Wheelchair users often sit for 12 to 16 hours per day resulting in unrelieved pressure over weight bearing tissues that can result in tissue trauma and pressure sore development. Tissue trauma is a multidimensional process (Sprigle et al., 1990a; Brienza & Karg, 1998). Two important risk factors that have been identified are externally applied pressure and tissue distortion. The use of custom contoured cushions to improve pressure distribution and reduce tissue distortion should result in a safer sitting surface (Sprigle et al.1990).
Occurrences of pressure ulcers caused by prolonged sitting for persons with SCI are estimated to occur in 50% to 80 % of the SCI population (Brienza & Karg 1998). Current clinical practice for wheelchair cushion prescription is based on the perceived risk of a particular patient or patient group for developing pressure ulcers.
Sprigle et al. (1990a) conducted two studies to determine the use of custom contoured cushions (CCC) as a safe sitting surface. One study fabricated contoured foam cushions for 11 SCI subjects and compared mean pressures on two flat and two contoured foams with varying degrees of stiffness. Study results are in agreement with the Hertz theory that pressure increases with the stiffness of the material. Sitting on a CCC resulted in lower pressure distribution than sitting on flat foam. The force deflection curve of a thinner (1”) cushion is lower than the force deflection curve of a thicker (3”) cushion. Three important attributes of CCC were identified: increased enveloping provides more uniform pressure distribution and stable sitting surface and a decreased foam compression. CCC seat interface pressure is potentially less damaging to soft tissue as compared to flat cushions. Also, CCC have reduced damaging effects of external loading, reduced deflection and lower pressure distribution when compared to flat cushions.
Sprigle et al. (1990b) compared CCC to subjects’ usual wheelchair cushions using pressure and clinical variables. CCC provided seating support at lower interface pressures. Use of CCC seemed to improve posture and balance without impeding the users’ functional abilities. However, several disadvantages and cautions were identified with the use of CCC. Persons at high risk for pressure sores, or without the ability to complete pressure relief or repositioning, need to be fitted and monitored on initial use of CCC and trained in the ongoing use of CCC. Disadvantages identified with using CCC include: the user must be positioned in one location on the cushion, must recognize proper positioning within contour of cushion, and protect the foam from wetness and monitor foam fatigue over time.
Brienza and Karg (1998) had subjects sit on flat foam, initial contour or final contour cushions and measure the interface pressure using a pressure-sensing pad. Interface pressures were higher for the SCI group for all cushions tested. Pressure distributions for the SCI group are more sensitive to support surface characteristics (e.g. shape and compliance) than for the elderly group. Custom contouring foam cushions have positive effects on interface pressure as compared to flat foam cushions of the same density.
There is level 2 and level 4 evidence (from one prospective controlled trial and two repeated measures studies; Brienza & Karg 1998) to support that custom contoured cushions (CCC) have attributes that promote their use as a safe sitting surface for the SCI population. However, disadvantages and cautions are identified for the actual use of CCC.
- Contoured foam cushions compared to flat foam cushions seem to provide a seat interface that reduces the damaging effects of external loading and tissue damage.
Knowledge of wheelchair and seating products is essential for clinician’s to assist clients in the selection of the most appropriate equipment based on their needs. Lack of scientific evidence to guide clinical judgment remains an issue (May et al. 2004). Clinicians view the introduction of a wheelchair in the rehabilitation process as a progression in independence and mobility; however, the individual participating in rehabilitation often views it as a symbol of disability (Minkel 2000). Regardless, the immobile SCI population must perform their daily living activities from the seated position. Studies support that wheelchair and seating equipment needs should be determined on an individual basis and modified to meet the needs of the user (Hastings et al. 2003; Janssen-Potten et al. 2001). Clinicians should utilize objective evaluation, clinical judgment and subjective feedback in the prescription and set-up of the equipment (Garber & Dyerly 1991; Garber 1995; May et al. 2004).