Confirmatory factor analysis and validation of the Hip Disability and Osteoarthritis Outcome Score for Joint Replacement in Italian patients: a tool for functional assessment in rehabilitation

Purpose: The Hip Disability and Osteoarthritis Outcome Score for Joint Replacement (HOOS, JR) is used to assess hip health in individuals undergoing total hip arthroplasty (THA). This study assesses the validity of the Italian version in a THA population. Materials and methods: Psychometric evaluation included: confirmatory factor analysis (CFA) whose model fit was evaluated by Comparative Fit Index (CFI), Tucker Lewis Index (TLI), Standardized Root Mean Square Residual (SRMR), and Root Mean Square Error of Approximation (RMSEA); reliability through internal consistency (Cronbach’s α) and test-retest reliability; construct validity via hypothesis testing with the Numerical Rating Scale (NRS), the Visual Analogue Scale (VAS), and the EuroQol instrument; interpretability by calculating the Minimum Detectable Change (MDC). Results: Eighty patients who had undergone THA were enrolled. CFA indicated a 1-factor 5-item structure of the HOOS, JR yielding satisfactory model fit indices (CFI = 0.977; TLI = 0.966; SRMR = 0.045; RMSEA = 0.082 [90%CI 0.00–0.190]). Internal consistency was good (Cronbach’s α: 0.77), and test-retest reliability was adequate (ICC2.1: 0.75). The MDC was estimated at 4.91 points on the 20-point scale. Conclusions: The HOOS, JR showed unidimensionality, test–retest reliability, associations with pain intensity and quality of life outcome measures, and interpretability.