The Henry Ford Approach to Custom Made Seating and Back Support
Steve Cousins, PhD, SCRS
Richard Hannah, MSc

Introduction
   
    Henry Ford pioneered the use of mass production techniques to produce
identical cars (in any colour as long as it was black!) In this Course we
will explore the structural matrix concept, the opposite of the Henry Ford
approach, that is, the use of mass-produced components for one-off,
custom shaped, non-identical products (that can also be made in black).
The concept of structural matrices was proposed for use in
rehabilitation1,2,3 about 25 years ago. About 5 years later serious clinical
application of these concepts was started with a 125 patient trial with a 5
year follow-up4, which has lead to worldwide fittings (about 23 countries
at one point) of over 30,000 matrix seating systems. 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.” The concept was later restated4
“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.”

Developments

The concept of Structural Matrices will be described using seven designs
that fall into two categories:
• Rigid, lockable segments
• Flexible, lockable segments
The subsequent clinical compromise that results from these design
choices are that you can have (1) a flexible system that shapes well to
the body, but is inherently structurally weak, or (2) you can have a rigid
system that will support the loads on it (and/or impart corrective forces)
but does not fit as easily to the body contours. Part of the reason for
the improved design, the 2nd Generation Matrix, is to overcome these
difficulties.

Components

The supply of a Matrix seating shell or back involves five processes.
These are, generally, (1) assessment, (2) fitting, (3) reinforcement, (4)
finishing and (5) re-adjustment. The system is composed of four main
elements: (1) Clamp and 4-ball repeating structural elements, (2) Flexible
4-ball interconnectors in soft, medium and hard grades, (3) 3D, 2-ball
connectors, and (4) Cladding reinforcement. Examples of how these
components are combined to produce a finished seating system are
described using pictures of completed systems.
In summary, the four main system elements give the following benefits:

General Features: (compared to original system)
• About 4 mm thinner (25%) and 2.3 times stronger
• About 20% lighter (less reinforcing framework needed)
• 3 vs 6 components in the clamp (production speed improvement)
• Larger flat surfaces (pressure risk reduction)

Flexible Components:
• Spasm trigger reduction
• More responsive shell
• Hinging for spinal de-rotation
• Dynamic mounting
3D Capability:
• Better fit to compound curves
• Improved production speed
• Easier post delivery adjustments
Reinforcement Cladding:
• Reinforcement where needed (without planning ahead)
• Thin, cosmetic reinforcement (if needed)
• Reinforcement if shell is split, seat from back

Fitting Techniques

Of the fitting techniques in use the three most basic are, (1) indirect,
using a evacuated bean bag and plaster cast, (2) direct shell fitting (on the
patient) of a one piece Matrix seat, in a fitting frame, and (3) direct back
fitting (fitting only to a patient’s back) with a prefabricated Matrix back
using special mounting hardware, in a wheelchair.
Indirect Fitting Method: By using a bean bag system, where the shape can
be captured by drawing a vacuum separately on at least the seat and back,
a corrected shape can saved with a plaster bandage cast. The Matrix
sheet can be draped over the cast (suitably reinforced) and screwed in
place along the centreline (each Matrix sheet has a green centreline; the
remaining material is black). This helps maintain symmetry (if the patient
is symmetrical) during fabrication. Any corrections can be made at an
intermediate fit or delivery stage.
Direct Fitting with Pre-measurements Method: Seven measurements can
be taken from patient and, with suitable formulae, transferred to a Matrix
sheet laid out on a table. The resulting shaped sheet can be formed up
into a seating shell and suspended in an adjustable fitting frame (with or
without bean bag seat cushion). The patient sits directed on the preshaped
shell and it is tightened around them.
Direct Back Fitting Method: This technique is similar to the one above
but the backs are all pre-shaped and selection is made by one patient
measurement, the ASIS to top of shoulder. The other difference is that
the back is mounted to hardware that allows it to be fitted to the patient’s
wheelchair. The direct fitting of the back to the patient is started at the
pelvis, shaped up the back and out to the laterals. The Matrix is then
tightened in columns starting from the centreline and working outward
(medial to lateral tightening).

