Defining disabling foot pain in older adults: further examination of the Manchester Foot Pain and Disability Index

Objective. To identify a practical definition of disabling foot pain in older adults for clinical and research use, using the Manchester Foot Pain and Disability Index (FPDI). Methods. Adults aged 550 years registered with three general practices were mailed a two-stage cross-sectional survey. A total of 1342 respondents who reported foot pain in the previous 12 months and completed the FPDI and 58 participants in a test-retest repeatability study were included. Results. Confirmatory factor analysis verified the three-construct FPDI structure (pain intensity, functional limitation and appearance). Internal consistency for the three constructs was good (Cronbach's alpha 0.74, 0.92 and 0.77, respectively). A total of 1320 (98.4%) of those persons with foot pain reported disability (at least one of the 17 FPDI items experienced on at least some days-Definition A). After restricting this definition to problems experienced on most/every day(s) (Definition B), 996 (74.2%) of those with foot pain reported disability (percentage difference 24.2%; 95% CI 21.9, 26.5%). For each of the three constructs, the prevalence of disability among persons with foot pain was significantly higher under Definition A than under Definition B. Test-retest repeatability for the individual constructs ranged from fair to substantial. Physical function, measured by the SF-36 physical function sub-scale, was poorer in those who reported problems within the function construct compared with those with problems in pain and/or appearance constructs only. Conclusion. A practical definition of disabling foot pain [at least one of the 10 FPDI function items experienced on most/every day(s)] is proposed, which appears valid, repeatable and suitable for use in older adults.