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Degenerative intervertebral discs (technical)

A degenerative intervertebral disc is a collective term that is used to broadly describe the changes within an intervertebral disc. These changes may occur during the normal ageing process or be sped up with lifestyle, sporting, occupations and hereditary factors. Inflammatory diseases, chronic wear and tear, and cancer that affect the disc could certainly speed this degeneration (break down) up too. These are known as pathological changes.

For a disc to be termed or classed as degenerative there are three things that must be seen. One or all of these subcategories should be seen, and include:

  1. Intervertebral disc annular fissures
  2. Intervertebral disc degeneration
  3. Intervertebral disc herniation

A chiropractor, physiotherapist or medical specialist may swap and change between these terms. However, with more and more studies into intervertebral discs and intervertebral disc pain, consistency when using these terms is becoming more common.

1. Intervertebral disc annular fissures

Annular fissures are sometimes called annular tears. Tear is not the correct term to use in a degenerative disc, as there has not been an injury, the word ‘tear’ implies this. Therefore, annular fissures are the accepted term. In years past, tear was acceptable. An annular fissure is the term used to describe either a separation between the fibres of the outer disc (annulus fibrosis – annulus for short) or a separation between the annulus and the vertebral bones (ring apophysis). Annular fissures can be described by their orientation (the way they tear). These include:

  • Concentric or circumferential. Fissures are between the layers of the annulus. Imagine layers of an onion separating.
  • Radial fissures. Fissures go straight through the annulus. These fissures can run horizontally, obliquely or vertically. Imagine just cutting the onion straight through in any way.
  • Transverse fissures. Transverse fissures sometimes get their own category as this is the type of fissure that can separate the disc (annulus) from the bone (apophyseal bone)

If these fissures get really big and separation of annular fibres is large, these are now commonly called annular gaps. Although annular fissures may happen from injury, such as whiplash, they can also occur through the normal ageing process.

Diagnosing intervertebral disc fissures

There are three different types of disc fissures that include radial, transverse and concentric fissures (described above). These are named depending on where they are and the direction of the fissure. Disc fissures occur in the annulus of the intervertebral disc. The annulus is the hard outer layer of a disc. On MRI any dehydration (looks black on MRI) suggests at least one fissure. There may be several. Bright white appearance of a disc on MRI (high intensity zones – HIZ) suggests fluid or granulation tissue (young repair tissue) and this means inflammation following a fissure (tear). This white appearance can be highlighted by injecting gadolinium into a disc and taking another MRI. The most important aspect of diagnosing a disc fissure is to realise that some fissures will not show up as high intensity zones (white) on a MRI and this means they will not be visualised. Discography may show more fissures however not all tears are seen on discography either. With this information two things should be unequivocally noted.

  • Painful fissures may not be seen on either MRI or CT scan. Clinical diagnosis if very important for a chiropractor and physiotherapist.
  • If a tear is observed on MRI or CT scan this does not mean that it is causing neck or back pain or producing symptoms. Non-painful discs also contain tears observable on MRI and CT discogram. Therefore to assume all tears in disc are painful is incorrect.

2. Intervertebral disc degeneration

Intervertebral disc degeneration really just means wear and tear or break down of a disc. It can be natural or pathological (caused by a disease). As a disc ages and breaks down, one or more of the following will be seen.

  • Intervertebral disc desiccation (dehydrated – Black on MRI)
  • Intervertebral disc fibrosis (lots of scar tissue within it)
  • Intervertebral disc space narrowing (disc becomes thin and loses its suppleness)
  • Intervertebral disc bulging (Bulges out from losing its ability to support weight)
  • Intervertebral fissuring (tears within a disc, as the disc breaks down)
  • Mucinous degeneration of the annulus (change in the material of the disc – now easier to tear)
  • Intervertebral disc intradiscal gas (gas accumulates in the gaps that tears create in the fibres of the annulus)
  • Osteophytes of the vertebral apophyses (This is the where the disc joints the vertebra bone above and below, inflammation leads to bone spurs – osteophytes)
  • Sclerosis of the end plates (The vertebral bones that above and below the disc become stiffened and hardened with changes in their material)

3. Intervertebral disc herniation

The term disc herniation simply means there has been some displacement of intervertebral disc material beyond the intervertebral disc space. The intervertebral disc space is bordered by the vertebra (end plates above and below) and around its circumference the outer edge of the ring apophyses (ring that marks where the annulus joins to the vertebral body above and below). Now, remember that a disc has a number of associated structures including the nucleus, cartilage, apophyseal bone and annular tissue. The displaced material may be one of these structures or a combination of these. Therefore, it should be unequivocally noted that a disc herniation is not a synonym for a nucleus pulposus herniation as it may contain other structures.

Disc bulging

Disc bulging is not a synonym for a disc herniation. Technically speaking it has nothing to do with a disc herniation. Disc bulging is the term used to describe the extension of the whole circumference of the disc extending beyond to ring apophyses (generally more than 25% of disc fibres). This doesn’t have to be symmetrical. It may be localised and focal (bulging of less than 25% of fibres – not as common). Asymmetrical focal bulging is common where there is deformity above or below the level of the bulging disc. When evaluating any spinal segment, including the morphology of the disc, the level above and below must be considered.

Herniated discs

There are 2 types of herniated discs and are classified on the basis of their shape (of displaced material).

  • Disc protrusion

A disc protrusion takes up less than 25% of the disc circumference. The term for this is ‘focal’. The criterion to determine whether it is a disc protrusion on image (CT, MRI) is simple. When you look at the protruded disc, it is wider at the base (origin, at the start of the protrusion within the disc) than the width of the protruded material coming out of the disc. The protruded intradiscal material must be continuous with the protruded disc material. That is, none has broken off.

  • Disc extrusion

This is almost exactly the opposite of a disc protrusion (above). In that, the width of the herniated material is larger outside the disc space than inside the disc. A subcategory of disc extrusion is disc sequestration and this is when there is no longer continuity between the intradiscal substance and the extruded disc substance. I.e. The extruded disc has broken off.

We have spoken only of disc herniations that occur about the circumferential periphery of the disc. However disc herniations may also occur in a vertical direction. Vertical herniations will go through a gap in the vertical body endplate. Sometimes called Schmorl nodes. The other terms that are readily used when describing discs are contained and uncontained disc herniations. Contained disc herniations are those still contained within the outer annulus or posterior longitudinal ligament. Uncontained disc herniations are no longer within the outer annulus or posterior longitudinal ligament.

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