Optimization of rocker sole footwear
current work which supports the idea of a common
footwear design for people with diabetes prior to
first ulceration. This group-optimized design would
incorporate an apex angle of 95°, an apex position of
52% of shoe length and a rocker angle of 15° or 20°.
Diabetes participants only
We sought to understand footwear performance in
the context of the 200 kPa threshold suggested by
Owings et al. [9]. This threshold was suggested based
on mean in-shoe pressures from individuals with a
prior history of ulceration who had remained ulcer
free for a prolonged period (0.4–14.4 years). The
feet of those pre-first ulceration are less likely to be
at comparable risk of ulceration. As such 200 kPa
may be a conservative target and, if the goal is to
prevent primary ulceration, this target could perhaps
be increased. Re-analysis of our data with a revised
threshold of 220 kPa (i.e. 10% higher threshold)
demonstrated a 5–7% decrease in the proportion
of feet at risk with the group-optimized design (for
example the percentage under the threshold increased
from 81% to 87% in the 2-4th MTH region). However,
importantly, the differences in the proportion of
people under the revised threshold between the
group optimized design and the personalized design
were very similar to those observed with the 200 kPa
threshold.
A clinical trial rather than a laboratory study is
needed to test the clinical efficacy of footwear for
the prevention of first ulceration. In their recent
systematic review, Van Netten et al. [1] advocated
evaluating interventions on the cohorts for which they
are intended and, in the context of interventions to
prevent first ulceration, this would involve individuals
deemed at high risk of first ulceration. A limitation
of this current study is that most participants would
be considered low risk as they did not demonstrate
sensory loss. However, our cohort did include 17
50
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who demonstrated evidence of neuropathy and we
quantified the proportion of this subgroup for whom
the group optimized rocker design reduced pressure
beneath the 200 kPa threshold. These data showed
very similar trends (Table 3) compared to the full
cohort with diabetes. This provides some evidence
that our proposed rocker design may be appropriate,
or at least a good starting point, for a higher-risk
population. Nevertheless, people with diabetes can
also present with deformity, Charcot arthropopathy, or
digit amputations, all of which will affect gait and foot
function. These may therefore influence the response
to footwear designs too. We acknowledge, therefore,
that our proposed design may not be immediately
transferrable to feet affected in different ways by
diabetes.
It is important to recognize that even if the pattern
of response to the footwear designs is insensitive to
diabetes, elevated pressures, and neuropathy, as we
suggest, the actual pressure values in people with
neuropathy and at higher risk would differ to those
we report. This limitation is important because the
proportion of individuals over the 200 kPa would
likely be higher than we report. Nevertheless, as
explained, 200 kPa is likely to be a conservative target
for those without prior ulceration and so the use
of the group-optimized footwear design would still
decrease the proportion of individuals considered at
risk.
There are a number of other limitations to the
current study which should be highlighted. Firstly,
due to the practicalities of experimental testing, we
chose to focus on a specific shoe design, varying two
specific design features across a number of discrete
levels. Our findings are therefore only valid for
curved rocker footwear. Nevertheless, our approach
of systematically varying independent design features
in order to identify a group-optimized shoe design
could be applied in other footwear designs. A further