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.”