Early Postoperative Measures Predict 1- and 2-Year Outcomes After Unilateral Total Knee Arthroplasty: Importance of Contralateral Limb Strength

Abstract

Background Total knee arthroplasty (TKA) has been shown to be an effective surgical intervention for people with end-stage knee osteoarthritis. However, recovery of function is variable, and not all people have successful outcomes. Objective The aim of this study was to discern which early postoperative functional measures could predict functional ability at 1 year and 2 years after surgery. Design and Methods One hundred fifty-five people who underwent unilateral TKA participated in the prospective longitudinal study. Functional evaluations were performed at the initial outpatient physical therapy appointment and at 1 and 2 years after surgery. Evaluations consisted of measurements of height, weight, quadriceps muscle strength (force-generating capacity), and knee range of motion; the Timed “Up & Go” Test (TUG); the stair-climbing task (SCT); and the Knee Outcome Survey (KOS) questionnaire. The ability to predict 1- and 2-year outcomes on the basis of early postoperative measures was analyzed with a hierarchical regression. Differences in functional scores were evaluated with a repeated-measures analysis of variance. Results The TUG, SCT, and KOS scores at 1 and 2 years showed significant improvements over the scores at the initial evaluation (P<.001). A weaker quadriceps muscle in the limb that did not undergo surgery (“nonoperated limb”) was related to poorer 1- and 2-year outcomes even after the influence of the other early postoperative measures was accounted for in the regression. Older participants with higher body masses also had poorer outcomes at 1 and 2 years. Postoperative measures were better predictors of TUG and SCT times than of KOS scores. Conclusions Rehabilitation regimens after TKA should include exercises to improve the strength of the nonoperated limb as well as to treat the deficits imposed by the surgery. Emphasis on treating age-related impairments and reducing body mass also might improve long-term outcomes.