Introduction - Preventive Biomechanics - page 1

Chapter 1
Introduction

It all started with a seat cushion given to me (first author) by a former colleague
12 years ago. This particular cushion, said my colleague, was not a regular cushion
but a professed anti-decubitus cushion and asked me if I had use for it. Since I had
always worked with technical materials, characterizing the polymeric soft foam
cushion material properties was the most obvious task to a materials scientist. How
the particular material and the cushion might interact with human body tissue
became increasingly preoccupying. After contacting the manufacturer for medical
bedding systems (generally referred to as aid devices or therapeutic appliances),
I learned that the term decubitus refers to ulcerated tissue (or pressure sore) which
recumbent patients or wheel-chair patients with strongly limited mobility are
likely to develop.
The more I learned about the development and design of such therapeutic
appliances, the more I questioned whether such devices could possibly fulfill their
claimed purpose, namely to prevent pressure sores. Even when these devices
fulfilled requirements such as efficient microclimatic conditions and toxicological
acceptability, it seemed unclear whether they could adequately reduce compres-
sive and shear loading at pressure sore prone body regions such as head, shoulder
or tail bone. Were they really designed and optimized to minimize peak pressure?
Although mattresses and cushions employed in anti-decubitus (and comfort
related) systems are mechanically tested in the lab with compression tests to
evaluate their mechanical properties, these tests do not involve human subjects.
Human subjects are, however, the ones meant to be well supported by such
devices. Only a few certified institutes employ physical dummy models (technical
materials in pelvic form) or abstract testing devices (cf. Fig. 1.1 ). The properties of
these dummies have very little in common with realistic anatomical and biological
properties of human material, such as skin, fat and muscle tissue.
Pressure mapping devices are still the method of choice (cf. Fig. 1.1 ) in testing
medical mattresses and cushions, as well as for automotive seating and sport shoes.
The imparted information is limited to contact pressure information between the
sensor system and the subject at the (skin) surface level. Pressure mapping devices
cannot

provide information about the complex three-dimensional interaction