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As part of an anatomical research study investigating the function of sinuses in vertebrate animals, finite element analysis is being used to simulate the effects of headbutting on the skull of Capra hircus, the domesticated goat. (Photograph courtesy of Luis C. Tejo, Buenos Aires, Argentina.) |
Farke used ALGOR FEA software to analyze the effects of strain on the brainpans of goat skulls. Testing a commonly held, but essentially untested, hypothesis that sinuses act as shock absorbers for the brains of horned, head-butting vertebrates, the FEA results led Farke to conclude that, to the contrary, the presence of sinuses in the skulls of horned vertebrates have little to do with shock absorption and, in fact, may actually weaken the skull roof and increase strain within the cranium. Apparently, the large sinuses of goats play no major role in protecting the brain from blows to the head caused by headbutting. These preliminary findings have opened up other questions and possible answers about sinuses in goats—and probably in humans too.
Evolution of a Research Project
Farke wanted to answer some basic questions about sinuses in vertebrate animals. What purpose is served by the sinuses? What is their function and why did they evolve? What, if anything, is the unifying principle that explains their presence? As a student of anatomical development, Farke knew that bovids, the group of horned animals including the goat, have evolved sinuses on three separate occasions in the course of their existence. Given this persistent presence, he reasoned that the sinuses must have some definite function. He chose to study the domesticated goat because primary research has been done on their skulls and data is available from strain-gauge experiments. In 1995, Carolyn Renzulli Jaslow and Andy Biewener did research by dropping lead weights on dead goat skulls and measuring the impact with strain gauges.1 While their data would serve as a baseline for comparison, they were unable to place strain gauges within the sinuses and there is no way to get information from the brain cavity without damaging the skull. Given earlier research using ALGOR for the study of monkey skulls at New York College of Osteopathic Medicine and the practical and ethical limitations of doing physical testing on live goats, Farke decided to use FEA to study the impact of headbutting on goat braincases.
Modeling Three Versions of the Goat Skull
The decision to use ALGOR software for the testing phase of Farke’s research was based on an extensive evaluation of several FEA programs. He chose ALGOR based on its compatibility with a large number of CAD solid modelers and for its portability across various hardware platforms and operating systems—he planned to run all of his simulations on a laptop computer running Windows XP. With funds from the Jurassic Foundation, a not-for-profit organization dedicated to providing funding for research on dinosaur paleobiology, which is also part of Farke's research, he purchased ALGOR FEA software.
After obtaining a fresh goat skull with its soft tissue intact, the next step was to run a CT scan for an image of its internal geometry. Using SolidWorks, Farke then began to model the skull based on the CT scan. He decided that three distinct models would be necessary in order to test the hypothesis that the sinuses act as shock absorbers for the brain. The first model was a skull with solid bone in place of the sinuses. The second model included the sinus cavities, but without the bony sinus struts or bony septa that act as supports for the sinuses. In the third, he modeled the sinus cavities with the bony septa —or in other words, the actual goat skull. The three skulls allowed for a comparison of deflection and strain in terms of the lack or presence of sinuses and their bony septa.
CT scan information of a goat skull with its soft tissue intact was used to generate a CAD solid model in SolidWorks. |
Defining and Analyzing the Skulls
Next, Farke opened the skulls in ALGOR. He defined the material properties of the skull using bone data determined in the primary literature. The loads and constraints for the analyses were taken from estimated values also found in the literature for the peak impact event of headbutting.
He fixed the base of the skull as a boundary condition on the assumption that at the time of impact, the neck was stiff. Such a fixed variable was necessary in order to conduct these preliminary tests on the skulls themselves, without complicating factors. He then applied the impact as a single, static stress event and measured the deflection of the craniums.
An ALGOR FEA results display shows contours of von Mises stress in the goat skull from the impact of headbutting. Preliminary FEA results indicate that the presence of a sinus actually weakens the skull roof and increases strain within the skull. |
Farke compared results from the first two skulls to see what effect, if any, the sinus cavity had on the strain impact to the brainpan. With a future analysis of the third skull, Farke will be able to compare the skull with no sinuses to the skull with sinus cavities as well as the actual skull with sinuses and their bony septa.
Conclusions
Given a comparison of the results from the first two skulls, Farke's preliminary FEA simulations indicate that the presence of a sinus actually weakens the skull roof and increases strain within the skull. Thus, the large sinuses of goats apparently play no major role in protecting the brain from blows to the head. Rather, Farke's research indicates that the sinuses may compensate for the added weight of the horns, thus serving the function of making the goat's head light enough to be supported by the animal's neck. Farke's research suggests that sinuses are not shock absorbers, but rather nature’s way of compensating for excess bone mass. In humans, the sinuses may similarly compensate for the heavier upper, maxillary jaw bones required for the support of the brain and the omnivorous diet.
Andrew Farke is a Ph.D. candidate in the Department of Anatomical Sciences at Stony Brook University in Stony Brook, New York. As part of his doctoral dissertation research, Farke used CAD and FEA software to model and simulate the effect of sinuses on the strength of a domestic goat skull during headbutting. |
When asked about the importance of ALGOR software for his research, Farke is unequivocal: "ALGOR made it possible. Without ALGOR, I would never have been able to study the role of sinuses in domestic goats nor gain insights about their function in other vertebrates. Given its CAD compatibility and portability across various hardware platforms and operating systems, ALGOR is an essential research tool. I will continue to use it for my dissertation research and beyond."
1 Jaslow, C. R., and A. A. Biewener. 1995. Strain patterns in the horncores, cranial bones and sutures of goats (Capra hircus) during impact loading. Journal of Zoology 235: 193-210.
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