Quadriceps weakness is common after total knee arthroplasty (TKA) as is longterm disability. We hypothesized that preoperative quadriceps strength would be the best predictor of postoperative functional ability when compared to preoperative pain or knee range of motion (ROM).
Forty subjects (mean age 63 +/- 8 yrs, body mass index 29.4 kg/m2 +/- 4.2) were tested 2 weeks before and one year after TKA. Quadriceps strength was measured isometrically, pain was quantified using the Medical Outcome Study Short-Form 36 (SF-36) bodily pain subset, and knee flexion range of motion (ROM) was assessed by goniometer. Performance based functional assessment included the Timed Up and Go test (TUG) and a timed Stair Climbing Test (SCT). The Knee Outcome Survey (KOS) and the SF-36 questionnaires were used to quantify perceived function. The ability of preoperative factors to predict postoperative outcomes was analyzed using hierarchical regression. Differences in means before and one year after surgery were analyzed using paired t tests.
Significant improvements were found in all functional measures assessed (p < 0.001). Preoperative quadriceps strength accounted for the bulk of the variance in the one-year SCT and the TUG (p < 0.001), but did not achieve significance in predicting one-year questionnaire scores (p > 0.05). Neither preoperative pain nor knee ROM were significant predictors of any functional measure (p > 0.05).
Preoperative quadriceps strength plays a dominant role in predicting one-year SCT and TUG functional measures, but it is not a good predictor of score on self-report questionnaires. Preoperative bodily pain and knee flexion ROM are poor predictors of all functional outcome measures.