Reliability of Foot Posture Index individual and total scores for adults and older adults

Background: Previous studies have suggested that the Foot Posture Index (FPI-6) is valid and reliable to evaluate foot posture of adults and children. However, studies with adults had some important limitations. In addition, it is not clear if FPI-6 is reliable for older adults. Variations in foot structure, such as edema, bone callosity and bunions, are more frequent in older adults, which may compromise FPI-6 reliability for this population. Objectives: To investigate test-retest and inter-rater reliability of FPI-6 total and individual scores for the assessment of foot posture of adults and older adults. Methods: Twenty-one adults and 19 older adults participated in this study. The examiners performed FPI-6 on two days of data collection. We used Cohen Weighted Kappa and Intraclass Correlation Coefficient for categorical and continuous variables, respectively. Results: For adults, FPI-6 scores demonstrated test-retest reliability varying from fair to substantial and inter-rater reliability varying from fair to almost perfect. For older adults, FPI-6 scores demonstrated test-retest reliability varying from not reliable to moderate and inter-rater reliability varying from fair to almost perfect. The examiners demonstrated more than 80% of agreement in all FPI-6 scores for adults and older adults. Conclusions: The relatively low reliability in light of this high level of agreement suggest that the current version of FPI-6 can be a useful tool to assess foot posture for adults and should be further examined. On the other hand, FPI-6 should be cautiously used for older adults.