Physical Function in Hip Osteoarthritis: Relationship to Isometric Knee Extensor Steadiness

Pua Y-H, Clark RA, Bryant AL. Physical function in hip osteoarthritis: relationship to isometric knee extensor steadiness. Arch Phys Med Rehabil 2010;91:1110-6. Objective: To evaluate, in a community hip osteoarthritis sample, the cross-sectional associations of isometric strength and steadiness of the knee extensors and their interaction with physical performance measures of physical function. Design: Cross-sectional. Setting: Human movement laboratory of a university. Participants: Sixty-seven adults (27 men and 40 women; age, 61 +/- 10y) with radiographically confirmed symptomatic hip osteoarthritis. Interventions: Not applicable. Main Outcome Measures: Participants performed isometric knee extensor steadiness and strength testing on a dynamometer. Physical function was assessed by using the habitual timed walk test and the self- and fast-paced stair-climbing tests. Results: In the hierarchical regression models, although there were clear main effects of knee extensor steadiness on fast-paced stair performance, greater knee steadiness predictively associated with faster stair-climbing performance particularly in individuals with high knee extensor strength. In contrast, knee extensor steadiness was not related to gait speed regardless of knee extensor strength levels. Conclusions: In patients with hip OA, knee extensor steadiness was positively associated with stair-climbing performance, particularly in those with high levels of knee extensor strength. These findings are of importance in developing intervention strategies, but they call for further study.