Lumbar disc degeneration is part of the ageing process. Bulging of the fibre ring, and even frank herniation or extrusion of the inner nucleus, are the result of progressive wear and tear, not a single injury. 6% of lumbar discs are degenerate in the under-20s, 80% in the over-60s.
Bulging intervertebral discs are no more abnormal than skin-wrinkles.
In separate studies of symptomless volunteers under 40, more than a third had at least one bulging lumbar disc on Magnetic Resonance Imaging (MRI) scanning, . In two studies 20% had a herniated disc on MRI or Computed Tomography (C-T), .
In the absence of demonstrable encroachment of fragments of nucleus on nerve roots producing sciatica, the connection between pain and abnormalities on diagnostic imaging examinations is often tenuous and speculative. Despite the commonness of low back pain, the anatomical structures originating it are largely unknown.
The cause of most low back pain is unknown.
Where a degenerate intervertebral disc is thought to be the origin of disabling pain, discography may precede discectomy: back pain is mimicked by injection into the suspect disc and diagnostic imaging is abnormal.
10 healthy volunteers each had discograms at three levels, followed by interview and MRI. When the studies were reviewed, interspersed with those of patients complaining of low back pain, 5 of the 30 discs, in 5 of the 10 healthy subjects, were confidently interpreted as abnormal.
Although an accident may cause a degenerate intervertebral disc to become symptomatic for the first time, objective evidence of causation is rarely possible.
In Germany, Insurance Law has recently been modified to reflect these medical concepts: not only must symptoms first appear after the accident, and the forces be adequate to cause substantial damage to an intervertebral disc, but the onus is on the plaintiff to show that the disc in question was not previously degenerate, , .
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