Studying the Unstudiable
From ancient ancestors to clinical insights, Dr. Amanda L. Smith, PNWU’s new assistant professor of anatomy, bridges disciplines.
I am Dr. Amanda L. Smith, and while I teach anatomy at PNWU, I also study the unstudiable.
What do extinct human ancestors and modern human patients have in common? We can’t do experiments on them.
Or can we?
My background is in paleoanthropology and evolutionary biomechanics. In my work, I have had to make inferences about the relationships between anatomical form (shape) and function (behavior and performance). This is made especially challenging by the fact that I can’t observe the behaviors I’m interested in -- because the animals are extinct. I can’t even test these relationships with fossils directly: the fossil remains of the specimens I study are delicate and irreplaceable, so I can’t run mechanical experiments on them.
That’s where methodological innovation comes in. New technology allows me to build virtual 3D models of fossils and even patients!
To build these models, I use high resolution CT scans to capture external and internal anatomical details. Part of this process can be done automatically, but it nearly always requires manual input by someone who understands the anatomy of the structure to build a clean, three-dimensional model.
Why build 3D models? Once I have a three-dimensional model, I prepare it for finite element analysis. This is an engineering technique that helps us understand how intricate structures respond to loads, like muscle and bite forces. It’s the same technique that engineers use to evaluate the structural performance of bridges and airplanes. Finite element analysis (FEA) requires that I partition our complex model into many simple geometric elements. By doing so, I can approximate stresses and strains in the model in ways that were exceedingly analytically expensive or even impossible without the aid of modern computers and commercially available software.
Thus I can simulate different feeding behaviors, like chewing and biting, and look at how different factors like skeletal shape, the force and direction of muscles, and the material properties of the bone affect strain distribution.
Biomechanists are interested in strain, not only because it can cause bone to fail, but also because it can cause bone to grow! I work with bone biologists to understand how bone cells respond in different ways to different types of strains. This helps us understand how bone responds dynamically to loads during use, which is especially important if we want to help patients maintain healthy bone quality and function. Some of the data on bone properties goes directly into my models; some of it is used to interpret my results.
From Lab-Bench to Bedside
My background in paleoanthropology sparked an insatiable evolutionary curiosity, which led to a lot of questions. Questions like, “Did these giant zygomatic arches and robust paranasal pillars and struts make our beefy-skulled ancestors better able to eat hard and tough foods?”
This methodological toolkit can also be applied clinically to help living patients right now. We can use 3D modeling and finite element analysis (FEA) to ask how changes in shape due to injury or surgery (like cleft palate and jaw fracture repair) lead to changes in the way someone chews.
One of the research projects I’ve been working on for the last few years is a broad comparative analysis of the mandibles of anthropoid apes, including humans, chimpanzees, gorillas, and orangutans. These are closely related species that are similarly shaped overall, but they have differences in their diets, and each have subtle anatomical features that scientists have considered dietary adaptations. I want to know whether any of the differences in shape are related to differences in function, like strain pattern and magnitude or bite force efficiency.
Digital experiments like this can both bolster the basic science and help us understand whether subtle differences in the shape of the jaws may influence feeding function in humans.
The first paper related to that project, Comparative Biomechanics of the Pan and Macaca mandibles during mastication: finite element modeling of load, deformation and strain regimes, was just published in Royal Society Interface Focus.
Much of what we know about orofacial mechanics is based on experimental work done on macaque monkeys. Scientist have worked with macaques because they have similar jaw shape and chewing behavior to humans. This research has driven clinical treatment for more than 50 years, and the foundational knowledge has allowed clinicians to successfully treat countless patients.
But we haven’t been able to evaluate precisely how similar the masticatory dynamics of macaques and other great apes (including humans) are because we can’t repeat those in vivo experiments on humans or other great apes. With FEA, however, we can repeat them in silico! So, we can evaluate differences on a species level to ask: How good are macaques as models for human feeding? And we can evaluate differences between individuals to ask: How good is a single human “template” as a model for feeding in all humans, or in a particular patient?
That leads to another exciting project I’m working on: Looking at cleft palate mechanics, which enables me to use 3D modeling and FEA to help clinicians and their patients. By analyzing cleft shape from several hundred patients, we can identify shape variation that we can then incorporate into our models. From there, we can characterize differences in palate mechanics related to cleft shape that may influence the success of specific repair techniques.
With access to high-quality medical imaging, we can simulate different types of interventions to build data-driven, patient-specific treatment plans, increasing the likelihood of positive outcomes!
I plan to maintain my active collaborations with colleagues in evolutionary biomechanics, not only because I love the research, but because I’m enthusiastic about pivoting to pursue answers to more clinical questions here at PNWU. I look forward to working with students and building collaborative relationships with local clinicians.
P.s. It doesn’t have to be all about jaws! Let’s do some biomechanical science!!
Amanda L. Smith, PhD
Assistant Professor of Anatomy
Pacific Northwest University of Health Sciences College of Osteopathic Medicine (PNWU-COM)