City Centre Chiropractic

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The Intevertebral Disc

Disc disease, degenerated discs, slipped discs and herniated discs are common terms often related to back pain. What do these terms mean? How do these things happen?

We at City Centre Chiropractic have inculded some anatomy to get us on the same page: The spinal column is made up of 24 bones called vertebrae. Each vertebra has six joints; four at the back of the bones that allow and control spinal movement. These are called facet joints and are aligned vertically, parallel to the direction of the spine. The other two joints are at the top and bottom of the vertebrae themselves. These joints are horizontal joints in orientation and weight-bearing in function. Between each pair of the vertebrae is an intervertebral disc, except between the top two vertebrae in the neck. The discs become progressively smaller as you go up the spine. They also change shape as they go up, simply because the bones also change shape.

The most problematic discs are the lower back ones. The lower back is also known as the lumbar region. The typical lumbar disc is almost circular in shape, but looks more like a flat car tire or mushroom head. It's flat across the back when you look down from the top.

A disc is made up of two things: the soft central area is called the nucleus, and the tough outer cartilage margins are called the annulus. The nucleus is roughly spherical in shape and is made of a material with a similar consistency to crab meat. The nucleus works like a ball bearing, allowing the bones to flex and extend around its shape, much like exercising over a gym ball in Pilates. The weight of the body causes a considerable amount of pressure to be built up in the nucleus. One of the things that builds the most pressure in a disc is when you sit, especially in poorly supportive furniture, or when you slouch. Surprisingly, the pressure in the nucleus is twice as great while sitting than it is while standing. This may explain why those in sedentary, seated occupations experience pain in their lower back.

The annulus is wrapped in layers around the nucleus to contain its pressure. These layers are somewhat like the layers of an onion. The fibers of one layer are at right angles to the next layer. These layers have to be tough and non-yielding; otherwise the softer nucleus would lose its shape and spill all over the place. In fact this is indeed what does happen if the annulus breaks down. This incident is known commonly as a slipped disc but more correctly, a herniated disc, a disc protrusion, or a disc bulge. These terms often depend on the degree of nuclear movement, which depend on the degree that the annular cartilage breaks down.

Annular tears (disc injuries) become painful when they extend into the outer one third of the annulus, as once this occurs scar tissue attempts to plug the gap. However with this scar tissue comes nerve endings. The disc is designed not to have nerves within it, and act as a shock distributor/ absorber, but if you tear a disc you end up with a pain sensitive structure

Two blood vessels enter the disc from the back and these vessels angle towards the centre and supply the nucleus with oxygen and nutrients. As we age, these two blood vessels dry up. That leads to two problems: Firstly, without a blood supply, the discs only get the sustenance they need by diffusing it from its surrounding environment, which is greatly aided by spinal movement. And most patients report a difficulty in moving once they have a disc injury, and so the problem perpetuates. The second factor in the drying up of these blood vessels is the fact that the vessels leave a channel through the annulus to the nucleus thereby creating a weakness in the disc.

So as you can see a disc injury is a lot more complicated than you might have thought and this is why something that seems like a simple injury can take so long to heal and be so painful.

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