Custom Body Support Using the 2nd Generation Matrix System
Steve Cousins, PhD, SRCS
Denis May, PhD
Ron Clarke

Introduction
    The concept of structural matrices for use in rehabilitation (1,2,3) has
lead to worldwide fittings of over 30,000 matrix seating systems (a type
of sitting orthosis). The concept was to “design a universal structure,
or structural matrix … defined as an array of small components that can
be linked, shaped and locked to form a strong enclosing or supporting
structure.” Additionally the “matrix approach takes advantage of massproduction
techniques for producing standard components.” The vision
was that the “frequency of patient visits may be reduced, as changes
to the shape and strength of the orthosis can be made while the patient
waits. The comfort of the patient will be increased by the provision of
lightweight and cool structures that conform and respond to their needs.”
The concept was later restated (4) “to speed production, lower costs and
reduce the reliance on skilled technicians for the custom fitting processes
in orthotics and prosthetics, it was proposed to divide support surfaces
into load bearing, interlockable, segmented structural elements that could
be mass produced.”
    From this worldwide experience design improvements were proposed.
This paper reports on component re-design and the resulting laboratory
and clinical evaluations. The re-designed (2nd Generation vs Original
Matrix) components are thinner (about 25%), flatter (three times the
surface area), stronger (nearly 3 times), lighter (due to less framing
and material changes), simpler (6 parts down to 3) and more corrosion
resistant (stainless steel). The new components have true 3D forming
capability (2-ball) by adding a translatory degree of freedom to the ball
and socket joint. The 3mm thick cladding allows reinforcement to be
applied anywhere on the Matrix shell compared to the old bulky frame.

Evaluation
    Pre-production evaluation was conducted on 10 patients followed by
post-production evaluation with 60 patients, 20 full shell and 40 back
support fittings using indirect (casting) and direct (to the patient) fitting
methods. In parallel destruction testing of nearly 450 structural elements
before and during all stages of the design’s evaluation were undertaken.
A further detailed retrospective measurement was made of eight casts
and finished shells of the Original Matrix to determine part orientation
and the distribution of custom components. The direct fitting method
was improved by taking eight ‘orthotic’ measurements that results in a
reduction of patient fitting time to about 30 minutes. From a workshop
perspective the new design reduces fabrication and subsequent alteration
time by about 30 to 40%. Equally, post delivery re-shaping times were
reduced.

Conclusions
(1) Increased strength means,
(a) less framing with reduced weight and bulk (improved cosmesis),
decreased production/adjustment time,
(b) flexible components now possible because slippage is eliminated,
(c) ‘off the shelf’ back supports – no custom frame.
(2) 3D capability
(a) speeds the production process (less special threaded connectors),
(b) strengthens the final product (metal core to 2-ball), (c) allows
major adjustments directly on the patient at fitting and post
delivery,
(3) Cladding allows
(a) reinforcement to be easily added anytime,
(b) a thinner and more cosmetic structure.

References
(1) Cousins SJ, Tredwell SJ, Cooper DG, Cousins SK. A Body Support
System for Seating Children with Disabilities. Proceedings of the
Interagency Conference on Rehabilitation Engineering. Atlanta Georgia,
1979.
(2) Foort J, Hannah RE, Cousins SJ. Rehabilitation Engineering as the
Crow Flies. P&O International, April 1978, Vol. 2, No. 1
(3) Cooper DG, Foort J, Hannah RE. Structural Matrices for use in
Rehabilitation. P&O International, April 1983, Vol. 7:25-8
(4) Cousins SJ, The Design of Segmented Structural Surfaces, Ph.D.
Dissertation, University College London, January 1988