Skull‐Brain Biomechanics of Headbutting. An XROMM Pilot Study on Goats

Abstract

In humans, the coup‐contrecoup injury occurs opposite the site of impact when the brain meets the skull, causing intracerebral hemorrhage. It makes up a significant portion of traumatic brain injuries (TBI) and can often lead to neurodegeneration. Bighorn sheep and related bovids are known for their impressive headbutting rituals performed during the rut, the general belief being that these animals come away unharmed from these encounters. However, a recent immunohistochemical study revealed TBI in bighorn sheep and muskoxen in relation to headbutting. With a large gyrencephalic brain, repetitive headbutting, and a pathology pattern resembling early chronic traumatic encephalopathy in humans, bovids present themselves as a significant model for TBI. It is, however, uncertain whether bovids sustain coup‐contrecoup injury due to the oblong shape of their braincase and tight fit to the brain. We aimed to investigate whether cranial and neuroanatomical aspects of the bovid head anatomy contribute to TBI reduction, using goats as a model to measure brain movement independent of the skull upon impact.Four cadaveric goat heads were implanted with radiodense tantalum beads in the skull and brain. A weight‐drop system was used to create an impact within the field of view of a biplanar fluoroscopy system. The heads were CT scanned and the recording was reconstructed as an animated 3D model using x‐ray reconstruction of moving morphology (XROMM). The brain markers were tracked relative to each other to account for soft tissue deformation and marker migration and relative to the skull markers to account for brain movement. We were able to visualize how the brain moves in relation to the skull for the first time in bovids, providing a better understanding of skull‐brain biomechanics.