Wheelchair seating is typically comprised of the primary support surfaces of a seat and back, as well as any secondary supports the client may require. Secondary supports may include pelvic positioning belts, lateral chest pads, hip guides and head supports. Cushioning for the seat and back varies, from off-the-shelf cushions and backs, to custom-designed linear systems, to seating systems molded to the client's body.
An appropriate cushion provides adequate support and stability, pressure distribution and relief, as well as comfort in the degree required by an individual client. There is not one "best" cushion, just as there is not one set of client requirements.
Cushions categories include those designed to reduce risk of pressure-ulcer development, to provide postural support, and to address both. Cushion performance is primarily based on shape/design, on the materials it is comprised of, and the cover.
Cushions vary quite a bit in price and can be very expensive. Usually, more expensive means better quality. Have you ever sat on an inexpensive couch? When the couch is new, it feels firm and comfortable. After a short time, however, that inexpensive foam quickly compresses and loses stiffness, resilience, damping and envelopment properties. The couch is now less comfortable and more difficult to stand up from, partially because the surface is now lower and partially due to decreased resilience.
Density. Higher density usually increases the weight of the cushion, but also its firmness. Higher density also limits the tendency of the cushion to bottom out, which occurs when the bony prominences of the pelvis (ischial tuberosities or ITs) protrude through the cushion material and actually contact the wheelchair base under the cushion. This can lead to discomfort and increased pressure over these small areas, dramatically increasing risk of pressure ulcer development.
Stiffness. A cushion that is very stiff will limit pelvic sinking into the cushion (envelopment). Increased envelopment increases pressure distribution as more of the cushion is actually in contact with body surfaces.
Resilience. This important property allows the cushion material to recover its shape and properties during movement. Let's say a cushion envelops or molds to a client's shape. If the client moves on the cushion, high resilience will allow the cushion to quickly reform to the client's shape. Low-resilience cushions do not change shape quickly, but may hold a client in place better as the material conforms well to the seated shape.
Damping. A material that dampens helps minimize vibration and impacts that come up through the wheelchair base. Vibration and impacts, over time, can lead to discomfort, fatigue, muscle spasms and pain.
Envelopment. As mentioned above, this is basically the opposite of stiffness.
Shear. Shear is the force created as the body moves across the surface of the cushion, such as during transfers.
Thermal. Some materials retain heat or cold. Heat is a contributing factor to pressure ulcer development. Certain material properties can change when very cold, such as increased stiffness, decreased envelopment and decreased resilience in viscoelastic foam and viscous fluids.
A cover has multiple purposes. First, it protects the cushion materials. Foam, in particular, deteriorates more quickly when exposed to air, sun or moisture. Urine will permeate foam, leading to quicker deterioration and odor. Other liquids, such as that chocolate milk from lunch, are hard on cushions and lead to bacterial growth and resultant odor.
Covers also prevent entry of unwanted guests. Depending on your area of the country, certain critters are more prevalent. Cockroaches tend to like foam, so that cover needs to protect the entire cushion.
If liquids are going to be a problem, an incontinent cover is indicated. This doesn't limit you to vinyl. Many covers have a rubberized under-surface that prevents liquids from being absorbed, or at least slow absorption to allow for clean up (example: Rubitex). Other cushions utilize a "shrink wrap" type plastic over the cushion materials and under the actual cover.
In addition to protecting cushion materials, a cover also helps the cushion perform optimally. For example, the Roho cushion is comprised of a series of air filled "pickles." These pickles tend to splay out without the cover to hold them in proper alignment. The cover may stretch in two or four directions so the client sinks down into the cushion materials. A thick vinyl cover is easy to clean, but masks the material properties.
Finally, a cover may allow airflow to decrease heat and moisture. It is less common for a cover to both allow airflow and prevent liquids from entering the cushion.
Hundreds of cushions are available. Here are a few manufacturers of cushions commonly used in rehab:
Comfort Company. This company makes cushions out of high-quality viscoelastic foam in a variety of styles, including hybrids that place gel under the ITs. Their Vicair is a very unique cushion filled with wedge-shaped, air-filled packets. The cushion allows the ITs to immerse into these packets. The less packets present, the more the cushion will envelop the client. This cushion provides moderate to maximum pressure relief and minimal to moderate postural support and stability.
