Performance tests and self-reported questionnaires capture different domains of function in patients with lower extremity osteoarthritis, but the impairments related to each of these domains have not been elucidated. The purpose of this study was to determine how strength and joint pain influence performance-based tests and self-reported questionnaires of functional ability of individuals with end-stage hip osteoarthritis.
Fifty-six patients scheduled to undergo unilateral total hip arthroplasty were included in this cross-sectional analysis. Subjects completed the Hip Outcome Survey (HOS) and pain in the affected hip was quantified on a scale from 0-10. Performance-based tests included the Six-Minute Walk Test (6MWT), the Timed Up & Go (TUG), and the Stair Climbing Test (SCT). Isometric strength of the hip abductors and knee extensors was tested and recorded. Hierarchical linear regressions were created to determine the contributions of pain, knee extensor strength, and hip strength for each outcome measure (TUG, 6MWT, SCT, and HOS). Height and body mass index were entered first, followed by pain, then knee extensor strength, and then hip abduction strength.
Greater pain significantly predicted lower HOS scores, but hip strength did not significantly improve the model. Hip pain was also significantly related to TUG, SCT, and 6MWT values, but hip and knee strength explained additional variance for these performance-based measures.
Self-report and performance-based measures capture different aspects of disability and are influenced by different underlying impairments. Both types of outcome measures should be used in studies that evaluate functional changes in patients with hip osteoarthritis.