Evaluation of the reliability, validity and sensitivity to changes of the Short Musculoskeletal Function Assessment Questionnaire (German version, SMFA-D) in the inpatient rehabilitation of patients with conservatively treated rheumatoid arthritis

Background: Modern patient-based outcome measures such as the Short Musculoskeletal Function Assessment Questionnaire (German version, SMFA-D) are able to detect both impairments and functional capacity in musculoskeletal disorders. The SMFA-D can be classified between disease-specific and generic instruments. It has been successfully evaluated in several patient cohorts treated operatively for osteoarthritis of the knee and hip, rotator cuff tears and rheumatoid arthritis. The aim of this study was to evaluate the SMFA-D among inpatient rehabilitation patients undergoing conservative treatment for rheumatoid arthritis. Patients and Methods: The SMFA-D, SF-36, Health Assessment Questionnaire and the "Funktionsfragebogen Hannover" were used in a prospective cohort study among 56 patients treated conservatively for rheumatoid arthritis. Patients' ratings of their pain, health status, functional ability of the musculoskeletal system and physicians' judgements of functional status and disease severity were performed. All measurements were carried out at three time points. Results: Analysis of reliability showed good to excellent results (Cronbach's alpha: 0.93 to 0.98; ICC: 0.87 to 0.93). Both indices of the SMFA-D showed significant correlations at all time points with the FFbH-P (r = -0.72 to -0.86), HAQ (r = 0.75 to 0.85), and SF-36 (r = -0.27 to -0.84), indicating construct validity. There was also a significant correlation with the functional ability of the musculoskeletal system and the rating of the physician, confirming criterion validity. The effect sizes of the SMFA-D were comparable to those of the other instruments used. The responsiveness of the SMFA-D can thus be judged as good. Conclusion: The SMFA-D represents a reliable, valid and responsive instrument also in conservatively treated patients suffering from rheumatoid arthritis. The use of the SMFA-D can be recommended in these patients.