When you have a prolapsed disc (commonly called a slipped disc), a disc does not actually slip. What happens is that part of the inner softer part of the disc (the nucleus pulposus) bulges out (herniates) through a weakness in the outer part of the disc. A prolapsed disc is sometimes called a herniated disc. The bulging disc may press on nearby structures such as a nerve coming from the spinal cord. Some inflammation also develops around the prolapsed part of the disc.
Any disc in the spine can prolapse. However, most prolapsed discs occur in the lumbar part of the spine (lower back). The size of the prolapse can vary. As a rule, the larger the prolapse, the more severe the symptoms are likely to be.
Bouts of back pain are very common. However, less than 1 in 20 cases of acute (sudden onset) back pain are due to a prolapsed disc. (Most cases of back pain are classed as simple low back pain. This is thought to be caused by a minor problem in a muscle, ligament, or other structure in the back for example, a strained muscle.) The most common age to develop a prolapsed disc is between 30 and 50 years. Twice as many men as women are affected.
It is not clear why some people develop a prolapsed disc and not others, even when they do the same job or lift the same sort of objects. It seems that some people may have a weakness in the outer part of the affected disc. Various things may trigger the inner softer part of the disc to prolapse out through the weakened outer part of the disc. For example, sneezing, awkward bending, or heavy lifting in an awkward position may cause some extra pressure on the disc. In people with a weakness in a disc, this may be sufficient to cause a prolapse. Factors that may increase the risk of developing a prolapsed disc include: a job involving lots of lifting, a job involving lots of sitting (especially driving), weight-bearing sports (weight lifting, etc), smoking, obesity, and increasing age (a disc is more likely to develop a weakness with increasing age).
The pain is often severe, and usually comes on suddenly. The pain is usually eased by lying down flat, and is often made worse if you move your back, cough, or sneeze.
Sciatic pain or sciatica
Sciatica is the pain that occurs because a nerve coming from the spinal cord is pressed on (trapped) by a prolapsed disc, or is irritated by the inflammation caused by the prolapsed disc. Although the problem is in the back, you feel pain along the course of the nerve in addition to back pain. Therefore, you may feel pain down a leg to the calf or foot. Sciatic pain can range from mild to severe, but it is often worse than the back pain. With a prolapsed disc, the sciatic nerve is the most commonly affected nerve. The sciatic nerve is a large nerve that is made up from several smaller nerves that come out from the spinal cord in the lower back. It travels deep inside the buttock and down the back of the leg. There is a sciatic nerve for each leg.
Other nerve root symptoms
The irritation or pressure on the nerve next to the spine may also cause pins and needles, numbness or weakness in part of a buttock, leg or foot. The exact site and type of symptoms depend on which nerve is affected.
Cauda equina syndrome
Cauda equina syndrome is a particularly serious type of nerve root problem that can be caused by a prolapsed disc. This is a rare disorder where the nerves at the very bottom of the spinal cord are pressed on. This syndrome can cause low back pain plus: problems with bowel and bladder function (usually unable to pass urine), numbness in the saddle area (around the anus), and weakness in one or both legs. This syndrome needs urgent treatment to preserve the nerves to the bladder and bowel from becoming permanently damaged. See a doctor immediately if you develop these symptoms.