Between each lumbar vertebra is an intervertebral disc IVD (meaning disc in between the vertebra).
This disc consists of 3 parts:
- An articular endplate (how the disc attaches to the bone of the vertebra)
- A nucleus pulposus (a semi-liquid gel like substance in the back/middle of the disc)
- The annulus fibrosus (the strongest portion of the disc that binds the disc together
The role of the IVD is to assist with movement and shock absorption.
The disc is like a sponge, in that it retains water to stay hydrated so it can work effectively as a shock absorber and also assist with lumbar movement. From 45-50 years old onwards the disc begins to dry out as its ability to hold water in diminishes. Likewise if the disc is damaged (torn) before this period it also reduces the discs ability to hold in water.
The most common way to injure a disc is through simultaneously lifting and twisting or stooping.
The 2 most common injuries to a disc are:
- Disc Bulge-where there is a tear in the annular fibres (usually the outer 1/3).
- Tearing doesn’t require a traumatic force and don’t generally compress the central or lateral spinal nerves.
- Protrusion-there is movement of the nucleus pulposus into the surrounding annular fibres but there is no migration outside the annulus.
- Extrusion-the nuclear material penetrates outside the annular fibres and this material can then migrate either up or down the spine.
- Both can lead to compression of the central and/or lateral spinal nerves.
- Sequestration-is a free fragment of nuclear material in the spinal canal which can occur after an extrusion herniation and can also migrate up and down the spine.
Lower back pain associated with disc injuries can come from a series of structures:
- The outer 1/3 of the disc (only this region of the disc can detect pain)
- Damaged ligaments, muscles and tendons (in particularly the posterior longitudinal ligament)
- Disc material compressing either the central or lateral nerve roots
- This commonly results in true sciatica which includes, numbness, tingling, burning pain down the back of the thigh, leg and into the foot
- Inflammation as a result of the bodies immune response to a sequestration or extruded nuclear material
Other symptoms following a disc injury include:
- Restricted movement
- Radiating pain into the buttock, back of the thigh, calf and foot
- Change in posture due to the pain
- Muscle spasm
- Loss of power in the leg and/or foot
If not looked after an injured disc can result in degenerative changes in that region of the spine (OsteoArthritis) which can ultimately result in Neurogenic Claudication (a decrease in the size of the central canal which houses the spinal cord or the lateral canal which houses the spinal nerve roots resulting in compression of the spinal cord and/or spinal nerves).