This article was originally published in Positive Health issue 64 – May 2001

The term ‘slipped disc’ is a misnomer, since intervertebral discs (IDs) do not and cannot slip out from their vertebral position. Nor can they slip back, which means that no amount of manipulation, however skilful, can cure sciatica (leg pain originating from the low-back) by pushing back a disc into its normal position. With a phrase such as ‘slipped disc’, one could be forgiven for thinking that IDs are like bars of soap. But, as we will presently see, they are not.

Our spine is made of 24 movable vertebrae. Thankfully, vertebrae do not have to sit ‘bareboned’ on each other, as nature, in its kindness, has provided them with cushions which come between all vertebral bodies (front part of the vertebra) apart from the first and second ones. These 23 cushions or discs account for one-quarter of the total length of our spine. But their raison d’être goes beyond the trivial matter of height. Their main function is to act as a shock-absorber mechanism and a ball or swivel joint which contributes to the overall flexibility of the spine by allowing three types of movement: tilting, rotating and gliding.

A disc is a compound structure made of two distinct parts:
a tough peripheral part, the annulus fibrosus or intervertebral annular ligament (the ‘hard disc’), composed of layers of collagen fibres; and
a soft central part, the nucleus pulposus (the ‘pulpy disc’) which is made of a gel-like substance containing about 88% water.

The ID does not ‘slip’, herniate or prolapse en bloc. It is only the central part (nucleus pulposus) that does so. Its extrusion can only happen if a tear occurs in the cartilaginous annular ligament, which engirdles and encloses it. So, a ‘slipped disc’ is not by definition a disc and it does not slip. It is a blob of semi-liquid substance that bursts or leaks out from its encasement.

Now a tough tissue like the annular ligament does not crack and fissure spontaneously. There can be two main causes for a torn intervertebral ligament: a severe trauma, or the summation of repeated micro-traumas. The first one is relatively rare; the second is common and is itself caused by misuse. Misuse, by shortening the back muscles and distorting the spine, puts a lot of undue pressure on the lowest IDs, which, although tough, eventually end up weakened. At this stage of disc degeneration, a simple wrong movement, even a cough, can become the last straw that breaks the annular ligament. Instead of thinking ‘slipped disc’, we should think ‘split disc’!

It is commonly thought that the discomfiture of a disc is the cause of much discomfort, mainly in the form of sciatica. It’s generally bad news for patients when they are told that they have a herniated disc; this often means that they have to contemplate the prospect of back surgery. Since 1932, when, for the first time in history, W Jason Mixter operated on a patient to obtain a cure for sciatica by removal of a protruded disc, there has been much scapegoating of the herniated disc. Orthopaedic surgeons found a new part of the body on which to exercise their cutting skills. With enthusiasm, they have repeatedly sharpened their scalpels in order to reach and remove the offending discs. Laminectomies, discectomies, laminotomies, nuclectomies, foraminotomies and fusions galore have been and still are performed. Unfortunately, recent studies reveal that they have been cutting their teeth on yet another innocent part of the body.

That a lot of people go under the knife unnecessarily is most unfortunate, as low-back surgery, like any kind of surgery, can lead to painful and disabling complications with complex names such as arachnoiditis and epidural fibrosis (post-surgical scarring). If surgery can make your spine disc-less, it rarely makes it painless. Worse, it can cause chronic and irreversible iatrogenic pains. This being said, there are cases of a traumatic origin where a massive extrusion of a disc causes what is known as cauda equina syndrome. In these fortunately rare cases, surgery is urgently required to avoid irreversible damage to bladder function. A surgeon who operates advisedly is indeed a much needed person.

But before they draw their knife when they suspect the presence of a herniated disc, surgeons should asked themselves why many patients with a herniated disc recover spontaneously; why large numbers of people with disc bulges or herniations have no symptoms; why one-third of herniated discs are calcified; why many cases of sciatica do not show any disc pathology; why some herniated discs are found on the side opposite to where the pain is felt, etc.

The consensus among specialists is that disc surgery is appropriate only when symptoms from a herniated disc fail to respond favourably to six weeks of treatment. The problem is that symptoms are often falsely attributed to herniated discs; that the six weeks can be spent receiving the wrong kind of treatment; and that the consensus is not always respected in practice.

Next month we will have a closer look at this blob of gelatinous material called nucleus pulposus and we will discover that it is rarely the villain in sciatica and other lower-back troubles. The body is able to discard its pulpy ‘disc’ without much discomfort. It is the peripheral part of the disc that we should worry about – so, don’t let your hard disc get floppy.