Preoperative Frailty Correlates With Progression of Lateral Compartment Osteoarthritis After Medial Unicompartmental Knee Arthroplasty: A Mean 70-month Follow-up Study

PURPOSE: Lateral compartment osteoarthritis progression (LOP) is a major cause of mid to long-term failure after medial unicompartmental knee arthroplasty (mUKA). This study investigated whether preoperative frailty predicts LOP after mUKA over a mean 70-month follow-up. METHODS: We retrospectively identified consecutive patients who underwent Oxford Phase III mobile-bearing mUKA between March 2016 and December 2020. Preoperative frailty was assessed with the Clinical Frailty Scale (CFS), and patients were classified as robust (Clinical Frailty Scale ≤ 3) or frail (CFS > 3). To minimize mechanical confounding, cases with postoperative coronal overcorrection and those with preoperative lateral meniscal extrusion on MRI were excluded. Outcomes included hip-knee-ankle angle, lateral compartment Kellgren-Lawrence (K/L) grade, Oxford Knee Score, Forgotten Joint Score, Kujala score, perioperative complications, and revision or conversion to total knee arthroplasty. Univariate and multivariable logistic regression identified risk factors of LOP. RESULTS: A total of 203 knees (101 robust; 102 frail) from 177 patients were analyzed (mean follow-up, 70.8 months). Baseline characteristics were comparable except for age. At the final follow-up, the frail group had lower OKS (39.39 vs 43.06; P < 0.001), FJS (79.56 vs 89.40; P < 0.001), and Kujala scores (59.88 vs 67.71; P < 0.001), and a smaller OKS gain (13.47 vs 18.72; P < 0.001). Five-year standing radiographs were available for 99 of 203 knees (48.8%): 26 of 99 (26.3%) showed a 1-grade increase in lateral K/L, while 73 of 99 (73.7%) remained unchanged. LOP was more frequent in frail versus robust knees (41.7% vs 11.8%; P = 0.001). On multivariable analysis, frailty independently predicted LOP (OR = 4.36; 95% CI, 1.37-13.90; P = 0.013). LOP increased across higher CFS strata within the frail subgroup (P = 0.043). CONCLUSION: Preoperative frailty is common and independently associated with a higher midterm risk of lateral compartment progression after mUKA, with risk escalating at higher frailty levels. CFS-based stratification provides a practical adjunct for preoperative counseling, expectation setting, and perioperative planning in candidates for mUKA.