Intervertebral discs are located between the vertebrae in the front of the spine and act as shock absorbers. Discs have two components and are often compared to a jelly donut. The outer part of the disc is called the annulus and is formed of rings of fibrous tissue like a tire. The inner part of the disc is called the nucleus. Protein molecules in the nucleus attract fluid that acts as a cushion or shock absorber between the vertebrae.

Disc herniation means that some of the nucleus material that is in the center of the disc has moved out of the disc through a tear or a crack in the outer annulus. Most often the defect in the annulus is at the back of the disc and the nucleus material squirts out into the spinal canal where it can compress or irritate a nerve root resulting in sciatica, which means leg pain. Sciatica is a very severe type of leg pain. People often say that it is worse than kidney stones or childbirth. Most people with disc herniations experience the sudden onset of severe leg pain. In most cases there is no specific injury or event that causes a disc herniation. It can occur in people of all shapes and sizes and affects people who have desk jobs as often as those with work involving physical labor. It is most common in people between the ages of 20 and 50. Some people experience a period of back pain prior to the onset of the leg pain, which is probably due to the tear in the outer part of the disc.

The distribution of the leg pain depends on which disc is herniated, which determines which nerve root is affected. The two most common levels where disc herniations occur are the two lowest discs in the spine, between the 4th and 5th lumbar vertebrae (L4-5) or between the 5th lumbar vertebra and the sacrum (L5S1). Both of these usually result in pain that runs from the buttock to the calf or the foot. Some people experience numbness in the leg or foot, and sometimes people experience weakness in their leg. Fortunately, eighty to ninety percent of people recover without any specific treatment. Most people recover within three months or less. Ten to twenty percent of people do not recover completely.

Treatment such as physiotherapy and chiropractic manipulation can sometimes help with the pain. The pain caused by the disc herniation will gradually improve in most people regardless of the type of treatment. This is called the natural history for this condition. In some people the disc herniation completely disappears, while in others it does not disappear, but the pain does. Studies have suggested that the pain is due to the release of inflammatory chemicals that work to dissolve the disc and also irritate the nerve. Once this inflammatory process resolves, the pain goes away. While the nerve is being compressed, activities such as stretching the leg will often irritate the nerve and aggravate the pain. It is important to remain as active as possible but to do activities that do not aggravate the pain. Pool therapy, walking or cycling can often be done without aggravating the pain. Remaining active has a low risk of causing nerve damage. Nerve damage occurs in less than ten percent of people with disc herniations and can result in weakness or numbness in the leg. In most cases the damage occurs at the time of the disc herniation when the pain first starts. It is uncommon for nerve damage to occur later on.

Surgery can be performed to remove the herniated disc fragment to relieve the pressure on the nerve. This results in almost immediate relief of the leg pain in eighty to ninety percent of people. There are potential risks to surgery such as infection or injury to the nerve. Therefore, surgery is usually the last resort. However, complications from surgery occur in less than 1% of operations. Approximately one person in a hundred will experience some permanent nerve damage caused by the disc herniation. This can result in weakness, numbness or even permanent pain.

People who experience an episode of sciatica are often afraid to return to full activities because the pain is so severe that they don’t want it to occur again. The risk of a recurrent disc herniation after symptoms resolve is approximately 10 percent. Recurrence can occur whether the person has had surgery or not, and can occur early on, or years after the first event. Most people completely recover from a disc herniation and are able to return to full activity including work and recreational pursuits. Doing regular exercise to develop a strong core helps prevent recurrent disc herniation or the onset of back pain.