Sitting pretty: wheelchair cushions and seating.
When you consider seating, it is not enough to just think of a wheelchair cushion. You must view the cushion as part of a seating system, which includes the wheelchair seat under the cushion, the wheelchair back, the arms, and the foot rests. How well these components do their job depends on how they fit and support you and how they are positioned in realtion to the drive system and the ground.
Goals of a Seating System
Wheelchair seating systems have three goals:
* To support and position users for optimal stability and use of their trunk, arms, and head
* To correct and/or prevent deformity
* To distribute pressure to minimize the tendency for skin breakdown
These three goals sometimes work against each other. For example, the cushions that distribute pressure often give the least stable seating surface. If the seating surface is not stable, it is difficult to maintain good posture, and reaching or leaning over become difficult. On the other hand, cushions that provide the best support and stability often distribute pressure poorly.
Because individual needs are different and because the considerations in developing a seating system are quite complex, each user who spends the majority of the day in a wheelchair must have a careful evaluation by a knowledgeable professional, and a custom system must be ordered specifically for that user. There is no one "best" seat or cushion for everyone.
Although many cushions do a good job of distributing pressure over the seated area, it is important to remember that no cushion will eliminate it. The pressure over bony prominences in the seating area, even with the best systems available, is greater than that of the blood flowing through the skin and muscles. This causes the blood flow to be cut off and the tissues to suffocate from lack of oxygen if the pressure is not relieved regularly. Therefore, it is vitally important for everyone to do regular, frequent weight shifts for pressure relief while sitting in the wheelchair, no matter what kind of cushion is used.
People who have normal sensation and movement shift their weight about every four minutes. If they don't, they become uncomfortable because the skin, nerves, and muscles in the seated area are not getting enough blood circulation.
Pralyzed people should also shift weight frequently, even though they don't feel discomfort. In general, it is recommended that people who are paralyzed perform pressure relief every ten minutes. This is the key to maintaining healthy skin, and no amount of special seating or cushioning will take away the need to regularly get the weight off the seated area.
Sometimes a person, particularly someone who is newly injured or young, can avoid skin sores without doing frequent weight shifts. An examination of the seated areas of these individuals, however, almost always shows that the tissue over bony prominences is wearing away and becoming thin. This comes from relative starving of the muscle and fat tissue from pressure on this area, and it is often only a matter of time before the skin breaks down.
Weight can be shifted by doing wheelchair push-ups, by leaning to one side or the other, or by leaning forward. If an individual cannot adequately relieve pressure by any of these means, a motorized reclining system is usually needed. These systems can allow an individual to lie flat or tilt back, keeping thighs and trunk at 90[degrees] to one another.
For people who need a reminder to do pressure reliefs, a small automatic timer is now available in most hardware stores, for less than $ 3. It will make a soft beeping sound at a set interval and does not have to be reset. This small investment will go farther toward skin protection than many hundreds of dollars worth of wheelchair cushions.
A seating system protects the skin by distributing weight over areas that have the most padding by fat and muscle (such as the back of the thighs) and by taking some of the weight off the bony places (such as the ischial tuberosities and the tailbone). This is accomplished by optimally adjusting the seat angle, back support, and leg rests and by providing a cushion that best meets the individual's needs for positioning, stability, and pressure distribution. When a person has a history of skin problems, the rehab practitioner may use a special device to measure pressure over areas at risk and make adjustments to minimize pressure over those areas.
Support and Positioning
A seating system should put your heels, arms, and head where you need them to be! Most people find that 1-2" of clearance under their footplates is necessary to get over rough ground. At the same time, the footplates should carry the weight of the lower legs and feet but be low enough so the backs of the thighs rest on the cushion.
Footplate position will often determine the minimum seat height. The combined height of seat and cushion should, if possible, fit under the desks and tables that the individual will be using. People with long legs will often want to use the thinnest cushion that meets their other needs.
