How Evolving Testing & Standards Could Impact the Future of Adjustable Cushion Codes

testing a cushion


The first design requirement for adjustable wheelchair seat cushions is to meet the “skin protection” test required by the PDAC [Pricing, Data Analysis & Coding contractor], which is a method of immersion testing defined internationally by ISO 16840-2 and specifically in the United States by RESNA Standard for Wheelchairs — Volume 3: Wheelchair Seating, section 2.

This simple test uses four cylinders connected by a strap to represent the ischial tuberosities and greater trochanters with the idea that with an applied weight, the cushion should be tall enough or contoured enough to immerse and support this fixture, which represents the general dimensions of the pelvic bones, without “bottoming out.”

Some other requirements about the cover, flammability and moisture resistance are common across all skin protection cushions. But to be distinguishable as “adjustable,” thankfully there is guidance language in the code that wasn’t there a few years ago.

The PDAC has clarified that adjustability must be “related to skin protection properties of the cushion,” so the adjustability must be clinically beneficial, essentially in the pelvic loading region of the cushion. This can be accomplished with a variety of materials that can be added or removed, including the addition or removal of foams or other materials, such as fluids (air, gas, liquid or gel) that provide immersion. In all cases, the cushion must be adjustable “out of the box” (with all pieces or mechanisms included) and be likewise adjustable over time, to continue to provide skin protection as the person gains or loses weight or muscle tone.

Variation in Performance & Clinical Outcomes

The tests and guidance language appropriately allow for a wide variety of material and product solutions, but unfortunately, the performance and clinical outcomes of the cushions in these codes vary greatly, as do the costs.

Since they are all categorized together, it’s easy to assume the performance is identical, and we know from published clinical trials, and from bench tests of pressure mapping and other measures, that the benefits (and risks) across this category are drastically different.

For example, just performing a simple pressure mapping with an ISO indenter can reveal a very surprisingly broad range of contact areas (an indication of envelopment), as well as average and peak pressures. Clearly these cushions are giving varying levels of performance and protection. Costs of course vary widely with the quality, and unless providers have a deep understanding of the cushion choices in the code, they may often choose the lowest-priced option, assuming it’s “just as good” as any other.

The ISO wheelchair seating committee (WG11) and the RESNA standards committee on Wheelchair and Related Seating recognize there are “opportunities for improvement” to better test and assess the benefits of cushions, especially those that provide skin and soft tissue protection. For example, the updated RESNA WC-3 standard now includes a standardized test for envelopment, to provide additional insight into the cushion’s ability to not just immerse, but to envelop the person, which is critical for prevention of pressure injuries, including deep tissue pressure injuries. This method mirrors the ISO 16840-12 envelopment method, and we hope that new data collected from this method can help us better understand the varying performance levels of cushions in this code.

Durability: Year Five vs. Day One

Another requirement that needs more clarification is regarding durability of cushions over time.

Most beneficiaries can only receive a new cushion every five years, so it’s important that a cushion performs as well at year five as it did on day one. The PDAC recognizes this, and in fact requires the immersion testing to be performed twice on a cushion — before simulated aging, and after. The problem is that the code doesn’t indicate how to do this aging. The ISO wheelchair seating committee published a simulated aging standard just a few years ago, ISO 16840-6, which offers a selection of tests to measure key characteristics of a cushion, followed by a way to simulate aging (via cyclic loading, laundering, disinfecting, simulated soiling, ozone exposure, and more), followed by re-testing. The thought is that after going through these challenges, the cushion should still give the same performance, as indicated by similar test results, before and after. A U.S. version of this standard was also approved by the RESNA committee for publication in WC-3.

Common Goals for Cushions

As chair of the RESNA Wheelchair and Related Seating standards committee, it has been wonderful to have so many clinicians, researchers, educators, end users, and manufacturers working together to develop tests we hope are meaningful and clinically relevant, with the goal of assisting providers and clinicians in selecting the best solutions for their clients, beyond the current coding classifications.

What has been particularly exciting is that we have had consistent committee participation by two FDA representatives keenly interested in this same goal. Our hope is that as we develop new standards, they can be properly applied to prescription, regardless of the material or technology that is used, based on the objective, clinically relevant performance measures. We welcome anyone who has an interest in this work to join our committee!

This article originally appeared in the January 2019 issue of Mobility Management.

About the Author

Kara Kopplin is Director of Regulatory Science for Permobil.

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