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 are cited as a major contributing factor to the development of pressure sores.
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 a 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 XSENSOR 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.
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 improve spinal alignment, reduce lumbar angles and reduce 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.
- Individual attention to spinal/pelvic positioning for SCI clients is essential for appropriate wheelchair prescription and set-up.
Use of lateral trunk supports in specialized seating improve spinal alignment, reduce lumbar angles and reduce muscular effort for postural control.