ATP Series

Demystifying Cushion Standards

What They Mean, What They Don't Mean & How They Impact Seating

• By Laurie Watanabe
• Apr 01, 2022

To seating teams immersed in clinic appointments and documentation, seat cushion standards might seem esoteric, understood only by a relative handful of academic and research professionals.

But the goals of seating standards are to support clinicians, suppliers, and consumers in their quests to achieve optimal outcomes when choosing from the enormous number of wheelchair seat cushions currently on the market.

So understanding what seating standards do — and just as importantly, what they’re not meant to do — can make the cushion selection process more efficient.

Creating a Common Language

Kara Kopplin, B.Sc. Eng, Director Regulatory Science, Group R&D for Permobil, is the Chair of the RESNA Standards Committee on Wheelchair and Related Seating.

Asked to define seating standards, Kopplin said, “In the U.S., our standards are developed by RESNA committees — and on the RESNA Web site, the different committees are spelled out, including wheelchair and related seating, where the cushions and backs are. And that’s the one that I chair. These are standards that are developed first to make sure we’ve got a common language in the way that we talk about seating and positioning. And then building upon that, it’s a way to do some mechanical testing in a lab, just to understand the properties of the cushions. And those tests are tied to the properties that we know are important for pressure injury prevention, primarily.

“So for example, with the clinical practice guideline, we know pressure injuries are caused by pressure or pressure in combination with shear. And pressure and shear are both properties that we can measure in a lab. We have those tests developed to try to assess that. And [testing] also gives us a very neutral way to look at the products, objectively compared to each other.”

The focus of standards, Kopplin said, is on function, regardless of what a cushion is made of, or what its shape or contouring is. Standards aren’t about criticizing foam and praising air cells, or vice versa. Function — regardless of the materials used in the cushion — is what’s being measured.

“We don’t write standards specifying materials, for example,” Kopplin said. “We just care about how [a cushion] functions with the body. So, developing objective tests that can try to capture that function — that is what we’re doing.”

Asked why it’s important to have seat cushion standards, Tom Hetzel, PT, ATP, co-founder and CEO of Ride Designs, said, “There are so many elements of the Complex Rehab Technology (CRT) industry that will benefit from the development and adoption of these standards. As a physical therapist, I have been doing nothing but seating, development, design, and education for over 30 years and have always been involved, to some degree, in the idea of the development of standards. It’s been exciting over these past few years to see the industry coalesce around really making this happen under the guidance of RESNA. Its coordination with international standards is going to be fantastic as well.”

Using Standards in the Real World

Hetzel pointed out that seating standards serve many purposes. “Even if a manufacturer is self-certifying with some of these standards, at least there’s ability to do some comparison there and truly look more objectively at how different cushions or different postural support devices perform,” he said. “So it’s imperative that this happens. And also, as we are looking at regulatory and governmental affairs, funding, reimbursement and trying to boost the validity of our industry — they require this level of standards if we want to proceed and have success with being awarded a separate [Medicare] benefit category.”

It’s just as important to establish what cushion standards are not meant to do. For example, standards do not issue judgments on cushion materials: In the 2022 International Seating Symposium presentation “Adding ISO Standards to the Clinical Reasoning Process” — which Kopplin co-presented with Stacey Mullis, OTR/L, ATP, and Ana Endsjo, MOTR/L, CLT — Kopplin showed test results for three cushions. The plot twist: A foam cushion had the best scores, even though foam is often thought to be the most basic cushion medium (the two lower-scoring cushions were made of gel).

Thus, standards can provide an unbiased way to compare cushions without pre-conceived notions about cushion materials.

“That’s been part of the fun of applying these ISO standards to a wide variety of cushions, that you do get that reveal,” Kopplin said. “People might assume, ‘Oh, I need this type of cushion,’ like a foam cushion is always going to perform this way. Not necessarily. Same thing with air [cushions]. You may have ideas about what it does or doesn’t do. And we’ve seen with multiple tests that those material results are interspersed all the way across the spectrum. So we haven’t yet seen something where we can say, ‘Yes, this material always performs like that.’ They’re all different, because it’s not just the material — it’s also the construction and the design and adjustability and on and on. So until you test the cushion to an ISO standard, you really shouldn’t make those assumptions about what it does or doesn’t do.”

Similarly, seating standards aren’t an equation for determining the “best” cushion for a client.

“All of that [standards-related] information helps you narrow the field of choices, because there are just so many options out there and lots of good options, too,” Kopplin said. “But it is very individualized, what you’re trying to find for the particular person in front of you. And if you have these objective test measures, you can start to see what might be worth trialing. If you know you need good skin protection and you know from the clinical guideline that immersion and envelopment are important, then you can ask for immersion and envelopment data from different manufacturers, and the ones that are trending better are the ones that you might want to look at first and try those out. None of it ever indicates, Yes, it will work, but it helps you make a more informed decision. The therapist can say, ‘Clinically, I’m trying to reach this goal; what is it about the product in front of me that’s going to help me get there?’, and having data can help answer that question.”

