Let’s Get It Clear: Arm positioning
An arm support on a wheelchair is usually little more than an elbow rest. What do we really need for arm positioning?
Most standard wheelchairs come with what are frequently described as ‘arm rests’. These tend to be part of the wheelchair frame, and their function can often be wide-ranging, but of these functions, there is usually little to offer towards arm positioning.
What are these useful functions that the arm rests are offering? They can be providing ‘skirt guards’ to stop clothing getting caught up in or soiled by the wheels of a manual chair. They may be offering lateral thigh support to stop the legs from abducting too far from the midline.
They may be the means for mounting a joystick and other controls on a powered wheelchair. They may be elbow supports. But what they are not, in most cases, are arm supports.
A true arm support needs to be height adjustable to match the distance for the upper arm from the shoulder joint to the elbow, while for the lower arm they should support the elbow, forearm, wrist. and hand.
Arm support
What are the elements we need to offer arm support, and even more importantly, arm positioning? First, for support, we need something to encompass the elbow and the wrist, to hold them in place. Next, we need to consider what are the anatomically-preferable resting positions of the different components of the arm.
For the upper arm, it is critical that there are no forces on the gleno-humeral joint at the shoulder, and that the humerus is not pushed upwards by too high an arm support, nor (worse) that gravity is pulling the humerus out of the joint. This damage can lead to severe chronic pain. Attempts to accommodate this position are often far from ideal (Figure 1).
This is a common presentation post-stroke where early intervention to prevent the subluxation of the gleno-humeral joint is critical. The population of people who have had a stroke is important: the World Stroke Association reports that there are over 12 million new stroke cases each year.
Globally 25 per cent of people over the age of 25 will have a stroke in their lifetime. Just over half of the strokes each year are in people under the age of 70.
Fifteen to thirty per cent of strokes lead to the individual being permanently disabled. This means that there’s a very large number of people at risk of not receiving the early interventions that could lead to recovery of function and prevention of long-term harm and pain.
After resolving the need to get the elbow at the correct height – which needs the chair arm hardware to be height adjustable (ideally continuously rather than in stepped increments), we should address the support of the forearm and wrist.
If you lift you forearm up from your side, it will naturally bring your hands towards your midline, and with the palms facing inwards. What this tells us is that providing troughs that are parallel with the side of the chair, and that place the hand in a pronated position, are not encouraging a natural position (see Figure 2).
This position parallel with the chair arm support is where the joystick of a powerchair is usually placed: for the occupant this is not ideal for fine motor control (would you place your keypad over to your side?), and can lead to the occupant developing a scoliosis from leaning over continuously to reach the joystick.
A trough restricts movement of the forearm, whereas one thing that we should be looking for post-stroke is early resumption of movement in the affected parts of the body, to reopen neural pathways affected by the stroke.
We also need to facilitate hand movement to avoid the development of contractures in the wrist and hand.
Dynamic arm support
To achieve the anatomically correct position of the arm, therefore, we should have an arm positioning support which can be positioned at the correct height, and that supports the elbow, forearm, and hand in a position where they can be moved in front of the trunk. Such a support can be seen in the Bodypoint Dynamic Arm Support (Figure 3).
This support can be moved by the occupant in a 30 degree arc from outside the width of the wheelchair to across the body, or be locked into a fixed position as and when required. Alternatively, an elasticated strap can be tied between the support and the opposite side of the seat, whereby the occupant can exercise lateral arm movements against for the forces in the strap.
There is an adjustable support along the forearm to help keep the forearm in position. A critical element is the design of the hand support (Figure 4): the thumb is positioned away from the fingers to help resist tendencies towards contractures in the wrist and hand, and the fingers wrap around a flexible sprung support which allows the fingers to flex and extend. There is a strap to help to hold the hand in place.
Stroke ward applications
In the UK, on hospital stroke wards, the bedside seating provision on the whole is not best suited to help protect the individual from developing a subluxed shoulder joint, nor provide the immediate interventions required for optimal early recovery. What is on offer tends to range from transfer-type wheelchairs to upholstered static chairs – neither of which have the facility to get the elbow at an optimal height.
The Dynamic Arm Support is available with different attachment hardwares to fit the arm rests on most wheelchairs, which means that the support can be attached to existing wheelchairs, but the correct height adjustment needs to be incorporated into the design of the chair arm rests.
For a number of upholstered static chairs, BES Healthcare has been working with a couple of the manufacturers of these seating systems. Cura Seating has designed an adjustable height arm support that they can fit onto their chairs, to which the Dynamic Arm Support can be attached.
For the Careflex range, there’s now the byBES interface (Figure 5) that fits into the arm mounting systems which provides for continuous (rather than stepped) height adjustment, which also can be set up to accommodate increased or decreased flexion at the elbow.
Standing for at least an hour a day is recommended for all mobility impaired individuals. A number of therapists have added Dynamic Arm Supports to their patients’’ standers to provide additional upper extremity exercise.
ISO standardised safety testing
To date the ISO wheelchair seating standard ISO 16840-31 has not provided for static or repetitive load testing for arm positioning supports.
This is currently being addressed: at the recent meeting of the ISO Wheelchair Seating Working Group, tests were proposed that address static downward (1), upward (2), lateral (3), and angular (4) loads (Figures 6 to 8).
A failure mode arises if the maximum allowable deflection distance or angle is exceeded, or permanent deformation or breakage occurs.
Lateral forces arise from the seated user or the caregiver pushing against the arm support or pivoting it through a range of motion (Figure7).
For ‘dynamic’ devices (3a), repetitive forces can be especially useful tests to identify failures by shifts in position or loosening of fasteners. For fixed-position devices (3b), lateral forces are equally relevant, even though no movement is expected.
For occupants exhibiting lateral leaning or users with strong tone, the angular forces can be quite high (Figure 8), and therefore this has been addressed in the new tests.
A rig has been designed to address repetitive loads which might be experienced in dynamic supports (Figure 9).
In conclusion
The arm support supplied as part of the framework of a wheelchair is normally little more than a poorly positioned painful elbow rest.
Functionally, an arm support should be a positioning device which can be placed to optimise the individual’s function and well-being, and without risk of inducing long term harm. Appropriate solutions and their safety testing are becoming available.
References
- ISO 16840-3:2022 Wheelchair seating Part 3: Determination of static, impact, and repetitive load strengths for postural support devices
Further items can be found at www.beshealthcare.net. If you are interested in receiving further information on the topic, please contact barend@beshealthcare.net
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Dr Barend ter Haar has been involved in seating and mobility for over 30 years, including lecturing internationally and developing international seating standards.
