Wheelchair Cushion Selection and Pressure Ulcer Prevention Post SCI
Bogie et al (1995) stated that 47% of pressure ulcers occur at the ischial tuberosities or sacrum and are therefore more likely to have been initiated while seated. Provision of a wheelchair cushion that relieves and redistributes pressure and reduces risk of pressure ulcer formation is an important prevention recommendation. Historically, cushion design has been based on the belief that sitting interface pressure should be distributed evenly to reduce areas of high pressure underneath bony prominences (Yuen & Garrett 2001). Cushion selection can be difficult as there are numerous cushions on the market each citing specific characteristics along with various amounts of pressure reduction and redistribution that make a cushion “superior.” When assessing an individual for a cushion, factors such as the degree of pressure reduction and redistribution (Garber 1985), temperature effects (Fisher et al 1978; Seymour & Lacefield 1985); level of SCI, pressure relief abilities, transfer technique and lifestyle (Garber 1985; Markhous et al. 2007a) are typically considered. As well as a reduction in pressure ulcer risk, cushions must also promote adequate posture and stability for the individual with SCI (Sprigle et al. 1990). Seat cushions can be made from a variety of materials, can be static or dynamic (Garber 1985; Markhous et al. 2007a) and incorporated into a variety of wheelchairs. See Table 20.4.
Numerous authors have investigated various wheelchair cushions and seating systems to try and determine which offer the most pressure or risk factor reduction to prevent occurrence of pressure ulcers in individuals with SCI.
Makhsous et al. (2007b), in a case-control study, exposed subjects to two 1-hour protocols: alternate, where sitting posture was alternated dynamically every 10 minutes between normal (sitting upright with ischial support) and sitting upright with partially-removed ischial support and lumbar support (WO-BPS), and normal (normal posture plus pushups performed every 20 minutes). These investigators found that the anterior portion of the seat cushion had a larger contact area among those with tetraplegia compared to those in the other groups. It also was determined that those with a SCI had a larger contact area in the mid portion of the seat cushion. There were significant differences between the groups when looking at the average pressure over the whole seat (p<0.001) and the total contact area on the seat cushion. With the WO-BPS posture, the average pressure for the tetraplegia group was higher than it was for the other groups (p<0.001). Most importantly, the total contact area on the posterior portion of the cushion was less for the WO-BPS posture group. As well, peak interface pressure was lower for all groups, with the greatest decrease from normal posture seen in the tetraplegia group. The average pressure increased on the anterior and middle portion of the cushion in all groups.
In the study conducted by Burns and Betz (1999), 3 wheelchair cushions were tested: dry flotation (ROHO High Profile), gel (Jay 2), and dynamic (ErgoDynamic), the last consisting of two air-filled bladders (H-bladder, IT-bladder). These were compared to each other under high pressure conditions (upright sitting or IT-bladder inflated) and low pressure conditions (seat tilted back 45° or H-bladder inflated). When analyzing the pressure placed on the ischial tuberosities, it was found that the pressure was higher during upright sitting than in the tilted back position for both the dry flotation and the gel cushion (p<0.001), with the dry flotation cushion providing more pressure relief than the gel cushion during upright sitting (112 versus 128 mmHg, p=0.01). Mean pressure with the IT-bladder-inflated cushion (157 mmHg) was greater than upright pressures for either the dry flotation or gel cushions (111 and 128 mmHg, respectively p<0.01). Most importantly, ischial tuberosity pressure for the dynamic cushion during H-bladder inflation in an upright position was comparable to the pressure for the dry flotation cushion in a tilted back position (71 versus 74 mmHg, p=0.91) and significantly less than the pressure obtained with the gel cushion (71 versus 86 mmHg, p<0.05).
Brienza and Karg (1998) had subjects sit on 3 different surfaces (flat foam, initial contour and final contour). Interface pressures were measured using a pressure-sensing pad. Results indicated that when SCI subjects were compared to the elderly subjects without SCI, depth values increased and the mean maximum depth of the final contour was deeper for the SCI group, suggesting that pressure distributions for the SCI group were more sensitive to support surface characteristics than elderly subjects without SCI.
Seymour et al. (1985) evaluated 8 cushions for pressure, temperature effects and subjective factors influencing cushion purchase. While data indicated a wide variability in pressure measurements in individual subjects, the air filled cushion (Bye Bye Decubiti) had the best pressure readings. The alternating pressure and foam cushions had consistently higher temperature readings across both groups.
Gilsdorf et al (1991) studied subjects sitting on ROHO and Jay cushions. Normal force, shear force, centre of force, lateral weight shifts and amount of weight supported by armrests were studied under static and dynamic conditions. The ROHO cushion showed a tendency to carry a larger percentage of total body weight; have a more anterior centre of mass; and showed more forward shear force. There were more lateral weight shifts on the Jay cushion. Armrests supported a portion of body weight.
Garber (1985) evaluated 7 cushions based on amount of pressure reduction. The author also looked at how frequently each cushion was prescribed to subjects with quadriplegia and paraplegia. The ROHO cushion produced the greatest pressure reduction in the majority of subjects (51%) but was prescribed more often for subjects with quadriplegia vs. paraplegia (55% vs. 45%).
Takechi & Tokuhiro (1998) studied the seated buttock pressure distribution in six patients with paraplegia using computerized pressure mapping. Five wheelchair cushions were evaluated (air cushion, contour cushion, polyurethrane foam cushion, cubicushion, silicone gel cushion). Tests showed that if the area of contact was more widespread, the peak pressure was lower. The air cushion and the silicone cushion were found to have the lowest peak pressures.
These studies demonstrate that there are individual variations inherent in those with SCI (e.g. paraplegia vs. tetraplegia). As a result the need for objective measures such as pressure mapping is needed to assist with individualizing a wheelchair cushion prescription. Objective findings together with the clinical knowledge of the prescriber, individual characteristics and the client’s subjective reports need to be considered when prescribing a wheelchair cushion to minimize pressure ulcer risk factors. None of these studies included direct evidence of pressure ulcer prevention associated with a particular cushion type.
- There is level 3 evidence that various cushions or seating systems (e.g. dynamic versus static) are associated with potentially beneficial reduction in seating interface pressure or pressure ulcer risk factors like skin temperature.
- No one cushion is suitable for all individuals with SCI.
- Cushion selection should be based on a combination of pressure mapping results, clinical knowledge of prescriber, individual characteristics and preference.
- More research is needed to see if decreasing ischial pressures or decreasing risk factors such as skin temperature via the use of specialty cushions will help prevent pressure ulcers post SCI.