Effect of Rocker Sole Shoe on Foot Plantar Pressure: Is It Useful in Diabetic Patients?
Authored by Maryam Mirshahi
Abstract
It is well known that high plantar pressures have
a primary role in the pathogenesis of plantar ulcers in diabetic foot.
Rocker sole shoes
are designed to reduce pressure on high-risk areas on the plantar
surface in the foot. The hypothesis is that the rocker nature of sole
assists rolling of the body
over the ground, controls joint motion and reduces the need for movement
in the foot. Though the potential effectiveness of rocker shoes in
pressure reduction is
clear, but careful consideration need to be made. Since high-pressure
areas depend on the condition of the foot and pressure varies with
each patient, the design and prescribing of the rocker sole should be
specified based on the patient's status.
Introduction
Diabetes mellitus is an epidemic chronic condition in
worldwide [1]. There is considerable growth in the number of who have
diabetes [2]. One of
the most common complications of diabetes is neuropathy that affecting
50% to 70% of cases [3,4]. The loss of sensation in the foot due to
peripheral neuropathy may
often lead to muscle imbalance, delays in muscle activation patterns,
abnormal gait and alterations of plantar pressure distribution pattern.
Limited joint mobility
and changes in the structure of the foot can also cause the gait
abnormalities and elevated plantar pressure [4]. It is well known that
high plantar pressures are a
major risk factor in the pathogenesis of plantar ulcers in neuropathic
foot [5]. Among persons with diabetes, the lifetime risk of de
veloping an ulcer could be as high as 15-25% [6,7]. Ulcers are most
often seen on high-pressure areas of the foot, especially on the
metatarsal heads and toes [3].
According to the results of study by Merolli and
Uccioli, pattern of plantar pressure distribution in healthy subjects
demonstrated
rear-foot contact in the heel strike phase, followed by a uniform
distribution of load along the whole foot surface in the mid-stance
phase.
In the terminal-stance phase, the load was focused in the front of foot
and evenly distributed along the arch of the metatarsal heads. During
the toe-off phase,
the load was transferred to the toes and finally the tip of the toe.In
the diabetic neuropathic patient, interval between heel strike and
toe-off was prolonged.
In these patients, load was transferred very early from the rear to the
forefoot.Load was increased in metatarsal heads in both magnitude and
time. In the
terminal- stance and toe-
off phases, weight was not transferred under big toe, further increasing
load of the first metatarsal head [8].
Off-loading the forefoot is an important clinical
aspect in people with diabetes who are at risk of developing a foot
ulcer or who are healing an ulcer [5]. This Offloading essentially is
achieved by redistribution of pressure to other foot regions [6]. Shoes
adapted with rocker profiles are one of the most effective design of
shoe that has been shown decrease the plantar pressure in people with
diabetes mellitus. This type of shoe facilitate "rocking" of the foot
from heel strike to toe-off, helping the tibia to rotate over the foot
more easily and reducing both the range of foot joint motion and plantar
pressure [2,9¬10]. There are heel, ankle and forefoot rockers during
normal gait cycle. It has been hypothesized that all of three rockers
are unstable.
The concept of "unstable shoe" such as rocker sole has been modeled
after natural rockers of gait [11].
The general structure of the rocker shoes consist a
curve surface in the front for reducing stress in the push-off phase and
excessive bending of the metatarsal-phalangeal joint, a flat middle
part for preserving stability and support in midstance and a curve in
rear section for reducing impact force during heel
strike [12]. A rocker sole shoe has three principle design features:
apex angle, apex position and rocker angle [2]. The offloading
properties of rocker soles
depend on all of three features design. The offloading properties of
rocker soles depend on all of three features. Three of the most commonly
prescribed rocker soles are the toe-only, negative heel, and double
rocker soles [3,10]. It is necessary to comprehend how each of the three
design features influence plantar pressure.
The toe-only rocker shifts the loads of the
weight-bearing proximal to the metatarsal heads and reduces toe stress
on toe- off. During walking,
the toe-only rocker prolongs midstance at the hindfoot and midfoot
providing a stable midstance [3]. The negative heel rocker places the
heel below or at the same
level as the ball of the foot. The negative heel rocker through weight
shifting to posterior helps to accommodate fixed ankle dorsiflexion
[3,13]. Both type of
negative heel and toe- only rocker are prescribed to decrease pressure
on the forefoot with different biomechanics [3].
The double rocker decreases midfoot loading. In this
type rocker, the midfoot does not touch the floor during midstance
[1,3]. Double rocker effect
ively redistributes midfoot pressures [3]. This type rocker typically
prescribed to relieve midfoot problems such as rocker bottom foot or a
Charcot foot deformity
[1]. In all kinds of rocker shoes, the mechanism of action is transfer
of load from the forefoot to more proximal regions [6]. The hypothesis
is that the rocker
nature of sole assists rolling of the body over the ground, controls
joint motion and reduces the need for movement in the foot [11]. The
rocker sole shoes cause
smooth progression through the stance phase of gait while restricting
active dorsiflexion of the toes and therefore forefoot contribution in
propulsion [6,12]. One
of the biomechanical advantages of rocker-soled shoes is reducing
plantar pressure on specific parts of the foot [12]. But the results of
some studies have been shown
that this pressure reduction is accompanied with increased pressure in
the other areas of the foot. It has been reported the midfoot received
most of the load
transferred from the forefoot [14]. However, it seems rather than
increasing the load, pressures are effectively distributed over a large
midfoot surface area [6].
Discussion
There are a number of published studies that
investigate the effect of rocker sole shoes on plantar pressures in
diabetes patients [2,3-6,8-10,14,15]. Several studies have shown a
percent reduction of plantar pressures of the forefoot ranging from 10%
to 60%, demonstrating efficacy of rocker soles for decreasing pressure
of the forefoot [5]. Chapman et al suggest
that an outsole design with a 95° apex angle, apex position at 60% of
shoe length and 20° rocker angle may be an optimal choice for offloading
different regions of the forefoot [2] . Other authors demonstrated
different positions of rocker for optimal pressure relief [9].
Though a number of studies show the potential
effectiveness of rocker shoes [2,12,14] but comparison between the
efficiency of rocker sole shoes is challenging for
several reasons. These reasons include different equipment and methods
for measuring of plantar pressure, diabetic patients who studied and the
characteristics of
the rocker sole (axis angle, apex position and the rocker angle)
[14,15]. In fact, by adjusting in any design features, biomechanical
effect of rocker will be
change.
Walking comfort is also another subject that should
be noted. Since comfort during walking with this shoe is relatively low,
it may affect adherence and efficacy of intervention [6]. Despite these
limitations, rocker sole shoes are effective offloading interventions
if careful consideration to be made when prescribing such designs as to
people with diabetes [12]. Since high-pressure areas depend on the
condition of the foot and pressure
varies with each patient, the design of the rocker sole should be
specified based on the patient's status [3].
Conclusion
It is clear that rocker sole shoe is effective to
reducing pressure in the diabetic foot, but each of the design may have a
different effect on diabetic patients. In fact, no single configuration
of rocker sole shoe has been demonstrated to be optimal for all
subjects and in all areas of the forefoot. Depending on the patient, a
specific sole can be prescribed to reduce plantar pressure. The
toe-only, negative heel and double rocker soles can effectively reduce
plantar pressures, helping to prevent of ulceration. It may be
appropriate to e
ncourage all people with diabetes to wear pressure reducing footwear for
protect against plantar tissue damage.
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