Evaluating the responsiveness of the ICOAP following hip or knee replacement

Numerous measures of pain have been used clinically and in research in people with osteoarthritis (OA) of the hip. These most commonly include measures of pain intensity such as the numeric pain rating scale (1) and the Western Ontario McMaster Universities (WOMAC) pain subscale which measures pain on activity (2). However, recent work by Hawker and colleagues indicated that people with hip and knee OA experienced two distinct types of pain as OA progressed: a dull aching pain that is more consistent over time; and, intermittent pain that is often more intense, unpredictable and emotionally draining (3). Under the auspices of an OARSI/OMERACT initiative, the Intermittent and Constant Osteoarthritis Pain measure (ICOAP) was developed. Building on preliminary work demonstrating the reliability and validity of the ICOAP (4), this work evaluates the responsiveness of the ICOAP in people undergoing total hip (THR) and knee replacement (TKR). The ICOAP constant, intermittent and total scores demonstrate large effects as expected in this patient group with standardized response means (SRM) ranging from 0.80 to 2.31. Correlations of the change scores for the ICOAP, WOMAC, the Hip Disability and Osteoarthritis Outcome Score (HOOS) (5) and Knee Injury and Osteoarthritis Outcome Score (KOOS) (6) pain subscales and Chronic Pain Grade (CPG) (7,8) are moderate suggesting that the measures are evaluating different aspects of pain. This work further supports the growing body of evidence that the ICOAP is a valid and responsive measure for use in people with OA.This work was funded by an operating grant from the Canadian Institutes of Health Research, grant number 77518