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Relationship between the Western Ontario and McMaster Universities Osteoarthritis Index Physical Function Subscale
Alexis A Wright1, Chad E Cook, G David Baxter
1Centre for Physiotherapy Research, University of Otago, Dunedin, New Zealand. lexie.wright@gmail.com
Objective:
To examine the convergent and factor validity of the Western Ontario and McMaster Universities Osteoarthritis Index physical function subscale (WOMAC-PF) using a battery of physical performance measures (PPMs) in patients with non-end-stage hip osteoarthritis (OA).
Design:
Cross-sectional data.
Setting:
A university physiotherapy research center.
Participants:
Patients with a clinical diagnosis of hip OA (N=93) referred for participation in research.
Interventions:
Not applicable.
Main Outcome Measures:
Factor validity of the WOMAC-PF was evaluated by using confirmatory factor analysis (CFA). Exploratory factor analysis (EFA) was run to determine whether WOMAC-PF and PPMs were capturing separate aspects of physical function. Covariates including pain, depression, Pain Beliefs Screening Instrument, body mass index, hip flexion, use of an assistive device, and lower-extremity strength were included in the EFA as independent variables.
Results:
CFA of the WOMAC-PF yielded a 1-factor solution accounting for 84% of the variance in the data (eigenvalue=11). EFA yielded a 2-factor solution accounting for 68% of the variance in the data. The PPMs and the WOMAC-PF loaded on separate factors.
Conclusions:
We were unable to confirm a 4-factor solution model of the WOMAC-PF as previously reported. This suggests that the WOMAC-PF shows sufficient factor validity in capturing perceived physical function in patients with non-end-stage hip OA but captures a different construct than that of PPMs, confirming the need for both when evaluating functional outcome. Furthermore, we suggest a new standardized battery of physical performance measures to serve as the criterion standard against which self-report measures could be compared.
