Validation of the Foot and Ankle Outcome Score for Use in Infracalcaneal Heel Pain

Abstract

There is growing interest in adopting validated and reliable patient-reported outcome measures following surgery. While the Foot and Ankle Outcome Score (FAOS) has previously been validated for use in multiple foot/ankle conditions, it has not yet been validated in patients with infracalcaneal heel pain. In this study we aimed to validate the FAOS by looking at 4 psychometric properties of the survey: construct validity, content validity, reliability, and responsiveness, using patients in our practice with a clinical diagnosis of plantar fasciitis. A total of 150 patients (mean age 49.7 ± 12.1 years [36 men and 114 women]) were included in one or more of the 4 components of this study. All FAOS subscales demonstrated adequate construct validity when compared with the physical health component of the 12-Item Short Form Health Survey (SF-12), and 2 out of 5 subscales demonstrated moderate correlation with the mental health component of SF-12 (all Spearman rho >0.3, and p values <0.05). Most FAOS subscales demonstrated content validity and were found to contain relevant questions from the patient's perspective. All 5 subscales demonstrated good test-retest reliability with intraclass correlation coefficients ≥ 0.827. Finally, 4 out of the 5 subscales (all but other symptoms) were responsive to change at a mean follow up of 12.2 months after surgery (p < .05). We conclude that the FAOS is a responsive, reliable, and valid instrument for use in infracalcaneal heel pain. We believe that due to its ease of use and broad applicability, the FAOS could be more widely adopted in foot/ankle practices as patient-centered healthcare delivery and research becomes increasingly prioritized in the US and abroad.