The completely patient-reported version of the American Orthopaedic Foot and Ankle Society (AOFAS) score: A valid and reliable measurement for ankle osteoarthritis

Abstract

BackgroundThe American Orthopaedic Foot and Ankle score (AOFAS) is an outcome measure for ankle and hindfoot conditions, which requires scoring from both the patients and the physician. A completely patient-reported version has been developed and used before, but its measurements properties are unknown. Our goal was to determine the measurement properties and the minimally important change (MIC) of a completely patient-reported AOFAS (PR-AOFAS) in patients with ankle osteoarthritis. Additionally, the MIC of both the PR-AOFAS and the AOFAS was estimated, which had not previously been done. Materials and methodsThe PR-AOFAS of 112 patients was evaluated for reliability, construct validity (using the AOFAS, Foot and Ankle Outcome Score, Ankle Osteoarthritis Score, Visual Analogue Scale, and Short Form-36), and responsiveness. The MIC was estimated using the optimal cut-off point of the receiver operating characteristic curve. This was a substudy of a randomized clinical trial on the efficacy of platelet-rich plasma injections for ankle osteoarthritis (OA). ResultsThe PR-AOFAS had sufficient construct validity, internal consistency, test–retest reliability, and responsiveness. The smallest detectable change at group level was 2.34. The MIC was 6.5 points (95% confidence interval: 0.6–14.4). ConclusionsThe measurement properties of the Dutch PR-AOFAS were sufficient in patients with ankle osteoarthritis who are willing to participate in a trial on injection therapy. The minimally important change of the PR-AOFAS is smaller than its smallest detectable change, making it more suitable for use in groups of patients, such as a research setting. Level of clinical evidence1.