Herniated Disc or ‘Slipped’ Disc
A herniated disc is known by many names, bulging disc, compressed disc, herniated intervertebral disc, herniated nucleus pulposus, prolapsed disc, ruptured disc and, perhaps the most inaccurate of all, slipped disc. It is one of the better known spinal conditions and yet few know what it truly means. Let us that a look at the structure of the disc and understand what happens when a disc is said to herniate.
Structure of a disc
A spinal or inter-vertabral disc sits between two spinal vertebrae. It acts mainly as a cushion to take up the pressure off the spine. Most people imagine the disc as a rubber disc with a soft-jelly centre, much like a jelly donut. It is perhaps more accurate to imagine a ball of jelly wrapped around with a string over and over again until the jelly ball is completely covered. So instead of a solid rubber material, the soft center is actually covered by a ring of tough string or fibres. This ring of fibre is known as the outer annulus fibrosus, which surrounds the inner ball of jelly, nucleus pulposus.
How the disc works
Imagine that you have blown up a small red balloon and ‘sandwiched’ it between two slices of bread. When you squeeze the slices of bread together, the balloon resists the squeeze and expands out of the side of the sandwich. Your disc works in exactly the same way, only that the disc’s wall is much thicker and has a jelly center instead of air. Now, instead of squeezing the balloon down evenly on both side, squeeze down the sandwich at just one end. The balloon should expand out at the other end of the sandwich. If this position is held for long time, the balloon will becoming permanently stretched at one end. When you let go of the sandwich, the balloon end will not shrink back fully but will remainly slightly loose. The more often you stretch it and the longer you hold the stretch, the looser is gets over time. The jelly center bounces back but the tougher surrouding fibres won’t. If they are over-stretched, they either break or remaining stretched.
Stages of disc herniation
Like the balloon sandwich, the disc doesn’t burst immediately unless squeezed extremely hard. Instead it will get stretched gradually over time. More accurately, each disc fibre gets stretched over time. So it is a gradual process happening over each fibre at a time. It is rarely a sudden process. You don’t wake up one morning to find a bulging disc when the disc was perfectly fine the day before.
At this early stage, the disc is stretched and doesn’t completely return to its normal shape when pressure is relieved. It retains a slight bulge at one side of the disc. Some of the inner disc fibres could be torn and the soft jelly (nucleus pulposus) is spiling outwards into the disc fibres but not out of the disc.
At this stage, the bulge is very prominent and the soft jelly centre has spilled out to the inner edge of the outer fibres, barely held in by the remaining disc fibres.
Herniated Disc or Extrusion
Herniation is a term to mean protrusion. In the case of a herniated spinal disc, the soft jelly has completely spilled out of the disc and now protruding out of the disc fibres.
Here some of the jelly material is breaking off away from the disc into the surrounding area.
Can discs heal?
Unfortunately, a damaged disc cannot heal itself. It has little blood supply (only at the flat top and bottom of the disc) and the disc tissues cannot regenerate themselves. Once the disc fibres are stretched, it is currently not possible to un-stretch back to their original state.
Is there pain?
There are few nerve endings in the spinal discs, mainly in the edge of the disc facing out from your back. So there is often little or no direct pain felt from a degenerating, bulging or herniated disc.
Pain felt from a herniated disc is more often caused by the disc or its soft jelly core pressing on its surrouding tissues which have more nerve endings. So it is possible to have a herniated disc and yet experience no pain if the herniated disc does not pressed against any nerves
Another source of pain is when the disc first herniates, the nucleous pulposus reacts with the blood supply surrounding the disc to produce chemicals that can also irritate to the surrouding tissue causing inflammation.
- P. Prithvi Raj MD, FIPP, ABIPP (2008) Intervertebral Disc: Anatomy-Physiology-Pathophysiology-Treatment , Pain Practice 8 (1) , 18–44 doi:10.1111/j.1533-2500.2007.00171.x
- Medline Plus, http://www.nlm.nih.gov/
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