CUSHIONS

Wheelchair cushions are typically prescribed based on the needs of the client and the abilities of the cushion to disperse pressure, especially under the ischial tuberosities and sacrum. Advances in technology have enabled new cushion development, increasing therapists’ options.

Cushions aid in the dispersement of pressure, postural support, and body positioning. By allowing the body to conform or contour to the seating surface, the likelihood of developing pressure points is decreased as surface area is increased. The properties of the cushion itself determine how well the body will conform to the seating surface and distribute pressure. For instance, placement of a soft pillow or foam insert will allow the individual to sink into the seat but promotes pressure point development on the ischial tuberosities as the cushion bottoms out. On the other hand, some individuals may overinflate an air-filled cushion in an attempt to prevent this bottoming out but in the process negate the benefits of the cushion as the individual can no longer conform to or sink into the seating surface.

Selection Process

The selection process for a cushion depends on the individual. The presence of fixed versus flexible deformities, the amount of time spent in the wheelchair, a current or past history of skin breakdown, the client’s sitting balance, sensory status, and the ability to perform weight shifts are all factors to take into consideration when selecting a cushion. Cushions also provide comfort and aid in the prevention of pressure ulcer development. For comfort, cushions must absorb shock and decrease vibration as a result of propulsion over different surfaces. Wheelchair users are exposed to regular shocks and vibrations during propulsion that may lead to pain and injury to the back and pelvis. In addition, shocks and vibration can induce fatigue and reduce sitting tolerance. For pressure ulcers, cushions may reduce friction and shear forces between the buttocks and seating surface, by preventing excessive uniaxial pressure and the development of excessive heat or moisture at the seating interface.

Cushions can be classified into two main systems: linear systems and nonlinear systems. Linear systems are planar and conform to the weight of the individual, whereas nonlinear systems provide some contouring or postural control surfaces. Nonlinear cushions can be classified as contoured (typically standard shapes), custom contoured, and modular. Custom-contoured systems are sculpted to accommodate the human body, and are used for people who cannot be accommodated by off-the-shelf products. Cushions are also made from a variety of materials including foam, dry flotation (air), gel, visco-elastic fluid, honeycomb, or combinations of several materials. With so many to choose from, how do you know which cushion is the best for your client and will withstand wear and tear? The best can be determined by weighing the pros and cons. For example, an air-filled cushion may provide adequate pressure distribution but it may not provide the appropriate stability for the individual.1

Establishing Standards

Unlike wheelchairs, standards do not exist for wheelchair cushions. The International Standards Organization (ISO), the American National Standards Institute (ANSI), and the Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) have primarily developed the wheelchair standards. The US Food and Drug Administration (FDA) uses these standards to aid in its own evaluation of wheelchairs as medical devices and commonly gives its approval for devices that pass the standards. Unfortunately, wheelchair cushions and seating systems have not had the same level of consideration as wheelchairs. No standards currently exist for the cushions, and no tests have been developed to ensure quality and reliability of the product. However, ISO is in the process of developing wheelchair cushion standards to help combat this issue. Standards could possibly include tests on resilience, biocompatibility, ways to fatigue a cushion, and permeability of covers. Until these measures are in place, little information concerning quality, comfort, or usefulness is available to manufacturers.

Ideally, medically used items should undergo standards testing as well as evaluation through clinical trials. Clinical trials are often used most frequently in drug studies to determine if one type of medicine is better (more effective with less side effects) than another. The best clinical trials are conducted with a large subject pool from varying geographic locations, with different trials examining the effectiveness of the device in different patient populations, ie, spinal cord injury, multiple sclerosis, traumatic brain injury. Unfortunately, the concept of multicenter randomized clinical trials is still emerging in the field of rehabilitation and assessment of assistive technology. This is probably due to the lack of money to support the research. Cushion manufacturers may do some market research on their cushions, but it is not as intensive as a large clinical trial. As drug companies need FDA approval to market their medications, they will fund clinical trials to achieve their goal. Cushion manufacturers do not need FDA approval and, therefore, do not necessarily fund evaluations of their cushions.

Rehabilitation researchers do make efforts to complete studies on various assistive technologies, including cushions. Review of the literature for the past several years indicates a continued effort to ascertain benefits of different cushions in different populations. Burns and Betz2 examined seating pressures using three different types of cushions (gel, dry flotation, and dynamic) in a population with tetraplegia. Results indicated that the dynamic cushion produced similar pressure relief compared to the gel and dry flotation cushions as well as a tilt-in-space wheelchair.

Other research has confirmed the belief that air cushions are much better at dispersement of pressure than foam.3,4 DiGiovine et al5 examined ride comfort as measured over an activity of daily living (ADL) course. The ADL course consisted of various surfaces including: carpeting, sine wave bumps, rectangular bumps, simulated door thresholds, and curb drops. The study focused on wheelchairs and the participants using their own cushions as opposed to examinations of different cushions and seating systems. As an extension of that study, different combinations of cushions and backrests have been examined. Preliminary results indicate that the cushion with a combination of foam and air has the highest comfort rating whereas the combination cushion of foam and gel (under the ischial tuberosities) has the lowest comfort rating.

The components for evaluating wheelchair-seating cushions are being established; advances in technology enable new cushions to be developed. The next step is for cushion manufacturers to take part in the research process and gain further knowledge of their products’ quality and reliability.

The benefits of active participation can be multifold. Manufacturers can gain increased knowledge of their products’ performance, which provides data that can be included in product information. Consumers and clinicians would then have relevant, clinical product information to aid in the decision process for appropriate cushion selection. Research data can also be used to justify product recommendation to third-party funding agencies. The end user is provided with safe and appropriate products, which may contribute to quality of life, improved function, and overall well-being. N

Shirley G. Fitzgerald, PhD, is the Associate Director of Research, VA Research and Development Center of Excellence on Wheelchairs and Related Technology, Human Engineering Research Laboratories, VA Healthcare System, Pittsburgh, and assistant professor, Department of Rehabilitation Science and Technology, University of Pittsburgh. Tricia Thorman, OTR/L, is clinical coordinator, Human Engineering Research Laboratories, VA Healthcare System, Pittsburgh. Rosemarie Cooper, PT, is the study coordinator, Human Engineering Research Laboratories, VA Healthcare System, Pittsburgh. Rory A. Cooper, PhD, is the Director, VA Research and Development Center of Excellence on Wheelchairs and Related Technology, Human Engineering Research Laboratories, VA Healthcare System, and Chair and professor, Department of Rehabilitation Science &Technology, University of Pittsburgh.

References

1. Cooper RA. Wheelchairs: A Guide to Selection and Configuration. New York: Demos Medical Publishers; 1998.

2. Burns SP, Betz KL. Seating pressures with conventional and dynamic wheelchair cushions in tetraplegia. Arch Phys Med Rehabil. 1999:80:566-571.

3. Takechi H, Tokuhiro A. Evaluation of wheelchair cushions by means of pressure distribution mapping. Acta Med Okayama. 1998;52:245-54.

4. Visser C, Eksteen CA. The efficacy of the simplified air cushion compared to the polyurethane foam cushion with regard to ischial tuberosity interface pressure relief. S Afr J Physiother. 1999;55(4):3-6.

5. DiGiovine MM, Cooper RA, Boninger ML, Lawrence BM, VanSickle DP, Rentschler AJ. User assessment of manual wheelchair ride comfort and ergonomics. Arch Phys Med Rehabil. 2000;81:490-494.