BACKGROUND: The aim of this study was to evaluate whether preoperative medial proximal tibial angle (MPTA) influences clinical outcomes following mobile-bearing medial unicompartmental knee arthroplasty (UKA).
METHODS: This retrospective study included 454 consecutive patients who had antero-medial osteoarthritis and underwent mobile-bearing medial UKA performed by two surgeons at a single institution between August 2016 and May 2023. Patients were stratified into three groups according to preoperative MPTA: ≤ 83° (n = 84), 84 to 86° (n = 229), and ≥ 87° (n = 141). Within each group, clinical outcomes were further compared according to postoperative tibial component alignment (TCA) using group-specific varus thresholds. Clinical outcomes were assessed using the Oxford Knee Score (OKS) preoperatively and at three months, one year, and two years postoperatively. Pairwise comparisons of changes in OKS were conducted using a general linear model with Bonferroni-adjusted post hoc tests, and adjusted mean differences were calculated after controlling for age, sex, and body mass index.
RESULTS: Improvements in the OKS from baseline to three months, one year, and two years were comparable among the preoperative MPTA groups. Postoperative TCA also did not differ significantly between groups (P = 0.280). In the MPTA ≤ 83° group, varus TCA was associated with significantly greater improvements in OKS at each time point.
CONCLUSION: Preoperative MPTA did not significantly influence clinical outcomes following UKA, suggesting that increased proximal tibial varus may not adversely affect two-year outcomes. Alignment strategies tailored to preoperative MPTA may help optimize postoperative outcomes.
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