%. Good and moderate responses according to the EULAR criteria were obtained in 61 and 36% of the patients, respectively. The biologic-naïve group had a significantly better DAS28 (2.1 vs. 2.8) and a significantly higher "good" response rate (86% vs. 54%) than the biologic-exposed group. Although the TCZ + MTX treatment group and the TCZ monotherapy group had a good response rate of 71 and 48%, respectively, the difference was not significant. Based on these results, we conclude that TCZ is able to significantly alleviate disease symptoms in a wide range of patients with RA in a normal clinical context.

Shape of the joint gap for 90 degrees and 120 degrees knee flexion after total knee arthroplasty.

BACKGROUND: The joint gap is set rectangular at 90 degrees flexion during total knee arthroplasty (TKA). However, the condition of the joint gap in deep knee flexion is obscure. METHODS: The method for obtaining a posteroanterior view radiograph of the knee at 90 degrees flexion (the epicondylar view) was modified, and a method to obtain an anteroposterior view radiograph at 120 degrees flexion (deep flexion view) was established. With this method, subjects lie on the radiography table with their thighs placed on a device so their lower legs hang down in neutral rotation with a 1.5-kg weight attached to the ankle. The joint gap angle and medial and lateral joint space widths were measured on epicondylar view and deep flexion view radiographs in 20 normal male subjects, 20 normal female subjects, and 20 subjects after TKA. RESULTS: The joint gap was almost rectangular at two flexion angles in normal subjects. In the implanted knees, the gap angle was 1.4 degrees varus +/- 3.3 degrees (mean +/- standard deviation), and no significant difference was found between medial and lateral joint space widths at 90 degrees flexion. In contrast, the gap angle was 2.5 degrees varus +/- 2.5 degrees and the lateral joint space width was significantly wider than the medial joint space width at 120 degrees flexion (P < 0.001). The gap angle was more varus with a significant difference in the implanted knees than that in the normal subjects at 120 degrees flexion (P < 0.001). CONCLUSIONS: The joint gap was trapezoidal with a wider lateral side at 120 degrees flexion even though it was almost rectangular at 90 degrees flexion after TKA.

Femoral shaft bowing influences the correction angle for high tibial osteotomy.

BACKGROUND: The optimal femorotibial angle (FTA) after high tibial osteotomy (HTO) is still controversial. Our hypothesis was that FTA itself may not be reliable because FTA cannot represent the accurate alignment of the whole lower extremity. METHODS: Non-weight-bearing radiographs of the lower extremities were taken in 100 Japanese subjects with medial osteoarthritic knees, and seven anatomic parameters were assessed. The correction angle by FTA was calculated so that the postoperative FTA was set at 166 degrees (14 degrees valgus). Another correction angle was calculated so that the mechanical axis passed through the lateral one-fourth of the tibial articular surface after HTO. After the correlation between two correction angles was assessed, influences of anatomic parameters on the discrepancy between two correction angles were assessed. RESULTS: There was a high correlation between two correction angles (R2 = 0.777, P < 0.001). The mechanical axis passed through the lateral one-fourth of the tibial articular surface when the postoperative FTA was set at 166 degrees in 80% of subjects. However, discrepancy between the two correction angles was 3 degrees or larger in 20% of subjects. Femoral shaft bowing and tibial shaft bowing significantly influenced the correction angles. Even though FTA was the same, the femoral head shifted medially in cases with lateral bowing of the femoral shaft, and the correction angle by FTA should be set larger. On the other hand, the correction angle by FTA can be set smaller in knees with medial bowing of the femoral shaft. Tibial shaft bowing also influences the correction angle by FTA. CONCLUSIONS: The correction angle by FTA for HTO should be calculated taking femoral and/or tibial shaft bowing in the frontal plane into account.

The extramedullary guide of the proximal tibia resection should be seen straight in front during total knee arthroplasty.

If surgeons see the shaft of the extramedullary guide from lateral to the guide during preparation of the proximal tibia resection during total knee arthroplasty, the tibial component may be implanted in varus position in the frontal plane. In order to clarify the effect of the angle of the surgeons' sight relative to the sagittal plane and the posterior slope angle of the resected surface on varus position of the tibial component in the frontal plane, mathematical analysis was performed. Three-dimensional coordinate system was utilized so that the central axis of the tibial shaft on the Z-axis and the shaft of the guide were skew. The relationship between two lines was analyzed solving equations on three dimensional planes. When the posterior slope angle is 10 degrees, and if surgeons see the shaft of the guide 10 degrees, 20 degrees and 30 degrees lateral to the sagittal plane, and the shaft and the central axis of the tibial shaft would seem to be parallel, the true varus tilt angle of the shaft on the frontal plane is 1.8 degrees, 3.7 degrees and 5.8 degrees, respectively. The extramedullary guide should be seen straight in front of the guide.

