midfoot were not included. The ability of a
static postural measurement to predict dynamic
midfoot function may be reduced as movement
occurs across multiple joints simultaneously
with individual axes of motion. The midfoot FPI
measurements also concentrate on medially
located structures, (talo-navicular congruence
and medial arch height) however, during gait
movement occurs across the entire midfoot.
There are several limitations to this study
that should be considered. This study was
restricted to normal and pronated foot types
as determined by FPI score. A supinated foot
type, classified by a score -5 to 0 on the FPI
scale, was not included. Due to the nature of
the ordinal scale used in the FPI, i.e. evenly
distributed categories and directional, it
suggests that the predictive capacity of the FPI
may extend to a negatively scored supinated foot
type however this is currently an assumption.
In this study the investigation of the effect of
planar dominance, (identified by a breakdown
of the FPI scores), assumed the measurement
of curvature above and below the lateral
malleolus to be a frontal plane measurement. In
reality, the FPI scoring system identifies this as
a combination of frontal and transverse plane
position [9] . Therefore, this study potentially
overestimates the strength of the relationship
between dynamic frontal plane motion of the
rearfoot and frontal plane dominance in the FPI
score.
Analysis was restricted to the frontal plane
due to frontal plane motion of the rearfoot
being adequately demonstrated by calcaneal
motion allowing comparison between
static measurements and dynamic function.
Components of the FPI related to the static
transverse plane position (assessed by palpation
of the talar head) were not compared to
dynamic motion as talar head motion cannot
be accurately or reliably measured by skin
mounted markers. There is no component of
sagittal plane position included in the rearfoot
FPI scoring system therefore this could not be
included.
Conclusions
The FPI is a validated, quick and simple clinical
measurement which can be easily applied. The
findings of this study suggest that it may be
an important and convenient screening tool
in evaluation of foot function and subsequent
predisposition to injury. Historically, research
into the effect of foot orthoses and footwear
on dynamic foot function has been hampered
by difficulty in reliably classifying foot type
for inclusion in studies, possibly contributing
to subject-specific findings and lack of
homogenous response to specific orthotic styles
[17,18]
. The results of this study suggest that the FPI
has a strong positive relationship with maximum
eversion of the rearfoot and is capable of
predicting 85% of the variance in maximum
eversion during the stance phase of gait. This
suggests the FPI has significant predictive ability
for dynamic rearfoot function which may assist
in clinical screening and in the future research
of the effect of orthotic prescription on foot
function in specific cohorts. Positive correlations
between frontal plane rearfoot measurements
and maximum rearfoot eversion suggests the
FPI may also have a role in identifying dominant
planar components of dynamic rearfoot motion
and warrants further investigation.
–end
Current Pedorthics | May/June 2019
27