Well, if you have been following this series, you will know that I have written about different aspects of wheelchair cushions, such as the material, design, and cushion cover, and how these may affect skin protection for a person using the cushion. You will also know that I have said that no one cushion will work best for all people. This month, I would like to write a reminder for everyone to consider wheelchair configuration and how this may influence the effectiveness of the cushion in providing skin protection. Sometimes when a client is beginning to show signs of skin breakdown, we trial different pressure relieving cushions and when one cushion does not seem to work, we blame the cushion and want to move on and trial the next one with the client. Have we ever considered how the wheelchair is configured and how that may be effecting pressure distribution? What do I mean by this? Well, for example, if the footrests are not at the appropriate height for the client to allow the client to take load through the femurs, there may be increased pressure in the area of the pelvis as this area takes more of the load. Look at the examples below of pressure mapping.
(If you are not familiar with reading pressure mapping, the pictures show the effects of pressure at the back rest – the area represented above the grey line – and at the cushion – the area below the grey line.)
The example on the left shows the effects on pressure mapping when the foot plates are too high for a client, which results in the femurs not taking load. Notice the increased pressure at the ischial tuberosities and the greater trochanters, represented by the lighter green colours in the area of the buttocks. The example on the right shows pressure mapping when the footplates are too low for a client, which results in increased pressure on the thighs distally (as illustrated by the light green areas at the end of the cushion).
Also notice how a change in height of the footrests also changes the pressure distribution on the backrest. If the footrests are too high for a client, the client is more likely to sit in a posterior pelvic tilt and have a kyphosis. This is why the pressure mapping shows increased load or pressure at the low back or the bottom part of the back rest (i.e. the area just above the grey line). If the footrests are too low for a client, the client’s pelvis may be brought into an anterior pelvic tilt, creating a lordosis. This is represented in the pressure mapping by the absence of load being taken on the back rest at the lumbar region.
So, we have seen the effect that the height of the footrest will have on the loading and pressure distribution on a cushion. The cushion will not be able to work optimally if the footrests are positioned either too high or too low for a client. Sometimes only small adjustments of ½ an inch are required to optimize the load bearing through the femurs.
Let’s also think about the back rest. In both pressure mapping pictures above, the back rest is not taking the load of the client’s trunk fully or evenly. As I have said in past Clinical Corner articles, we are trying to maximize the seated footprint to redistribute load and minimize peak pressures. The amount of load taken through the backrest will influence the pressure distribution through the cushion. Something to keep in mind is that anytime we change one component of the seating, whether it is the cushion or the backrest, we may be altering the load distribution through the other component. We need to ensure that both the cushion and the backrest are taking load optimally and working together.
One final thought is the influence of the use of armrests on pressure redistribution over the seated surface. The upper extremities represent 10 per cent of a person’s body weight. The use of armrests to support the upper extremities when the upper extremities are not required for function can help to reduce peak pressures over the buttocks.1
In summary, a pressure relieving cushion does not work in isolation. It is important to consider the seating and wheelchair configuration as a whole as the components should work synergistically to maximize the seated footprint and minimize peak pressures.
As always, please provide your comments, questions and suggestions regarding Clinical Corner on my blog at www.clinical-corner.com. I look forward to hearing from you!
Sheilagh Sherman, OT Reg. (Ont.)
Clinical Rehab Product Consultant
1. Consortium for Spinal Cord Medicine Clinical Practice Guidelines. (2000). Pressure Ulcer Prevention and Treatment Following Spinal Cord Injury: A Clinical Practice Guideline for Health-Care Professionals. Paralyzed Veterans of America.
Note: The content of this blog is not meant to be prescriptive; rather it is meant as a general resource for clinicians to then use clinical reasoning skills to determine optimal seating and mobility solutions for individual clients.