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Wheeled Mobility and Seating Equipment

Postural Implications of Seating Equipment Set-up

The loss of voluntary trunk stability and the postures imposed by the configuration of the wheelchair contribute to the development of spinal deformities and an abnormal sitting posture in the SCI population. These changes result in a kyphotic C-shaped thoracolumbar spine, extended cervical spine, flattened lumbar spine, and posteriorly tilted pelvis (Hobson & Tooms 1992; Janssen-Potten et al. 2001). Prolonged sitting results in application of pressure over bony weight-bearing prominences and is cited as a major contributing factor to the development of pressure sores.

Author Year
Country
Research Design
Score
Total Sample Size
Methods
Outcome
Shields & Cook 1992
USA
Prospective Controlled
Trial
N=36
Population: SCI group: Age range: 21-38 yr; Gender: males=13, females=5; Weight range: 45-66 yr; Height range: 158-177 cm; Level  of injury: paraplegia=12, tetraplegia=6; Chronicity=chronic; Control group: Age range: 21-52 yr; Gender: males=7, females=11; Weight range: 51- 71 kg; Height range: 156-178 cm.

Intervention: Lumbar support thickness adjustment (0, 2.5, 5, 7.5cm).

Outcome Measures: Highest and lowest seated buttock pressure, Hip angle.

1. In the able-bodied group, only the 5 cm and 7.5 cm lumbar support thicknesses caused a decrease in highest seated buttock pressure.
2. The adjustment of lumbar support thickness did not influence highest seated buttock pressure in the SCI group.
3. The area of highest seated buttock pressure was significantly higher in SCI than control group.
4. SCI had a reduced pelvifemoral angle for all lumbar thickness adjustments.
Hobson 1992
USA
Prospective Controlled
Trial
N=22
Population: SCI group: Mean age:40.9 yr; Gender: males=10, females=2; Mean weight=59.8 kg; Level of injury: paraplegia=7, tetraplegia=5; Severity of injury: complete=12; Mean time since injury=19.5 yr; Able-Bodied group: Mean age: 39.2 yr; Gender: males=6, females=4.

Intervention: Nine typical wheelchair sitting postures.

Outcome Measures: Tangentially induced shear, Pressure distribution, Oxford Pressure Monitor Device.

1. Mean maximum pressure was on average 26% higher in the SCI group versus the able-bodied group.
2. Forward trunk flexion reduced the average pressure for both groups; however, SCI group encountered a 10% increase in pressure at the initial 30° of forward flex before a reduction occurred.
3. SCI subjects had a mean peak pressure gradient that was 1.5-2.5 higher than able-bodied subjects. Maximum decrease of pressure gradient from a neutral position happened after the backrest reclined to 120°.
4. When a sitting position change occurred, a similar shift to the anterior/posterior midline location of maximum pressure was experienced in both groups. From neutral, a forward trunk flexion at 30° and 50° produced a 2.4 and 2.7cm posterior shift. When the backrest reclined to 120°, the greatest posterior shift occurred at 6cm.
Hobson & Tooms 1992
USA
Prospective Controlled
Trial
N=22
Population: SCI (n=12): Level of injury: paraplegia=7, tetraplegia=5; Able-bodied (n=10).

Intervention: Three standardized sitting postures: P1M, neutral position; P1R, trunk bending; P2,  forward trunk flexion.

Outcome Measures: Spinal and pelvic alignment.

1. Disabled group on average has more lumbar lordosis in upright sitting position compared to the normal group.
2. Person with a SCI will sit in neutral posture with posteriorly tilted pelvis (-tilted on average 15° more than non-injured), forward trunk flexion (30° from neutral posture), forward rotation of the pelvis (8° normal and 12° SCI).
3. In neutral seated posture posterior pelvic tilt causes ITs of SCI to be displaced anteriorly on average 4cm.
4. Kyphotic spinal deformity occurs mainly in thoracolumbar/thoracic spine with compensation in cervical spine – implications for backrest height and lumbar pads.
5. Changes in angle of pelvis and IT location have implications for tissue distortion and/or mechanical abrasion of buttock tissue.
Janssen-Potten et al.
2001
Netherlands
Case Control
N=30
Population: High SCI (T2-8, n=10), Low SCI (T9 12, n=10), Able-bodied controls (n=10). Age range: 25-53 yr; Gender: males=28, females=2; Height range: 1.7-1.9 m; Weight range: 52.1-87.3 kg.

Intervention: Standard chair and chair with 10° forward seat incline.

Outcome Measures: Pelvic tilt, Center of pressure displacement (COP), Muscle activity, Reaching task.

