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As deadly as pressure ulcers can be, it is remarkable how poorly they have been understood and how common they remain. But some groundbreaking research coming out of the laboratory of Dr. Amit Gefen at Tel Aviv University in Israel is changing that.

Dr. Gefen is a Ph.D. in biomedical engineering whose lab has done industry-changing work over the last decade in the etiology of pressure ulcers, in coordination with other leading scientists around the world. The work has provided a much better understanding of a particularly dangerous and difficult-to-detect kind of pressure ulcer -- the kind caused by deep tissue injury, or DTI. The key insight: these injuries are caused primarily by tissue and cell deformation, not ischemia. Ischemia, or lack of blood flow, acts as a secondary factor, rather than a primary cause.

This new study from Dr. Gefen’s lab revealed important insights about the best ways to prevent these deformations -- and therefore these DTIs -- in wheelchair users. The findings are significant not only because of the size of the wheelchair user's population – about 3.3 million Americans (over the age of 15), but also because of the healthcare system’s cost in treating pressure ulcers – over $11 billion annually. The study is also an important development to guide clinicians because of the dearth of information in recommending the best cushion to protect their clients. The new study offers the first tissue deformation comparison between two commonly used cushion technologies – foam-based (representing the largest number of cushions in use) and ROHO's air-cell-based (ACB) technology.

The research was published in Journal of Tissue Viability’s February 2014 issue. I partnered with Ayelet Levy, a graduate student in Dr. Gefen’s lab, as well as Dr. Gefen to author the article. Dr. Gefen holds an unparalleled level of subject matter expertise and is the current president of the European Pressure Ulcer Advisory Panel (EPUAP).

This study required that the investigators analyze data far beyond mere contact pressure measurements, which assess pressure at the skin-cushion boundary and literally give only superficial information. Understanding what happens deep within the body, where DTI’s occur, makes it necessary to use a sophisticated analytical tool that evaluates internal soft tissue loads in the buttocks.

That tool is called finite element (FE) modeling. A complex but well-established way of using computer models to predict mechanical stress and strain outcomes in the engineering and medical worlds. FE modeling has previously been used to analyze the biomechanical performances of basic foam cushions. However, this latest study was the first to use the technique to evaluate the performance of one of the most complex cushion structures on the market --ACB.

The new study specifically provided a detailed performance comparison between a ROHO QUADTRO SELECT HIGH PROFILE Cushion and two flat, foam-based cushions with varying stiffness properties (7 kPa and 10 kPa) for individuals with a spinal cord injury (SCI). SCI patients represent a key segment of the wheelchair user population. Many have been victims of accidents and face their entire future using a wheelchair. Yet roughly one in ten of these patients will die from a pressure ulcer, and many others will be affected and suffer a reduced quality of life.

The investigators therefore used an MRI slice from a 21-year old SCI patient to develop an anatomically-realistic model of the patient’s left buttock.  15 variants of the computer model were created to represent the different kinds of muscle atrophy, spasticity and bone-flattening that occurs in patients with SCI, as they live their lives seated.

For all three cushions, immersion was calculated as the percentage of skin surface in full contact with the cushion. Higher figures represent more surface area for load transfer, and potentially lower internal tissue loads. The different mechanical stresses – compressive, tensile, shear and effective stress – were calculated. Measures were recorded for each individual model, in the muscle, fat, and skin tissues under the ischial tuberosities during sitting, to determine the risks for the specific internal conditions.

The results were dramatic. For the ROHO's ACB cushion, immersion was consistently in the 91-93 percent range; for the foam cushions, the range was 58-65 percent. And the consequence was that all of the peak stress components were four orders of magnitude – 10,000 times -- lower for all three kinds of tissues in the ACB cushion than for the foam models.

Moreover, bone flattening led to higher peak stresses on muscle tissue in the foam cushions, but lower stresses for the ACB cushion. Likewise, muscle atrophy substantially increased fat and skin stresses on foams, but substantially decreased them on the ACB cushion. Both of these sets of results demonstrate that as the patient’s condition worsened, the ACB cushion decreased the risk even further in comparison to a foam support.

More research is needed to understand how body movements and positions affect internal tissue deformations and stresses. Additionally, research needs to explore how other cushion technologies, such as custom foam, gel and honeycomb-like cushions, affect the patient’s risk. In the meantime, these findings clearly suggest that the ROHO's ACB cushions provide much longer safe sitting times than foams for wheelchair cushion users.

This new understanding of the role of tissue deformations in the formation of DTIs needs to be applied to wheelchair cushion policies. The current standards for wheelchair seating and the cushions are inadequate in delivering appropriate protection. Even cushions categorized as "adjustable skin protection cushions” can present a wide range of risk or protection, since unfortunately, they are not categorized by how well they minimize tissue deformations.

With the existing broad cushion categories, and this new, yet evolving understanding of the causes of DTI, clinicians often treat cushions as commodities. Therefore they can be lead to recommend the cushions that have the lowest possible price, thinking all cushions are equal, and not realizing the hazardous situation they might be prescribing to their clients.

A policy of choosing the cheapest solution without evaluating the risk to the patient is extremely shortsighted and even irresponsible. Other than the suffering and life-risking conditions, the total cost for managing a single full-thickness pressure ulcer can be as high as $70,000. More importantly, such an approach can lead to needless maladies and death.

This new and groundbreaking work is already providing the evidence for a critically needed change in direction, toward prescribing better and safer sitting solutions.

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