Bob VogelQ. I’m a T8 Para, 15 years post-injury. My handcycling friends are giving me a hard time because I haven’t replaced my cushion in eight years. I check my skin from time to time and it looks fine. If I do decide to replace it, how do I go about it, and what should I look for?
— Curt

A. Every cushion has a finite lifespan. Eventually, every brand, make and model will wear out and break down, and the cushion will no longer support and protect your skin the way it was designed to, putting you at risk of a pressure sore. It is vital to replace your cushion before this happens.

Your question is timely because a study published in a recent issue of Journal of Tissue Viability used “finite element” computer modeling to measure and compare the effectiveness of two common types of cushions: foam-based and air cell-based. The results provide important clinical data to look at when choosing a cushion. It also found that deep-tissue injury — a serious type of pressure ulcer that starts below skin level and is not visible until it opens up

[see Para/Medic, March 2011] — is caused in a different way than was previously thought. Choosing the right cushion is crucial to preventing DTI.

The study, led by Dr. Amet Gefen of Tel Aviv University, explains that the appropriate cushion is critical for protecting wheelchair users from pressure ulcers, and there is a wide variety of cushions from which to choose. This study offers a tool to define, using computer analysis, how a particular cushion will protect skin.

An MRI of a 21-year-old person with SCI was used to create an anatomically realistic replica of the model’s left buttock. Measurements were recorded at 17 sites in the muscle, fat, and skin tissues under the ischial tuberosity, and computationally documented how each cushion affects loading on the internal tissues — not just the surface area, the way a pressure mapping system does. It measured different types of tissue stress — overall, tensile, and shear stresses — comparing a ROHO Quadtro Select High Profile cushion (air cell-based) with flat foam cushions of varying densities.

This is the first study to look at internal tissue loads comparing flat foam cushions to a sophisticated complex rehab cushion.

Physical therapist Darren Hammond, certified wound care specialist and senior director for ROHO Institute for Education, explains that to understand the results of the study, it is important to understand a central goal of a cushion — immersion. By providing the greatest amount of immersion (sinking into the cushion without bottoming out) peak pressures on bony areas are reduced, and the pressure is spread over the greatest possible area.

Hammond adds that immersion is not the only way to manage force. Some cushions manage it by off-loading the force — taking the force at a specific site (usually over a bony prominence) — and distributing it over areas that can manage a greater amount of force (thighs and trochanter, for instance).

The study concludes that stresses in tissues and skin are “orders of magnitude” lower on the ROHO cushion compared to non-adjustable foam cushions. Immersion for air cell-based cushions was in the 91-93 percent range compared to 58-65 percent for foam cushions. In addition, stresses on tissue around the ischium were significantly decreased with the air cell-based cushion compared to the foam cushion.

Deep-Tissue Injuries
The study really honed in on looking at pressures in deep tissues, which can cause deep-tissue injuries. This type of wound actually begins beneath intact skin, usually near the interface between the ischial tuberosity (sit bone) and soft tissue, so a mirror check won’t reveal a problem until it gets severe enough to push to the surface of the skin. “There has been a paradigm shift in the understanding of DTIs, and Gefen’s work has had a great deal to do with it,” says Hammond. “The thinking used to be that DTIs were caused by ischemia (lack of blood because of sitting pressure) and/or shear that tears capillaries.” The current thinking is DTIs are caused by tissue deformation.

Individual cells and membranes become deformed and stretched because of prolonged periods of pressure, which makes them weak and permeable (leaky). If this is repeated over time, more cells and membranes become damaged, lose their ability to retain nutrients, aren’t protected from waste, and begin to die off, creating a “spiraling” mechanism for a potentially life-threatening DTI. Because finite element uses computer modeling to compare cushion performance, especially how well they alleviate pressure loads in deep tissue — something that pressure mapping can’t do — the system should be able to identify cushions that reduce the risk of DTI.

In looking for an appropriate cushion, Hammond also says in addition to immersion, look for envelopment — how a cushion surrounds the surface area after you have become immersed in the medium. This helps reduce pressure and manage force as well as reduce side to side movement, which causes harmful shear.

Most important is to get an evaluation from a physical or occupational therapist at a seating clinic, advises Jim Munson, district manager for Permobil TiLite and the ROHO group, and a T9 para. “You can get set up for a seating eval through your primary care physician, or you can contact your local DME supplier and tell them you need a new cushion. They will be happy to walk you step by step through the process of getting a cushion based on your insurance,” says Munson. Make sure they are an accredited member of NRRTS — The National Registry of Rehabilitation Technology Suppliers. To find out if a DME is registered with NRRTS, go to

Also, work with an assistive technology professional (ATP) certified through the Rehabilitation Engineering and Assistive Technology Society of North America,

Munson stresses to have the evaluating therapist write a Letter of Necessity, and make sure it states the exact type of cushion you and your therapist decided upon, the exact manufacturer, model, and size. Be sure you get the cushion you were evaluated for, and not one that “is in the same criteria” but has a better mark-up for the seller. A lot of cushions “look” the same, but don’t perform equally well.

Hopefully, this study will lead to more studies on other cushions, and the end result will give each of us more information on the best cushions for all of us.

• An air cell-based cushion for pressure ulcer protection remarkably reduces tissue stresses in the seated buttocks with respect to foams: finite element studies:
• March 2011 Para/Medic: Deep Tissue Pressure Sores:

Advice in this column is supported by Craig Hospital’s SCI Nurse Advice Line, a toll-free hotline for people living with spinal cord injury, a community service partially funded by grants from the PVA Education Foundation, Craig H. Nielsen Foundation and Caring for Colorado Foundation. For non-emergency nursing information about SCI health, call 800/247-0257 between 9 a.m. and 4 p.m. Mountain Time. If you have a health question, contact Bob Vogel at