Wheelchair users should be able to make use of all of their abilities of head, arm, or trunk movement while in the chair. They should be able to reach, lift things, and perform all necessary tasks without "holding on." In addition, they should be able to lean to the side or forward, if they can, to relieve pressure on the seated area without fear of falling out of the chair.
In general, if a peson has enough arm use and trunk stability to do a side-to-side weight shift, tying the person into the chair with lateral supports or a chest strap should be avoided. Proper contour and angle of the back and a well-fitting lap belt should be all that are needed to keep the person safely in the chair.
Maintaining a good posture will prevent back and neck pain, make breathing easier and stamina better, and improve a person's appearance. A loose sling seat and back and a soft cushion will often cause a person to slouch forward in the chair (Figure 1A). If you look like this, or if you require a series of straps, belts, leg spreaders, and hooks to keep yourself upright and in position, chances are that you need an adjustment in your seat and back support.
A number of individuals who have been paralyzed for a long time have developed some deformities of the back and pelvis. Sometimes these deformities are flexible and can be corrected, and sometimes they are solid, or fixed.
In general, a seating system should correct a flexible deformity, but if the deformity is fixed, the system should adapt to it. To figure out which way to go, the health care professional must carefully examine the individual, both in the chair and in bed or on a mat table, to see how much correction can be done. Then, trials of various combinations of seat tilting, wedging, and special cushions are often necessary to figure out the best way to get the user sitting comfortably and aligned properly.
When a person has been sitting with poor posture for a long time, an improved posture often does not feel comfortable at first. It is a good idea to make posture changes in small stages and to give each change a week or two to become comfortable.
Are Armrests Necessary?
Armrests are a matter of user choice. Individuals with good trunk and arm-muscle function often choose not to have armrests on their chairs. Armrests can be a significant help, however, if trunk stability and arm function are not normal and greater support and balance assistance are needed. In combination with push handles, they can assist in pressure relief and can also carry the weight of the arms, somewhat reducing the pressure over the seated area.
If a person puts significant weight on armrests, the devices should be wide enough and well-padded enough to prevent nerve injury.
Good and Bad Aspects
Many types of cushions are available, ranging in cost from $10 to over $600. The price of a particular cushion is not necessarily related to its quality, durability, or appropriateness for a particular user. Price is often determined by the maximum that the consumer, insurance carrier, or government will pay.
It is a fact, however, that someone--either the user or the person who pays insurance premiums or taxes--must pay for the cushions. Therefore, purchase cost and replacement costs must be a consideration. It makes no sense to purchase a $300 cushion when a $60 cushion will meet the individual's needs just as well.
* Is there a history of skin breakdown, or is the skin particularly sensitive? How much natural padding is over bony prominences? How easily can the person do weight shifts? Does the user have much spasticity? How old is the user? (Often skin will become more fragile as a person grows older, so that cushioning needs will change with time.)
* How is the person's posture? Does any deformity need to be corrected or accommodated?
* What is the person's lifestyle? Are there special height needs? Does the person frequently go out in subzero weather or live in a hot, humid climate?
* Has the person experienced difficulties with particular cushions in the past?
Armed with this information, the potential user has a wide variety of cushion types to choose from. Some types available are as follows:
* Foam Cushions
Foam is the most widely used cushioning material and provides good stability and pressure relief for many individuals. These cushions come in a wide variety of styles and prices and are generally made of polyurethane or latex rubber. They are most often 1-4" thick.
The firmness of the foam may vary from a low-density, soft material to a firm, dense foam that "gives" very little. Foam ay be open-celled like a sponge or closed-celled (made up of many individual bubbles). Open-celled foam absorbs liquids and breaks down easier, while closed-cell foam often distributes pressure less well. Some foam cushions are made of two or more types of foam in layers or patterns to take advantage of the best properties of each kind of material.
One of the advantages of foam is that it can be custom molded or carved to conform to a fixed dformity or special pressure need. The new computer-assisted, cushion-carving systems promise to solve some difficult seating problems at a relatively low cost.
