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 cervical spines. Objectives. This study examined the baboon as a potential model for in vivo and in vitro atlantoaxial research. Summary of Background 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 humans. Methods. Twenty baboon and seven human normal adult cadaveric upper cervical spines were studied morphologically. C1-C2 motion segments were analyzed biomechanically using a flexibility method of testing with physiologic range, nondestructive loading. Motion and load-deformation relationships were studied during flexion, extension, bilateral lateral bending, and bilateral axial rotation. Results. The bones and ligaments 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 was 50% to 60% of the human specimens. There were several minor anatomical differences. Baboons had more horizontal C2-C3 facet joints and more vertical C1-C2 articular surfaces; the vertebral arteries were encased in a continuous bony canal in C1. Biomechanical testing demonstrated that baboons and humans had similarly proportioned neutral zones and elastic zones. Compared with humans, baboons had a 2-degrees to 9-degrees wider range of motion in all directions. Conclusions. The baboon and human upper cervical anatomy and biomechanics are similar. The baboon may be useful to study atlantoaxial biomechanics and pathology.