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.