The Intervertebral Discs 
The intervertebral discs are a prevalent source of lower back and neck pain as they are one of the most frequently irritated spinal structures either through repetitive trauma or as part of the aging/degerative process. The discs connect adjacent spinal vertebrae together and provide a degree of shock absorption in the torso.
Disc Structure
The structure of the spinal disc resembles a jelly filled doughnut. The inner aspect of the disc contains a gel-like substance called the nucleus pulposus. Surrounding the nucleus are tough fibrocartilagenous fibers called the annulus fibrosis. These annular fibers contain the inner nuclear material similar to a basketball skin containing the air within.
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Causes of Disc Injury
Disc injury occurs when the annular fibers of the disc are torn. Because the inner regions of the annulus lack "pain" innervation, injuries contained to the inner annulus occur without one's knowledge.
Common causes of annular disc tears include:
- prolonged sitting
- poor postural habits
- poor lifting habits
- improper workstation setup and ergonomics
- improper lifting techniques
- extended periods of vibratory forces (truck and auto drivers, jack hammer operators, etc.)
- Other factors have been shown to increase the susceptibility of disc injury:
- inadequate diet and nutrition
- smoking
- obesity
- lack of physical activity
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Types of Disc Injury
There are 3 main types of disc injuries. The first disc injury consists of annular fiber tears which do not extend to the outer aspects of the disc. Thus, the inner nuclear material is prevented from completely escaping the disc.
The second type of disc injury, commonly referred to as a disc herniation, consists of annular tears which run from the innermost aspects of the annulus (where the nucleus is) to the outermost aspects of the annulus. In this type of injury, the pressurised nuclear material can squeeze through the tears in the annulus and escape to the outside of the disc. When this occurs, the nuclear material may come in contact with nearby spinal nerves and even the spinal cord.
In the third type of disc injury, referred to as a disc bulge, the inner nucleus loses hydration; common in those with prolonged spinal stress and the elderly. This results in "bulging" of the disc much like a tire "bulges" when it contains inadequate amounts of air. Similar to the previous injury, the nearby spinal nerves and spinal cord may become impinged from the bulging disc.
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Symptoms of Disc Injury
The symptoms of disc injury depend upon the location of the disc tears and whether or not the spinal nerves or spinal cord are affected.
When tearing of the annulus occurs within it's inner portion only, generally pain is not experienced. As previously stated, this is because the inner regions of the annulus lack pain receptors. When tearing of the annulus occurs in the outer annular fibers, mild to excruciating pain is felt in a generalised manner. If a lumbar disc is affected, for instance, diffuse low back pain with associated paraspinal muscle spasm is typical.
When numerous partial tears coalesce to form tears which run clear through the thickness of the annulus, the gel-like nucleus is able to escape the disc. If a spinal nerve or the spinal cord is contacted the individual may experience symptoms of pain, numbness, tingling and/or weakness within either or both lower extremities.
In extremely rare cases patients may lose the ability to control bowel and bladder functions (you would possibly urinate or defecate yourself). If this occurs, immediate medical intervention is required and you should urgently proceed to A&E as the condition can become permanent without rapid surgical intervention.
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