This single-center cohort study explored preoperative determinants—specifically physical function and the quantity and quality of the quadriceps femoris muscle—for physical activity (PA) status at 1 year following total knee arthroplasty (TKA). A total of 204 individuals with knee osteoarthritis scheduled for TKA were enrolled and subsequently stratified into groups based on PA increase or decrease. Variables exhibiting significant between-group differences, including non-operative-side quadriceps strength, the Knee Injury and Osteoarthritis Outcome Score (KOOS) Sport/Rec dimension, the cross-sectional area (CSA) of the vastus medialis (VM) on the operative side, and computed tomography attenuation values (CTV) of the vastus lateralis (VL) on the operative side, were incorporated into a multiple logistic regression model. Receiver operating characteristic (ROC) curve analysis was employed to establish the threshold for preoperative VM CSA required to surpass the necessary PA score at the one-year postoperative mark. The multivariate logistic regression demonstrated that non-operative-side quadriceps strength, KOOS Sport/Rec, operative-side VM CSA, and operative-side VL CTV each maintained a significant independent association with enhanced PA after TKA. The cutoff value determined by ROC analysis was 10.2 cm². The data suggest that preoperative muscle quantity and quality, particularly the VM, may be critical factors influencing postoperative PA outcomes following TKA.