Foam cushions will deteriorate over time, and users must frequently check to make sure that bony prominences are not "bottoming out." These cushions often need to be replaced every 6 to 12 months. They usually have covers that may or may not be waterproof. A waterproof cover will protect the cushion but may cause heat and moisture to build up in the seated area. If the cushion absorbs liquids easily, it can be prone to developing odors and to early deterioration.
Foam cushions are lightweight and good in cold or hot climates. They are often the least expensive cushion available; however, replacement costs must also be considered.
* Air-filled Cushions
There are three types of air-filled cushions: (1) single or compartmentalized air bladder, (2) single bladder filled with air and foam (self-inflating), and (3) multiple villous (finger-like) air-filled projections.
Air-filled cushions are lightweight and easy to clean. All are susceptible to puncture and come with repair kits. The simple air-bladder cushions are durable, stable, and inexpensive. They do not distribute pressure very well, but a number of active users who are careful about pressure relief have found they meet their needs adequately.
The self-inflating, foam-filled air cushions distribute pressure a bit more evenly and cost quite a bit more.
The villous air-filled cushions distribute pressure extremely well, but some models provide little stability. They are expensive. These cushions can be customized for special seating needs and are often useful when an individual has a combination of scarred or delicate skin and a severe bony deformity of the spine or pelvis.
* Gel, Water, or Dry Polymer Flotation Cushions
These types fo cushions have fairly good stability and good pressure-distribution characteristics. All are heavy and hard to lift but easy to clean and good for heat dissipation in hot climates. Most will harden in extremely cold temperatures and/or will become cold enough to freeze the user's skin if appropriate insulating covers are not used. Their cost is moderate to high.
* Hybrid or Combination Cushions
These usually combine a firm base made of foam or plastic with a top layer of gel, dry polymer or other viscous material, or villous air pockets. Other less common arrangements can have a gel center sandwiched between foam or can mix foam into a matrix of water or gel. The goal of these cushions is to provide good stability with a firm base and maximize pressure distribution with the viscous layer or insert. Some of these cushions accomplish this goal successfully.
In addition, a number of this type of cushion can be customized for special positioning and pressure needs. The cushions are expensive and some are quite heavy. Some hybrids are also fairly thick and can raise the user's lap area to an unacceptably high level.
* Alternating-pressure Cushions
Alternating-pressure seating systems user air pumped by an external power source to vary the shape of the seated surface at specified intervals. Their goal is to continuously shift pressure from side to side or from one area to another to avoid the need for the user to do pressure relief.
There is no reason for individuals who are capable of shifting their own weight to use one of these divices, since they are extremely expensive and require an outside energy source, which adds inconvenience, bulk, weight, and unnecessary energy use to the seating system. For people who cannot shift their weight independently, however, these devices would seem to be a cost-effective alternative to a reclining system. A few individuals have used the devices successfully in this way.
Alternating-pressure cushions have not, unfortunately, been effective for a large number of users in eliminating the need for pressure relief. As we learn more and more about the dynamics of pressure and shape change in the seated area, modifications of these types of systems promise to be of great use to the person with high-level quadriplegia.
Even with the best seating system and the most careful pressure relief, almost everyone eventually has some skin breakdown. If a pressure area is identified and proper measures are taken early, the resultant "down time" and disability will be minimized. The bigger a pressure sore is, the longer it will take to heal, and the worse the scarring and resulting fragility of the skin will be. A scarred area is much more likely to break down again after a minor injury or increase in pressure.
How To Get Your
Seating Needs Met
With all of the wonderful variety and continuing advances in seating systems, two things are apparent: There is a good likelihood that a seating system exists that will allow you to sit comfortably and safely all day, but the whole business is complex and potentially expensive. You should get help from a qualified expert in this area.
Not all health care practitioners--and not even all rehabilitation professionals--are skilled in the area of seating. To get your seating needs met, you must often visit a spinal cord injury center that cares for a large number of SCI individuals.
The optimal seating solution will be the result of careful and effective teamwork between the user, the physician, the therapist, the manufacturer, and the vendor.
Dr. Britell is assistant chief, SCI Service, at the VA Medical Center in Seattle.