Associations of self-report physical function with knee strength and knee range-of-motion in total knee arthroplasty possible nonlinear and threshold effects.

This study aims to examine, in patients before and following a total knee arthroplasty (TKA), whether knee extensor strength and knee flexion/extension range-of-motion (ROM) were nonlinearly associated with physical function. Data from 501 patients with TKA were analyzed. Knee extensor strength was assessed preoperatively and 6 months postoperatively. Knee ROM and Short Form-36 (SF-36) physical function data were collected from each patient preoperatively, and at 6 and 24 months postoperatively. Knee strength was measured by handheld dynamometry and knee ROM by goniometry. Restricted cubic spline regression was used to examine possible nonlinear associations. At all assessment points, the associations between knee measures and function were not always linear. Some of the associations revealed distinct threshold points. These findings have potential clinical and research implications.