Specific Assessment

In addition to all the normal special seating assessments techniques that
professions use to arrive at a prescription, a ‘decision support’ rating scale
can be used to help in selecting general special, custom-made seating
system. For example, it would help you choose between a foam carved
system and a structural matrix. This tool is still under development. The
score of the Physical and General Factors are added together to give the
Special Seating Rating Scale total.
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Physical Factors
1. Pelvis – impact of deformity, tone, sensation on:
Score up to 6
•Obliquity
•Posterior tilt/Anterior tilt
2. Hips - impact of deformity, tone, sensation on:
Score up to 6
•Unequal flexion
•Flexion less than 90
3. Lower Limbs - impact of deformity, tone, sensation on:
Score up to 8
•Abduction/Adduction/Windsweeping
•Leg length discrepancy
4. Trunk - impact of deformity, tone, sensation on:
Score up to 16
•Lateral flexion
•Scoliosis
•Kyphosis
•Increased/decreased lordosis
•Rotation
General Factors
1.Postural deformity management Score up to 3
2.Medical condition Score up to 2
3.Continence Score up to 2
4.Agitation/Excessive movement/Insecurity Score up to 2
5.Current Weight Score up to 2
6.Future Weight Score up to 2
7.Growth Score up to 2
8.Autonomic function Score up to 2
9.Others?
•Sitting ability (eg. inverted Chailey Sitting Scale)
•Postural competence (eg. Pauline Pope’s assessment)
Possible ‘decision support’ from rating scale:
Score < 20 Custom seating not indicated
Score 21 – 30 Foam Carve indicated
Score >31 Matrix indicated
Trunk Score =>6 Matrix Back indicated
Case Study

Objectives: For this 39 year old male, with a diagnosis of Cerebral Palsy,
our objectives were to provide a wheelchair and seating system that will,
at minimum risk:
• Accommodate fixed deformities
• Provide lower limb alignment
• Accommodate knee flexion difference
• Accommodate plantar flexion
Patient Details: He was admitted to the hospital in 1991, initially to a
rehabilitation and subsequently transferred to a continuing care ward.
He has been throughout severely disabled by a dense, spastic tetraplegia,
kyphoscoliosis with rotation of the trunk, choreo-athetoid movements
of the upper limbs, head and neck, and tongue with repetitive facial
grimacing and epilepsy. His disabilities arise from congenital athetoid
cerebral palsy. Some basic and physical information is listed below:

Contraindications Epilepsy
Medication Carbamazepine; Bisacodyl
Height 1.64m
Current Weight 57.9kg (this is an increase of nearly 10kg since
1999. NB: this weight has been stable for 12 months+)
Target Weight 55-60kg
BMI 21.5 kg/m2
Method of propulsion Attendant pushed
Visual status Can inconsistently track objects
Auditory status Normal auditory stimuli response
Communication None established
Cognition Follows verbal commands inconsistently,
low concentrations levels
Respiratory status No problems noted
Sitting tolerance 6-8 hours
Skin integrity Intact
Ability to pressure relieve None
Method of transfer Hoist
Continence Doubly incontinent
Feeding / swallowing PEG fed
Transportation issues Travels in a wheelchair in an ambulance/
adapted vehicle
Environment Indoor and outdoor
Future placement Long term care facility
Pelvis
• Raised and forwards on the Right – fixed
• Fixed in posterior tilt
• Unequal weight distribution
Hips
• Bilaterally adducted and internally rotated – limited correction
• Resting angle of Right hip is 120º but can achieve 110º
• Resting angle of Left hip is 110º
Knees
• Left rests at 50º flexion
• Right rests at 45º flexion but can achieve 90º
Feet
• Bilaterally plantar flexed – Right can be corrected to plantar grade but
Left is fixed
Trunk
• Left convex scoliosis – see photographs
• Flexed lower and upper spine
Shoulder Girdle
• Bilaterally protracted
• Rotated forwards on the Right
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Upper Limbs
• Active but non-functional movement
• Left arm rests in a flexed and pronated position
• Right arm tends to rest in extension
Head / Neck
• Flexed
• Rotated to the Left
• Good passive ROM
• Good active head control

Discussion: He was admitted with a MSI (one piece moulded seating
insert – vacuum formed). He has had two Matrix sitting shells (Original
Matrix) made during his stay in the continuing care facility with a new
system (2nd Generation) completed recently. His 24-hour physical
management will be discussed, supported by a review of his physical
condition and treatment all in conjunction with a review of the recent
seating systems (with photographs).
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