1. There was no significant influence of incline on pelvic tilt in any group.
2. Able-bodied controls had a significantly larger reaching  position than the SCI groups (p<0.001).
3. The COP was not significantly different between the two hairs, or the groups.
Mao et al. 2006
Taiwan
Pre-Post
N=17
Population: Mean age: 35.4 yr; Gender: males=10, females=7; Level of injury: C5- T11; Chronicity=chronic.

Intervention: Adjustable seating system with lateral trunk supports (LTS).

Outcome Measures: Spine radiographs, Cobb angles, Relative change in angle.

1. LTS improved spinal alignment in frontal plane.
2. LTS reduced lumbar angle in sagittal plane resulting in more erect posture.
Alm et al. 2003
Sweden
Pre-Post
N=30
Population: Mean age: 25.8 yr; Gender: males=30, females=0; Injury etiology: complete C5-C6 tetraplegia.

Intervention: Documentation and evaluation of wheelchair sitting (i.e., type of wheelchair, seat angle, backrest height, type and height of cushion).

Outcome Measures: Pelvo-femoral angle (deg), Pelvic tilt (deg), Upper body height. Frontal trunk alignment, Pelvic obliquity.

1. In SCI subjects, the pelvo-femoral angle was statistically significantly smaller in the wheelchair as compared to the standardized surface in relaxed (p<0.001) and upright (p=0.005) sitting positions.
2. In the relaxed sitting position, there were no significant differences among SCI patients in the pelvic anterior tilt
between the standardized surface and wheelchair, regardless of seat angle. In the upright sitting position, the pelvic anterior tile was statistically significantly less (p=0.004).
3. In SCI patients, the mean vertical acromion-trochanter major distance in the sagittal plane was statistically significantly larger in upright than in the relaxed sitting position on both the standardized surface (mean increase: 5%, p<0.001) and in the wheelchair (mean increase: 4% p=0.001).
4. Results showed a statistically significant decrease in mean heights in wheelchair for both relaxed (p<0.001) and upright (p<0.001) sitting positions.
5. For SCI patients, there were no significant differences observed in the horizontal C7 deviation in the frontal plane between relaxed and upright sitting positions, for either the
standardized surface or in wheelchair.
Bolin et al. 2000
Sweden
Pre-Post
N=4
Population: Mean age: 25.8 yr; Gender: males=4, females=0; Injury etiology: complete thoracic spinal cord injury (SCI), Mean time since injury: ≥2 yr.

Intervention: A new wheelchair prescription with  features to support sitting, stability, and improve balance, pelvic posterior tilt.

Outcome Measures: Modified Functional Reach Test (MFRT), Functional Independence Measurement (FIM), Ashworth Scale (AS).

1. There were no changes in the level of spasticity observed for ¾ participants. One participant perceived a decrease in his level of spasticity.
2. Except for improved balance in one participant, the MFRT did not show any significant differences in ¾ participants’ balance. Two self perceived an improvement in balance and one expressed a further deterioration in balance.
3. No changes were observed in respiration for two participants; two perceived an improvement and one perceived deterioration.
4. Two participants stated their wheelchair propulsion improve, even though this was not supported by Cooper’s test or uphill slope propulsion.
5. Wheelchair skills improved for one participant and remained unchanged for two participants. Three participants perceived their wheelchair skills to be improved.

Summarized Level 5 Evidence Studies

The following level 5 evidence studies have been reviewed, and the overarching findings from the studies are highlighted in this section. As noted at the start of this chapter, these types of studies are not included in the discussion or in the conclusions.

Hong et al. (2016) described levels of comfort using the Tool for Assessing Wheelchair discomfort (TAWC) for rigid and sling style back supports. 131 participants rated their discomfort for different body regions (back, neck, buttocks, legs, arms, feet and hands) for their current back support. The authors found a trend towards more discomfort reported for rigid back supports; however, they did not account for the fit and positioning of the participants in the rigid back support which may influence discomfort levels.

Discussion

Shields and Cook (1992) compared the effects of different lumbar support thicknesses on seated buttock pressure. Results of the study suggest that use of a lumbar support was not effective in reducing seated buttock pressure areas in individuals with chronic (≥three yr) SCI. Subjects with SCI were positioned with the pelvis placed as far back in the chair as possible, however, the chronic SCI group had significantly reduced pelvifemoral angle (hip flexion angle) for all lumbar support conditions as compared to the nondisabled group. SCI subjects were not able to sit with an initial hip flexion angle or anterior tilted pelvis as compared to control subjects likely due to shortened hamstrings or hip extensor musculature or structural changes of the spine in chronic SCI.