Standards can also support efforts to improve reimbursement — and can help to distinguish medically necessary products from general consumer goods. “First of all, having the standards helps the company that’s developing the product have some baselines,” Kopplin said. “Then as they’re evolving their products, they can measure the effect of the changes: ‘We improved the design in these ways, and we can measure the results.’ And that type of R&D, of course, has a cost associated with it and requires that kind of analysis and that engineering discipline.

“And then same thing for the regulators: We want them to be able to weed out the products that really were never intended to be medical devices. Maybe it is just a thin slab of foam that was meant to be thrown on an office chair, and that’s as far as the thinking went. That’s why it’s $30 — but does it even pass this cursory immersion test? No. So even setting some relatively low bars is important so that we make sure our products are safe and effective for the users.”

Hetzel added, “The other area is internationally. I am hopeful that adoption of these standards or use of these standards will start to remove some of these extremely arbitrary product definitions that create different coding structures and reimbursement structures in other countries. It’s very difficult for a manufacturer to enter new markets when you have a product that, by all standards in the U.S., has been successful, has been proven successful through good clinical practice and experience. But then, to go to [another country] and find out that their requirements for the product are not only inconsistent with what we’re doing — but they’re not science based.”

The Limitations of Cushion Standards

Cushion standards are a work in progress, with other factors that would ideally be part of the cushion selection process.

“One of my concerns is the application of these standards as well,” Hetzel said. “First of all, one of the reasons the standards are so difficult is that what we’re trying to do as a committee is work within our knowledge right now of biomechanical risk for pressure injury and what influences the risk. And we support, financially, Georgia Tech and [Dr.] Sharon Sonenblum’s efforts to define biomechanical risk for skin breakdown. Her ultimate goal is to create a tool that will allow a clinician, very quickly and very accurately, to evaluate you and go through a simple battery of tests that are clinically relevant and proven that could assign you a number for risk.

“That risk number would then be tied to your cushion design. So the problem right now with standards is it’s all about what is deemed salient to what we were able to control in seating. The forces, the temperatures, the humidity — we know these things influence skin breakdown, but there’s not the peer-reviewed research relative to the standards. There’s not that ‘If you get a cushion with these standard measures, this will be tied to this skin outcome or this postural outcome.’”

Current standards, Hetzel said, are tied not to clinical outcomes or to direct biomechanical risk of skin breakdown. Rather, today’s standards are “tied to what we know from the research as contributing factors to pressure injury. So, how do we manage those, what is our level of knowledge relative to that, and what performance characteristics of cushions can be measured to help to determine if it should be deemed at least a safe tool to assess and try? Will it hold up over time? Are the immersion and envelopment qualities sufficient for my client? And are the secondary supports strong enough for the degree of spasticity or dystonia that I’m working with in my client base?

“All these things — if all of us manufacturers are speaking the same language relative to the same standards — are going to allow people to make more objective decisions.”

No Substitute for Clinical Judgment

Since every client who uses a wheelchair is different — not just in diagnosis and potential progression, but also in age, environment, etc. — seating standards can’t replace clinical expertise.

“What we need to recognize is that [standards] aren’t going to be a substitute for clinical judgment,” Hetzel said. “What we don’t want is people or legislative or regulatory agencies to say, ‘Okay, all these cushions need to go through all these tests,’ and then determining what’s going to be funded or what’s going to be prescribed because of how they do on the full battery of tests — that’s simply not appropriate. That’s been one of our challenges: trying to discern, within these standards, what constitutes minimum performance standards. Is there a battery of minimum tests that every product should, to some point, at some degree, be able to meet a standard?”

As an example of how clinical judgment is then needed, Hetzel said, “Think about your active paraplegic living in Orlando, Fla., in that climate, versus my great grandmother, who sits in a climate-controlled environment most of the day in Idaho. So, it’s going to be a matter also of clinicians and manufacturers looking at this battery of tests and determining what is appropriate, what tests are valid and need to be done. I’m looking forward to having these standards in place. I want them to be used judiciously. I want people to understand that there’s really no guarantee of a clinical outcome by meeting a certain standard.”

Kopplin added that consumer preferences and perspectives must also play a key role in successful cushion selection. “As much as you might have data that says, ‘It looks like this should work pretty well for you,’ if for whatever reason the user says, ‘I don’t feel stable,’ or, ‘I don’t feel comfortable,’ or, ‘My position’s not quite right’ — whether the data says otherwise or not, it’s not the right cushion. And I think it’s a good point that there are multiple characteristics to these cushions, and there are multiple needs for the user. And so we’re also very careful about explaining, ‘Don’t look at any one test result in isolation.’

