The association of WOMAC, HSS and isokinetic strength and fatigue of knee muscles in people with osteoarthritis following total knee replacement

Abstract

BACKGROUND: Osteoarthritis (OA) is the most prevalent joint pathology and an important cause of disability among people over 65 years of age. Following total knee replacement (TKR), which may be the only curative intervention, function is mainly affected by quadriceps weakness whose extent can accurately be assessed using isokinetic dynamometry. AIM: To evaluate the association between the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the Hospital for Special Surgery Score (HSS) scores and knee muscle isokinetic strength and fatigue findings in TKR patients 2-5 years postoperatively as well as assess the reproducibility and validity of the isokinetic test findings in this cohort. DESIGN: Twenty-four women who underwent TKR filled in the WOMAC and HSS questionnaires. The isokinetic test was carried out at 120 and 180 • /s in concentric flexion/extension. The maximal isokinetic strength was evaluated as the peak torque (PT). Isokinetic fatigue was measured using the fatigue index and calculated based on 40 repetitions at 120 • /s. The same protocol was performed 7 days apart. Test-retest reproducibility was analyzed using intraclass correlation coefficient (ICC), the standard error of measurement (SEM) and Bland Altman plots. HSS and WOMAC internal consistency was tested with Cronbach's alpha; questionnaire validity and correlations were obtained using Spearman's rho. RESULTS: The HSS Function sub-score was significantly correlated with quadriceps PT but not with fatigue isokinetic scores. Excellent reproducibility was indicated for all outcome measures, with the exception of the HSS Knee subscore and the fatigue index. CONCLUSIONS: Isokinetic dynamometry of the quadriceps can provide objective and useful information regarding the functional status of patients following TKR due to OA of the knee.