Valgus positioning of the femoral component does not compromise short-term clinical outcomes in fixed-bearing unicompartmental knee arthroplasty.

Abstract

In unicompartmental knee arthroplasty (UKA), the tibial component tends to be placed in a mildly varus position because of the expected improvement in stress distribution and load transfer across the tibia. With the spacer block technique in UKA, if a tibial osteotomy is performed in the varus position, the femoral component is placed in the valgus position. Therefore, this study aimed to evaluate the impact of valgus positioning of the femoral component on the short-term postoperative clinical outcomes in fixed-bearing UKA using the spacer block technique. We analyzed 77 knees of 70 patients who underwent fixed-bearing UKA using the spacer block technique for medial compartment osteoarthritis and spontaneous osteonecrosis of the knee. Patients were categorized based on femoral component alignment: the neutral group (-3° to + 3°, mean 0.5° ± 1.7° valgus) and the valgus group (> 3°, mean 5.7° ± 1.7° valgus). Postoperative outcomes, including the femorotibial angle (FTA), component sagittal alignment, knee range of motion, and 2011 Knee Society Score (KSS), were compared between the two groups. No significant differences were found between the neutral and valgus groups regarding the postoperative FTA, component sagittal alignment, knee range of motion (neutral vs. valgus group; extension,°: - 1.9 ± 2.9 vs. - 1.6 ± 2.9; flexion,°: 133.0 ± 6.9 vs. 131.3 ± 7.9), or 2011 KSS (objective knee indicators: 95.0 ± 8.9 vs. 96.8 ± 3.5; functional activities: 78.9 ± 15.3 vs. 78.2 ± 12.9). These findings support the safety of valgus positioning in fixed-bearing UKA, offering flexibility in component placement without compromising short-term clinical outcomes.