Biomechanics of seating for the spinal injury patient

Biomechanics of seating for the spinal injury patient

1986; 1: 147-149 Clinical Biomechanics 147 Printed in Great Britain Brief Reports Biomechanics of seating for the spinal injury patient R J Minns...

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1986; 1: 147-149

Clinical Biomechanics

147

Printed in Great Britain

Brief Reports

Biomechanics of seating for the spinal injury patient R J Minns Pm Regional Medical Physics Department,

Dryburn Hospital, UK

Summary Pressures under the ischial tuberosities have been measured using a specially adapted seat in which the footrest length and backrest position can be adjusted so as to allow spinal injury patients to sit in a position identical to sitting in a wheelchair. The information on the area and values of underseat pressures are used in monitoring the effect of surgery, as a feedback device to obtain the optimum posture whilst sitting in a wheelchair and the design of wheelchair cushions to relieve pressures under the ischial tuberosities.

Introduction A

pedobarograph

Dryburn

has been

Hospital

developed

at

deflects

light

of pressures

camera.

The electrical

and built

for the measurement

under the foot and buttocks and for evaluating materials.

cushion

A similar device for clinical use in the mould-

ing of cushions for spinal injury patients in wheelchairs has been built’. Helen

Furthermore.

Hayes Hospital.

a device has been used at

New York

in which the under-

through

a

calibration

from

voltage

the

detecting

comparator

photography

to provide a permanent

or for studying

Using

a combination

the Pedobarograph been designed frame is formed with adjustable

adjustable

of a portable

technique.

by a

wheelchair.

wheelchair

an ‘Ischiobarograph’

and is based at Hexham,

England.

mal circumstances

this light is reflected

internally.

A

norA

plastic foil is placed on the upper surface and the whole assembly is covered with black material light. Pressure applied

to exclude stray

to the upper surface causes the

plastic foil to come into contact with the glass and the internally through mounted with

a

reflected

light

the glass. Within television Newvicon

is

deflected

the frame

camera (National S4075

tube).

An

the effect

pattern

of posture

of underseat

downwards

is a horizontally

can be calibrated

change

pressure

pressure ranges can be plotted tive monitoring

Durham

DHI

by using

and used for compara-

purposes.

The use of the lschiobarograph design service The lschiobarograph pressure patterns

for a wheelchair cushion

has been used to produce

of spinal cord injury

patients

ischial at the

mobile stage to highlight areas at risk to tissue damage. We also use this data to monitor the effect of treatment either

by surgery

using rotation

flaps to cover

the

ischium with or without carbon fibre pads (Figure 2), or by wheelchair

cushions designed to accommodate

cut-

WV-1350

CCTV

out areas corresponding to the underseat pressures seen on the device. We also use the lschiobarograph to

angled

mirror

monitor

md reprinr requesfs 10: Dr R J Minns. Regional Durham Unit. Dryhurn Hospital. STW. UK.

Medical PhysicsDepartment.

on the

distribution.

and adjusted

pressure

relief

under

the ischial tuberosities

with posture changes using the adjustable Correspondence

device.

compressed air on the detecting surface so that zones of

polished

tubes. Under

resulting

I)

record (Figure

as a feedback

The machine

on all surfaces and edges. Light is shone at these edges 13-W fluorescent

value.

has

angles. and foot rests. The detecting surface on the frame

from two domestic

after

full size

and

by a wheelchair frame; being portable arm heights. back rest depths and

contains a sheet of glass 12 mm thick optically

which

monitor

the

passes

The pictures on the monitor can be recorded by light

on the edges by fluorescent

lamps’ and viewed

into

zones of pressure above a certain predetermined

or used in the dynamic situation

placed under a modified

circuit

shows on a large colour

seat pressures are detected by a thick plexiglass sheet lit mirror

surface

signal from the camera

footrests to reduce asymmetry The wheelchair resilience

cushions are designed

polyurethane

foam

backrest and

effects. using a high

(DHR236--Dunlopillo)

148

C/in Biomech. 1986; 1: No 3

Figure 2. Pre (left) and post (right) operative underseat pressure profiles of a patient with a carbon fibre implant under the right ischium. Figure 1. Photographic underseat pressure record of a seated clothed subject.

Cut-outs for chair frame

wear properties to date suggest that the foam component needs replacing every year, but this can be done without the patient attending the Ischiobarograph Clinic; a gross shift of position and change of posture may have the patient sitting away from the cut-out areas. Clinical use

Reconstituted

foam base

lschlobarograph

Figure 3. Design of the wheelchair cushion utilizing data obtained from the Ischiobarograph.

kg/m.‘, hardness value of 124-150 Newtons to BS 3379: 1975 class of ‘V’ (very severe), and flame-resistant treated to the DOES flame test. The base is made of flame-resistant chip foam of 1 inch thickness and the upper 2 inch layer has tapered cut-outs corresponding to the ischial pressure patterns seen relatively positioned to the backrest (Figure 3). We fmd this design has many advantages over other cushion systems, but. it does have certain shortcomings over more expensive cushions: individually made and needs the lschiobarograph to obtain the cut-out data;

A current device is available to produce a cut-out type wheelchair cushion. This consists of a cushion sandwich of foam rubber with the top layer cut out in the regions of high pressure to the shapes and positions displayed on the Ischiobarograph much in the same way as the construction of the ‘synergistic’ cushions’. Pressure relief is confirmed by sitting on the modified cushions with a thin (3 mm) capacitive pressure measuring pad of 2 inch diameter. Photographs of the pressure regions are also taken for permanent recording as assessment records. It is possible for the therapist or nursing staff to use the device competently in a very short training period.

which has a density of 33-38

References

Minns RJ.

Sutton RA. Duffus A, Mattinson R. Underseat pressure distribution in the sitting spinal injury patient.

Paraplegia 1984; 22: 297-304 Mayo-Smith W. Cochran GVB. Wheelchair cushion modification device for locating high-pressure regions. Arch Phys Med Rehabil 1Y81 :h2: 135-6 135-6 Synergistic Tri-Pod. Everest & Jennings Ltd.. USA