Changes of Postural Steadiness Following Use of Prefabricated Orthotic Insoles

Abstract

Orthoses are designed to assist a malaligned foot in adapting to the environment and reduce the frequency of injury. Literature is divided on the benefits of orthotics insoles for postural stability. The current study was conducted to determine the effect of prefabricated orthotic arch supports on postural stabilization. Twelve healthy young adults participated in this study and were tested with and without prefabricated orthotics. Different variables were computed from movement of center of pressure (COP) during orthotic use as suggested in the literature. The mean position of COP was significantly shifted forward and toward the dominant side. Neither the COP movement nor the velocity changes following the use of orthotics revealed significant differences. Mediolateral range of COP movement and the 95% confidence circle area of sway was significantly reduced (P = .022 and 0.048 respectively), but changes in 95% confidence circle and ellipse areas of fractal dimension were not significant (P = .053 and P = .057 respectively). In conclusion, orthotic insoles significantly improved postural sway initially by reducing mediolateral range of postural sway and 95% confidence circle area of sway at the cost of increased fractal dimension area variables and power.

Full text

Journal of Applied Biomechanics, 2013, 29, 174-179
© 2013 Human Kinetics, Inc. An Official Journal of ISB
www.JAB-Journal.com
ORIGINAL RESEARCH
174
Hamid Bateni (Corresponding Author) is with the Physical
Therapy Program, School of Allied Health and Communicative
Disorders, Northern Illinois University, DeKalb, IL.
Changes of Postural Steadiness
Following Use of Prefabricated Orthotic Insoles
Hamid Bateni
Northern Illinois University
Orthoses are designed to assist a malaligned foot in adapting to the environment and reduce the frequency of
injury. Literature is divided on the benets of orthotics insoles for postural stability. The current study was
conducted to determine the effect of prefabricated orthotic arch supports on postural stabilization. Twelve
healthy young adults participated in this study and were tested with and without prefabricated orthotics. Dif-
ferent variables were computed from movement of center of pressure (COP) during orthotic use as suggested
in the literature. The mean position of COP was signicantly shifted forward and toward the dominant side.
Neither the COP movement nor the velocity changes following the use of orthotics revealed signicant dif-
ferences. Mediolateral range of COP movement and the 95% condence circle area of sway was signicantly
reduced (P = .022 and 0.048 respectively), but changes in 95% condence circle and ellipse areas of fractal
dimension were not signicant (P = .053 and P = .057 respectively). In conclusion, orthotic insoles signicantly
improved postural sway initially by reducing mediolateral range of postural sway and 95% condence circle
area of sway at the cost of increased fractal dimension area variables and power.
Keywords: orthotic devices, postural balance, rehabilitation
Orthoses are designed to assist a malaligned foot in
adapting to the environment and reduce the frequency of
injury; they are prescribed for various reasons.1 Studies
have shown that orthotic insoles potentially can improve
postural stability and the quality of sensory information
required for postural control.2–4 In contrast, there are some
who have reported that the use of foot orthotic devices
may not have a benet for postural stability.5,6
It has been shown previously that orthotic insoles
improve the scores of Berg Balance Scale signicantly.3
It is also reported that use of custom-made orthotics
improves balance and proprioception among profes-
sional golfers4 and reduces the velocity of sway among
individuals with rear foot malalignment.2
Most studies reporting benets of foot orthotics
studied custom-tted arch supports. The only study that
focused on prefabricated insoles5 reported no signicant
effect of insoles on postural stabilization in professional
soccer players. The only study that reported no benets
in the use of both prefabricated and custom-tted orthotic
insoles on postural sway6 studied 15 athletes with acute
ankle injuries. Whether the lack of signicant changes of
postural sway velocity in the study of Hertel et al (2001)
resulted from the use of orthotics or was a consequence
of ankle injury is unknown.
This study aims to compare postural sway of young
adult individuals with and without orthotic insoles in the
time domain distances and area measures, fractal dimen-
sion, and frequency domain variables. Postural control
often has been used as a measure of lower extremity
function and is dened as the process of maintaining
the center of gravity with the body’s base of support.7,8
Postural stabilization is often quantied by measurement
of postural sway, which is the movement of the center
of pressure (COP) while participants are standing on a
force platform.6,9 Postural sway provides an indication
of postural control during quiet stance.6,9 Normal limita-
tions of postural sway are about 12 degrees in the sagittal
plane and 16 degrees in the frontal plane.10 Numerous
studies have shown that poor postural stabilization can
be identied by an increase in time-domain distance
and area variables of sway.11,12 It also has been shown
that postural control can be characterized by frequency
domain variables such as power of the sway.13,14 More
recent studies have suggested that fractal dimensional
variables of sway signal are valid and reliable measures
of postural steadiness.15–18
The purpose of this study was to examine the
effects of prefabricated orthotics on postural stability in
young healthy subjects with a neutral hind foot. It was
hypothesized that prefabricated orthotics would shift
the mean antero-posterior (AP) position of COP and
decrease postural sway as reected by total excursion
and mean distance and root mean square distance from
the mean COP. Furthermore, it was hypothesized that

