Task-specific determinants of one-year performance after unilateral primary total knee arthroplasty.

AIMS: This study aimed to investigate the associations between performance-based outcomes (walking, sit-to-stand, and stair climbing) and impairment-level measures one year after primary unilateral total knee arthroplasty (TKA) using an analytic framework that mitigates multicollinearity. METHODS: Prospectively collected data were analyzed in a cross-sectional design. We included 142 patients who underwent primary unilateral TKA. The performance-based outcomes one year postoperatively were the 40 m fast-paced walk test (FPWT), 30 s chair stand test (CST), and 11-step stair-climbing test (SCT). Explanatory variables included age, sex, BMI, one-year postoperative muscle strength (bilateral quadriceps and hamstring strength), pain visual analogue scale (VAS) score, and knee flexion range of motion (ROM; SCT model only). We performed multivariate analyses using multiple linear regression and additionally applied ridge regression to mitigate multicollinearity. Relative importance was quantified using the Lindeman-Merenda-Gold (LMG) method. RESULTS: For the FPWT, the primary determinants were bilateral quadriceps strength, contralateral hamstring strength, and age, while sex and pain VAS scores were lower-importance contributors. For CST, bilateral quadriceps strength, age, and contralateral hamstring strength were the primary determinants, with BMI contributing secondarily. For SCT, contralateral quadriceps strength and age were the main determinants, whereas pain VAS score and knee flexion ROM were additional, lower-importance contributors. CONCLUSION: One year after TKA, bilateral quadriceps strength played a central role across all tasks. Walking and sit-to-stand performances were additionally associated with contralateral hamstring strength and age, whereas stair performance was influenced by pain control and adequate knee flexion ROM. These findings support personalized rehabilitation strategies that prioritize bilateral quadriceps strengthening and layer-task-specific requirements.