Seat Cushion Special

Form & Function

How Design Elements Impact Cushion Performance

Seat Cushion Form & FunctionContours, cut-outs, profiles, bladders…not to mention a host of different materials choices. Size and weight wise, the cushion is a relatively small part of a wheelchair seating system. But it’s also critical to the overall performance of the entire seating & mobility system, which is why so much time and money are invested in creating various cushion choices.

Cushions According to Medicare

Today’s wheelchair seat cushion is expected to achieve a long list of goals, from providing comfort to helping to maintain the end-user’s overall health. For billing purposes Medicare has distilled this list into categories for cushions — general use, skin protection, positioning, and skin protection & positioning — and then further differentiates the categories according to size and adjustability or lack thereof.

Manufacturers who want their cushions to have HCPCS codes — required for cushions to be reimbursable by Medicare, as well as many other funding sources — apply to Medicare’s Pricing, Data Analysis& Coding contractor (PDAC) for coding verification. The application filled out by the manufacturer or distributor includes information such as the components and accessories included in the base product; a description of how the cushion functions; indications for cushion use; the media used in the cushion; and which codes the manufacturer is applying for, with test results to back up the application.

Susan Cwiertnia, PT, MS, clinical education specialist at VARILITE, says a general use cushion “needs to have a loaded contour depth of at least 25mm and then overload deflection of at least 5mm” during the required testing. The loaded contour and overload defl ection tests, she says, look at “basically how well it’s going to envelop somebody’s body, and to make sure that the cushion is not going to bottom out when somebody sits on it.”

Testing — simulation types or using human subjects — becomes more complex for cushions applying for skin protection and/or positioning codes.

For skin protection cushions, for example, Cwiertnia says the PDAC requires “loaded contour depth (to be) at least 40mm, so they have to be able to immerse into it a bit further and still have that same overload deflection of 5mm.”

For skin protection & positioning cushions, she adds, PDAC requirements state that “the cushion has to meet the components for the skin protection cushion. But it also has to have positioning components, such as a pre-ischial bar or ridge in front of the ischial tuberosities to prevent forward migration, and lateral pelvic supports. It also has to have a medial thigh support and other components as well, such as a certain height at a preloaded state, including the planar surface, and then features that make the material firmer within the cushion. So it’s going to give you those contours for that positioning, to get that medial and lateral support.”

Additionally, skin protection and skin protection & positioning cushions can be non-adjustable or adjustable. Says Cwiertnia: “Adjustable means the cushion meets all of the characteristics for that skin protection code, but then it has the ability to adjust by the addition or removal of air, liquid, gel or some other fluid medium, and it has to be in areas of the cushion appropriate to promote pressure redistribution.”

Adjustability, she notes, “gives you the ability to customize that cushion or adjust that cushion better to meet that patient’s skin protection needs, because I can let in or let out a certain amount of air, or I can take out fluid packs or add fluid packs to give them what I feel they need for appropriate skin protection for their specific case.”

Of course, a clinician or provider working to find the right cushion for a client may have additional goals or considerations in mind.

“A cushion has to do pressure management,” Cwiertnia says. “It also has to do positioning. A cushion also needs to work for stability, and it needs to work to absorb vibration and impact. Flammability can be a big issue, or the amount of maintenance can be a big issue.”

Other medical issues such as psoriasis or eczema, a client’s lifestyle, environment, climate and activities can also impact cushion choice. As Cwiertnia pointed out, “Traveling is a huge deal. If you take an air cushion (onto an airplane), that air is going to expand, and they might have to let some of the air out when they’re on the plane. When they land, that cushion is going to be underinflated, and they’re going to have to readjust it.”

How Design Impacts Function

Product descriptions of today’s seat cushions for complex rehab clients include discussions of contours and profiles, as well as multiple media being used within a single cushion. How do design elements affect how a cushion performs?