Effect of Arch Supports on Postural Sway 17 5
use of orthotic insoles would cause a reduction in the
95% condence circle, which consists of 95% of COP
positions. We expected no signicant changes on fractal
dimension or total power of sway following the use of
orthotics.
Methods
Following approval from the Institutional Review Board
of Northern Illinois University, twelve healthy young
adults (5 males, 7 females) between the ages of 22 and
27 (mean = 23, SD = 1.4) were recruited to participate
in the study. Participants were included if they (a) had
neutral rear-foot alignment with less than 5 degrees of cal-
caneal varus or valgus as measured by the angles formed
between the midline of the posterior aspect of the distal
third of the leg and the midline of the posterior aspect
of the calcaneus,19(p859) (b) had no physical or mental
disability which could potentially affect their balance
and (c) could stand on a single limb for 30 seconds.
Individuals with any visual or vestibular decits and
those with a history of injury or surgery on the lower
extremities in the past 6 months were excluded from
the study. All recruited participants were right handed
and right legged. To determine whether participants
were right handed and right legged, they were asked two
questions: (a) which hand do you use to write? (b) if you
were to kick a ball which leg would you use? Participants
were asked to sign a consent form before participation
in the study.
ProFoot Super Sport Arch supports (Profoot, Inc.,
Brooklyn, NY) that were used in this study are differently
sized for men and women. All participants were using
gender-appropriate ProFoot Super Sport Arch supports
for orthotics trials. ProFoot Super Sport Arch support is
a typical orthotic insole that supports both longitudinal
arches as well as the transversal arch of the foot. The
insole covers the plantar surface of the foot under the heel
up to the head of metatarsals. The reason for selection
of this model of orthotics was availability and low cost.
Previous studies have shown that there are no signicant
differences between different brands of prefabricated
orthotic insoles.20,21 The Kistler-9287BA force platform
(Kistler Co., Winterthur, Switzerland) was used to col-
lect position data of the COP at 100 Hz. The Matlab
program was used to compute several variables derived
from postural sway.
Participants were randomly assigned to 4 trials (2
conditions: with and without orthotics, 2 repetitions),
each lasting 30 seconds. Participants were instructed
to stand on the platform as quietly as possible, looking
straight ahead, toward a black circle (1 inch in diameter)
located on the wall 6 feet distant in the anterior view.
Landmark lines were drawn on the force platform to
ensure participants would stand at the same location
on the force platform during all tests. During the tests,
participants stood in a standard position determined,
from literature, to represent a typical self-selected
stance (14 degrees between medial foot margins,
heel-center spacing = 11% of body height.22 For the
orthotics trial, prefabricated orthotics were placed under
each foot.
Force platform data were collected for a period of
30 seconds. Anteroposterior and mediolateral time series
data were ltered through a fourth-order zero-phase
Butterworth low-pass lter with cut-off frequency of 5
Hz as suggested in the literature.23 The rst 10 seconds
of data were cut off following the method of Prieto and
colleagues23 to remove potential lead-in effect on the
postural sway. The last 2 seconds also were cut off
to avoid any sway effect due to anticipation of the
end of the trial. The middle 18 seconds was used in
the analysis. An in-house-developed Matlab program
was used to compute several variables of postural sway
in both time and frequency domains as reected by the
movements of the COP. A detailed explanation of time
and frequency domain variables computed in this study
is provided in the literature.23–27 To compute the fractal
dimension, the algorithm of Myklebust and Myklebust
was adopted.23
Fractal _Dimension =log(N) /
log(Nd /([AP(n+1)−AP (n)]2+[ML(n+1) −ML(n)]2))
n=1
N−1
∑
where N is the number of data points included in the
analysis, d represents the maximum distance between
any two points, and AP and ML are coordinates of COP
position in mediolateral (ML) and anteroposterior
(AP) directions. Matlab and SAS statistical analysis
programs were used for data processing and analysis.
Resultant and direction characteristics of postural
sway in time and frequency domains were compared.
Repeated measures analyses of variance with a single
random effect of orthotic vs no orthotic with replicates
within subjects were performed to identify signicant
differences (P < .05). Analysis of normality assumption
was conducted for each response variable and results
showed normality.
Results
The mean position of the COP was signicantly shifted
forward and toward the dominant side when the orthotics
were used (PML = 0.001, PAP = 0.036) (Figure 1). Some
time domain variables changed signicantly following
the use of orthotics (Table 1). Movement of the COP,
resultant and directional (ML and AP) mean distance
from the mean COP and velocity of sway following the
use of orthotics did not change signicantly (P > .05).
The resultant root mean square (RMS) of the distance
substantially changes, but did not reach statistical sig-
nicance (P = .07). Changes in the mediolateral sway
range were statistically signicant (P = .02). Neither the
resultant nor the AP and ML directional total excursions
of the COP were signicantly changed (P > .05). From

