Selecting the Best Wheelchair Cushion
by: Maricon Williams
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 cushions.
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.
Cushion function
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 cushions
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 cushions
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 or dry floatation cushions
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 we sit.
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 sores.
Urethane honeycomb cushions
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.
Alternating pressure
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 pressure.
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.
Positioning systems
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.
About The Author
Maricon Williams
I love reading. Give me a book and I'll finish it in one sitting. Reading is the chance to be transported to a different world and so is writing. I'm more enthusiastic about writing however, since you can relay your ideas to someone else. I can only imagine that feeling when I hear a complete stranger talking about my ideas which read on an article somewhere. To relay my message to as many people is the same as touching people with music. Only mine's less harmonic. I try to make up for it with the color I bring with words. And most of the time, it's more than enough.
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This article was posted on March 18, 2005
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