Internal consistency and construct validity of the Short Musculoskeletal Function Assessment (SMFA) in older adults

Objective The primary objectives of this study were to 1) investigate the internal consistency 2) and construct validity of the Short Musculoskeletal Function Assessment Questionnaire (SMFA) in older adults commencing physical rehabilitation in an outpatient setting. Methods This cross-sectional study recruited older adults who had commenced physical rehabilitation in an outpatient setting. The SMFA consists of two indices: 1) dysfunction capturing the impact of musculoskeletal disorders on physical limitations, and 2) bothering capturing how the individual is emotionally affected by their disorder. SMFA holds four categories: 'mobility', 'daily activities', 'emotional status', and 'function of the arm and hand'. Participants answered the SMFA alongside other patient-reported questionnaires (such as the 36-Item Short Form Survey, SF-36) and similar) and objectively measured muscle strength for the upper and lower body and functional capacity. Results We included 115 older adults with a median age of 74 years (IQR 9). Adequate internal consistency was seen with Cronbach's alpha values of 0.90-0.94 for the SMFA indices and 0.77-0.91 for the SMFA categories. The strongest correlations between the SMFA indices were observed with the SF-36 physical component summary (SMFA-Dysfunction r = 0.74, p < 0.05, SMFA-Bother r = 0.72, p < 0.05). Only fair correlations were found between SMFA index scores and clinical outcome measures. Discussion This study demonstrated that the SMFA has adequate internal consistency and construct validity for self-reported health status in older adults, especially when considering components covering physical health status. However, we only observed fair correlations between SMFA and clinical outcome measures, indicating that SMFA does not adequately capture muscle strength and functional capacity.