Background Individuals with GOA typically suffer from limitations of both upper and lower extremity function. However, current OA specific instruments for activity limitations are usually site specific and do not involve activities of both upper and lower extremities. We hypothesized that the Health Assessment Questionnaire Disability Index (HAQ-DI), originally developed for patients with inflammatory arthritis, might be appropriate to measure functional limitations in GOA.

Objectives To evaluate the measurement properties (content validity, construct validity and reliability) of the HAQ-DI in patients with GOA.

Methods Data were used from a randomized clinical trial evaluating the effectiveness of a 6-week multidisciplinary treatment program for patients with GOA. 137 patients completed a standardized set of questionnaires before and directly after treatment. The measurement properties of the HAQ-DI were assessed according the Consensus Based Standards for the Selection of health Status Measurement Instruments Checklist¹. Floor and ceiling effects for each HAQ-DI category at baseline were considered present if >15% of patients scored the worst or best possible score. For content validity, 17 health professionals were asked to judge the relevance of each HAQ-DI item. Construct validity was assessed by computing associations (Pearson r) between HAQ-DI scores and scores on other clinical (un)related measures. Reliability was assessed by confirmatory factor analysis (CFA), Cronbach's alpha and intra-class correlation coefficient (ICC). The minimal important change (MIC) score was calculated using an anchor based method.

Results Of 137 patients (mean age 60 (SD 8) years; (85%) female), 93% reported to have complaints in both the upper and lower extremities. The mean (SD) HAQ-DI score was 1.27 (0.5) at baseline and 1.20 (0.5) at follow-up. 20% - 30% of patients reported the best possible score on the HAQ-DI categories eating, dressing and gripping; 16% reported the worst possible score on the category hygiene. The content validity was questionable since according to the health professionals the HAQ-DI encompasses 9 (out of 20) activities that are not relevant or too easy to perform for GOA patients. Construct validity was rated positive given the moderate to strong associations with related constructs and weak associations with unrelated constructs. The CFA confirmed the unidimensionality of the HAQ-DI (Root Mean Square Error of Approximation =0.057, χ²/df ratio =1.48). Cronbach's alpha was 0.90, confirming internal consistency and the ICC was 0.81, reflecting good reliability. The MIC was 0.25 points and the smallest detectable change was 0.60 indicating that important changes cannot be distinguished from measurement error in individuals.

Conclusions The HAQ-DI showed good construct validity and reliability to measure functional limitations in GOA. Yet, the content validity was unsatisfactory and we cannot support the use of the HAQ-DI to monitor individuals with GOA in daily clinical practice. Considering the unsatisfactory content validity, we recommend to update the items of the HAQ-DI when using the HAQ-DI in future research focusing on functional limitations in GOA. The latter might also be relevant for other arthritic populations.

References

1. Mokkink et al. (2010). Qual Life Res 19:539-549.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.3483