The following excerpt is taken from Chapter 9 of Choosing a Wheelchair:
A Guide for Optimal Independence, by Gary Karp,
copyright 1998, published by O'Reilly & Associates, Inc.
To order, or get more information about Gary's book, call
(800) 998-9938. Permission is granted to print and
distribute this excerpt for noncommercial use as long
as the above source is included. The information in this
article is meant to educate and should not be used as an
alternative for professional medical care.
Although your wheelchair and cushion are separate purchases, which chair you
choose is significantly affected by the type of cushion you will use. Chair and
cushion are a team, each influencing the other. The proper combination of chair
and cushion will enable you to sit in a neutral and stable posture and to
operate the chair safely.
Cushions come in various depths and sizes which need to be accommodated by the
size of your wheelchair frame. The actual length of footrests, the height of the
chair back, the position of armrests, and other features are influenced by how
high or low you will be sitting on a cushion. Clearly, you need to decide which
cushion is best for you before you can make a final decision about which chair
is best, certainly before you specify the exact dimensions of your chair.
Wheelchair cushion development is quite lively, as designers and engineers
continue the quest for the ideal cushion. A number of manufacturers, such as Jay
and Roho, exist solely for the design and production of seating and support
systems for wheelchairs. Most of the major wheelchair makers, including Everest
& Jennings, Invacare/Pindot, and Otto Bock Reha also offer an assortment of
Cushion design is by no means a simple topic, and there are many choices to make
as you decide on the right one for you. This chapter discusses the four basic
types of cushions--foam, gel, air floatation, and urethane honeycomb--as well as
designs and systems for more specialized needs.
What kind of cushion you choose will depend on a variety of factors, including
how much time you spend in your chair, how much you move around in your chair,
and how stable your posture is.
One important task of the wheelchair cushion is the prevention of pressure
sores. Since, when we sit, only one third of the body's surface is supporting
all of its weight, blood flow is restricted. In the presence of muscle
atrophy--which is experienced in particular by many people with spinal cord
injuries--circulation is limited further by the loss of muscle which once served
as a sort of natural cushion. An additional risk of sitting is shear force, as
we tend to slide forward in the cushion, causing stress across the surface of
the skin. Resulting pressure sores (decubitus ulcers) can be very serious,
leading to hospitalization, surgery, and--though rare--even death. The right
cushion is a primary tool for maintaining the health of your skin.
The other crucial task for a cushion is postural stability. Even if you are able
to walk or are an amputee with sufficient built-in cushioning, the right cushion
helps to support your spine. If you already have some asymmetry in your body,
you need to be supported in a way that will not increase any spinal deformity.
For manual chair users, greater stability in your chair also means you can push
the wheels with more confidence and strength.
It can't be repeated often enough--posture is key. Bob Hall of New Hall's Wheels
puts it well:
The wrong seating system leads to poor posture, which leads to physical
problems, which leads to becoming more sedentary, which leads to a negative
emotional and personal experience. It's a dangerous chain of events.
Foam technology has come a long way. No longer just the soft, airy stuff of the
past, foam now comes in a range of densities and with varying degrees of
"memory," holding its shape as you sit, contributing to your stability. The new
foams can adapt to any shape, and still provide even support, spreading pressure
across the sitting surface. Different foams are often used in combination,
layered for their various properties of softness, even support, and memory.
Foam is relatively inexpensive, and it is easy to cut. A therapist can
experiment with shapes free of financial risk. If you have an area of skin that
is broken down or on the verge, pressure can easily be reduced by cutting out a
portion of the cushion. (You should not do this on your own, though, because
only a doctor or therapist can identify the changes in your cushion that will
help relieve pressure while still maintaining appropriate support.)
On the downside, foam wears out faster than other materials and loses its shape,
but because of its lower price, this might not concern you. If you choose a foam
cushion, be sure to replace it when its time is up. Old foam that is compressed
can allow pressure points to form that can lead to a sore.
If you choose a gel or air flotation cushion for daily use, it is a good idea to
have a backup foam cushion since gel and air flotation cushions can leak.
Gel cushion designs attempt, in effect, to replace the consistency and support
of atrophied muscle tissue. Highly engineered gel fluids are placed in pouches
and usually attached to a foam base, so that the cushion conforms to the
pressures placed on it. As a result, gel cushions provide excellent pressure
distribution and are very comfortable. Many gel products also offer supplemental
inserts to stabilize your legs. Your knees might tend to fall together
(adduction) or apart (abduction), so such an accessory can help keep your legs
straight which also aids your overall posture.
Unfortunately, gel cushions are much heavier than other types, which can cancel
out some of the benefits of your lightweight wheelchair. Gel suppliers such as
Jay and Flofit offer lighter, active-use designs, but these might not be
appropriate for you if you are unable to do your own pressure-relief lifts.
If you bounce up and down curbs, or commonly experience similar impact in your
chair, a gel cushion might not be ideal. When you sit in a gel cushion, there is
no further "cushiness" to absorb impact, a concept known as impact loading.
Other cushion types are better able to absorb impact.
Another drawback to gel cushions is the possibility of them "bottoming-out" as
the gel is pushed aside by your weight. You can help prevent this distribution
problem by kneading your gel cushion once a day, keeping the fluids loose and
spread evenly. Look for a design that divides the gel portion into several
sections so that all of the gel cannot push to the sides.
There is also the chance of the gel leaking. While cushions arrive with patching
kits, patches are ineffective when the breach is at a seam, which is often the
case. A leak might be very minor, or it could be an extremely messy affair.