Importance of the lateral anatomic tibial slope as a guide to the tibial cut in total knee arthroplasty in Japanese patients.

Using three-dimensional computed tomography in 50 osteoarthritic knees, we simulated at various cutting angles the tibial cut for total knee arthroplasty. Cutting angles of 0 degrees, 3 degrees, 5 degrees, 7 degrees, 9 degrees, and 11 degrees were used. We then calculated the anterior and posterior thicknesses, the medial-lateral widths, and the medial and lateral condylar depths of the resected tibial bone at each cutting angle. Each set of measurements was evaluated according to a comparison between the cutting angle and the anatomic posterior slopes. The cutting angles showing the smallest anterior-posterior difference at the medial and lateral plateaus were 9 degrees and 7 degrees, respectively. The mean anatomic posterior slopes at the medial and lateral plateaus were 9.0 degrees and 8.1 degrees, respectively. When the tibia was cut at the cutting angle closest to the medial anatomical posterior slope in each knee, the thickness of the lateral posterior plateaus resected from 12 knees (24%) was more than 10 mm. Among these 12 knees, the cutting angle was more than 9 degrees in 9 knees (75%). In contrast, when the tibia was cut at the cutting angle closest to the lateral anatomical posterior slope, only one resected medial posterior plateau was more than 10 mm. The cutting angle of this case was 7 degrees. Therefore, in consideration of the thickness of bone resection from anatomic posterior slope, we demonstrated the importance of using the lateral anatomic posterior tibial slope as a guide to the tibial cut. There was no significant difference with respect to resected bone morphology at any cutting angle.

Anatomical analysis of the femoral condyle in normal and osteoarthritic knees.

It is important to understand anatomical feature of the distal femoral condyle for treatment of osteoarthritic knees. Detailed measurement of the femoral condyle geometry, however, has not been available in osteoarthritic knees including valgus deformity. This study evaluated femoral condyle geometry in 30 normal knees, 30 osteoarthritic knees with varus deformity, and 30 osteoarthritic knees with valgus deformity using radiographs and magnetic resonance imaging (MRI). In radiographic analysis in the coronal plane, the femoral joint angle (lateral angle between the femoral anatomic axis and a tangent to femoral condyles) was 83.3 degrees in the normal knees, 83.8 degrees in the varus knees, and 80.7 degrees in the valgus knees. In MRI analysis in the axial plane, the posterior condylar tangent showed 6.4 degrees of internal rotation relative to the transepicondylar axis in the normal knees, 6.1 degrees in the varus knees, and 11.5 degrees in the valgus knees. These results suggested that there was no hypoplasia of the medial condyle in the varus knees, but the lateral condyle in the valgus knees was severely distorted. Surgeons should take this deformity of the lateral femoral condyle into account when total knee arthroplasty is performed for a valgus knee.

Distal femoral cut perpendicular to the mechanical axis may induce varus instability in flexion in medial osteoarthritic knees with varus deformity in total knee arthroplasty: a pitfall of the navigation system.

Two factors that influence the external rotation angle of the femoral rotational axis in total knee arthroplasty (TKA) were assessed in 40 medial osteoarthritic knees with varus deformity. First, the anatomic configuration of the femur was assessed using standardized radiographs of the patients' lower extremities before TKA. Second, the degree of medial soft tissue release was assessed during TKA. The radiographs showed that the characteristics of the femur were lateral bowing of the shaft and external rotation of the condyle in the coronal plane. Therefore, when the distal femur is cut perpendicular to the mechanical axis, the cut surface may be in too much of a valgus position. Furthermore, some degree of medial soft tissue release was necessary in all knees. Medial soft tissue release rotates the femur externally in extension in the coronal plane, and it rotates the femur externally around the femoral axis in flexion relative to the tibia. A distal femoral cut in too much of a valgus position and medial soft tissue release induces varus instability in flexion in knees with lateral bowing of the femoral shaft. Anatomic variation such as femoral bowing should be considered when a navigation system is used for TKA because the navigation system shows only the mechanical axis.