Horn and horn core trabecular bone of bighorn sheep rams absorbs impact energy and reduces brain cavity accelerations during high impact ramming of the skull.

UNLABELLED: Bighorn sheep (Ovis canadensis) routinely experience violent impacts to the head as part of intraspecific fighting. Dynamic 3D finite element models of the skull and horns of a male bighorn sheep were developed to gain an understanding of the roles that the horn and bone materials and structure play in absorbing the impact that occurs during ramming. The geometry and volume mesh of the model were derived from CT scan images. The models included the horn, bony horn core, and bone of the skull. The horn core fills a portion of the hollow horn and consists of a thin cortical bone shell filled with foam-like trabecular bone. Two modified models were also created: one with the distal half of the horn length removed to assess the effects of the tapered spiral geometry of the horn, and one with the internal trabecular bone material of the horn core removed. The trabecular bone material stored three times more strain energy during impact than the horn material in the intact model. Removing half of the horn length had the effect of increasing translational accelerations in the brain cavity by 49%. Removing the trabecular bone in the horn core resulted in a 442% increase in rotational accelerations within the brain cavity. These findings support the investigation of novel bioinspired materials and designs that could be used in mitigating brain injuries and in other applications involving high-impact collisions. STATEMENT OF SIGNIFICANCE: Bighorn sheep routinely experience violent impacts to the head and horns without apparent negative consequences to the brain or horns. A portion of the horn is filled with a thin cortical bone shell containing foam-like trabecular bone. We developed novel dynamic finite element models of the skull and horns of bighorn sheep to gain an understanding of the roles that the horn and bone materials play in absorbing the impact that occurs during ramming. The study revealed that both horn and bone materials and the structures made from these materials (i.e., tapered spiral horns and foam-like trabecular bone struts) are important for absorbing impact energy and reducing brain cavity accelerations.