Development of a foot impact scale for rheumatoid arthritis

Objective. To develop a new foot impact scale to assess foot status in rheumatoid arthritis (RA) using established qualitative methodology and the latest item response techniques (Rasch analysis). Methods. Foot problems in RA were explored by conducting qualitative interviews that were then used to generate items for a new foot impact scale. Further validation was undertaken following postal surveys and Rasch analysis. Results. Analysis of the first postal survey (n = 192 responses) produced a 63-item binary response, 4-subscale instrument. The 4 subscales covered the domains impairment, activities, participation, and footwear. Following test-retest postal surveys and additional analysis, the instrument was reduced to a 2 subscale, 51-item questionnaire covering the domains of impairments/shoes and activities/participation. Initial results of these subscales indicate good psychometric properties, external validity, and test-retest reliability. Conclusion. A foot impact scale to assess the impact of RA and to measure the effect of interventions has been developed. The 2 scales comprising the instrument demonstrate good psychometric properties.