Completion of a thorough seating and mobility assessment is the key to identifying client’s specific seating needs. Based on the assessment specific cushion features can then be determined.

Determination of Client’s Seating Needs

The following issues must be addressed in order to determine the client’s optimal seated position:

Positioning
Balance
Pressure management
Function
Comfort

Client position is integral to both comfort and function. The purpose of the seat cushion is to provide a stable base of support to offer both safety to skeletal and muscular structures and stability from which movement of trunk and limbs can originate. Ideally, this level base of support should promote postural alignment. Where possible the cushion is used to promote a level pelvis (correcting flexible pelvic obliquity) reducing unbalanced muscle forces contributing to the development of scoliosis. The cushion should support the pelvis in a neutral position (decreasing posterior/anterior tilt) to reduce development of kyphotic or lordotic spinal postures. This correction is only possible where flexibility exists. If the client presents with fixed asymmetries/deformities, the cushion will have to accommodate the client’s position but offer orientation to allow the client best access to his/her functional activities.

“Dynamic Stability” is an important goal of the cushion. Although the seating system provides a static position for the pelvis and lower extremities, it is also provides the basis for movement. Stability and support at the pelvis and lower trunk will allow freedom of movement in the upper trunk and extremities and allow maximal energy to be translated into movement rather than in stabilizing the body. In order for the client to function within their wheelchair they must have the freedom to access their daily activities, propulsion, joystick access, transfers etc. Movements must be considered when looking at client position in order to allow for maximal strength, range of motion, and protecting joints from overuse injuries.

Cushion support is also necessary to promote client’s balance in the wheelchair. Orientation of the cushion within the wheelchair frame, contour of the cushion and cushion materials are important factors in providing stability. Ideally, the cushion should “grip” the pelvis reducing forward sliding and shear forces. The client will then experience greater comfort and safety within the wheelchair system.
The cushion surface must also assist in reducing risk of tissue trauma. In the sitting position, the pelvis becomes the primary weight bearing structure. There are many bony prominences on the surface of the pelvis, thus there is an inherent risk of skin. Skin breakdown increases as clients display additional risk factors:

The goal of seating products traditionally has been to reduce pressure by increasing surface area. Even pressure distribution contributes to circulation and positioning as long as the forces are not significantly higher in a small surface area. Immersion of the bony structures into a viscous material assists in distributing forces over a greater surface area. Contouring of the cushion surface allows for increased weight distribution over larger weight bearing areas such as the thighs and gluteal surfaces. This reduces the pressure over bony pelvic structures eg. ischail tuberosities, coccyx and greater trochanters. New technologies are re-introducing the concept of “offloading” i.e. translating pressure to muscular areas i.e. gluteal and posterior thigh areas and eliminating pressure from ischail tuberosities and coccyx. This reduces risk of skin breakdown and promotes healing where breakdown has occurred. This concept must be utilized with caution ensuring that pressure is still evenly distributed over these muscular structures so as not to develop areas of high pressure elsewhere.

Client comfort is still of utmost importance. Although subjective comfort is essential in ensuring that client’s use the products prescribed and are able to maintain their daily routines without additional pain and fatigue caused by the cushion.

Which Cushion is Best?

Many cushions have been developed over the years combining different shapes and materials. This is indicative of the fact that our client’s are all individual’s with unique shapes and seated postures. Which cushion is best can only be determined by identifying and prioritizing clients’ postural and skin management needs.

Cushion factors to be considered:

Interface with the wheelchair is important in determining cushion size. Height will affect transfers and environmental access. Depth will affect chair balance, positioning of lower extremities on the footrests and possible access to removal of footrests. Weight is important when considering client maneuverability and propulsion, portability, and caregiver lifting and pushing.

Contour and shape of the cushion should match the client as closely as possible to reduce excessive pressure buildup on bony prominences and areas at risk for skin breakdown. Pressure mapping is one tool which can assist in the determination of contour matching. Custom cushions may be considered, if the client displays asymmetries, deformities, sliding, postural instability or skin breakdown. It is also important to consider heat and moisture build-up as a potential risk when prescribing a highly contoured cushion.

Foam cushions have been developed over the years as foam was easily carved and molded to create contours. With the development of viscoelastic foams, immersion of bony prominences is attainable to increase surface area. Layered foams of different densities is essential for the cushion to maintain its shape. Foam cushions are popular as no maintenance is required, the material is light weight and cost is not exorbitant. Foams are temperature sensitive so cushions should not be left in areas of extreme cold. New foams with breathable properties are now being used to allow for custom contoured cushions without the heat buildup. Use of material technologies from outside industries is now providing the seating industry with alternatives although cost may be a significant factor.

Polymer gels provide shear reduction as the material moves with the skin but due to the density does not allow for much immersion. The material is not temperature sensitive and tends to assist in cooling the skin. These gels are very heavy and are often used in conjunction with a foam based cushion.

Fluid gels promote immersion and shear reduction as they allow bony prominences to move within the fluid. Constant movements within the fluid may cause the fluid to redistribute allowing for “bottoming out” and increase risk of pressure points. Movement of the fluid will also limit stability provided by the cushion and may affect client balance and position. Fluid gels will need maintenance to ensure that the client is always sitting in a pocket of fluid and is not sitting in an exaggerated posture after each transfer to the chair. As with the polymer gels, fluid cushions are heavy.

Air provides the perfect medium for immersion. The limitation is containing the air for stability. A variety of air cushions have combined the positive use of flotation technology with various means of limiting instability of the surface by containing air in quadrants and pockets. Air also helps to reduce buildup of heat and moisture. Air cushions are light but require maintenance as the air must be maintained to allow for proper immersion.

Although cushion materials are important, cover materials are equally essential to allow immersion of the body into the contour of the cushion. Significant interface pressures have been identified when non-stretchy materials are used over contoured cushion surfaces. It is Therefore essential that multiple stretch fabrics be used. It is important also that covers “wick” moisture away from the client’s skin as well as preventing moisture from deteriorating cushion materials.

As cost is a significant factor in equipment selection the ideal parameters of the system should be identified and prioritized. Lower priority items can be deleted from the system to save cost if necessary.
In choosing cushions, client postural and skin integrity needs should be assessed and identified by the therapist. Functions of specific cushions and materials as well as compatibility with the mobility base should be identified by the provider and manufacturer. Working as a team, these professionals must educate the client and caregivers on the benefits of positioning, material maintenance and the effect of cushion choice on future function. The client ultimately makes the final decision based on comfort, function, aesthetics and cost.

References

Hetzel, T., Padgitt, J., “Seating, The Next Generation”, proceedings of the 21st International Seating Symposium, 2005.

Mogul-Rotman, B., “I’m Not Comfortable, Fix It!”, proceedings of the Canadian Seating & Mobility Conference, 2005.