Discectomy is partial or complete removal of a disc's central part, or nucleus
During the decades when the mythology of the ‘slipped disc’ reigned supreme it was not unusual to see bulging discs removed almost willy-nilly, with no neurological signs of nerve damage and in some instances where pain had been present for a matter of days only.
It was the Cochrane Review, first published in 1999* that fostered the beginnings of change. The conclusion of their study on the outcomes of surgery for acute disc prolapse was sober reading: "limited direct evidence on the efficacy of surgical discectomy". Just as serious was their conclusion about surgery for degenerative spinal problems: "no acceptable evidence on the efficacy of any form of decompression for degenerative disc disease or spinal stenosis".
The lever of change most instrumental in bringing about the decline of the 'dynasty of the disc' was the advent of MRI (magnetic resonance imaging). Unlike X-rays and old-fashioned myelography MRI is not invasive, allowing large populations not suffering back problems to be screened without risk. The outcomes were dramatic. One study revealed 80% of those screened had ‘bulging discs’ and as many as 1 in 3 over the age of 60 had ‘ruptured discs'. None of those scanned had symptoms: no pain, no muscle weakness, no leg or foot numbness.
Even so, both the orthopaedic and radiology worlds have been slow to change their ways. And still, on a daily basis, I read radiology reports nominating prolapsed discs and minor bulges as the cause of their back pain. Surgery to remove a bulging disc, simply because it is there, is still happening today.
All discs bulge more when they are dehydrated. This lowers their pressure, and like a car tyre lacking air, they always bulge more. Discs that have been operated upon (discectomy) also bulge more, as evacuating the nucleus causes a drop of disc pressure by as much as 45%. This makes it only too clear why repeat surgery (or re-operation) because ‘the disc has slipped again’ is usually inappropriate.
Often the disc of a problem spinal level bulges more than its neighbours. This happens because the muscles are actively protecting this level (we call this ‘raised tone’) which compresses the spinal link and milks it of fluid. The bulge is invariably a consequence, not the progenitor, and in most cases it is not pain making.
Most disc bulges are benign, but sometimes they are not! Where a back is in acute crisis, over-protective muscles can become a problem in their own right. They alone can make everything worse.
Discs have a very slow metabolic turnover and even at the best of times struggle to remain viable. Discs break down rapidly under the compression of acute muscle spasm. The protective clench smothers the disc to death within a couple weeks - which is why it's so important to get acute backs out of spasm. Even if the problem was not originally of the disc, the massive muscle clench keeps the disc buckled down and can lead to the disc devouring itself through its own enzymatic reaction.
In the final stages of breakdown a disc can go one of two ways, both of which may require surgery. With primary breakdown of the nucleus, inflammatory products seep out through the walls of the disc, like a leaking hessian bag. Their chemical toxicity scalds the nearby nerve root, causing excruciating leg pain (sciatica). Surgery to remove a toxic nucleus quickly eradicates leg and back pain.
With advanced disc degeneration, nerves grow in from the outside, looking for trouble
The other mode of disc breakdown is primarily via the walls. The nucleus is at the heart of the disc. With marked degeneration it shrinks by up to 50%, making the walls bear the brunt of loading. Over time, they develop clefts and fissures that allow blood vessels to grow in from the outside. Where blood goes, nerves follow. So, extremely degenerated discs can develop another nervous network that literally grows into the disc looking for trouble. These discs make a very painful back and are ideal for resection through laminectomy.
Equally rare - in about 3-5% of cases of low back pain - it's possible to have a discreet focal bulge in the back wall of a
disc. These usually develop in the back (posterior) or the diagonal
back corners (postero-lateral) as an acute disc prolapse.
True prolapse, or ‘slipped' disc, develops as part of a degenerative cascade when the nucleus loses cohesion - but this process takes time. While the disc is breaking down, chinks and cracks start opening up in the wall as a result of excessive loading (caused by disc dehydration). In fits and starts the de-nourished nucleus burrows out through the layers of wall towards the back.
Bending and twisting movements add to the back pressure on the runaway nucleus, squeezing it through radial cracks and circumferentially between adjacent layers of wall. As the migrating nucleus nears the the last retaining layers of wall the pain becomes intense because these layers are innervated, unlike the rest of the disc. The pent up pressure causes a deep-seated central back ache.
Acute prolapse may also cause leg pain and neurological signs, such as weakness and numbness in the leg as the bulge exerts pressure on the nearby spinal nerve root. The nerve is also irritated by the toxic chemicals that leak from the disc, more so as it deteriorates. The pain and symptoms in the leg are caused by a combination of the physical pressure and the chemicals around the focal bulge.
Degenerated nuclear material usually tracks out through the disc wall in the back (postero-lateral) corners
prolapse has both a physical squashing effect on the nerve root and a chemical one, in the manner described above.
Sometimes, in a spinal condition called disc fenestration (also called sequestration) the de-nourished nucleus bursts right through the
retaining few layers of disc wall into the spinal canal.
The wall has excellent self-sealing properties and this is a good natural outcome for a degraded disc. Rather like a boil bursting, it rids the disc of its rotten nucleus and creates the best chance for it to get healthy again - and the best circumstances for disc regeneration. Read this personal account of a disc fenestration event.
And although it's a great relief that the back pain goes away (from released internal pressure internally against the wall) the leg becomes much more painful from the chemical scalding of the nerve. Very importantly, these cases do not need surgery ! They get better of their own accord. The extruded or sequestrated disc material is reabsorbed by the blood stream in a matter of weeks - and the leg pain subsides.
Escaped nucleus does not need surgical removal. The body absorbs it with a few weeks
Or, you can download 'Complete Back Pain Video Package' to see Sarah explain about the causes of back pain and how you can treat it yourself.
Ref: *(Gibson J N, Grant I C, Waddell G 1999 The Cochrane review of surgery for lumbar disc prolapse and degenerative lumbar spondylosis Spine 24: 1820-1832)
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