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.