Basic wheelchair measurements include the shoulder width, chest width (from armpit to armpit) and hip width. These width measures must be considered and accommodated when prescribing the wheelchair chassis and corresponding modular seating options to optimise:
- Functional ability for self-propelling, without limiting shoulder range of movement,
- Immersion into the back support for pressure offloading and distribution to prevent tissue deformation and skin integrity risks,
- Support where it is biomechanically required to meet the unique postural needs of the wheelchair user’s body shape, and
- Configurability for changes to body shape requirements.
The main purpose of the back support in the wheelchair is to offer posterior support to the trunk – it is a primary posterior support surface allowing weight-bearing and reinforcing support against the effects of gravity to reduce the effort of sitting. It can also provide support behind the pelvis, helping to align the pelvis into a more neutral position.
Availability of off-the-shelf back supports that allow for responsiveness to complex body shapes can be a challenge – Spex seating technology aims to provide modular off-the-shelf solutions that can be ordered and configured to respond to increased complexity.
Much like the height of a back support, the width can vary based on the level of support required. An additional factor which can affect the width of the back support is if the back support and shell need to have the ability to move between the wheelchair back posts to allow for seat depth adjustment and/or recline.
|Spex (Height-Adjustable and Classic) Back Supports||Spex Mantaray Back Support|
In some cases, we may want a back support that is slightly wider than the trunk. This can be for the following reasons:
1. Provide greater stability
Less contact surface between the body and the back support because of changes to body shape and non-contourable surfaces in response to these changes will lead to instability to the trunk. This will affect available movement and function of the upper limbs and control of the head and neck.
Instability might also lead the body to respond by attempting to ‘fix’ or stabilise elsewhere in order to facilitate freedom of movement in other body segments (e.g. arms or head and neck) – this can lead to secondary postural deformity if stability doesn’t support optimal alignment. We need stability in body segments to allow for movement in others; core stability allows us to move our arms and legs more freely.
This can lead to avoidable postural deformity occurring to alleviate experienced pain over those pressure sites and because the postural control against gravity, whilst seated in the wheelchair, becomes more difficult to control.
The back support can be used to provide postural support to the pelvis at the level of the posterior superior iliac spine (PSIS) – this can help to maintain a neutral pelvic alignment in tandem with the contouring of the seat cushion.
The back support can also allow for immersion and envelopment and provide soft, yet stable, lateral contouring around the chest wall for improved alignment and stability against gravity. In this way it can offer a little bit of a ‘hug’ for comfort and for improved support.
Figure 1 Example of Spex Supershape to accommodate to body shape and provide posterior and lateral support to the trunk
2. Provide more directed support and sensory feedback
There are times when a standard rectangular back support may need additional shaping to better respond to the user’s body shape and accessories required.
For example, increasing the width behind the shoulders and/or pelvis but not around the trunk to better accommodate lateral trunk supports.
This allows greater contouring and shaping around the shoulder girdle and pelvis for stability of these areas.
Figure 2. Surface or ‘I’ shaped modification to Spex Back Support
Figure 3. T-shaped modification to Spex Classic back support (without outer cover) to meet contouring needs and increased support at the shoulders
3. A greater contact surface can help advise our sense of body position (proprioception) and body schema
Most of us know where we are in space and have an internal awareness of our body and how our body parts are related to each other (body schema). This develops as we learn to move and make sense of how our body feels as we develop as a child. Our vestibular (balance) system, vision, muscle activity, tendon stretch, and sensation help inform us of where we are in space and how our bodies needs to work to perform our chosen activity. When we are unstable, we may increase our muscle tone to ‘fix’ or stabilise certain body parts in order to allow movement in other body parts (think of the effort of reaching whilst standing on one leg compared to reaching whilst sitting down) – we do this largely without thought because our brains automatically process how we are positioned and how the muscles need to work together (anticipatory postural adjustment) to allow for us to complete the required action.
