Cervical Vertebral Morphology and Neck Mobility in Gibbons (Hylobates lar) and Humans

Abstract

The form and function of the primate cervical spine is poorly understood. Specifically, how the bony morphology of the cervical vertebrae facilitates spinal range of motion within primates is not known. Within mammals, primate cervical vertebrae present relatively unique morphologies, such as the uncinate processes. The objective of this study was to investigate the relationship between vertebral morphology and range of motion in the cervical spine of gibbons and humans. Vertebral morphology is variable within the cervical column (i.e. the morphology of C3 is different from that of C7). Range of motion also varies between intervertebral joints. These variations allow us to explore the relationship between form and function intraspecifically. We predict that range in flexion will be greater in vertebrae with taller bodies, extension inhibited by long spinous processes, and the range of lateral flexion will be lesser in vertebrae with longer transverse process length and taller uncinate processes. These hypotheses were tested using humans and gibbons (Hylobates lar).Morphological variables were quantified by digitizing cervical vertebral specimens (n=130) using a Microscribe 3DS and measured using Rhinoceros 3DM. Gibbon range of motion was measured from radiographs of maximum flexion, extension, and lateral flexion movements (n=1) and human range of motion was collected from the literature. Ordinary least squares (OLS) regression was used to test the intraspecific relationships between vertebral morphology and ranges of motion. In both gibbons and humans, regression results indicate a relationship between the range of lateral flexion and the length of the adjacent transverse process (p<0.1) but no relationship between the other variables. It may be that soft tissue influences ranges of flexion and extension more so than bony morphology. It is also possible the intraspecific differences are too minute to show a significant pattern. An interspecific comparison could elucidate a pattern.Support or Funding InformationThis project was supported by the National Science Foundation's East Asia and Pacific Summer Program.