Choosing the Cushion to Match the Buttocks

Photo of Sharon Sonenblum Editor’s Note: Ride Designs has graciously donated their blog post space to Sharon Sonenblum, a rehabilitation engineer and Senior Research Scientist at Georgia Tech, to share her thoughts and research findings on some very important topics: sitting mechanics, pressure ulcers, wheelchair cushions, and butts. Sharon is Senior Research Scientist at Georgia Tech, and she has been studying wheelchair use, ulcer prevention, and the response of buttocks to loading for over a decade. This is the second in a series. To read the first blog, What Butts Tell Us About Biomechanical Risk, click here
Wheelchair cushions serve many roles for the individuals sitting on them for more than 10 hours per day. Identifying a cushion that will provide sufficient protection from pressure ulcer development while meeting the other goals such as comfort, stability, and postural support can be very challenging, and there is little scientific evidence available to support those decisions.
What do we know about skin protection cushions? Skin protection cushions are covered by insurance for pressure ulcer prevention. Currently, entry into this class of cushions requires that that the cushion experiences a minimum level (40 mm) of immersion using a standardized test. The immersion measurement was developed by Dr. Stephen Sprigle at Georgia Tech as a multi-part test to describe cushion features and characteristics. While informative, it does not offer enough sensitivity to represent a cushion’s ability to support the buttocks tissues. In fact, as of right now, no standardized test exists to evaluate the Shape Compliance of a wheelchair cushion, or the ability of a cushion to support the buttocks with minimal buttocks deformation.
So how do we match an individual (and their distinct buttocks) with an appropriate wheelchair cushion? Clinicians certainly have strategies they use, but wouldn’t it be great to have a tool that clinicians (especially new clinicians) could use? Pop a few demographics and some measurements about the clients’ Biomechanical Risk into your mobile device, and out comes a list of cushions that should support the clients’ buttocks adequately. Now the clinician can focus on other practical and functional concerns to narrow down the options.  
My colleagues and I are very interested in developing just such an app. First, that will require some investigation into the factors that best predict an individual’s Biomechanical Risk. We would appreciate your feedback on these questions: 
  • What factors do you use to pair someone with a wheelchair cushion?
  • Would you be willing to measure someone’s tissue compliance if it required a mat exam? If it took only 3 minutes?
  • Would you use interface pressure mapping if you knew what to do with the resulting pressure map?
Thanks for your feedback!


Submitted by Michael Kostie,... (not verified) on

What factors do I take to chose a cushion, many factors are taken to make this decision, Time patient in in the chair, any history of pressure ulcers, environment the patient lives in, ( being home or a facility ) clothing the patient normally wears, ( different fabrics are able to breathe, or not ) does the patient have an incontinence problems, body size of the patient ( thin / thick ) the chair that they are looking into will it have a tilt/ recline option. is the patient able to pressure relief on his / her own, and how often,

I do not think testing a patient's skin tissue is something that should be done by anyone other than a Doctor, or nurse, during an office visit. Most of the time the eval is done in the home, and not having the proper and safe environment to do this might not be in the patient's best interest. If it was given as part of the face to face note or as a clinical note that would help.

I do have a FSA pressure mapping system that I carry with me at all times, and I do use it when needed. I can show the patient the difference between cushions, and most of these people are already in a chair, so they have an idea of what works for them, I am able to show them in color, and numbers what the cushion is doing and how it is important for them to pressure relief as much as possible, show them the difference between gel , air, or foam cushions. and even print out those photos to present to the insurance to prove a ROHO cushion is better than a gereral use cushion, or a certain back rest is more supportive with the patient kyphotic posture.

Submitted by Tamara Vos-Drap... (not verified) on

Excellent article, Sharon. You propose interesting potential solutions to the pressure management dilemma. I'm excited to see your work with the mobile app! Our team at Mayo Clinic is also very interested in this challenging problem. We are currently advancing the development of our pressure mapping system with mobile app (for use at home) to address some of the issues you describe in your article. Through two federal grants awarded this year, we are using feedback from veterans with SCI and conducting other tests to learn how to best use a pressure mapping system in daily life. There are challenges for sure! Thank you for the important contributions you and your team have made in this area.

Immersion and envelopment are not necessarily or exclusively active events. A cushion (seat or back) can be pre-shaped for envelopment yet possess qualities that allow additional immersion. This is the perspective we embrace every time (36 years) we fabricate a custom cushion. Tissue deformation is also a key component in our designs. Selective repartitioning and compartmentalizing pressure to reflect known tissue tolerance variances along the contact interface is also key to skin/wound management and promotion of healing, while seated.

The population we serve are largely without cognitive or physical ability to: avoid pressure limits, realign posture, reorient alignment or request assistance. Lastly, noting a persons tone anomalies and manner of postural collapse (including causation) is also key to our design protocols.

An app that can acknowledge these facts and note these factors would be wonderful.

Submitted by R. H. Graebe, BEE (not verified) on

Pressure doesn't cause a pressure sore.
Ischemia over extended time cause the death of tissue cells. These cellular deaths, over time, develop into a wound incorrectly called a pressure sore.
The question needing an answer is what external forces cause ischemia. Deformation of tissues is one cause of ischemia. This can be demonstrated by placing a fingertip against a pane of clear glass and observe that those tissues are blanched lacking blood and flow.
Wheel chair cushions that match the shape of the patient minimize deformation maintaining blood flow keeping local weight bearing tissues healthy.
Measuring how well the support surface complies with a shape presented to it should make evaluation of wheel chair support surfaces. A bench test can be created to conduct the evaluation creating a quantitative measure/rating of shape compliance for that cushion.
A means to measure the deformation resistance of the patient's soft tissues to establish how good or poor the support surface must be in its shape compliance rating. Deformation resistance of the involved tissues also must be made to aid in making a choice of the best cushion for that patient.

Add new comment