“The reason that people are using contours is pressure distribution,” Cwiertnia says. “Pressure distribution is just a simple formula. It’s a person’s body weight divided over the amount of the surface area of the cushion they’re sitting on. You can’t make pressure go away. The only thing you can do is redistribute it, and the more closely the cushion shape matches the person’s body contour, the more surface area you have for distribution, and the more immersion you have.

“You also have more area for pressure distribution, so that’s why people are trying to do the contours. And then the contours also help with positioning as well, like the positioning of the legs and the pelvis.”

The potential pitfall of using contours? “Pre-contoured cushions are taking a contoured shape that’s going to match a majority of the population most of the time, but it’s not going to fit everybody, because everybody’s body shape is different,” Cwiertnia says. “So that’s also a consideration, too, if you’re choosing a cushion that’s pre-contoured. Is that going to fit your client’s shape?”

The choice between a high profile and a lower profile generally involves the issues of pressure distribution and stability…among others.

“With a higher-profile cushion, usually you have more room to immerse into it,” Cwiertnia says. “You’ve got more surface area that you’re distributing the weight over.” Depending on its materials, however, a taller cushion might make the user feel less stable.

Lower-profile cushions might be preferred by users who want to feel more stable in their wheelchairs, and may want their chairs to respond more efficiently to even minor input.

“Some of the more active users say because they’re more stable in their wheelchairs, they have more control over their movements,” Cwiertnia says. But she also points out, “Sometimes it’s just a matter of your floor-toseat-height ratio. You might need that lower height just to fit underneath your desk. You’re looking at the overall height and weight of the cushion, too: Is it going to fit in the wheelchair? What’s it going to do to the system? How is it going to change the geometry on the wheelchair?”

Multiple Media for Multiple Goals

Another common design element among today’s cushions is using multiple media within a single cushion.

“There are different reasons for using multiple media,” Cwiertnia says. “In the case of a gel fluid cushion, that gel fl uid pack itself is very heavy, and it doesn’t have a lot of shape. It requires (a) stiffer foam base to give it its shape, and also it’s going to lighten up the overall weight of the cushion. So they’re sort of using the best of both worlds: They’re using that fl uid for the skin protection, and then using that foam to get the positioning and lighten the overall cushion.

“Same thing with the (use of) air and foam. The air is going to give you really good skin protection, but it’s not going to give you the stability and the positioning that you want. So we put the lightweight foam in there. We’re trying to get the best of both worlds, getting that positioning and that skin protection.”

That “best of both worlds” approach is also popular among foam cushions, Cwiertnia says: “With some of the foam-only cushions that are made out of multiple thicknesses and densities of foam, that design is to get the skin protection and the positioning that you need, but also making it comfortable. The really soft, comfortable foam is next to the skin, where the user feels it. It feels comfortable and it contours to their shape. But if it’s really soft, it’s going to bottom out. So you put a medium firmness of foam underneath that, and then a really stiff foam underneath it to give the shape to the cushion for the positioning.”

A Form for Every Required Function?

Ultimately, the goal of all these different choices is to give seating clinicians and providers a larger arsenal of potential solutions for clients with highly individualized needs.

“When you’re picking out a cushion, not all clients have the same priorities,” Cwiertnia says. “Thirty to 80 percent of people with a spinal cord injury are going to get a decubitus ulcer in their lifetime, so skin protection would definitely be a priority. But it’s not the only thing, because I don’t want to just give them skin protection. If I’ve got a client with a higher level of spinal cord injury, they don’t have any trunk control; positioning and stability are going to be really important for them, too. So I need to find a cushion that’s going to do both of those.

“If it’s somebody with cerebral palsy, maybe skin protection is not going to be such a big issue with them, but I really need to look at their positioning and their stability and how easy it is to maintain that cushion, because they may not be able to do that very easily.”

Despite all the choices available, there is no magic bullet, Cwiertnia says. “All cushions have several characteristics. Some of them perform better than others. You have to match up the characteristics of the cushion with what meets your client’s needs the best, based on your evaluation.”

This article originally appeared in the May 2011 issue of Mobility Management.

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