The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Variation in number of vertebrae in humans


Geography and Anthropology, Louisiana State University

March 27, 2015 , Archview Ballroom Add to calendar

Species differ in variability in number of vertebrae; humans are among those species with higher variability. This study uses human skeletons from the Hamann-Todd and Robert J. Terry Collections to quantify variability in number of presacral vertebrae and to consider correlates with this variability. A total of 1,020 individuals (259 females and 761 males) between ages 20 and 49 were studied; all individuals have a 5 segment sacrum. Results show that the sexes differ significantly in number of presacral vertebrae (modal number is 24), with 5% of females and 10% of males having a nonmodal number; males have a higher prevalence of 25 vertebrae. An extra vertebra is positively associated with presence of a nearthrosis between the last lumbar and first sacral vertebrae; nearthrosis is associated clinically with pain in the lower back and leg. Conversely, an extra presacral vertebra is negatively associated with presence of a cervical rib; cervical rib is associated clinically with thoracic outlet syndrome. Using the sample of males, individuals with 25 presacral vertebrae have significantly lower means than those with 24 vertebrae for these variables: (1) summed height of vertebral bodies for vertebrae 2-24, (2) length and width of sacrum, and (3) anteroposterior diameter of pelvic inlet. The two groups of individuals do not differ significantly for these variables: (1) lengths of femur and clavicle, (2) femoral head diameter, and (3) other pelvic measures, such as transverse diameters of inlet and outlet. Number of vertebrae has clinical implications; etiology of numerical variation is discussed.