Preoperative medial‐compartment osteophytes do not adversely affect the outcome of lateral unicompartmental knee arthroplasty

PURPOSE: Lateral unicompartmental knee arthroplasty (UKA) is an effective treatment for isolated lateral-compartment osteoarthritis, yet detailed evidence-based indication criteria remain poorly defined. Therefore, this study evaluated the association between preoperative medial-compartment osteophytes and reoperation-free survival, implant survivorship, medial-compartment disease progression requiring reoperation, and postoperative functional outcomes following lateral UKA. METHODS: A total of 900 lateral UKAs (830 patients) performed between 2016 and 2021 with a minimum follow-up of 2 years (mean 5.1 ± 1.8 years) were retrospectively analysed. Using the OARSI (Osteoarthritis Research Society International) atlas, knee radiographs were stratified into no medial osteophytes (n = 601), small osteophytes (n = 180) and moderate/severe osteophytes (n = 119). Kaplan-Meier survival analysis estimated 9-year survival for the endpoints reoperation, implant revision and disease progression requiring reoperation. Functional outcomes were assessed using the Oxford Knee Score (OKS) and University of California, Los Angeles (UCLA) Activity Score. RESULTS: Reoperation-free survival at 9 years was 94.2% (95% confidence interval [CI]: 91.6-96.8) for knees without osteophytes, 93.0% (95% CI: 88.5-97.5) for small osteophytes, and 91.8% (95% CI: 86.5-97.1) for moderate/severe osteophytes (p = 0.489). Implant survivorship was comparably high across groups (98.3%, 98.1% and 98.0%), respectively (p = 0.972). Medial-compartment disease progression was not associated with radiographic medial osteophyte status (97.6% [95% CI: 96.1-98.5], 98.7% [95% CI: 95.0-99.7] and 96.9% [95% CI: 93.4-98.5]; p = 0.616). Functional outcomes improved significantly across groups without differences between groups (OKS: p = 0.389; UCLA: p = 0.353). CONCLUSIONS: Clinically relevant medial-compartment disease progression requiring reoperation after lateral UKA is uncommon at mid-term follow-up and appears to be independent of the presence or severity of medial-compartment osteophytes. These findings suggest that medial-compartment osteophytes alone should not preclude appropriately selected patients from undergoing lateral UKA when indications are based on stress radiographs. LEVEL OF EVIDENCE: Level IV.