176 Bateni
Figure 1 — Box plots of mean position of COP in both AP and ML directions. Two conditions of no orthotics (NO) and with
orthotics (WO) were compared. The line at the middle of the boxes represents medians and diamond shape represents mean value.
Notches on each box indicate 95% condence intervals of median values. Plus signs on the graph represent outliers. Overlap of
notches between two boxes shows that no signicant difference at 95% condence exist between medians. *Shows signicant dif-
ference (P < .05) between mean values.
Table 1 Descriptive statistics of the COP-based measures of postural sway, comparison of with
orthotics, without orthotics, and overall
Measure No Orthotics, mean (SD) Orthotics, mean (SD) Overall, mean (SD)
P
Value
Mean ML position (mm) –15.33 (7.62) –13.81 (9.05) –14.57 (8.31) .0011
Mean AP position (mm) –1.92 (2.85) –2.96 (2.27) –2.44 (2.6) .0364
Mean distance (mm) 2.94 (0.85) 2.71 (0.472) 2.83 (0.69) .2242
RMS distance (mm) 3.43 (0.91) 3.14 (0.52) 3.29 (0.75) .0745
ML range (mm) 21.99 (7.12) 20.68 (7.33) 21.34 (7.18) .0228
Total excursion 182.72 (54.66) 186.84 (33.84) 184.78 (44.97) .634
Mean velocity 10.14 (3.03) 10.37 (1.87) 10.26 (2.49) .634
95% condence circle area (mm2) 112.67 (58.99) 90.68 (32.31) 101.68 (48.34) .0484
Mean AP frequency (Hz) 0.90 (0.28) 0.98 (0.21) 0.94 (0.25) .0495
Mean ML frequency (Hz) 0.82 (0.20) 0.82 (0.23) 0.83 (0.31) .7297
Fractal dimension-CC 1.58 (0.08) 1.62 (0.06) 1.61 (0.08) .0530
Fractal dimension-CE 1.67 (0.12) 1.71 (0.09) 1.69 (0.11) .0574
Total AP power 82.63 (35.95) 102.13 (43.39) 92.38 (40.63) .0248
Note. Mean ML and AP positions are the position of COP from the center of the force platform. For all other measures, ML and AP positions are
normalized based on the mean ML/AP positions of COP. Table also indicates P values resulting from comparison of two conditions: with or without
orthotics.

