Proximal external femoral torsion increases lateral femoral shaft bowing: a study based on 3D CT reconstruction models

Abstract

Purpose Femoral bowing influences the genesis and management of knee osteoarthritis (OA). The aim of this study was to investigate the relationship between the femoral torsion angle (FTA) and femoral bowing angle (FBA) in a southern Chinese population. It was hypothesized that a greater FTA would lead to a greater lateral FBA. Methods A total of 381 lower extremities from 381 osteoarthritic patients (298 women, 83 men; 201 left, 180 right; mean age 66.5 ± 8.9 years) were retrospectively reviewed. Age, sex, body mass index (BMI), side, height, femoral length (FL), hip-knee-ankle angle (HKA) and FTA were set as FBA-related factors. The three-dimensional (3D) FBA, the angle between the anatomical axis of the proximal femur and the anatomical axis of the distal femur in the plane they form, and its projection on the coronal (lateral FBA) and sagittal (anterior FBA) planes were measured on 3D computed tomography (CT) models. The correlation of the 3D, lateral and anterior FBAs with each of the FBA-related factors was explored using multiple linear regression analysis. The correlation between the FBA and FTA was explored and verified after using propensity score matching to control for the other FBA-related factors. ResultsThe mean lateral and anterior FBAs were 5.5°, with 53.5% greater than 5°, and 12.7°, with 70.3% greater than 11°, respectively. 3D FBA was positively correlated with age (Std.Co = 0.113, P < 0.05) and HKA (Std.Co = 0.129, P < 0.05). Lateral FBA was positively correlated with age (Std.Co = 0.118, P < 0.05), female sex (Std.Co = 0.206, P < 0.05), HKA (Std. Co = 0.184, P < 0.05) and FL (Std.Co = 0.220, P < 0.05). Anterior FBA was positively correlated with age (Std.Co = 0.108, P < 0.05) and male sex (Std.Co = 0.108, P < 0.05). When the related factors were balanced between the two groups (NS), FTA did not significantly affect 3D FBA or anterior FBA (NS), while FTA was positively correlated with lateral FBA (Std. Co = 0.165, P < 0.05). Conclusion External torsion of the proximal femur increases the lateral FBA by twisting a partial anterior FBA into a lateral FBA, especially in the female population. If a patient is found to have a large lateral FBA preoperatively, one should be alert to the possibility of a concomitant large FTA, as there are implications for femoral orthopedics, TKA and patellofemoral pressure distribution. Level of evidence III.

Surgical Transepicondylar Axis Is Not a Reliable Reference when there Was Lateral Femoral Bowing

“…The posterior condyle line was the tangent line of the most posterior apexes of two posterior condyles. According to previous studies, 3 the angle between the anatomical axis of the proximal femur and the anatomical axis of the distal femur in the plane they formed was the actual femoral bowing angle (FBA; Fig. 1 ).…”

“…Malalignment and malrotation of femoral components cause dissatisfaction after total knee arthroplasty (TKA). 1 , 2 Surgical transepicondylar axis (sTEA) is the line between the most prominent of lateral condyle and the most concave of medial condyle, 3 , 4 which is believed to be close to the true femoral rotating axis. 5 , 6 In the axial plane, sTEA is considered a reliable axial reference for cutting the posterior condyle and rotating the femoral component compared to other osseous landmarks.…”

Functional knee phenotypes appear to be more suitable for the Chinese OA population compared with CPAK classification: A study based on 3D CT reconstruction models

“…All observers were trained in measurement and standardized on measurement criteria. To ensure enough forgotten time, an interval of not less than 2 weeks between measurements was required [21]. For anatomical parameters, the intraobserver correlation coefficients were greater than 0.9 for all three observers, and the interobserver correlation coefficients were greater than 0.85, indicating excellent intra‐ and interobserver reliability.…”