Optimization of rocker sole footwear
Introduction
Background
Van Netten et al. [1] highlighted that studies
investigating “the specific role of therapeutic footwear
in preventing a first foot ulcer in at-risk patients
with diabetes are lacking and are therefore urgently
needed”. Indeed, use of appropriate footwear by
people with diabetes without prior ulceration is
widely advocated [2–4] and motivated by a need to
reduce plantar pressures that are one of the many
risk factors for ulceration [5, 6] . In addition to reducing
plantar pressure, however, changes in footwear
habits prior to first ulceration would allow more
time for footwear related behavior change to become
permanent prior to a serious foot or limb threatening
event. At that stage adherence with footwear advice
or prescriptions is known to affect ulcer healing and
risk of reulceration, but effective behavior change is
often not achieved. This was demonstrated in a recent
trial which observed a significant (19%) reduction
in re-ulceration at 18-month follow, but only in
the subgroup with good adherence and who wore
customized footwear as recommended [7] . Changes
in footwear choices and use prior to first ulceration
might therefore mitigate the risk of a first ulcer by
reducing pressure and improve longer term adherence
if ulcers do occur.
Prior to investigating the potential reduction in
the risk of a first ulcer due to pressure relieving
footwear as Van Netten advocates [1] , it is important
to optimize the design of the footwear. Indeed,
following a systematic review, Bus et al. [8] called for
more standardized procedures to inform the design
of footwear used in ulcer prevention. To optimize
an intervention, it is important to have an objective
measure of performance. In cases of re-ulceration,
reducing plantar pressures to <200 kPa has been
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the target for optimizing footwear design [9– 12] . A
corresponding pressure target does not yet exist for
first ulceration, but 200 kPa forms a logical initial
target. Unfortunately, use of this threshold in practice
relies on the use of pressure measurement at the point
of footwear provision [7] , and this may not always be
feasible. This is especially true prior to first ulceration,
when many of the footwear choices made, and
implicated in subsequent ulceration, occur in a retail
rather than a health care setting.
A preferable approach would be use prefabricated
footwear incorporating a standardized design (i.e.
same for all patients) which is known to reduce
pressures <200 kPa for the majority of individuals.
This will be referred to as group-optimized footwear.
However, no such group-optimized design exists at
present and current evidence for footwear achieving
the <200 kPa threshold relates only to footwear
selected/customized using individual plantar pressure
data [7, 10, 12] . We refer to this as personalized footwear.
Producing personalized footwear for individual
patients is expensive and unlikely to be justified prior
to a first ulcer unless there are significant risk factors.
Therefore, in order to meet the 200 kPa target using
footwear to prevent a first ulcer, it is important to
understand whether group-optimized footwear that
could be mass produced might suffice or whether
personalized footwear is required.
In terms of the most appropriate footwear outsole
designs for pressure relief, most clinical studies have
investigated shoes with some form of stiff rocker
outsole [7, 10] . This design has been shown to reduce
peak plantar pressures at high risk sites [13] . However,
a full description of the design features of the rocker
outsole, or indeed the rest of the shoe, is often
limited [14] . This is important because it limits our
understanding of the relationship between design
features (independent variable) and changes of
pressure (dependent variable), limiting our ability to