Asymmetric transepicondylar axis between varus and valgus osteoarthritic knees in windswept deformity can be predicted by hip-knee-ankle angle difference

Purpose Studies regarding the best strategy to determine appropriate femoral component rotation during bilateral total knee arthroplasty (TKA) in wind swept deformities (WSD) are very limited. The purpose of this study was (1) to evaluate whether femoral rotational profiles differ between varus and valgus osteoarthritic knees in WSD and (2) to analyze the correlation between femoral rotational profiles and coronal radiologic parameters. Methods A total of 40 patients who were diagnosed with bilateral knee osteoarthritis with WSD between January 2010 and December 2020 at a single institution were retrospectively reviewed. On axial computed tomography scans, femoral rotational profile parameters such as the clinical transepicondylar axis (cTEA) and anterior-posterior (AP) axis were compared between valgus and varus osteoarthritic knees. In standing full-limb AP radiographs, coronal radiographic parameters including hip-knee-ankle angle (HKA), valgus correction angle (VCA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and joint line convergence angle (JLCA) were measured in both knees. The correlation between the varus-valgus cTEA difference, and differences in coronal radiologic parameters was analyzed. Results In valgus osteoarthritic knees, cTEA was significantly increased compared to varus osteoarthritic knees by 1.5 degrees (valgus: 7.65 degrees +/- 1.82 degrees, varus: 6.15 degrees +/- 1.58 degrees, p < 0.001). All coronal radiologic parameters, including HKA, LDFA, MPTA, JLCA, and VCA, were significantly different between valgus and varus knees. In correlation analysis, the varus-valgus cTEA difference was significantly correlated with LDFA (r = 0.365, p = 0.021), MPTA (r = 0.442, p = 0.004), and HKA differences (r = 0.693, p < 0.001), with the HKA difference showing the strongest correlation with the cTEA difference. Conclusion In bilateral knee osteoarthritis with WSD, valgus knees showed significantly increased cTEA compared to varus knees, and the cTEA difference positively correlated with the HKA difference between valgus and varus knees. To determine the optimal femoral component rotation during TKA in WSD, assessment of cTEA with pre-operative CT scans or careful intra-operative measurement is recommended, especially in patients with large HKA difference.