This study aimed to translate and adapt the intermittent and constant osteoarthritis pain (ICOAP) measure into the Chinese language (ICOAP-C), and to study its psychometric properties in patients with knee osteoarthritis (OA).
The ICOAP was translated and cognitively pretested following internationally recommended guidelines. The reliability, including the internal consistency and the test-retest reliability, was then evaluated in 108 outpatients with knee OA. The validity was assessed by comparing the ICOAP-C with the Western Ontario and McMaster Universities Osteoarthritis Index Pain Subscale (WOMAC-PS), the Knee Injury and Osteoarthritis Outcome Score Pain Short-Form (KOOS-PS), and pain on a visual analogue scale (VAS). Seventy-four patients undergoing total knee arthroplasty (TKA) participated in the evaluation of the responsiveness of the ICOAP-C over a 6-month period.
All participants completed the questionnaires, and no floor or ceiling effects were found. All ICOAP-C scales exhibited satisfactory internal consistency. The intraclass correlation coefficients (ICCs) were excellent, i.e., 0.932 for "total pain", 0.908 for "intermittent pain" and 0.892 for "constant pain". Regarding the convergent validity, the ICOAP-C scores exhibited strong correlations with the WOMAC-PS and moderate correlations with the KOOS-PS and the VAS. The responsiveness of the ICOAP-C at 6 months after TKA was good [standardized response mean (SRM) range: 0.94-1.20; effect size (ES) range: 1.41-1.71].
The ICOAP-C exhibited good reliability, validity, and responsiveness. This scale is a reliable instrument for evaluating the pain experiences of patients with knee OA and is useful for outcome measurement in clinical research.