Isolated lateral compartment cartilage changes on preoperative magnetic resonance imaging should not automatically preclude medial unicompartmental knee arthroplasty: A cohort study of 100 magnetic resonance imaging scans

Abstract Purpose Magnetic resonance imaging (MRI) frequently detects lateral compartment abnormalities in patients considered for medial unicompartmental knee replacement (UKR). The long‐term prognostic significance of these findings remains unclear and may influence patient selection. The purpose of this study was to investigate whether lateral compartment cartilage changes identified on preoperative MRI are associated with an increased risk of revision following medial UKR. Methods This retrospective cohort study included 100 knees undergoing medial UKR between 2006 and 2013 with available preoperative MRI. Lateral compartment cartilage changes on MRI were assessed using a predefined scoring system. The primary outcome was revision for any cause. Competing risk analysis using the Fine‐Grey method was applied to estimate cumulative revision risk, accounting for death as a competing event. Results Mean follow‐up was 9.6 years (standard deviation [SD 4.8]). Lateral compartment cartilage changes were observed in 34 cases, including both partial‐ and full‐thickness cartilage loss. During follow‐up, six revisions occurred, with progression of lateral osteoarthritis accounting for 50% of cases. At 10 years, the cumulative incidence of revision was 9.1% (95% confidence interval [CI] 1.5–16.8) in patients without and 3.0% (95% CI 0–8.9) in patients with lateral compartment changes on preoperative MRI. No statistically significant association was detected between lateral cartilage changes on preoperative MRI and revision risk (sHR 0.40, 95% CI 0.05–3.42; p = 0.40). Conclusions No statistically significant association was detected between lateral compartment cartilage changes on preoperative MRI and revision risk following medial UKR. When radiographic and intraoperative findings are consistent with established indications, isolated lateral MRI abnormalities should not automatically preclude consideration of medial UKR. Level of Evidence Level III, retrospective cohort study.