Psychometric properties of the foot and ankle outcome score in a community-based study of adults with and without osteoarthritis.

Abstract

Foot and ankle problems are common in adults, and large observational studies are needed to advance our understanding of the etiology and impact of these conditions. Valid and reliable measures of foot and ankle symptoms and physical function are necessary for this research. This study examined psychometric properties of the Foot and Ankle Outcome Score (FAOS) subscales (pain, other symptoms, activities of daily living [ADL], sport and recreational function [sport/recreation], and foot- and ankle-related quality of life [QOL]) in a large, community-based sample of African American and white men and women ages ≥50 years. Johnston County Osteoarthritis Project participants (n = 1,670) completed the 42-item FAOS (mean age 69 years, 68% women, 31% African American, mean body mass index [BMI] 31.5 kg/m(2) ). Internal consistency, test-retest reliability, convergent validity, and structural validity of each subscale were examined for the sample and for subgroups according to race, sex, age, BMI, presence of knee or hip osteoarthritis, and presence of knee, hip, or low back symptoms. For the sample and each subgroup, Cronbach's alpha coefficients ranged from 0.95-0.97 (pain), 0.97-0.98 (ADL), 0.94-0.96 (sport/recreation), 0.89-0.92 (QOL), and 0.72-0.82 (symptoms). Correlation coefficients ranged from 0.24-0.52 for pain and symptoms subscales with foot and ankle symptoms and from 0.30-0.55 for ADL and sport/recreation subscales with the Western Ontario and McMaster Universities Osteoarthritis Index function subscale. Intraclass correlation coefficients for test-retest reliability ranged from 0.63-0.81. Items loaded on a single factor for each subscale except symptoms (2 factors). The FAOS exhibited sufficient reliability and validity in this large cohort study.