Textured foot orthoses impair postural stability

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September 2007 Biomechanics Magazine

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Textured foot orthoses impair postural stability

By: Lori Rochelle Roniger

Wearing textured insoles worsened postural control in individuals

with chronic ankle instability, according to a poster presented at

the National Athletic Trainers' Association annual meeting in

Anaheim, CA, in June.

" We were surprised by this finding, " said Jay Hertel, PhD, ATC, an

assistant professor of human services at the University of Virginia

in Charlottesville, and one of the study's authors. " We had done a

previous study on healthy individuals with these same textured

inserts and found that traditional force plate-based measures of

postural control were enhanced by the inserts. "

Studies conducted by Hertel and his colleagues have suggested that

traditional foot orthoses improve balance in healthy people by

enhancing plantar cutaneous stimulation, which in turn might boost

lower extremity neuromuscular activation.

In the current study, the researchers tested whether wearing

textured insoles in the laboratory would improve the balance of

individuals with chronic ankle instability. This condition may arise

from proprioceptive deficits stemming from damage incurred to the

ankle joint capsule and ligamentous mechanoreceptors during an

initial ankle sprain, Hertel explained.

" In an effort to replace this diminished articular proprioceptive

information, we wanted to provide cutaneous stimulation to the

plantar aspect of the foot using the textured insoles, " he said. " It

is possible that chronic ankle instability creates constraints on

the neuromuscular system that prevent the heightened plantar

cutaneous stimulation from positively affecting balance. "

Twelve men and eight women whose average age was 21.5 and who self-

reported chronic ankle instability served as study subjects. They

had experienced at least one substantial ankle sprain, had their

ankle repetitively give way by rolling over, and scored less than

90% on both the activities of daily living and sports subscales of

the Foot and Ankle Disability Index.

The subjects' postural control was measured as they stood on one

foot on a force plate for 10 seconds, while wearing their own low-

top athletic shoes, under six conditions: with their eyes opened or

closed while wearing textured shoe inserts, sham inserts, or no

inserts.

The textured inserts, which were designed to offer minimal

mechanical support to the foot, were constructed from a plastic

matting material and had four 2-mm raised nodules per cm2. The sham

inserts were made from 1.5-mm rubber foam.

The researchers recorded time-to-boundary measurements in the

mediolateral and anteroposterior directions.

Time-to-boundary data provide a spatiotemporal representation of

center-of-pressure excursions by illustrating the time it would take

for the center of pressure to reach the foot. Center-of-pressure

data were collected at 50 Hz and provided 500 data points, from

which time-to-boundary statistics were calculated.

" We then performed a number of different statistical analyses on the

data points at the valleys or minima because these represent the

instances of greatest postural instability, when the subjects are

closest to losing their balance, " Hertel said.

Anteroposterior time-to-boundary minima measurements recorded while

the subjects had their eyes open were significantly lower when they

wore the textured insoles (12.2 sec) than when they wore the sham

insoles (13.6 sec) or no insoles (14.2 sec), indicating poorer

postural control under the textured insoles condition. When the

subjects closed their eyes, the measurements were not significantly

different. Mediolateral time-to-boundary minima were significantly

lower when the subjects wore the textured insoles (2.9 sec) compared

with the sham insoles (3.2 sec) or no insoles (3.3 sec). This also

suggests that the subjects experienced worse balance while wearing

the textured shoe inserts.

Hertel noted that the textured insoles may have been slightly

uncomfortable, which could have negatively affected the balance of

the subjects. His research team may conduct future studies on the

effects of textured insoles with shorter raised nodules.