Higher prearthritic activity is associated with higher long‐term activity after medial unicompartmental knee arthroplasty

Abstract Purpose To evaluate long‐term sport participation after medial unicompartmental knee arthroplasty and determine whether recalled prearthritic activity was associated with activity at final follow‐up. Methods This retrospective study included 76 knees in 70 patients evaluated at a mean follow‐up of 116.3 ± 31.9 months. The Tegner Activity Scale was recorded for the retrospectively recalled prearthritic period, immediately before surgery, and final follow‐up. Final Tegner score was the primary outcome. Return to sport was assessed among the 54 knees with prearthritic sport participation. Multivariable linear regression used patient‐clustered standard errors, and a sensitivity analysis excluded seven revised knees. No a priori sample‐size calculation was performed. Results Of 54 previously sport‐active knees, 53 returned to at least one sport (98.1%). Across all 76 knees, 61 (80.3%) participated in sport and six (7.9%) reported vigorous activity at final follow‐up. Mean Tegner score decreased from 4.00 ± 1.03 prearthritically to 2.3 ± 1.5 preoperatively ( p < 0.001) and increased to 3.88 ± 0.78 at final follow‐up ( p < 0.001 vs. preoperative; p = 0.227 vs. prearthritic). Prearthritic Tegner score was associated with final Tegner score (regression coefficient, 0.531; 95% confidence interval, 0.242–0.821; p < 0.001), and the association persisted after excluding revised knees (regression coefficient, 0.519; 95% confidence interval, 0.224–0.814; p < 0.001). Conclusion Sport participation was high at nearly 10 years after medial unicompartmental knee arthroplasty, although vigorous activity was uncommon. Higher prearthritic activity was associated with higher final activity, but retrospective recall and substantial attrition limit causal and prognostic interpretation. Level of Evidence Level IV.