Biomedical Engineering Reference
In-Depth Information
Fig. 7.46 Optimized cushion
shape contour to minimize
shear stress lateral to the
ischial bone of the transversal
plane strain model.
Optimized contour is
highlighted in red
The shape aims to reduce direct stress beneath the ischial tuberosity. Shear
stress
information
is
not
included
and
thus
does
not
influence
the
derived
geometry.
To verify validity of the derived three-dimensional shape cushion loading was
simulated using the lower leg model BoMo 9 introduced in
Sect. 5.3.5
. The effects
on the tissue were evaluated and compared to a 3D-block-shaped cushion of
s = 140 mm thickness. Comparison of tissue stress shows that also in three
dimensions, using the optimized cushion geometry, reduction of direct stress at
skin level as well as inside fat and muscle tissue in the ischial bone region is
achieved, Fig.
7.49
.
Clearly, if tissue stress is reduced at the ischial bone region, stress must increase
at some other tissue location since the total body weight is supported. In this
context an increasing contribution of the upper legs to body weight support using
the derived sagital shape can be observed, accompanied by an increase in tissue
stress in this region.
A quantitative comparison of tissue stress on the lower body model, simulated
using a block-shaped cushion and the optimized cushion shape, is shown in Fig.
7.50
.
The stress distribution along a nodal path originating at skin level and progressing
through the fat and muscle tissue towards the bone was considered. Element corner
results are averaged at the selected nodes using a simple averaging method.
