Blame chimps for your persistent back pain

Persistent lower back pain could be the result of bones in your spine that share similarities in shape to non-human primates like chimpanzees and orangutans.

New research suggests that the relatively quick evolution of the ability to walk on two legs had a substantial impact on modern human health owing to the stress placed on the spine.

The findings indicate why some individuals are more prone to back problems.

"Our study is the first to use quantitative methods to uncover why humans are so commonly afflicted with back problems compared to non-human primates," said post-doctoral researcher Kimberly Plomp from Simon Fraser University, Canada.

For the study, researchers studied the vertebrae of humans, chimpanzees and orangutans to examine links between vertebral shape, locomotion and the appearance of "vertical disc herniation" in humans.

A widespread cause of back pain, 'intervertebral disc herniation' has a high prevalence rate worldwide.

It is caused by the prolapse of a gelatinous substance inside the disc and when the herniation is vertically directed, it is often characterised by protrusions of cartilage called "Schmorl's nodes".

The researchers compared 141 human vertebrae, 56 chimpanzee vertebrae (a knuckle-walking primate), and 27 orangutan vertebrae (a climbing primate that uses all four feet which are modified as hands) and found significant differences in their shape.

This could be explained by the different modes of locomotion and contributes to the understanding of the human evolution of bipedalism.

Of the human vertebrae they studied, 54 had "Schmorl's nodes", the skeletal indicators of vertical disc herniation.

The researchers found that human vertebrae with "Schmorl's nodes" shared more similarities in shape with chimpanzee vertebrae than the healthy human vertebrae shared with those non-human primates.

"This suggests that vertical disc herniation preferentially affects human individuals with vertebrae that are towards the ancestral end of the range of human shape variation," Plomp noted.

These individuals may, therefore, be less well adapted for bipedalism and suffer more from load-related spinal disease.

The findings may help in preventative care by identifying individuals such as athletes, who may be at risk of developing the condition.

"This could help clinicians investigate an individual's vertebral shape and predict their susceptibility to the spine disease,'" the authors noted.

Future research will include larger sample sizes and multiple human populations from different ancestral backgrounds, the team concluded in a paper published in the journal BMC Evolutionary Biology.