Optimization of rocker sole footwear
was motivated by our previous study [16] which showed
marked plantar pressure increases when apex position
was increased to 70% of shoe length.
For each of the nine shoes, in-shoe plantar pressure
was collected using Novel Pedar-X system (50 Hz)
whilst participants walked at 1 m/s along a 20 m
walkway. Speed was monitored during each trial
Rocker angle is the angle between the floor and sole
under the toe area (Fig. 1). Previous research has
demonstrated that plantar pressure decreases as rocker
angle is increased [15, 16] and increasing rocker angle is
also a customization option [12] . However, increasing
the rocker angle from 15° to 20° has a pronounced
effect on the appearance of the shoe as the thickness
of the outsole must be increased. It is therefore
possible that use of a 20°rocker angle would reduce
adherence especially if the footwear was to be used to
prevent a first ulcer (when motivation for a change in
footwear habits might be lower than once ulceration
has been experienced). Furthermore, our previous
research suggests that the benefits of increasing rocker
angle above 15° may be marginal, especially if the
apex position is chosen appropriately [16] . Therefore,
we studied a 15° rocker angle (aesthetic design) and a
20° rocker angle (less aesthetic design) in the hope of
achieving the target pressures in the former.
A total of eight shoes were designed in which rocker
angle (15° and 20°) and apex position (52, 57, 62 and
67%) were independently varied. All footwear was
manufactured with the same outsole thickness (Fig.
1) sufficient to accommodate a 20° rocker angle at
all apex positions. This meant that the outsole of
some designs (especially those with a 15° rocker) was
unnecessarily thick but ensured that all shoes were
of the same weight. In addition, a control shoe was
designed with exactly the same upper as the rocker
footwear but with a flexible outsole, similar to that of
a running shoe [21] . The outsole of all rocker footwear
was manufactured using EVA (ethyl vinyl acetate)
and incorporated a 5 mm thick layer of folex which
ensured that the outsole was rigid. All footwear
were produced by Duna® (Italy) using CAD/ CAM
technology.
40
Pedorthic Footcare Association | www.pedorthics.org
using optical timing gates and only those trials within
10% of the target speed used for further analysis.
Shoe order was randomized, using a custom Matlab
program, and participants completed a familiarization
period of three-four minutes before data collection.
A minimum of 25 steps was collected for each shoe.
Following collection, the data was visually checked to
identify the steps at the start and end of each walking
trial which were then removed. Peak plantar pressures
were calculated for each shoe design in three high-
risk [10] regions: 1st metatarsophalangeal (MTP)
joint, 2-4th metatarsal heads (MTH) and hallux.
The Pedar sensors corresponding to each region were
defined following Cavanagh et al. [22] and the peak
pressures, calculated for each region, averaged across
all steps to give a single value for each region and
shoe. This process was repeated across all participants
using custom Matlab software. The statistical analysis
(outlined below) showed similar trends for both the
left and right sides and therefore only data from the
left side are presented in this paper.
Statistical Analysis
A two-way ANOVA model with repeated measures was
used, in each anatomical region, to explore the effect
of apex position and rocker angle on plantar pressure
in the people with diabetes. This analysis was used
to test for main effects of apex position and rocker
angle and also to identify any possible interactions.
If significant differences in main effects were
observed, pairwise differences were investigated using
a Bonferroni correction for multiple comparisons.
Before testing, all data was checked for normality and
homogeneity of variance. A significance level of α <
0.01 was chosen for all ANOVA analyses.