Sit-to-stand power predicts functional performance and patient-reported outcomes in patients with advanced knee osteoarthritis. A cross-sectional study

BACKGROUND: Lower limb muscle power is positively associated with functional performance and patient-reported outcomes (PROMs) and suggested as an important variable to evaluate in patients with advanced knee osteoarthritis (OA). OBJECTIVES: To explore the association between muscle power derived from the 30-sec sit-to-stand test (STS power) with functional performance and PROMs compared to maximal isometric knee extensor strength (KE MVC) in male- and female patients with advanced OA. STUDY DESIGN: Cross-sectional design. METHODS: Eighty-six patients (66.6 64.9-67.7years) with advanced knee OA were included. Dependent variables were STS power and KE MVC. Independent variables were Timed Up&Go (TUG), 40-m fast-paced walk test (40mFWT), Knee injury and Osteoarthritis Outcome Score (KOOS) subscales. COVARIATE: Age. ANALYSES: Simple linear- and multiple regression analyses with and without adjusting for age. Pitman's test was used to evaluate differences in correlation strength among dependent variables. RESULTS: STS power demonstrated a statistical relationship with TUG and 40mFWT for both sexes (β coefficients -1.11 to -4.36 (p < 0.05), r2 = 0.47-0.55 (p < 0.05)), and with KOOS Pain, ADL, and Sport for male patients (β coefficients 6.53 to 7.17 (p < 0.05), r2 = 0.29-0.33 (p < 0.05)). Knee extensor MVC demonstrated no relationship with any outcomes for male patients or female patients. STS power displayed statistically stronger correlation to functional performance. CONCLUSION: STS power was associated with functional performance in both male patients and female patients suffering from advanced knee OA. Moreover, STS power was associated with KOOS Pain, Sport, and ADLin male patients. The assessment of STS power should be considered in the evaluation of patients with advanced knee OA. TRIAL REGISTRATION NUMBER: NCT04081493.