Functional quadriceps endurance, dynamic balance, and patient-reported recovery after total knee arthroplasty: a cross-sectional analysis of functional capacity and perceived disability

Background Functional quadriceps endurance is a key determinant of physical function after total knee arthroplasty (TKA), yet its relationship with patient-reported outcomes and the potential mediating role of mobility and balance performance remain underexplored. Objectives To (1) examine the associations between functional quadriceps endurance and patient-reported outcomes (PROMs) after TKA, and (2) test whether dynamic balance and mobility mediate the relationship between endurance and disability. Methods A cross-sectional study was conducted in 136 individuals (mean age 67.45 ± 6.83 years; 58 males) between 6 and 18 months post-TKA. Participants completed physical performance tests–including the 30-Second Chair Stand, Straight-Leg Raise (SLR), Timed Up and Go (TUG), Four-Square Step Test (FSST), Single-Leg Stance (SLS), and Y-Balance Test–along with PROMs (WOMAC, KOOS, PROMIS Pain Interference, LEFS). Participants were stratified into tertiles based on quadriceps endurance. Analyses included ANOVA, ANCOVA, multiple linear regression, and mediation models using Sobel tests. Results Higher quadriceps endurance was significantly associated with better PROMs across all domains ( p < 0.001). Regression models showed endurance independently predicted WOMAC Function (β = −0.87, p < 0.001), PROMIS Pain Interference (β = −0.39, p = 0.006), and KOOS ADL (β = 1.15, p < 0.001). Mediation analyses indicated significant indirect effects through TUG (β = −0.19, Sobel p = 0.001), FSST (β = −0.15, p = 0.003), and Y-Balance (β = −0.14, p = 0.004), supporting dynamic balance/mobility as mediators. Conclusion Quadriceps endurance is an independent predictor of pain, function, and daily activity outcomes in TKA patients, with dynamic mobility and balance mediating its effects on disability. These findings support targeting endurance and mobility in postoperative rehabilitation.