“We also are conscious that we don’t want someone to look at cushion A and cushion B and say, ‘Well, this one is 0.2 better’ — whatever the value is, square millimeters of contact area or millimeters of immersion. We don’t want people to rule things out and specifically rank them. We do want people to think about, ‘This family of cushions functions in a similar way. So let’s look at those for this individual.’”

The Future of Cushion Standards

What’s coming next for standards? Current cushion standards focus on immersion and envelopment, two factors linked to pressure management. But of course, many cushions are also called upon to help with positioning.

“Maybe you’re going to choose skin-protection cushions with good immersion and envelopment, but what about stability?” Kopplin asked as an example. “And that’s an area where we have a new ISO standard developed just for that — it was published last year, 2021. It’s an indication of how well the cushion will return [the user] to their center position if they’re functioning in a lean, if they’re reaching for something and coming back.

“So there’s another set of data: These cushions seem to have good skin protection. I know I need something really stable for this client. If I look at the stability data — well, maybe these two [cushions] are kind of bottom of the list now, because their stability results were on the low end. And again, not saying they’re good or bad, but trying to find something more ideal. Knowing what the person needs might point me to something that did well with skin protection and with stability.”

Hetzel again referenced a client living in a warmer, damper environment: “If you are that active paraplegic in Orlando, and you know you’ve had issues with skin maceration and level one or level two pressure injuries relative to heat and moisture — I want to be able to look objectively across my options and see how those specific cushions tested relative to microclimate. So of all these options, it seems there are four cushions now that seem to do that well. Then, we can start having that clinical discussion about what other elements need to be in place.”

And Hetzel referenced the current focus on immersion and envelopment: “These standards are, very much with respect to performance, based on immersion and envelopment knowledge. And we know at Ride Designs that immersion and envelopment isn’t the only answer, and there’s a growing body of evidence that supports what I just said. So, we know at Ride Designs that our participation in the standards is very, very important so that we know what the industry is speaking to as far as the state of the knowledge. Again, looking at peer-reviewed research and looking at skin outcomes and tying biomechanical risk to these things is still off in the future, but this is a really, really good step.”

Coming up, Kopplin added, “is that stability test, which is relatively new, and we are excited about that because that’s really the first one we’ve had that has been related to dynamic function of the person. And the second one is about flammability.

“We’ve been on this long road toward improving a previous standard that was developed just for wheelchair seating to simulate an electronic cigarette and replace the open-flame testing that’s used for furniture, mostly in Europe. Even in the U.S., open-flame testing is pretty much abolished for all furniture. And the reason we’re so passionate about that is because it will allow new materials to be developed if they no longer have to pass this incredibly aggressive fire-retardancy requirement. So it opens it up for smart textiles and low-shear surfaces and all kinds of different high-tech solutions that we haven’t had access to as designers and developers.”

Kopplin is also excited about shear research: “There have been a lot of presentations clinically about shear, and then from an engineering standpoint, explaining shear, forces, stresses, and strains outside the body and inside the body, causing that tissue deformation that causes deep tissue injury. But we haven’t had a good way to measure interface shear forces in the lab with our ISO indenter and a cushion. So we’re doing this in two steps.

“The first is we have a draft document right now that’s taking that clinical terminology and engineering terminology and putting it together in an accessible way, especially so people understand what’s happening outside the body, how it translates inside the body, what we’re talking about when we say shear. And then the next step will be to develop a test sensor that we can do this evaluation in the lab. So if you are looking for that localized low-shear interface on your cushion cover, we’ll have a way that you can use this tool to design and develop it, and you will have this tool to be able to have evidence behind those claims once it’s out in the market.”

Given that cushion standards are a tool that can benefit the entire seating team and cushion selection process, Kopplin encouraged interested stakeholders to get involved.

“Just reach out,” she said. “We’d love to have you join a meeting as an observer to see if it’s something you’d like to participate in. We do really want that wide variety of input. We need those checks and balances of different perspectives, and we definitely need more end users right now. We would really welcome that perspective and input. So whether you’re a therapist or a manufacturer or a policymaker, or you work in a large facility or a small practice, we probably could use some advice from you, and we’d love to have you.”

“We need standards, and we have to recognize that there’s limitations relative to them,” Hetzel said, in summarizing standards’ role. “They are qualitative, they’re quantitative, they do provide a standard by which you can compare different things, performance wise. Unfortunately, you cannot say for certain that, if I take the highest-scoring cushion with these standards, I can just put that underneath client B and let them go and know that they’re going to be safe. It’s just not going to happen.

“But when you look at that category of cushions and look how it does in standards, it can help you to do a more accurate side-by-side comparison and add that to your toolbox of things you can be considering in making a choice or helping a consumer towards the best choice.”

This article originally appeared in the Mar/Apr 2022 issue of Mobility Management.