Page 24 - Mobility Management, February 2017

ATP Series
What We Know About Pressure
Gefen: Human beings are not symmetrical to start with. But sometimes, a condition or a comorbidity may worsen that or make differences larger.
People have used pressure mapping a lot in the past to capture asymmetries in posture and in the structure of the buttocks. Some of the information you wouldn’t be able to capture with a pressure map because the pressure map only shows you asymme- tries that present themselves on the surface of the skin, because that’s where the measurement is taking place. Asymmetries deep within the body — for example, an asymmetry in the left to right
It is the anatomy that has the strongest influence on the state of mechanical loads in tissues, particularly the peak loads in tissues —Amit Gefen
ischial tuberosities, say in the sharpness or the shape of the bones — wouldn’t necessarily manifest in a pressure mapping measure- ment. Because you have all these soft tissue thicknesses that kind of mask the information in the deep tissues. So you may have serious differences and exposure to mechanical loads around these bony prominences because they’re not identical (because they’re asymmetric), but you can’t really detect that informa- tion when you’re far away from that site, that is, when you’re measuring quantities on the surface of the skin.
Akins: As an example of that, there are cases in this study where we found that some people sat on muscle on one side of their buttocks and did not sit on muscle on the other side. They sat on adipose tissue, on fat tissue.
Gefen: Pressure mapping wouldn’t necessarily show you that. Because the pressure mapping doesn’t know that on one side there is muscle tissue, and on the other side, the bone is actually covered by fat.
Q: How Do MRI & Ultrasound Differ in the Information They Provide?
Akins: I think one thing to pull back into consideration is the sharpness of the ischial tuberosity, and that can play into that asymmetry. One of the interesting findings is how we were able
to use ultrasound more reliably to obtain the radius curvature compared to our T1-weighted MRI images. We found actually poor reliability between raters of obtaining a “good” radius curvature. And that was due to the inability to differentiate between cortical bone and the musculotendinous junction. We could have used a different type of MRI image, T2 weighted, to potentially solve that issue, but we can easily see that and measure that structure with the ultrasound.
So from a clinical perspective, that could be something very
useful: to not only see that asymmetry of how they sit, but what is that sharpness, that radius curvature between the two sides?
Brienza: How the tissue compresses and how the loads are distributed varies based on posture and how the pelvis is tilted at any particular point in time. But those anatomical features of the bone itself are going to be constant. So if you find a person with
a very high radius of curvature, indicating a high-risk situation, then you know to take some special precautions for that case. Pressure mapping might not detect this risk factor.
Maybe they were leaning to their good side when you took that pressure map. So you didn’t see that stress concentration, that pres- sure concentration because the weight was distributed away from it.
Consider the bone shape as a fundamental piece of informa- tion that’s going to help determine how the load is going to be distributed in the tissue beneath that bone. And the other thing that Jon said that is really important: The ultrasound is perhaps a better methodology for measuring bone curvature because you can’t distinguish between the muscle junction with the bone and the bone itself in the type of MRI imaging we performed.
Q: Does Ultrasound Technology Offer Practical, Operational Advantages?
Gefen: What we should also take into account with regards to imaging technology: MRIs are probably not going to be much smaller than they are today. There are some miniature MRIs, but I don’t see an MRI system going into someone’s pocket.
With ultrasound systems, there is huge potential — you can see the technology going there, where we end up with devices that look like pens that we can stick in our pocket. We can talk to our cell phone using a Bluetooth connection, and we will put that pen-like device on the [patient’s] skin, and you’ll see what’s going on internally on the screen of your cell phone.
So looking at where technology is going and trying to extrap- olate for the future, we should consider that risk assessment
tools as we know them today are going to be totally different 10 years from now, maybe five years from now. As technologies are able to look at deep tissues, I’m sure that ultrasound will play an important role. And essentially, we’ll end up with risk-assessment tools that are able to take into account anatomical features that we’re not taking into account using existing tools.
For example, in many of the existing risk-assessment tools,
you take the nutritional status of the patient into account by measuring the BMI [body mass index]. BMI is essentially an anatomical feature which is rather easy to assess: You just need
to measure the [patient’s] weight and height. If you could assess, for instance, the sharpness of the ischial tuberosities as easily as you would measure someone’s weight or height, you could have a critical piece of information for the risk assessment because you know the ischial tuberosities can be as sharp as a nail or as blunt as the bottom of a cup. If you can measure that, then you know this individual is at higher risk for developing a deep tissue injury because [the IT] looks like a sharp nail. That would immediately
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