Assessing structural validity of the oxford hip score in patients undergoing total hip arthroplasty

The Oxford Hip Score (OHS) is a patient-reported outcome measure (PROM) used to evaluate hip pain and function in patients treated with total hip arthroplasty (THA). Given the clinical utility and interpretability limitations of other hip-related PROMs, further scale assessment is warranted. The purpose of this study was to examine the structural validity of the OHS in patients undergoing THA. Data were obtained from the Surgical Outcomes System registry. Structural validity of the 12-item OHS was assessed using contemporary confirmatory factor analysis methods. As model fit criteria were not satisfied, exploratory factor analysis (EFA) was performed to identify a more parsimonious model. As model fit criteria were met, multigroup invariance testing was assessed across sex (males/females) and age groups (≤44, 45–54, 55–64, 65–74, and ≥75 years). Neither the one-factor comparative fit index (CFI) = 0.92, standardized root mean square residual (SRMR) = 0.05, Tucker–Lewis index (TLI) = 0.90, Bollen's incremental fit index (IFI) = 0.92, root mean square error of approximation (RMSEA) = 0.09 nor the two-factor (CFI = 0.94, SRMR = 0.04, TLI = 0.92, IFI = 0.94, RMSEA = 0.080) 12-item OHS met all recommended model fit indices. As such, EFA procedures identified a four-item short-form version with substantially improved model fit (CFI = 0.99, TLI = 0.98, RMSEA = 0.06, SRMR = 0.015). Measurement invariance was supported across sex and age subgroups. This study identified lack of scale validity of the original OHS at the pre-operative visit, indicating that this scale should not be used in its current form in clinical practice. However, subsequent analysis identified a modified short-form version with improved model fit and considered invariant across patients of different sexes and age groups. Prior to its use, further research is warranted in patients undergoing THA. • One-factor and two-factor 12-item Oxford Hip Score (OHS) did not meet recommended model-fit criteria. • A four-item short-form version of OHS met model fit criteria at the pre-operative visit. • The four-item short-form version of OHS was invariant across sex and age subgroups.