The juvenile arthritis foot disability index: development and evaluation of measurement properties.

OBJECTIVE: To develop a new juvenile arthritis foot disability index (JAFI) and to test it for validity and reliability.
METHODS: Samples of 14 children/adolescents and 30 children/adolescents with juvenile idiopathic arthritis (JIA) and 29 healthy children/adolescents participated. We used a questionnaire derived from the International Classification of Functioning, Disability and Health that included 27 statements divided into the dimensions Impairment, Activity Limitation, and Participation Restriction. Comments on the contents were invited from parents and adolescents. Convergent and divergent construct validity was examined by comparing the 3 JAFI dimensions to joint impairment scores, the Childhood Health Assessment Questionnaire (CHAQ), and self-rated, foot-related participation restriction. Known groups construct validity was assessed by comparing answers from children with JIA to those from healthy children. Test-retest stability was investigated over one week.
RESULTS: One item was added after suggestions from 2 participants. A consistent pattern of increasing JAFI scores was found with increasing joint impairment scores, CHAQ scores, and self-rated foot-related participation restriction. Foot-related disability as assessed by JAFI was more pronounced in children with JIA than in healthy controls. One statement showing a floor effect was excluded. No internal redundancy (rs > 0.90) between items was found, and internal consistency within each subscale was satisfactory (rs > 0.50) for all items but one. No systematic differences were found between test and retest, and weighted kappa coefficients for the 3 JAFI dimensions were 0.90, 0.85, and 0.88.
CONCLUSION: The JAFI appears to be valid and reliable for assessing foot-related disability among children/adolescents with JIA. Its sensitivity to change remains to be investigated.