Relationships between Foot Type
and Dynamic Rearfoot Frontal
Plane Motion
Abstract
Background: The 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.
Methods: 40 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.
Results: The 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).
Conclusions: The 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.
by Vivienne H Chuter, Ph.D
Current Pedorthics | May/June 2019
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