Hobson and Tooms (1992) investigated the presence of abnormal spinal/pelvic alignment(s) in the SCI population and the impact of the typical seated posture in a wheelchair. On average, the disabled group had more lumbar lordosis in the upright sitting position compared to the able-bodied group. Persons with an SCI tended to sit in a neutral posture with a posteriorly tilted pelvis and tilted on average 15° more than able-bodied group. A forward trunk flexion to 30° from neutral posture resulted in forward rotation of the pelvis – 8° in able-bodied compared with 12° in the SCI group. Lower spinal flexion occurred in the SCI group’s lumbar sacral joint with negligible movement at the sacroiliac joint. In a neutral seated posture, the posterior pelvic tilt caused the ischial tuberosities (IT) of the SCI group to be displaced anteriorly four cm, on average. The angle and rotation of the pelvis and the ischial tuberosity location and slide have implications for tissue distortion and/or mechanical abrasion of buttock tissue.

Use of radiographic evidence to measure spinal alignment of individuals in a seated position was investigated in the study by Mao et al. (2006). The effects of lateral trunk support on a SCI’s individual frontal and sagittal spinal alignment in the seated position were considered. Results showed that lateral trunk supports significantly improved spinal alignment in the frontal plane regardless of the severity of scoliosis. Lateral trunk supports also resulted in a more erect seating posture by reducing the lumbar angle in the sagittal plane. Improved head and trunk alignment with reduced muscular effort was also enhanced by the lateral trunk supports.

Hobson (1992) completed work on the comparative effects of posture on pressure and shear at the body-seat interface. Postures typically assumed by wheelchair users were studied. The pressure distribution findings suggest that individuals with SCI have higher maximum pressures for all postures studied than the able-bodied group. Maximum pressures can be reduced with postural changes – forward flexion to 50°, backrest recline to 120° and full body tilt.

Janssen-Potten et al. (2001) examined the effect of seat tilting on pelvic tilt, balance control and postural muscle use. Providing a standard wheelchair with a cushion creating 10° forward inclination of the seat had no effect on pelvic tilt for persons with or without a SCI. The study did not reveal a difference in pelvic tilt because of seat manipulation. However, the difference between pelvic position at rest and in the forward-reaching position was significantly greater in non-sensorimotor-impaired persons than in persons with SCI. The second purpose of the study was to determine if the forward inclination of the seat impacts balance control and alternative muscle use in the thoracic SCI Group. There were no significant changes in centre of pressure displacement between the standard chair condition and the forward inclined seat condition for all three groups (high thoracic, low thoracic and able-bodied). Review of the kinematics combined with the electromyography data did not provide evidence for development of a protocol for wheelchair prescription for pelvic positioning in persons with a SCI.

The effect of foot support height on ischial tuberosity pressure for 17 people with paraplegia SCI who used manual wheelchairs was examined by Tederko et al. (2015). A standard study wheelchair was used with the seat horizontal and the seat surface to back angle being set at 90°; the cushion was five cm thick foam to allow pressure changes to be observed. Foot supports were raised 10% and 20% of the participants’ fibula length using 5 mm thick mats was placed under the feet. Results of interface pressure mapping using the X-Sensor system indicated significant differences between each raised foot support position for all variables studied. As the foot support position was raised, the contact surface decreased and the average pressure at the IT increased significantly; authors report observations of raising foot supports also raising thighs off the seat surface which would contribute to reductions in contact surface noted in pressure mapping. The authors note that they did not examine coccygeal pressure changes or changes in the pelvic position with the raising of foot supports or differences on different seat cushions.

Conclusions

There is level 2 evidence (from one prospective controlled trial and one pre-post study: Hobson & Tooms 1992; Mao et al. 2006) that the typical SCI seated posture has spinal and pelvic changes/abnormalities.

There is level 2 evidence (from two prospective controlled studies: Hobson 1992; Shields & Cook 1992) that in sitting postures typically assumed by people with SCI, maximum sitting pressures are higher than in able-bodied people.

There is level 4 evidence (from one pre-post study: Mao et al. 2006) that use of lateral trunk supports in specialized seating improves spinal alignment, reduces lumbar angles and reduces muscular effort for postural control.

There is level 2 evidence (from one prospective controlled trial: Shields & Cook 1992) that the use of lumbar supports does not affect buttock pressure.

There is level 3 evidence (from one case control study: Janssen-Potten et al. 2001) that there is no difference in balance and postural muscle control between static positions on a level surface and a 10° forward incline for people with SCI; the pelvic position does not change as compared to able-bodied participants.

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