Slipped discs – not all bending and twisting

Some slipped disc injuries might be caused by movements other than the commonly blamed bending and twisting, according to new research by Flinders University.

It’s a finding that will lead to a better understanding of the motions that put people at greatest risk of a slipped disc and help develop more robust guidelines for safe lifting.

“It’s always been assumed that bending and twisting is the mechanism for a slipped disc,” says Dhara Amin, a PhD candidate at the Flinders University Medical Device Research Institute.

“We wanted to test this theory in the lab using the more advanced technology we now have access to.”

Slipped discs, which are technically known as lumbar disc herniations, are a common source of sciatica (radiating pain down the legs) in the young and middle-aged.

The ‘discs’ are made of an elastic casing around a jelly-like material (called the nucleus), which helps absorb shock and keep our spine stable by slotting between the vertebrae.

A slipped disc is like squeezing a jam doughnut: the jam oozes out.

If you pressurise and bend the disc, the nucleus bulges out of its casing, impinging the nerves coming out of the spinal cord and causing radiating pain down the legs and potentially back pain.

Magnetic resonance image of human spine showing disc herniation. Photo: iStock.
Magnetic resonance image of human spine showing disc herniation. Photo: iStock.

Ms Amin’s team used the University’s robotic hexapod at Flinders at Tonsley, which simulated a year’s worth of ‘lifting’ a 20kg box, with bending and twisting movements on sections of cadaveric human spine.

The hexapod robot was able to mimic human movements that previously weren’t possible using the standard mechanical testing devices.

The biomedical engineering researchers tracked the disc failure patterns and found that only half of the spines failed via slipped discs, while the others failed via bone injuries.

“The result was interesting. We expected all of the specimens to fail by slipped discs,”  says Ms Amin from the College of Science and Engineering at Flinders.

“This leads us to believe there are other motions that can cause a slipped disc, which may be worse than just bending and twisting.”

Further research on other combinations of motions will help us better understand what causes a slipped disc, she adds.

Professor Brian Freeman, Head of Spinal Surgery at the Royal Adelaide Hospital, also worked on this project.

“The prevalence of lumbar disc herniation is estimated at three-to-five per cent,” says Professor Freeman.

“Lumbar disc herniation often presents with acute low back pain, followed by severe leg pain.

“These symptoms can persist for some time, resulting in work absence with significant cost to the economy,” he says.

“Research like this is crucial if we are to reduce the incidence of disc herniation. It’s important for those involved in manual handling tasks to be educated in safe lifting practice.”

Ms Amin was the South Australian winner of Fresh Science, a national competition run by Science in Public, which helps early-career researchers find and share their stories of discovery.

Fresh Science in Adelaide is supported by the South Australian Museum, Flinders University, UniSA and the University of Adelaide.

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