What are spinal discs?
Spinal discs are robust structures between vertebrae (spine bones) made of fibrocartilage and a gel-like matrix, which provide shock absorption to protect the vertebrae, brain, spinal nerves, blood vessels and other soft tissue structures. The discs allow some vertebral motion: extension (backward bending) and flexion (forward bending). Individual disc movement is very limited; however, considerable motion is possible when several discs combine forces.
Disc herniation is a medical condition in which a small tear in the outer fibres (anulus fibrosus) allows the central portion of the disc (nucleus pulposus) to bulge out beyond the damaged tissue. A ‘bulging’ or ‘slipped’ disc usually precedes a herniation and is not associated with tearing of the annulus fibrosus.
Spinal disc herniation is a relatively common disorder affecting 1-3% of the population. It can occur in any disc of the spine, but it is most common in the low back, causing lower back pain and sometimes leg pain as well. Often this type of leg pain is due to irritation of the nerve root (nerve fibres that extend from the spinal nerve through a small space called the intervertebral foramen, which is made between two approximating vertebra). This condition is known as radiculopathy, or more commonly, ‘sciatica’. Lumbar disc herniation occurs 15 times more often than cervical disc herniation. 4.8% males and 2.5% females 35 years and older experience radiculopathy during their lifetime, and in 14% of patients, pain lasts more than 2 weeks. Generally, males have a slightly higher incidence of disc herniation than females.
There are many risk factors associated with disc herniation:
- Age: The most common risk factor is being between the ages of 35 and 50. After age 50 or 60, osteoarthritic degeneration (such as spondylosis) or spinal stenosis (narrowing of the spinal canal) are more likely causes of low back pain or leg pain. Interestingly, the condition rarely causes symptoms after age 80.
- Gender: Men have roughly twice the risk for lumbar herniated discs compared with women.
Physically demanding work: Jobs that require heavy lifting and other physical labour have been linked to a greater risk of developing a lumbar herniated disc. Pulling, pushing, and twisting actions can add to risk if they are performed repeatedly and with poor posture. The most common mechanism of injury is forward bending and twisting of the low back while lifting heavy loads.
- Family history: the medical literature has shown a hereditary tendency for disc degeneration, and disc degeneration is associated with an increased risk for a herniation. Family history of lumbar herniated discs is a good predictor of a future herniation.
- Previous history: Patients who have had a low back injury, a herniated disc or back surgery are also at a higher risk of developing further disc injury.
- Vibration: Exposure to constant vibration (such as driving a truck or operating a crane with poor suspension) is linked to disc irritation.
- Physical inactivity: Not exercising regularly, doing strenuous exercise for a long time, or starting exercise too strenuously after a long period of inactivity may increase your risk.
- Smoking: Nicotine and other toxins from smoking can keep spinal discs from absorbing all the nutrients they need from the blood, making disc injury more likely. Smoking also increases your sensitivity to pain.
- Being overweight/obese: Carrying extra body weight (especially in the abdominal area) may put additional strain on the lower back, although this has not been proven. But being overweight often also means being in poor physical condition, with weaker muscles and less flexibility. These factors can lead to low back pain and potentially disc injury.
To learn more about disc herniation, please follow the link to read an overview on herniated lumbar discs.