The bones of the spine are called vertebrae, and they are separated by small round, quarter-sized discs. Called intervertebral discs, these cushioning spinal components have a tough outer layer (annulus) that surrounds a gel-filled, watery nucleus. A herniated disc, also called a ruptured or slipped disc, is when the inner disc material pushes out the annulus and into the spinal canal.
The discs of the spine act as shock absorbers for the vertebrae (spinal bones). They allow for spinal motion and flexibility, and prevent bones from rubbing together.
With a herniated disc, a fragment of the nucleus pushes out of the annulus through a crack or tear in the tough, outer disc layers. Discs often herniated in early stages of degenerative disc disease (DDD). A single, excessive strain or traumatic injury can cause a disc to herniate. However, with age and wear-and-tear, the ligaments that hold discs in place begin to weaken. With degenerative progression, twisting or straining can lead to nucleus rupture through the annulus.
Anyone can suffer a herniated disc, and they most often occur in the lower spine. Research shows that herniated discs are more common in men, people who perform heavy labor duties, and those with a predisposition.
The symptoms of a herniated disc vary depending on the size of the herniation and location of injury. When a herniated disc does not impinge on nerves, most people report only mild back pain. When the nucleus material puts pressure on one or more spinal nerves, it can produce pain that radiates into an arm or leg, as well as weakness, and numbness of the extremity. With a lower back (lumbar spine) herniated disc, pressure often affects the sciatic nerve, which supplies each of the lower legs. This pressure can produce an electric shock-like pain that is more severe with walking or standing.
Diagnosis of a herniated disc is made based on the patient’s medical history, a physical examination, and diagnostic testing. Tests used to assess the spine include:
According to a recent study, symptomatic herniated lumbar disc affects around 2% of the general population. The highest prevalence is among persons aged 30 to 50 years. Men are affected twice as often as women (2:1 ratio), and 95% of herniated discs occur in the lower spine. Thoracic (middle spine) and cervical (neck) disc herniates are more common among persons age 55 years and older.
Jordon J, Konstantinou K, & O’Dowd J (2009). Herniated lumbar disc. BMJ Clin Evid, 1118.