Responsiveness of the short musculoskeletal function assessment (SMFA) in patients with femoral neck fractures

The aim of this study was to evaluate the internal and external responsiveness of the Short Musculoskeletal Function Assessment (SMFA), i.e. the instrument's ability to capture clinically important changes, in patients with hip fractures within the context of a randomized controlled trial. To evaluate the internal responsiveness of the SMFA, the observed change and the standardized response mean (SRM) in relation to the change in the Dysfunction Index and the Bother Index were calculated. In order to calculate external responsiveness, an external criterion (EC) was constructed by using the Harris hip score. Receiver operating characteristic (ROC) curves and logistic regression analysis were used in the evaluation. Both the Bother and the Dysfunction SMFA indices displayed good internal responsiveness as expressed by significant change scores and by moderate and large SRMs, 0.76 and 0.96, respectively. The ROC curve and logistic regression analyses showed that both indices had acceptable external responsiveness and were able to discriminate between patients with a less good outcome versus a moderately good or good outcome based on the EC while the ability to differ between patients with moderately good versus a good outcome was limited. The percentage of correctly classified cases was 64% (good/moderately good), 80% (good/less good), and 74% (moderately good/less good) for both the Dysfunction and Bother Indices. The SMFA had good overall responsiveness in patients with hip fractures and, based on our results, we conclude that the SMFA can be recommended for use as one of the measures to evaluate the outcome after a hip fracture.