German short musculoskeletal function assessment questionnaire (SMFA-D): comparison with the SF-36 and WOMAC in a prospective evaluation in patients with primary osteoarthritis undergoing total knee arthroplasty.

In a prospective clinical trial, the German short musculoskeletal function assessment (SMFA-D), the short form (SF)-36, and the Western Ontario and McMaster Universities osteoarthritis index (WOMAC) were evaluated in 63 patients with primary osteoarthritis undergoing total knee arthroplasty. All instruments were sensitive to change, demonstrating the effect of total knee arthroplasty at 1-year follow-up. The SMFA-D effect sizes in comparable scales were bigger than in the SF-36 and similar to those of the WOMAC. Significant correlations of the SMFA-D indices with the SF-36 and WOMAC scales preoperatively could be shown. After 1-year follow-up, all correlations between the SMFA-D indices and SF-36 scales were significant. In other comparison, only the correlation between the SMFA-D function index and the WOMAC function scales remained significant. The correlation of the SMFA-D function index with external validation criteria was higher than that using the other instruments. We recommend the SMFA-D for assessing change in functional status of patients with primary osteoarthritis of the knee following arthroplasty.