Reliability of the modified foot posture index

Background: The Foot Posture Index (FPI) has been advocated as a simple and convenient tool to assess static foot posture in a clinical setting. Although published studies have indicated that the FPI has good intrarater reliability and moderate interrater reliability, these studies were conducted on a previous version of the tool that used eight criteria to score a patient's foot posture. The revised tool has only six criteria (FPI-6). The purpose, therefore, of this study was to investigate the intrarater and interrater reliability of the revised version of the FPI. Methods: Three different raters used the FPI-6 to twice evaluate 92 feet from 46 individuals. Results: Intrarater reliability was high but interrater reliability was only moderate. In addition, using the raw score generated by the FPI-6 to classify feet into one of five categories did not improve agreement between raters. Conclusions: The FPI-6 should be used with extreme caution and may actually have limited value, especially from a research perspective.