MORPHOLOGY AND KINEMATICS OF THE BABOON UPPER CERVICAL-SPINE - A MODEL OF THE ATLANTOAXIAL COMPLEX

Study Design. Quantitative and qualitative analyses were performed to compare the anatomy and biomechanics of baboon and human upper cervica l spines. Objectives. This study examined the baboon as a potential mo del for in vivo and in vitro atlantoaxial research. Summary of Backgro und Data. A variety of animal models have been used for spine research ; however, no species have been used for C1-C2 research. Most species have remarkably different C1-C2 morphology compared with that of human s. Methods. Twenty baboon and seven human normal adult cadaveric upper cervical spines were studied morphologically. C1-C2 motion segments w ere analyzed biomechanically using a flexibility method of testing wit h physiologic range, nondestructive loading. Motion and load-deformati on relationships were studied during flexion, extension, bilateral lat eral bending, and bilateral axial rotation. Results. The bones and lig aments of the baboon and human upper cervical vertebrae have similarly proportioned structures, identical individual components, and similar geometric configurations. The average size of the baboon vertebrae wa s 50% to 60% of the human specimens. There were several minor anatomic al differences. Baboons had more horizontal C2-C3 facet joints and mor e vertical C1-C2 articular surfaces; the vertebral arteries were encas ed in a continuous bony canal in C1. Biomechanical testing demonstrate d that baboons and humans had similarly proportioned neutral zones and elastic zones. Compared with humans, baboons had a 2-degrees to 9-deg rees wider range of motion in all directions. Conclusions. The baboon and human upper cervical anatomy and biomechanics are similar. The bab oon may be useful to study atlantoaxial biomechanics and pathology.