Responsiveness of the foot function index, AOFAS clinical rating systems, and SF-36 after foot and ankle surgery

Abstract

Background: There is uncertainty regarding which outcomes tools should be used to report the results of treatment for patients with foot and ankle disorders. This study compared the responsiveness of the Foot Function Index (FFI), American Orthopaedic Foot and Ankle Society (AOFAS) Clinical Rating Systems, and Medical Outcomes Study Short Form-36 (SF-36) in patients with foot and ankle surgery.

Methods: Twenty-five patients were recruited at a tertiary referral foot and ankle practice. The mean age of the patient sample was 40 years (range 21 to 69) and 19 were women (76%). Thirteen patients (52%) had conditions affecting the ankle, hindfoot, or midfoot, while 12 patients (48%) had conditions affecting the forefoot. Patients completed packets preoperatively and 6-months postoperatively which included informed consent forms, the FFI, the AOFAS, and the SF-36 questionnaires. Standardized response means (SRM) and effect sizes (ES) were used as the measures of responsiveness and were calculated for the AOFAS scores, the three domains of the FFI, the eight SF-36 sub-scales, and the two SF-36 summary scales.

Results: The standardized response mean (SRM) for the AOFAS scores was 1.10 and the effect size (ES) was 1.12. The SRM for the three FFI domains ranged from -0.39 to -0.83, while the ES ranged from -0.55 to -0.86. The SRM for the SF-36 ranged from 0.09 to 0.72 (ES ranged from 0.09 to 0.77) with the highest values occurring with the Bodily Pain sub-scale (SRM 0.72, ES 0.77) and Physical Component Summary scale (SRM 0.76, ES 0.68).

Conclusions: This study demonstrated increased responsiveness of foot and ankle specific outcomes tools compared to the SF-36. However, the Bodily Pain sub-scale and Physical Component Summary scale of the SF-36 had levels of responsiveness approaching those of the FFI and AOFAS Systems after foot and ankle surgery. This suggests that the SF-36 may be used alone to monitor the outcomes in these patients without sacrificing adequate sensitivity to clinical change.