Offloading shoe sole designs could impair patients' balance

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April 2007 Biomechanics Magazine

Offloading shoe sole designs could impair patients' balance

By: Jordana Bieze

http://www.biomech.com/showArticle.jhtml?articleID=198800909

The pressure distribution benefits of rocker bottom and negative

heel shoe sole configurations may be offset by levels of instability

that could put neuropathic patients at risk of falling, according to

research from East Carolina University in Greenville, NC.

In nine young healthy subjects, investigators compared response to

force plate perturbations under three crepe-sole shoe conditions: a

rocker bottom, which was rounded at the toe and heel; a negative

heel, which was rounded only at the forefoot; and a control shoe,

with a full thickness flat sole. Four types of perturbations were

applied: horizontal forward shift, horizontal backward shift, toes-

up tilt, and toes-down tilt.

The researchers found that the horizontal backward-shift

perturbation resulted in significantly greater sway amplitude and

sway variance in both experimental shoes than in the control shoe;

the rocker bottom shoe was also associated with significantly

greater sway velocity than the control shoe. The other three types

of perturbations were not associated with significant differences

between shoe conditions.

" Postural responses with the experimental shoes reflected greater

destabilization and potentially rendered subjects more vulnerable to

postural imbalance, " said Bruce C. Albright, PhD, PT, professor of

physical therapy at ECU, who presented his group's findings in

February at the annual Combined Sections Meeting of the American

Physical Therapy Association.

The results may not be surprising to rehabilitation specialists,

since similar measures of instability have been reported to be

associated with the Masai Barefoot Technology shoe, which has a

rocker bottom sole and a negative heel (see " Barefoot-like designs

challenge footwear conventions, " February, page 20). In fact, this

instability-similar to that provided by a wobble board-is the

mechanism by which the Masai shoes are thought to strengthen the

small muscles of the foot; in-press research from the University of

Calgary even found that six weeks of wearing the shoes could

actually improve balance.

The Masai shoes, however, are not recommended for patients with

diabetic neuropathy because of balance impairments often associated

with loss of sensation (see " Neuropathy treatment may aid in

preventing falls, data suggest, " August 2004, page 19). Similarly,

the East Carolina researchers believe their results suggest that

neuropathic patients, in whom rocker-bottom or negative-heel shoes

can decrease the risk of ulceration by redistributing plantar

pressure, could be even more unstable in such shoes than the healthy

subjects they studied. A September 2004 study by researchers from

Milwaukee, presented at the annual conference of the IEEE

Engineering in Medicine and Biology Society, also suggested that

feelings of imbalance were responsible for changes in pelvic tilt

and hip rotation during gait observed in 40 subjects wearing double

rocker sole shoes.

The instability seen in rocker-bottom and negative-heel shoes

suggests that patients with diabetic neuropathy should undergo a

balance assessment before such shoe interventions are prescribed,

Albright said. Balance training may be beneficial for those patients

in whom impaired balance is detected.

Albright noted, however, that the study did not measure the extent

to which subjects might have become less unstable as they

accommodated to the shoes over time, although the researchers did

observe some accommodation by study subjects as five trials were

performed in each shoe condition. It is possible, he said, that

patients who wear rocker bottom or negative heel shoes for pressure

relief subsequently develop unique strategies to maintain postural

stability.