Varus tibial alignment is associated with improved joint awareness after lateral unicompartmental knee arthroplasty

Due to anatomic and kinematic differences between the medial and lateral knee compartments, findings from medial unicompartmental knee arthroplasty (UKA) cannot be directly applied to lateral UKA. In particular, optimal component alignment may differ between both compartments. Therefore, the study aimed to assess the potential association of femoral and tibial component alignment on clinical outcomes in patients undergoing lateral UKA and to determine whether recommendations for optimal component positioning can be derived from the findings.

This retrospective study analysed prospectively collected data from patients who underwent lateral UKA with a fixed-bearing implant. Radiographic alignment parameters were measured relative to the anatomical axes of the femur and tibia, including femoral varus/valgus angle (VVA-F), tibial varus/valgus angle (VVA-T), femoral flexion/extension angle (FEA-F) and tibial slope angle (TSA). Clinical outcomes were assessed using the Oxford Knee Score, Forgotten Joint Score (FJS) and range of motion. Statistical analyses included correlation and subgroup analyses to identify relationships between component alignment and clinical outcomes.

A total of 94 patients (97 UKA) were eligible for clinical and radiological analysis with a mean follow-up of 3.4 ± 1.9 years. Most component alignment variations did not significantly affect clinical outcomes. However, a varus-aligned tibial component correlated with an improved FJS (p = 0.021). Based on the findings, target alignment ranges for lateral UKA were proposed as safe thresholds: VVA-F: 3° varus to 13° valgus, VVA-T: 3° varus to 1° valgus, FEA-F: 3.5° extension to 16.5° flexion and TSA: 4.5°-10.5°.

Although previous studies have addressed component alignment in UKA, evidence specifically related to lateral fixed-bearing UKA remains limited. The present study contributes to this underexplored area by providing preliminary data suggesting that slight varus alignment of the tibial component may be associated with improved clinical outcomes in lateral UKA.

Level III, retrospective cohort study.