Selection of appropriate seating and wheelchair bases and components should include a thoughtful analysis of the clinical evaluation results in order to match equipment parameters to the person's unique needs. A crucial step in this process is identifying any postural problems and ascertaining the specific causes. Unfortunately, this last component is often overlooked. Merely providing generic solutions to a postural problem without identifying the cause is like putting a Band-Aid on a chronic wound without addressing its origin. Not only might this be ineffective in healing the wound, but also in the worst case, it could cause further harm. For each postural abnormality, several potential solutions might be appropriate. However, one cannot just start selecting from a catalog of interventions. The specific cause must be identified in order to address that specific postural issue. What exactly is causing the individual to sit like this and how can that cause be eliminated? Postural deformities have two basic types of causes. Equipment causes are related to improper adjustments, configurations, shapes, options and/or dimensions of the wheelchair, seating base or components. Physical causes are related to neuromuscular, orthopedic, tonal, cognitive or functional limitations of the individual. Postural deformities are also either fixed or flexible. It is critical that this status be identified to determine if the deformity should be corrected (flexible) or accommodated (fixed). Consider the common postural issue of a posterior pelvic tilt (PPT) as an example.
Physical Causes
A PPT can be the result of muscle weakness, paralysis and/or poor endurance that make it difficult or uncomfortable for the individual to maintain an upright posture against gravity while sitting. There will be a tendency to slide into a PPT because the resulting slouched posture requires less energy and effort. A variety of solutions can help hold the pelvis and trunk upright, make it easier to sit against gravity, encourage spinal extension and increase comfort. These could include: contour in the seat cushion and back support; an open or closed seat-to-back angle; a fixed tilt in the wheelchair frame; and/or a lumbar support, posterior pelvic supports or a back angle. A PPT might also be caused by contractures in the joints or muscles of the pelvis and/or hips that prevent the individual from sitting in a neutral pelvis and 90 degrees of hip flexion. If the wheelchair has a standard 90-degree seat-to-back angle, the hips cannot get to the back of the seat and the individual will be forced to slide forward. To accommodate this fixed deformity, an open seat-to-back angle might more closely match the person's fixed shape. Other options include an appropriately long contour in the seat cushion and a deeper contour in the back support. These interventions will increase contact with the seating surfaces, provide better pressure distribution and improve the person's visual field and comfort. For a unilateral hip extension contracture, an appropriate solution might be a leg trough cut into the cushion on the affected (extended) side or a split seat that is angled down on the affected side. Either solution can help to accommodate the deformity by allowing the extended hip to sit lower in the cushion, while maintaining the unaffected hip at 90 degrees. Many individuals of size will carry excess abdominal tissue. If this is significant enough, their ability to achieve a neutral pelvis and 90 degrees of hip flexion is limited, and they will sit in hip extension and a PPT. A standard 90-degree seat-to-back angle will not accommodate this reclined posture. A better solution would be an open seat-to-back angle that will match the person's shape and angles. In some cases, the slide into a PPT might be due to increased extensor tone in the trunk and legs. In this case, potential solutions might include angles, shapes, configurations and/or materials in the seating and wheelchair that help to manage the tone and prevent its triggers.
Equipment Causes
A PPT might also have a simple equipment cause that is relatively easy and inexpensive to remedy. For example, a PPT might be the result of a poor base of support. A cushion with a firm foam base, a solid board or pan under the cushion, or possibly just good tight upholstery might provide the stable base of support needed for the pelvis. Footplates, armrests and/or back supports that are too high or too low, can also cause a PPT. To prevent sliding into a PPT, the footplates must be high enough to support the feet while keeping the legs parallel to the seat surface. The armrests must be high enough to be easily accessible. And the back support must be high enough to provide stability, but low enough to allow movement of the arms for functional activities, as appropriate. An inappropriate angle in the footrest hanger or front frame might also result in a PPT. This might be the case if tight hamstrings or a knee flexion contracture prevents functional knee extension. If the angle of the hanger/front frame is not tight enough, the hamstring or knee joint will reach its limit of flexibility as the leg is extended to reach the footplate. At this point the only thing that can move is the pelvis, which will rotate back into a PPT. The solution in this case is to provide a tighter hanger/front frame that does not stretch the knee beyond its limit. Individuals who propel the wheelchair with one or both feet might slide into a PPT if the seat-to-floor height (STFH) of the wheelchair prevents them from effectively accessing the ground. Providing a lower STFH will allow the individual's heels to reach the ground while still maintaining an upright posture. Moving the rear wheels and casters up on the frame, using smaller rear wheels and casters, or providing an ultrahemi wheelchair frame might achieve a lower STFH. A seat depth that is too long will create pressure at the back of the knees. To relieve the resulting discomfort the individual will most likely slide forward into a PPT. The solution in this case is a seat depth that is appropriate for the person's anatomical measurement.
Treat the Cause and Not the Symptom
The cause of each postural problem and whether it is fixed or flexible must be identified so that the recommended solution will specifically address that cause and status. A solution that merely seems appropriate or simply has worked in the past is unlikely to solve the problem. In some cases this could actually exacerbate the existing problem or cause a new one. For example, suppose the PPT is due to a hanger angle that is inappropriate for the individual's tight hamstrings, but generic solutions—contour in the seat, a solid support under the cushion and a mild fixed tilt in the frame—are applied. These solutions might be appropriate if the PPT is due to poor core muscle strength but they will do nothing to help position the knee at the correct angle and prevent further sliding. Or consider that the PPT is due to extensor tone in the trunk and lower extremities but an open seat-to-back angle is selected. This solution might be appropriate if the problem was inability to maintain upright against gravity. However, in this case, it might actually trigger further tone and exacerbate the problem. What happens if a fixed PPT is due to chronic use of a seat depth that is too long? Solutions that focus on achieving an upright neutral pelvis will be unproductive in solving the current problem and might actually cause discomfort, skin breakdown and further postural issues. Identifying the specific cause of the postural problem will not only prevent inappropriate solutions that will be ineffective or harmful, but might also save considerable time, effort and money. In some cases the solution might be as simple as adjusting the footrest, armrest or back height. In other cases, it will be as complex as adding an open or closed seat-to-back angle or a fixed tilt in the frame. We must choose carefully and appropriately and not merely provide a Band-Aid. Read more about assistive technology and spinal cord injury at homecaremag.com/spinal-cord-injury
