Physical functioning before and after total hip arthroplasty: perception and performance.

BACKGROUND AND PURPOSE Self-report and performance-based measures of physical functioning in people before and after total hip arthroplasty seem to present different information. The relationship between these different measures is not well understood, and little information is available about changes in this relationship over time. The aims of this study were: (1) to determine the relationship between self-report and performance-based measures of physical functioning before and after total hip arthroplasty, (2) to assess the influence of pain on the relationship, and (3) to determine whether the relationship changes over time. SUBJECTS AND METHODS Seventy-five subjects admitted for total hip arthroplasty were included and examined before and 6 and 26 weeks after surgery. The relationships between the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical functioning subscale and walking speed and gait variability were examined by use of generalized estimating equations, which included interactions with time and the WOMAC pain subscale. RESULTS The relationship between self-report and performance-based measures of physical functioning was poor. Pain appeared to have a considerable influence on self-reported physical functioning. The relationship did not appear to change over time. DISCUSSION AND CONCLUSION The influence of pain on self-reported physical functioning serves as an explanation for the poor relationship between self-reported and performance-based physical functioning. When using a self-report measure such as the WOMAC, one should realize that it does not seem to assess the separate constructs--physical functioning and pain--that are claimed to be measured.