Preoperative coronal tibiofemoral subluxation does not affect 2-year outcomes after mobile-bearing medial unicompartmental knee arthroplasty for anteromedial osteoarthritis

INTRODUCTION: Coronal tibiofemoral subluxation (CTFS) is frequently observed in patients with medial knee osteoarthritis; however, its clinical relevance and the acceptable degree of CTFS when considering unicompartmental knee arthroplasty (UKA) remain unclear. This study aimed to determine whether preoperative CTFS influences short-term postoperative clinical outcomes in patients with anteromedial osteoarthritis (AMOA) undergoing medial UKA. METHODS: In this retrospective cohort study, 457 consecutive knees with AMOA who underwent mobile-bearing UKA performed at a single center between August 2016 and May 2023 were analyzed. CTFS, defined as medial translation of the femur relative to the tibia, was measured on preoperative weight-bearing anteroposterior radiographs and expressed as the percentage of tibial plateau width. Patients were categorized into mild (0-5%), moderate (≥ 5% to < 10%), and severe (≥ 10%) CTFS groups. Clinical outcomes were evaluated using the Oxford Knee Score (OKS) preoperatively and at 3 months, 1 and 2 years postoperatively. Pairwise comparisons of changes in OKS were performed using a general linear model with Bonferroni-adjusted post hoc tests, and adjusted mean differences were calculated controlling for age, sex, body mass index, and preoperative OKS. RESULTS: At 2 years, mean OKS improvements were 16.6 ± 8.9, 14.8 ± 8.3, and 16.0 ± 9.3 in the mild, moderate, and severe CTFS groups, respectively. Adjusted mean differences between groups were small, with confidence intervals including zero. The severe CTFS group demonstrated greater joint line convergence angle than the mild and moderate groups (both p < 0.001). Mean bearing thickness did not differ among groups (p = 0.428). CONCLUSIONS: Preoperative CTFS was not associated with worse outcomes in mobile-bearing UKA for AMOA with correctable deformity. Within the setting of correctable deformity and appropriate patient selection, preoperative CTFS was not associated with inferior 2-year outcomes. Longer-term survivorship and radiographic progression analyses are warranted.