Jay. Manufactured by Sunrise Medical, Jay cushions have been around for a long time and use viscous fluid packs on a firm, pre-contoured base. The Jay GS pediatric cushion includes growth in the ischial well. The Jay Deep has additional fluid to provide maximum pressure relief. The newer Jay 3 cushion provides a choice of air or gel in the pelvic well.
These cushions provide moderate pressure distribution and relief, moderate comfort and minimal postural support. The gel packs tend to retain heat, become firmer if cold, are heavy, and allow pelvic movement. If the client does not have a lot of pelvic movement, this cushion is fine. If the client tends to extend into a posterior tilt, the fluid will not significantly limit that movement. It is important that the base is placed correctly in the wheelchair and that the fluid packs are always used with the base.
Otto Bock. The Cloud cushion is comprised of many components and uses a viscous fluid called Floam, which does not conduct heat or cold. This cushion provides moderate pressure relief, comfort and postural support. The cushion is very heavy and, because this cushion has so many components, it can be time consuming to take apart and clean. One version of this cushion includes an additional material on top of the Floam that cools on contact to reduce the seating surface temperature.
Ride Designs. Ride has two cushions that address pressure and positioning. The Forward cushion is made of a high-quality viscoelastic foam that is highly contoured. This cushion provides moderate pressure distribution and positioning. The cover provides very good air flow for a foam cushion. The Ride Custom Cushion is molded to the client and can be further modified from there. A clinician or supplier trained in the molding and ordering process is required. The client is literally "pressed" into a special foam block which is then mailed to the company, who makes the cushion out of a very unique foam called Brock foam. This allows moisture and air to pass through and is extremely lightweight. The cover also promotes airflow. This cushion provides maximum pressure relief and distribution, airflow, positioning and stability. The ITs can be completely unweighted, as needed.
Roho. Many configurations are available and all include air-filled "pickles." These cushions provide maximum pressure relief and good air flow. However, the Roho only provides good pressure relief if properly maintained. If the pressure is too high or too low, the cushion does not perform well. This must be monitored. The cushion allows a lot of movement, which can feel unstable for some clients and may not provide adequate positional support for others. Some hybrid versions combine air below the ITs with foam throughout the rest of the cushion to provide pressure relief where most needed and stability everywhere else.
Stimulite. These cushions, made by Supracor, are made of a plastic honeycomb. Various stiffnesses are available in layers. Some have a pre-contoured shape. These cushions are lightweight with good airflow and minimal to moderate pressure relief and stability. However, this cushion wears out fast, performing great for about 12 months; it wears out faster under heavier clients.
Varilite. Varilite makes a number of cushions, including the Evolution. The Evolution is a combination air and foam cushion. It has a valve that equalizes the pressure of the air in the cushion to that in the room. If the valve is open and the client sits down, the cushion will self-contour to the client as the air is displaced. The valve is then usually closed, but can remain open without risk of bottoming out. I usually recommend the valve be opened after the client gets out of the wheelchair to allow the cushion to recover. This cushion provides moderate pressure relief, good stability and does not retain a lot of heat. It can break down quickly if the valves are not opened regularly to allow the foam to recover.
Other high-quality viscoelastic foam and hybrid cushions include the Invacare Infinity series, Motion Concepts Matrix series and Quantum Rehab Synergy cushions.
As you can see, not all cushions are created equal! It is essential to be familiar with the product options to determine the best match for your client and to justify funding of these products. Talk to some suppliers in your area and see if you can borrow several cushions to try out. An optimal product match can provide your client comfort, stability and function, and help prevent pressure ulcers.
Michelle L. Lange, OTR, ABDA, ATP/SMS, is owner of Access to Independence in Arvada, CO. She has 25 years of experience in assistive technology. She is editor of Fundamentals of Assistive Technology, 4th Ed. She can be reached at MichelleLange@msn.com or visit her website at http://www.atilange.com/.