Deep Tissue Injury Research, Part I

Pressure Ulcers: A New Perspective

They’re not a new medical condition, and healthcare professionals have been dealing with them for so long that multiple terms have been coined for them. Bedsores. Decubitus ulcers. Pressure sores. Pressure ulcers.

But in research published in Mobility Management last year (JuneAugust and September 2014 issues), Amit Gefen, Ph.D., shed important light on the hows, whys, whens and wheres of tissue deformation and how this internal deformation can cause Deep Tissue Injuries (DTI) that can be even more insidious than traditional pressure ulcers — because they’re typically harder to identify and observe in the usual ways.

This year, we start a new research series based on new conversations with Gefen as well as with his colleague Kara Kopplin, BSc, the Senior Director of Efficacy Research, Standards & Compliance for ROHO Inc. The series will explore the role of tissue deformation on skin and tissue health, and will extrapolate from last year’s research.*

A Different Background, a Different Approach

Gefen is a professor of biomedical engineering at Tel Aviv University. His Ph.D. and master’s degrees are in biomedical engineering, while his bachelor’s degree is in mechanical engineering.

That background resulted in Gefen adopting an unconventional, but very effective approach in trying to understand the forces within the body that lead ultimately to skin breakdown. While studying chronic wounds during his master’s research, Gefen investigated how the bones of the foot and the soft tissues within the foot interacted. He also noticed that the chronic wound field lacked the large bodies of research that one could easily find in other healthcare specialties, such as orthopaedics or cancer. “I decided I would focus on that and try to bring the tools that mechanical engineers use, like computational modeling,” Gefen said. “Mechanical engineers use a lot of computational tools, computer tools, to try to describe how complex structures behave.”

Computer simulations offered a way “to look at how loads develop in tissues, not only on the surface of tissues, but also internally, where you can’t look,” Gefen explained. He also used laboratory-generated human tissue, subjecting that tissue to forces and loads that clinicians can expect to see in wheelchair users. Those tissues substituted for human subjects, thus circumventing a chronic challenge for researchers in the complex rehab industry: The relatively small number of clients to test and examine.

Gefen also called upon other tools common in the medical field, though not necessarily to the seating & wheeled mobility niche. One very helpful device was an “open” style of MRI machine, which enabled subjects to be scanned while sitting upright — first on a rubber tire, then directly on the flat MRI surface. When subjects sat on that surface, Gefen noted, “You can see that the muscle is deformed to at least 50 percent of its original thickness.”

Why Tissue Deformation Is Crucial to Pressure Ulcer Discussions

On this year’s series, Gefen said, “It all builds on the research that we discussed last year. If you remember what we discussed last year, it’s essentially the role of tissue deformation. And we covered the seating studies that we did with an MRI, looking at tissue deformation with the MRI being the tool to measure tissue deformation in human beings and how you extrapolate from these measurements of tissue deformation some measures of tissue tolerance by using, say, animal models or tissue engineering models — where you apply the same mechanical loads that you are observing in the MRI and then to approximate how the tissues respond to that and whether they stay viable or not.

“And then we went to the cellular level and looked at what exactly happens to the cells that kills them. We found that these deformations are basically compromising the control of transport through the plasma membrane of the cell so after certain times, the walls of the cell, the plasma membranes, become more permeable.”

That conclusion — that deformation eventually causes tissue damage that happens internally, where it’s difficult or impossible to detect using conventional observational methods such as checking for a change in skin color — sounds simple. But it potentially evolves how pressure ulcer formation and therefore prevention should be understood and approached.

“If you want to protect tissues, what you really need to do is to minimize tissue deformation,” Gefen said. “Minimize tissue deformation as opposed to minimizing interface pressures. It’s not the same thing. If you look at interface pressures, you basically look at just the skin. And you can’t really tell what’s going on in [the body].”

Taking Gefen’s findings into consideration, the commonly used term “skin breakdown” seems somewhat imprecise. Gefen suggested that “tissue breakdown” is a far more accurate term. But skin breakdown is really how the industry has come to think of pressure ulcer formation. HCPCS codes and related funding, for instance, describe wheelchair seat cushions as “skin protection” models. In reality, protecting skin doesn’t seem to even come close to ultimately understanding the entire picture.

As Kopplin pointed out, “Skin we can protect easily. But the internal damage….”

*Editor’s Note: Stay tuned for part II of this year’s series. Download a free pdf containing all three of the 2014 research columns.

This article originally appeared in the August 2015 issue of Mobility Management.

About the Author

Laurie Watanabe is the editor of Mobility Management. She can be reached at

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