The vertebral column is a complex anatomical structure in terms of form and function, and the majority of the loads applied to it during locomotion pass through the bodies of the vertebrae. Spontaneous vertebral fractures are a common skeletal pathology in humans, and are linked to low bone mineral density. In contrast, spontaneous vertebral fractures have not been reported in apes, even in cases of extremely low bone mineral density. Given these observations, it is likely that there is a structural difference in the vertebral bodies among humans and apes that causes humans to be more susceptible to spontaneous vertebral fracture. The focus of this study was to determine how the structure of the vertebral body in terms of gross morphology, trabecular microarchitecture and shell thickness differed among humans and apes, and whether these differences were related to body mass, locomotion and strength of the vertebral body.

Humans have larger vertebral bodies along the entire length of the vertebral column than would be expected for body mass, and the vertebral bodies increase in size along the length of the vertebral column similar to the much larger gorilla. However, when vertebral body size is normalized within the vertebral column, there are no differences among the species. Additionally, although humans have large vertebral bodies, they are still weaker than would be expected for their size. Humans have lower trabecular bone volume fraction than gibbons and African apes, and displayed a negative correlation between bone volume fraction and degree of anisotropy in the ventral vertebral body unlike the other hominoids. Humans have thinner vertebral shells than would be expected for their body mass and vertebral body height. The combination of tall vertebral bodies containing unsupported columnar, craniocaudally oriented trabeculae that do not support the thinner than expected vertebral shell may be the structural differences in vertebral bodies that account for the increased susceptibility to spontaneous vertebral fractures in humans. Evolution of larger, more trabecularized vertebrae with a thinner shell in humans is likely linked to the evolution of bipedalism;​ however, an exact mechanism is currently unclear and requires further investigation.