Reliability Of A Novel Digital Photographic Method Of Measuring Static Foot Posture: Clinical Application

Abstract

A plethora of research investigating the relationship between "abnormal" foot posture and numerous lower extremity (LE) injuries has been conducted. While a number of studies have reported significant relationships between "abnormal" foot posture and LE injury, others have failed to report significant relationships. Some of the inconsistencies between studies may be due to the measures used to quantify foot posture. Although a number of the measures have moderate-high intra-tester reliability, the inter-tester reliability is generally low. Low inter-tester reliability may not only contribute to between-study variability, but may also limit the clinical relevance of the measures. To be clinically relevant, foot posture measures must have moderate-high intra- and inter- tester reliability. A measurement that meets both criteria is the arch ratio (AR). There are, however, sources of error/variability associated with the caliper measurement method that may avoided with a digital measurement method. PURPOSE: Investigate the intra- and inter-tester reliability of quantifying static foot posture using a novel digital photographic measurement method (DPMM). METHODS: Twenty healthy individuals (10 women; age = 24 ± 2 years) participated in the study. Two investigators assessed each participant's foot posture three times during 10% and 90% weight bearing (WB) conditions. Foot posture was quantified using the AR, navicular ratio (NR), and longitudinal arch angle (LAA) measures. RESULTS: Intra-class correlation coefficients (ICC3, 1) were moderate-high for the AR (10%WB: 0.928; 90%WB 0.905) and NR (10%WB: 0.835; 90%WB 0.787), but low for the LAA (< 0.60). Inter-tester correlation coefficients (ICC2,3) were moderate-high for the AR (10%WB: 0.947; 90%WB: 0.961) and NR (10%WB: 0.926; 90%WB: 0.932), and moderate for the LAA (10%WB: 0.751; 90%WB: 0.793). CONCLUSION: The AR computed using the DPMM meets the intra- and inter- tester reliability requirements for clinical relevance. The DPMM also affords the clinician the ability to quantify foot posture using the NR with moderate-high intra- and inter-tester reliability which has not been the case using a caliper method. Future studies investigating the relationship between static foot posture computed using the DPMM and dynamic function are warranted.