Abstract
BackgroundThe Foot Posture Index (FPI) provides an easily applicable, validated method for quantifying static foot posture. However there is limited evidence relating to the ability of the FPI to predict dynamic foot function. This study aimed to assess the relationship between dynamic rearfoot motion and FPI scores in pronated and normal foot types.Methods40 participants were recruited with equal numbers of pronated and normal foot types as classified by their FPI score. Three dimensional rearfoot motion was collected for each of the participants. Dynamic maximum rearfoot eversion was correlated with the total FPI score across all participants and within the normal and pronated foot types. Linear correlations were performed between components of the total FPI scores measuring frontal plane rearfoot position and maximum rearfoot eversion. The capacity of the total FPI score to predict maximum frontal plane motion of the rearfoot was investigated using linear regression analysis.ResultsThe correlation between the total FPI score and maximum rearfoot eversion was strongly positive (r = 0.92, p < 0.05). Correlation performed on data subsets demonstrated the pronated foot type (FPI = +6 to +9) and maximum rearfoot eversion angle were more strongly positively correlated (r = 0.81, p < 0.05) than the normal foot type (FPI = 0 to +5) and maximum rearfoot eversion (r = 0.76, p < 0.05). Correlations between frontal plane rearfoot FPI score and frontal plane motion during gait were strongly positive, (r = 0.79 p < 0.05 pronated group, r = 0.71 p < 0.05 normal group), however were less strong than the total FPI score and rearfoot motion. Linear regression analysis demonstrated a significant and strong relationship between the total FPI score and maximum rearfoot eversion (r2 = 0.85, p < 0.001).ConclusionsThe results of this study suggest the FPI has strong predictive ability for dynamic rearfoot function. This will assist in clinical screening and research by allowing easy classification by functional foot type. Positive correlations between frontal plane rearfoot measurements and maximum rearfoot eversion suggest the FPI may identify dominant planar components of dynamic rearfoot motion and warrants further investigation.
Highlights
The Foot Posture Index (FPI) provides an applicable, validated method for quantifying static foot posture
The total FPI score was correlated with maximum rearfoot eversion angle for the entire subject population (Figure 3)
Correlations between the FPI score and maximum rearfoot eversion angle were performed on data subsets representing a pronated foot group (FPI = +6 to +9) and a normal foot group (FPI = 0 to +5)
Summary
The Foot Posture Index (FPI) provides an applicable, validated method for quantifying static foot posture. This study aimed to assess the relationship between dynamic rearfoot motion and FPI scores in pronated and normal foot types. Many static measures have been developed to describe foot posture and subsequently investigated as possible predictors of dynamic rearfoot motion [4,5]. Measures have included frontal plane calcaneal angle, (frequently referred to as rearfoot angle), medial arch angle and arch height, none has consistently been found to be accurate predictors of dynamic rearfoot motion for stance phase [4,5,6,7,8]. The six item Foot Posture Index, (FPI), uses a validated criterion-based observational measurement of the forefoot and rearfoot in a static position [9]. A score is allocated to each measure to give a total overall score indicative of foot posture with reference values provided for classification purposes [9]
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