Structural Validity of the Short Musculoskeletal Function Assessment in Patients With Injuries

Background. The Short Musculoskeletal Function Assessment (SMFA) is a widely used patient-reported outcome measure, originally having 2 elements of outcome: the function index and the bother index. In multiple studies, it has been argued that the SMFA should be scored using 3, 4, or 6 subscales instead. Therefore, there is inconsistency with the number of underlying dimensions of the SMFA.Objective. The aim of this study was to evaluate the structural validity of the various proposed subscale configurations of the SMFA in a broad range of Dutch patients with injuries.Design. This study used a prospective cohort design.Methods. Participants with injuries were asked to complete the Dutch SMFA (SMFA-NL) at 5 to 8 weeks postinjury. The structural validity of the 6 different factor structures that have been proposed in other studies was evaluated using confirmatory factor analyses. Internal consistency was analyzed using Cronbach alpha.Results. A total of 491 patients participated (response rate = 74%). A 4-factor structure showed an acceptable fit (root-mean-square error of approximation [RMSEA] = 0.070, comparative fit index = 0.973, Tucker-Lewis index = 0.971). Other models, including the original 2-index structure, showed insufficient structural validity in Dutch patients with injuries. The 4-factor structure showed sufficient discriminant validity and good internal consistency (Cronbach alpha = 0.83).Limitations. It is unclear whether conclusions are generalizable across different countries, people who are elderly, and people without injuries.Conclusion. In a broad range of patients with injuries, the SMFA-NL may be best scored and interpreted using a 4-factor structure. Other factor structures showed insufficient structural validity.