Air floatation cushions support the body entirely on air. A typical example is
the Roho cushion, designed with a group of small, interconnected rubber balloons
arranged in rows. Pressure is balanced by air shifting out to surrounding
balloons, spreading pressure evenly against your skin. The whole system is
closed so air floatation cushions can't bottom out the way gel cushions can.
If you have a pressure sore, you can tie off individual balloons to reduce
contact under that area, allowing you to spend more time sitting as the sore
heals. The Roho Quadtro allows the user to inflate four quadrants separately for
optimal positioning. Air cushions are relatively lightweight, and are
waterproof, allowing for double duty in the bathtub or on a boat.
Crown Therapeutics, maker of the Roho cushions, also offers air floatation
products for the wheelchair back, supplemental lumbar or sacral support, full
bed cushions, and even a product for a standard toilet seat. All are inflatable
to adjust to your needs.
A longtime presence in disability magazines has been an ad for the "Bye-Bye
Decubiti" cushion. It is inflatable, comes in many different sizes and shapes,
is made of heavy duty rubber, and--although different from the Roho balloon
design--is uniquely formed to minimize pressure at the bony protrusions on which
Air cushions can be less stable for those who move around a lot in their chair,
but recent designs offer either low profile or quadrant options that minimize
this problem. The balloons used in air cushions can be punctured, of course, and
leaks do occur, although a fairly heavy duty rubber is used. But patching them
is easier than with the gel design. The hard part is submerging the cushion
under water to find the leak (look for escaping air bubbles).
The biggest drawback to air cushions is that they require more maintenance. It
is necessary to check the pressure frequently, especially if you have pressure
Thermoplastic urethane honeycomb cushions are the most recent development in the
world of cushions. Because there are many individual cells--like a
beehive--these cushions are able to distribute weight evenly, but there is no
risk of leaking gel or of an air bladder being punctured. The many open spaces
in the beehive structure of the cushion allow air to travel more effectively.
This design helps to protect against skin breakdown because your skin is kept
cooler and moisture is prevented from collecting.
Urethane honeycomb cushions are very light, absorb shock, and a low profile
cushion can provide significant support. These cushions can even be thrown into
your washing machine and dryer, making them attractive for people with
incontinence problems where the cushion will be soiled from time to time despite
best efforts at bowel and bladder management.
Supracor of San Jose, California, makes several honeycomb cushions based on
their patent. One type uses multiple layers of varying stiffness to allow your
sit bones to sink into the cushion while deeper layers provide overall support
and weight distribution. Another type is contoured to provide adduction and
abduction, plus a rear dish for pelvic positioning. There is not much of a track
record for urethane honeycomb cushions because of their recent development, but
there appears to be good prospects for this type of cushion to evolve and become
more widely used.
The latest territory being explored in cushion design is the use of an air pump
to create alternating pressure, of particular interest to those with more severe
disabilities who are unable to perform their own weight shifts to relieve
Comes in range of densities.
Holds shape (memory).
Provides even support.
Can be cut to relieve sores.
Nothing to leak
|Wears out faster.
Loses its shape.
Old, compressed foam could lead to a sore.
||Excellent pressure distribution.
May have supplemental inserts to stabilize legs.
Chance of leakage.
Less able to absorb
Some designs allow gel to push out to sides.
Even pressure distribution.
Will not bottom out if properly inflated.
Can be modified to relieve pressure sores.
Some models inflate to user's specific needs.
Chance of puncture/leakage.
High maintenance: need to check pressure frequently.
Low profile in appearance.
Distributes weight evenly.
Keeps skin cooler.
No risk of leakage.
|Relatively new, so not much of a track record
Sitting for extensive periods of time without pressure relief causes the muscle
and fatty tissues to separate, putting the delicate skin layer in closer contact
with the bone. This creates even more pressure on the skin. Lack of air
circulation increases the temperature between you and the cushion. Moisture
collects and is trapped against the skin. All of this further increases the risk
of a sore.
One alternating pressure solution is the ErgoDynamic Seating System from ErgoAir
in New Hampshire. This system pumps air into and out of alternating portions of
the cushion. The product is contoured for pelvic stability, with a pre-ischial
cross-bar design that prevents forward slipping--and therefore shear--on the
cushion. Special vent holes serve to allow the flow of air and moisture. In a
five-minute cycle, compartments are inflated and deflated to shift support
alternately between the ischial (sit) bones and the hips. Both areas get regular
periods of complete pressure relief. The manufacturer likens it to a massage
while you sit, with the resulting promotion of blood flow. In some cases, the
makers suggest, a pressure sore can even heal while you sit. This cushion system
can be plugged into some power chair batteries or charged in a cigarette lighter
in your car.
Alternating pressure products are of course heavier--given their use of
batteries and air pumps--and, like air floatation cushions, prone to puncture.
However, the technology for these innovative systems is likely to evolve further
in the future, as new materials and batteries are developed.
Advanced needs such as significant spinal curvatures or asymmetries in your body
require more complex kinds of trunk support. For example, the Pindot system,
recently acquired by Invacare and available from suppliers around the country,
is a support system which customizes seat and back cushions to your exact shape.
First, a special chair takes an imprint of your body's shape. A therapist views
a computer image of the shape and can customize the contours of your cushion.
From your imprint and the therapist's specifications, a foam cushion that gives
you optimal support is manufactured specifically for you. The Pindot system is
of most value to people who will not move around much in their chair. Since the
cushion is formed to your shape, you will only be comfortable in it when you sit
in the right relationship to the customized contours.
Your needs might require the services of a rehab engineer who custom designs
your seating system. A rehab engineer might adapt existing products or build
something from scratch just for you. Your therapist or dealer should be aware of
such people in your area. Often they are working in a major hospital or
university. The Veteran's Administration is also involved in research and
engineering that addresses the need for customized positioning systems.