Relationship between Lateral Femoral Bowing and Varus Knee Deformity Based on Two-Dimensional Assessment of Side-to-Side Differences

Purpose The objective was to evaluate the relationship between side-to-side differences of lateral femoral bowing and varus knee deformity based on two-dimensional (2D) assessment in unilateral total knee arthroplasty (TKA). Materials and Methods A total of 143 patients with varus knee osteoarthritis who underwent unilateral TKA were enrolled. We evaluated the side-to-side differences of the frontal lower limb alignment by assessing lateral femoral bowing, anatomical medial distal femoral angle, and anatomical medial proximal tibial angle (aMPTA). Results The average values of all anatomical indices were significantly different between the operated side and the non-operated side (p＜0.05). The side-to-side difference in hip knee ankle (HKA) angle had a statistically significant correlation with that in lateral femoral bowing (intraclass correlation coefficient, 0.259; p=0.002) and that in aMPTA. Linear regression analysis showed 0.199° of side-to-side difference in lateral femoral bowing was associated with 1° of side-to-side difference in bilateral HKA angle. Conclusions The side-to-side difference in lateral femoral bowing showed a tendency to increase in proportion to varus knee deformity based on 2D assessment in unilateral TKA patients.