The development of a short measure of physical function for hip OA HOOS-Physical Function Shortform (HOOS-PS): an OARSI/OMERACT initiative

OBJECTIVE: To derive a cross-culturally valid, short measure of physical function using function subscales (daily living and sports and recreation) of the Hip disability and Osteoarthritis Outcome Score (HOOS). METHODS: Rasch analysis was conducted on data from individuals from multiple countries who had hip osteoarthritis (OA). Fit of the data to the Rasch model was evaluated by model chi(2) and item fit statistics (chi(2), size of residual, and F-test). Differential item functioning was evaluated by gender, age and country. Unidimensionality was evaluated by factor analysis of residuals. Individual data sets were analyzed and data pooled and re-analyzed for fit to the model. Regression modeling was conducted to derive a nomogram converting raw summed scores to Rasch derived interval scores. RESULTS: Seven data sets were included (n=2991), ages 19-96 years, male/female ratio was 1:1.23. The final model included five HOOS items. From the easiest to most difficult, the items (logit) were as follows: sitting (1.832), descending stairs (0.729), getting in/out of bath or shower (0.255), twisting/pivoting on loaded leg (-0.221) and running (-2.595). The separation index was 0.80. CONCLUSION: The daily activity and sports and recreational items of the HOOS were reduced to five items achieving a feasible, short measure of physical function with interval level properties. This tool has potential for use as the function component of an OA severity scoring system. Further testing of this measure is warranted.