• Cushion function
  
• Foam cushions
  
• Gel cushions
  
• Air or dry floatation cushions
  
• Comparison of Main Types of Cushions
  
• Urethane honeycomb cushions
  
• Alternating pressure
  
• Positioning systems
  

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

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 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

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

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

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.

Comparison of Main Types of Cushions

Alternating 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