Abstract
Background
Recent studies suggest there is a relationship between intervertebral disc herniation and vertebral shape. The nature of this relationship is unclear, however. Humans are more commonly afflicted with spinal disease than are non-human primates and one suggested explanation for this is the stress placed on the spine by bipedalism. With this in mind, we carried out a study of human, chimpanzee, and orangutan vertebrae to examine the links between vertebral shape, locomotion, and Schmorl’s nodes, which are bony indicators of vertical intervertebral disc herniation. We tested the hypothesis that vertical disc herniation preferentially affects individuals with vertebrae that are towards the ancestral end of the range of shape variation within Homo sapiens and therefore are less well adapted for bipedalism.
Results
The study employed geometric morphometric techniques. Two-dimensional landmarks were used to capture the shapes of the superior aspect of the body and posterior elements of the last thoracic and first lumbar vertebrae of chimpanzees, orangutans, and humans with and without Schmorl’s nodes. These data were subjected to multivariate statistical analyses.
Canonical Variates Analysis indicated that the last thoracic and first lumbar vertebrae of healthy humans, chimpanzees, and orangutans can be distinguished from each other (p<0.028), but vertebrae of pathological humans and chimpanzees cannot (p>0.4590). The Procrustes distance between pathological humans and chimpanzees was found to be smaller than the one between pathological and healthy humans. This was the case for both vertebrae. Pair-wise MANOVAs of Principal Component scores for both the thoracic and lumbar vertebrae found significant differences between all pairs of taxa (p<0.029), except pathological humans vs chimpanzees (p>0.367). Together, these results suggest that human vertebrae with Schmorl’s nodes are closer in shape to chimpanzee vertebrae than are healthy human vertebrae.
Conclusions
The results support the hypothesis that intervertebral disc herniation preferentially affects individuals with vertebrae that are towards the ancestral end of the range of shape variation within H. sapiens and therefore are less well adapted for bipedalism. This finding not only has clinical implications but also illustrates the benefits of bringing the tools of evolutionary biology to bear on problems in medicine and public health.
| Original language | English |
|---|---|
| Article number | 68 |
| Number of pages | 10 |
| Journal | BMC Evolutionary Biology |
| Volume | 15 |
| Early online date | 27 Apr 2015 |
| DOIs | |
| Publication status | Published - 27 Apr 2015 |
Bibliographical note
AcknowledgmentsWe thank York Osteoarchaeology, Pre-Construct Archaeology, Durham University, the Natural History Museum, and the American Museum of Natural History for access to the specimens used in the study. We also thank Helgi Pétur Gunnarsson for his assistance with the analyses. The study was funded by the Social Sciences and Humanities Research Council, Canada Research Chairs Program, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, MITACS, and Simon Fraser University. We thank the editor and two anonymous reviewers for their insightful comments and suggestions on this paper.
Keywords
- Back pain
- Disc herniation
- Vertebral shape
- Bipedalism
- Geometric morphometrics
- Schmorl's nodes
Access to Document
- The ancestral shape hypothesis
© 2015 Plomp et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.