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Wheeled Mobility and Seating Equipment

Custom Contoured Cushions

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 deformation. The following studies explore the use of custom contoured cushions (CCC) to improve pressure distribution and reduce tissue deformation (Sprigle et al. 1990b).

Author Year

Country
Research Design
Score
Total Sample Size

Methods Outcome
Li et al. 2014

China

Prospective Controlled Trial

N=32

Population: Non SCI group: Mean age: 35.2 yr. SCI group: Mean age: 38.3 yr; Level of injury: T7-L2.

Intervention: Patients in each group compared a flat cushion (FC) to a new custom contoured cushion (CCC) created through a method that employs interface pressure measurements representing the buttocks and upper-thigh topology to machining the cushion directly. A new optimized algorithm of converting pressure distribution to the cutting depth according to the load-deflection characteristics of the cushion foam.

Outcome measures: Subjective evaluation of pressure relief and comfort on lateral stability (LS), Anteroposterior stability and comfort degree, Objective evaluation of maximum pressure (MP), Average Pressure (AP), Average pressure gradient (AVP), Balance coefficient (BC).

Subjective Evaluation:

1.     For SCI group, the CCC had high-pressure relief scores than the FC on LS (p<0.01), APS (p<0.005), and CD (p<0.01).

2.     For control group, the CCC had higher-pressure relief scores then those of FC on LS, APS and CD, (p<0.005) for all.

3.     Across both groups the CCC allowed form pressure redistribution and decreased interface pressure between the buttocks and cushion.

Objective evaluation:

1.     Using a Tekscan sensor for both Fc and CCC. Parameters were calculated through MP, AP, APG and BC that assess pressure distribution.

2.     FC had increased pressure across all MP, AP, APG and BC.

3.     CCC produced a lower MP and AP (p<0.01), as well as APG and BC (p<0.05) compared to FC which shows how CCC would prevent pressure sores in high-risk individuals.

Brienza & Karg 1998

USA

Prospective Controlled Trial

N=12

Population: Age range: 21-52 yr; Gender: males=10, females=2; Level of injury: C4-5 to L1-2; BMI range: 17-32.3 kg/m2.

Intervention: Assessed forces for three different surfaces (flat foam, the initial contour and final optimized contour) with the force sensing array (FSA) pad between the cushion and buttocks. Compared SCI to seniors group.

Outcome Measures: Electronic Shape Sensor, Computer Automated Seating System.

1.     There was no difference in tissue stiffness between SCI and seniors group on any of the surfaces.

2.     There was a significant difference in pressure for the initial contour condition between SCI and seniors (p=0.027, p=0.017, respectively), but not within other conditions.

3.     The mean maximum depth was significantly deeper for the final contour as opposed to the initial contour (p<0.001). Also, the mean maximum depth was deeper in the SCI group than the seniors group within the final contour condition (p=0.016, p=0.053, respectively).

4.     Significant differences in interface pressure were found between flat and initial contour (p=0.023) and flat and final contour (p=0.006). No difference was found between the initial and final contour condition.

Sprigle et al. 1990b

USA

Pre-Post

N=10

Population: Level of injury: paraplegia, tetraplegia, C4-5 to T12.

Intervention: Personal wheelchair cushion and custom contour cushion (CCC), with two different foam stiffness (45 ILD, 55 ILD).

Outcome Measures: Pressure distribution; eight Clinical variables: balance, posture, level transfer ability, comfort, propulsion, pressure relief/repositioning, spasticity/posture effect, skin reaction.

1.      CCC significantly lower pressure as compared to the subjects’ usual cushion (p<0.05).

2.      Posture and balance were improved, without interfering with functional abilities, when using the CCC.

3.      CCC did not receive more than two negative responses regarding the eight variables.

Sprigle et al. 1990a

USA

Post-Test

N=11

Population: Level of injury: paraplegia, tetraplegia, C5 – L3.

Intervention: Two flat and two custom contour cushions (CCC) with two different foam stiffness (45 ILD, 55 ILD). (ILD Indentation Load Deflection)

Outcome Measures: Pressure distribution – Oxford Pressure Monitor TM700; ILD test.

1.       Pressure increased as the stiffness of the cushion increased (p<0.05).

2.       CCC had a significantly decreased pressure distribution (p<0.05), as compared to the flat cushion.

3.       CCC also had less soft tissue damage due to seat interface, less harming effects of loading and increased deflation, as compared to the flat cushion.

4.       Three important attributes to CCC found: increased enveloping; decreased foam compression; uniform pressure distribution.

Discussion

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.

Li et al. (2014) in an unrandomized trial compared custom contoured cushions (CCC) to flat foam cushions for SCI wheelchair users and healthy prolonged sitting subjects, both groups were at high risk of pressure ulcer occurrence. CCC were designed to optimize interface pressure distribution. After using the cushions, both groups reported that CCC improved their lateral stability, anteroposterior stability and degree of comfort relative to flat cushions. Mean pressure, average pressure, average pressure gradient and balance coefficients, were all in favour of CCC compared to flat foam cushions, suggesting CCC are better at redistributing pressure

Sprigle et al. (1990a) conducted two studies to determine the use of 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 (one inch) cushion is lower than the force deflection curve of a thicker (three inch) 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.

Conclusions

There is level 2 evidence (from two prospective controlled trials: Brienza & Karg 1998; Li et al. 2014, one post-test study: Sprigle et al. 1990a; and one pre-post test study: Sprigle et al. 1990b) to support that custom contoured cushions (CCC) have attributes that redistribute interface pressure better in comparison to other foam and/or flat foam cushions. However, disadvantages and cautions are identified for the day to day use of CCC.

Summary

Knowledge of wheelchair and seating products is essential for clinicians 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. 2003Janssen-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 1991Garber 1985May et al. 2004).

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