Refinement of interbody implant testing in goats: a surgical and morphometric rationale for selection of a cervical level

Abstract

Object The authors provide a surgical description of the ventral approach to the cervical spine in a goat model and identify selection of the most appropriate level for testing interbody devices. These constructs are designed for implantation in humans during anterior cervical discectomy and fusion. Such description and guidelines for level selection have never been published in either the medical or veterinarian literature. Methods The study comprised three phases: surgical, anatomical, and morphometric. Six goats underwent ventral approaches and were later killed; their necks were dissected and the cervical spines were processed to obtain clean specimens of the vertebral bodies. Measurements were made at each level using a contact digitizer. Results The anterolateral bone spurs, called alar processes, and the increased thickness of the longus colli muscle are the surgically relevant characteristics in the goat. The morphometric analysis showed that C2–3 is the most suitable level for implantation of interbody devices. The vertebral endplates at the C2–3 level are relatively flat and parallel to each other, and are perpendicular to the spinal canal axis. More distally, the endplates adopt a more curved arrangement, and the endplate angle becomes significantly greater than 90°. The authors describe anatomical landmarks that are important to safely and effectively perform a ventral cervical spinal approach in the goat. Conclusions The authors' model identifies C2–3 as the most appropriate level for animal testing of cervical implants because of its similarity to human anatomy. Further study with rigorous biomechanical range of motion evaluation of each caprine cervical level is needed.