Note: This article is written and published in Ukrainian and is a translated version of the original published here.
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The place of CAE in modern medicine.
Benefits of using CAE in medicine
- Development time: reduction up to 9 times
- Total amount of production costs: reduction up to 4 times
- Warranty service cost: reduction up to 89%
- Number of critical changes after the start of production: reduction to 2.5x
- Percentage of successful new product launches: an increase of 67%
What is the result? We have a number of figures that say that the efficiency of using calculation technologies is very high. These figures were not invented by the author of the publication. They are "brazenly" "torn out" from the reports of companies that conducted surveys among doctors and companies that use calculations (for the development of medical equipment). As you can see, the efficiency is sometimes even higher than that of machine builders. A little later it will be clear why.
The complexity of the prosthetic problem, from the point of view of computational mechanics
It is about why the efficiency is higher, we will now talk. Let's explain why various medical CAE calculations (using biomechanics as an example) are very, very complicated.
The fact is that, as already mentioned, each person is unique: we are all of different heights, different weights (someone has a "wide and thick bone"), different physiques. And, accordingly, we have different geometries (organs, bones, etc.) and different properties of the materials inside us. At the same time, even for people living in different regions of our world, the average "percentile" - 50 (average height/weight), 5 (minimum height/weight) and 95 (maximum height/weight) are also very different. That is, all the characteristics "jump" from person to person, finding any one solution that will help absolutely everyone, by default, is quite a difficult task. Moreover, even if we have one person (with approximately similar weight and geometric dimensions), over time, the characteristics of his internal organs, musculoskeletal system change in both directions, may improve, or may worsen. In general, even for the same person at different points in time, they are very different.
The complexity of the prosthetic problem, from the point of view of computational mechanics
We have a very big problem. It lies in the fact that when we list all the parameters that we have and which must be taken into account, then their values sometimes differ not in percentage, but by orders of magnitude. Not even at times, but by orders of magnitude, that is, we get a very large range in which we can get as a result. And the problem is that such a result is not suitable for a particular person. For him, you need to develop a specific object that will be inside him and will suit him (despite all possible variations in the values of the characteristics of his body) and only him.
That is, our task, as in the old proverb, is to pull a camel through the eye of a needle.
For a researcher who is not given a practical task, this is a "super" task! Everything is in order. Whatever you count, they hit everywhere ("and what is there to hit - 10 barrels and the whole sky in parrots" (c)). But for the practitioner, taking into account that it then needs to be implanted in a person... The task is difficult, because, as they say, you need to be "responsible for the bazaar".
The complexity of the prosthetic problem, from the point of view of computational mechanics
Another problem is that the geometry of humans is quite complex. Now we are getting it using MRI. The result is a bunch of cross-sections (with a fine pitch) of a person. And these sections show the density at each point. Accordingly, it is possible to restore the geometry of a person (and his organs, bones, etc.) with high accuracy.
The complexity of the prosthetic problem, from the point of view of computational mechanics
On the slide we see a large number of bones, cartilage and the rest. It can be seen that they are all curvilinear, but it is not entirely clear how "scary" it is in life.
The complexity of the prosthetic problem, from the point of view of computational mechanics
And in life, if we analyze the curvature of at least one "simple" vertebra, we will see that this geometry is very, very complex.
The complexity of the prosthetic problem, from the point of view of computational mechanics
And if at the same time we also remember that the vertebra is not integral (monotonous in characteristics), like any bone, there are several additional materials inside it (the vertebra) ... Of course, the task is further complicated. It becomes even more "fun" from the fact that the materials that we have in the vertebra, in particular in the entire musculoskeletal system, differ in characteristics by orders of magnitude (not only by themselves, but also among themselves). Let's say that the cortical layer of bone (outer) is about 20 times stiffer than the spongy tissue that is inside. And the disc that is placed between the two vertebrae differs from them in density by a bunch of orders of magnitude (from the spongy bone by more than 100 times). From the point of view of mechanics, we get different "scales" of deformations and stresses.
The final problem turns out to be extremely difficult, both in terms of building a finite-element grid (due to complex geometry, which also needs to be created), and in terms of obtaining correct results, and even their analysis.
The complexity of the prosthetic problem, from the point of view of computational mechanics
In addition, all these objects can "break", for example, a vertebra can break.