Our body schema can become impaired following damage to our neurological system (e.g. injury to the brain or our nerves that control the flow of sensory and movement information) from clinical conditions such as: stroke, brain injury. This affects the control we have over our body and the quality of our movement.
We can use the back support to help provide sensory information that can help inform our body schema. This can help reduce overactivity in muscles because the body feels unstable and can help prevent development of postural deformities because of impaired body schema.
4. Reduce pressure and associated pain over bony prominences around ribs and shoulders
For wheelchair users with complex body shapes resulting from progressive neurological conditions and gravity’s continuous effect on the body over time, the alignment and bony contouring of the trunk can change. For example, the bones of the ribs, or shoulder blades can become more pronounced causing areas of pressure risk against the contact surface. Similarly, the wheelchair user’s trunk dimensions may change, become narrower in width but deeper from front to back.
If some areas are pressing more into the back support, other parts will have limited or no contact back support. Greater force over a smaller area can contribute to pain and development of pressure areas.
Figure 4. Example of trunk shape changes that would affect optimal contact if on a flat back support surface and use of Spex Supershape back support to respond to unique body shapes
5. Reduce potential pressure risks because of extended lateral hardware or increased pressure on lateral hardware
Some users may have a total body support system in the form of custom moulded back supports offering posterior and lateral support to the trunk. Others will have modular solutions where different components can be configured to meet unique body shapes. Lateral trunk supports are often used to provide support in addition to the back support and, in some cases, may have exposed hardware (e.g. extended brackets to meet lateral pad positioning) or need to withstand increased force.
If body shape results in increased force/pressure onto lateral trunk support, and/or potentially exposed hardware that could pose pressure concerns, a wider back support can wrap around the body and provide additional lateral cushioning to the trunk to distribute pressure over a wider surface area.
Figure 5. Wider back support surface allows increased ‘wrap around’ to cover extended lateral hardware and provide lateral contouring for stability
Can Spex seating technology respond to this future-proofing need?
Children may grow more quickly in height than width initially, but width adjustments will need to be considered. Factors such as weight fluctuations, changes in clinical conditions, and growth must be considered to avoid incorrect fit of the wheelchair and result in postural instability.
It is possible to order the back support surface sizing to be a slim-fit, default fit or custom fit so that increased contouring and support is required. It is also possible to order a 1” wider back support shell and default fit padding and mount it onto a narrower chair with use of the width adjustable brackets (this would mean the back support being mounted in front of the back posts with no seat depth extension within the Spex hardware.
Figure 6 – Spex script form page 20 – available here
If the overall body width measurements are likely to change, then both back support shell and support surface sizes may need to be considered for future-proofing. This can help with changes if the back support shell is to move between different chassis, the back support needs to respond to growth or shape changes or there is a need for greater trunk width support for the user.
Figure 7. Width adjustable quad mount hardware for mounting a wider back support shell onto chair with a narrower seat width.
Spex seating technology offers both width adjustment considerations in the back support surface and the back support shell. These are both off the shelf solutions that come together as default for a set size or ordered separately for a more bespoke personalised fit.
Ordering a wider back support surface that is configurable/contourable to the user’s body shape can accomplish the following:
- Wrap around the trunk to provide a greater surface area for pressure distribution,
- Envelope and immerse the trunk for greater sensory feedback to inform the body schema,
- Provide additional cushioning to exposed lateral trunk support hardware,
- Meet individual body shape contouring, offering reinforced support against gravity,
- Improved posterior and lateral stability to the trunk to reduce the effort of sitting and optimise function of the arms, and
- Provide additional comfort when seated in the wheelchair.
The width of back support is dependent on the wheelchair user’s unique postural, functional, comfort needs and future needs – as indicated in your clinical assessment. Simulating the seating system is helpful to assess whether the selected back support width is correct and whether it allows necessary function with the appropriate biomechanical support.
If you have any queries, please do not hesitate to contact us.
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