Effect of Arch Supports on Postural Sway 17 7
the time domain area measures, the 95% condence circle
area of sway was signicantly reduced following the use
of insoles (P = .048).
The mean anteroposterior frequency of the COP
movement and total anteroposterior power also were
signicantly changed (P = .049 and 0.025 respectively).
Total power calculated as the integrated area of the
power spectrum in both directions showed a signicant
increase in AP direction (P = .025) following the use
of insoles (Figure 2). Fractal dimension circle area and
fractal dimension ellipse area did not show statistically
signicant differences in their mean (P = .053 and 0.057
respectively). The median value of fractal dimension
ellipse area, however, changed signicantly at the 5%
signicance level.
Discussion
Most studies in the literature have reported the effects
of the use of foot orthotics in athletes5 or in the presence
of a pathological condition (eg, References 2–4 and 6).
It is difcult to conclude from the literature, however,
whether the observed changes reported were attributed
to the orthotics or to the special conditions of partici-
pants. The focus of the current study was on the effect
of foot orthotics on postural steadiness of young adults
without the presence of any pathologies or conditions
that differentiated participants from the healthy young
adult population.
A limitation arises from the quasi-experimental
nature of this study. Participants of this study were not
randomly selected, although all were from the target
population of healthy, young adults, and none had been
prescribed or were using orthotic insoles at the time of
the study. Participants were not wearing shoes during the
tests, as footwear in general can contribute to changes in
postural sway as can differences in footwear.28 Lack of
footwear, however, could potentially deform the insole
and alter the proper functioning of the insole. Such
limitations must be given consideration when interpret-
ing the results.
Use of prefabricated orthotics shifted the mean
position of the COP anteriorly and laterally. This shift
in the COP has not been reported in previous studies on
foot orthotics. Small changes in the position of the COP,
however, have been found to result in large alterations
of forces and moments on knee joints.29 Changes in the
position of the COP per se, without being accompanied by
changes in the distance or velocity of the COP movement,
do not necessarily indicate changes in postural steadiness.
Such changes may be considered an issue of concern that
warrants further studies on more at-risk groups such as
older adults or pregnant women.
This study does not support signicant changes in
postural sway velocities in either AP or ML directions
and is in agreement with the nding of a previous study
on 15 college athletes with ankle sprain.6 In addition,
Percy and Menz (2001) reported that use of orthotics
does not signicantly affect postural sway, as measured
through optoelectronic devices that were recording
movement of the waist. They did note a trend, however,
in participants to sway less in the unipedal position when
prefabricated orthotics were used.5 The current study also
conrmed that participants tended to sway less when the
mean distance from mean COP position was measured.
Furthermore, the measurement of 95% condence circle
Figure 2 — The results of 95% condence fractal dimension circle and ellipse area in addition to total power computed based on
the power spectrum. Two conditions of no orthotics (NO) and with orthotics (WO) are compared. *Indicates statistically signicant
difference (P < .05). Note that nonoverlapping intervals in the fractal dimension ellipse indicate signicant differences between the
two medians at 5% signicance level.

178 Bateni
area of sway conrmed that individuals will sway in a
signicantly smaller area while wearing orthotics than
while not wearing orthotics.
Mediolateral range of postural sway substantially
decreased when orthotics were used (P = .023). Range
of postural sway is known to represent the most reliable
traditional variable of postural performance.30 Signicant
reduction in mediolateral sway of the COP is particularly
important to determine, since associations between
aging, lateral instability and the risk of falling is well
established.31–34 Studies of risk factors for hip fracture
have suggested that the ability to avoid lateral falls may
be equally if not more important than factors such as bone
quality or body mass index.35–37
The 95% confidence circle and ellipse areas of
fractal dimension were computed as suggested in the
literature.23,26,27 It appears that these variables have not
been measured in any other studies investigating the
effect of foot orthotics on postural steadiness. Fractal
dimension is a unitless measure indicating the potential
of the COP movement curve to ll out a metric space that
it encompasses. Fractal dimension measures are reported
to be more reliable than traditional measures of postural
sway30 since they provide additional information about
the underlying dynamics of the sway.
The 95% condence circle and ellipse areas of fractal
dimension were both measured in this study. Both values
showed a nonsignicant increase in the mean value
following the use of orthotics (P = .053 and P = .057
respectively). Fractal dimension ellipse area, however,
showed a signicant increase in median value (at the 5%
signicance level). Fractal dimension values technically
are derived from both velocity and movements of COP;
therefore, fractal dimension quanties the relationship
between the effort made by the central postural control
system and achieved postural steadiness.23 Substantial
increase in 95% condence circle and ellipse areas of
fractal dimension may indicate that when participants
were using orthotics, they may have put forth more effort
to reach the same level of postural steadiness as without
orthotics. Substantial increase in the mean frequency of
postural sway in AP direction (P = .0495) and total AP
power (P = .0248) also support the possibility of change
in mechanism of control when orthotics were used. This
may be due to the immediate change that participants
experienced under their feet and change of the mean posi-
tion of the COP as discussed earlier. One could speculate
that if the participants use orthotics long enough to get
used to changes in the mean position of the COP, fractal
dimension differences will be reduced to near original
values. So, after a given time, the presumed benets
and side effects of orthotic insoles may diminish due to
adaptation phenomenon.
In conclusion, the results showed that use of orthotic
insoles signicantly reduced mediolateral range of pos-
tural sway and 95% condence circle area of sway and
therefore improved postural steadiness initially. The
substantial increases in the 95% condence ellipse areas
of fractal dimension, however, suggest the possibility of
an increase in muscle activity to control posture. Future
studies should focus on the long-term effects of orthotic
insoles on postural control to determine whether initial
changes last over time.
Acknowledgments
The author would like to thank physical therapy students at
Northern Illinois University for their assistance on data col-
lection.
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