Formulation of problems of multivariate research
And then it needs to be replaced with some kind of prosthesis. The slide shows an example of a "cage" (endoprosthesis). And on the right, an example is shown not only of geometry or calculation, but of experimental research using holography (holographic speckle interferometry), because in life there are so small deformations that the results of computer calculations need to be measured with something highly accurate.
The complexity of the prosthetic problem, from the point of view of computational mechanics
And here is another example when it is not the vertebra that is broken, but the intervertebral disc. And instead of a disc, you can make a variety of designs. Some of them (including Western ones), unfortunately, do not guarantee the desired result. Ie. "Fashionable" and very expensive dentures for disc replacement lead to the fact that after a while they overgrow and as a result we have several "fused" vertebrae. At the Sytenko Institute, designs were invented, which are shown here in a very simplified way, because at the time of writing this patenting process was taking place and they asked not to show in more detail. But in this case, we are talking about the fact that, using modern calculation technologies, it is possible to create structures that will work as they should.
Formulation of problems of multivariate research
And what is the main idea of all these calculations? In the end, all decisions are made equally by the "surgeon". But without computer calculations, he takes them simply "by eye". And how does it happen? He underwent surgery. Did it go well? So they remembered. Did you have to reoperate? Something needs to be changed.
This, unfortunately, is not the best variant. However, the use of computer calculations allows you to better understand the processes taking place inside the body, and it is better to select the necessary parameters in order to correct the consequences of unsuccessful operations less times.
Formulation of problems of multivariate research
It should also be noted that problems are not only with the spine. We often have problems in our legs. It can be the hip joint, knee, ankle. And it is not always important to evaluate the complete replacement of some element. Sometimes we need to evaluate the structure that is needed for a while while the broken bone is fused.
There are also neck problems. I think many people have seen similar designs. This is a cervical orthosis. And they are very different. Unfortunately, people who walk in such orthoses, to put it mildly, are very uncomfortable. And therefore, we have the task of creating orthoses that are more pleasant to wear, at the same time not too hard, nor, on the contrary, too soft.
Formulation of problems of multivariate research
To do this, it is necessary to completely model the entire neck, along with the geometries of the orthosis, vertebrae, etc.
Formulation of problems of multivariate research
Thus, in order to select prostheses and choose a high-quality solution for a particular person, it is necessary to perform a fairly large number of calculations, because the parameters of the materials may differ by several orders of magnitude. And the surgeon cannot determine on the basis of MRI analysis alone what properties each material has in the current patient. That is, you have to take an approximate average value (based on MRI and experience) and vary within certain limits in order to get a whole range of different calculations. It is also necessary to vary the different geometric parameters of the prostheses and see if they correctly replace the damaged element.
Formulation of problems of multivariate research
Material parameters:
- Mechanical properties of RSA materials:
- Young's modulus: ± 5 - ±30%
- Poisson's ratio: ±5%
- Full-functional/damaged element
- A variety of prosthetic options
- Geometric parameters of dentures
- Mechanical properties of prosthesis materials
As a result, it turns out that we can do and get two fundamentally different (in terms of content) fields of results.
Formulation of problems of multivariate research
"Green" indicates results for an "ideal" (healthy) musculoskeletal system design or internal organs that work "like new". That is, we vary the parameters and get as a result the boundaries within which a good, normal "design" works. And we also model with various violations, and we get a "gray" area - the area of "bad" results.
To some extent, they can intersect, but in general, our task is to design the design of a prosthesis that will replace the damaged part of the body in such a way that it does not enter the "gray" zone and at the same time does not leave the "green" one.
Since such calculations are complex and large, many calculations are initially tried to be made as simplified as possible. The slide shows an example of such a simplification. This is not a sideways chair (as you might assume). It is difficult to guess what it is if you have not encountered such calculations. But these are two vertebrae, an intervertebral disc and an element that holds the vertebrae together. These calculations are given on the website of Algor (which was bought out at one time by Autodesk). Here you can clearly see that the vertebrae are "somewhat" different from the real ones, but these calculations are also important, because they allow you to weed out a large number of different incorrect (design options). That is, the transition to more accurate and complex calculations can be done at the end.
Some of the results obtained in Nastran In-CAD
The slide presents only examples of strains and stresses for only different types of one particular "cage".
Note: This article is written and published in Ukrainian and is a translated version of the original published here.
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