Minimally important change, measurement error, and responsiveness for the Self-Reported Foot and Ankle Score

Abstract

Background and purpose — Patient-reported outcome measures (PROMs) are increasingly used to evaluate results in orthopedic surgery. To enhance good responsiveness with a PROM, the minimally important change (MIC) should be established. MIC reflects the smallest measured change in score that is perceived as being relevant by the patients. We assessed MIC for the Self-reported Foot and Ankle Score (SEFAS) used in Swedish national registries. Patients and methods — Patients with forefoot disorders (n = 83) or hindfoot/ankle disorders (n = 80) completed the SEFAS before surgery and 6 months after surgery. At 6 months also, a patient global assessment (PGA) scale—as external criterion—was completed. Measurement error was expressed as the standard error of a single determination. MIC was calculated by (1) median change scores in improved patients on the PGA scale, and (2) the best cutoff point (BCP) and area under the curve (AUC) using analysis of receiver operating characteristic curves (ROCs). Results — The change in mean summary score was the same, 9 (SD 9), in patients with forefoot disorders and in patients with hindfoot/ankle disorders. MIC for SEFAS in the total sample was 5 score points (IQR: 2–8) and the measurement error was 2.4. BCP was 5 and AUC was 0.8 (95% CI: 0.7–0.9). Interpretation — As previously shown, SEFAS has good responsiveness. The score change in SEFAS 6 months after surgery should exceed 5 score points in both forefoot patients and hindfoot/ankle patients to be considered as being clinically relevant.