The most common cause of sciatica is a lumbar disc herniation, which causes compression or irritation of a nerve root in the lower back. Discs are spacers that are located in the front of the spine between the vertebrae, which are the blocks of bone in the front of the spine. The structure of a disc is often compared to that of a jelly donut. There are two parts. The outer part (donut) is called the annulus and is composed of layers of fibrous tissue similar to a tire that attach to the vertebrae. The centre of the disc (jelly) is called the nucleus, which is more fluid or spongy in nature and provides the shock absorber function. When a tear occurs in the outer annulus of the disc some of the nuclear material extrudes into the spinal canal where it can compress or irritate one of the nerve roots. This results in pain in the leg. The location of the pain depends on which nerve root is affected. Most people experience pain in the buttock on the affected side with pain that runs down the leg, often all the way to the foot. Some people develop weakness in the leg and/or numbness and tingling. Where in the leg the weakness or numbness is located depends on which nerve is being affected. Weakness and numbness indicate that the nerve has suffered some damage. Most people have pain without any nerve damage.

Sciatic is often very severe pain. Women often say that it is worse than childbirth and worse than kidney stones. The pain usually comes on suddenly which is when the disc herniation occurs. Some people report having back pain for hours or days prior to the onset of the leg pain, which is probably when the tear in the annulus of the disc occurs. In sciatica the leg pain is worse than the back pain. Many people do not have any back pain, just leg pain.

Most disc herniations occur without any specific accident or injury. Some people wake up with the pain. Sometimes it occurs when they bend over but most of the time it is not caused by a specific injury. It is due to wear and tear and bad luck. Fortunately the leg pain gradually gets better in 80 – 90 % of people usually within 6 – 12 weeks. The body works to remove the herniated disc material, relieving pressure on the nerve. Initially there is inflammation with chemicals that irritate the nerve, which gradually improves. There are 10 – 20 % of people who improve but do not completely get better. Those people are candidates for surgery for removal of the herniated disc material. The entire disc is not removed. The success rate of surgery is 80 – 90 %. However there are risks associated with surgery and therefore surgery is the last resort for treatment. Most people recover and can return to all of their normal activity including work and recreational activities. People are often afraid to do physical activity because the pain was so severe that they do not want it to come back. However there is a only a 10 % chance of having a recurrence due to more disc material (jelly) leaking out of the centre of the disc into the spinal canal. 90% of people recover and do not experience a recurrence of their pain. If people have surgery we recommend that they do not do any heavy lifting or jarring activity for 8 – 12 weeks after the surgery to reduce the risk of recurrence. By 3 months after surgery people can return to full activity.

Treatment for sciatica usually involves finding a way to manage the pain until it goes away. Drugs such as painkillers and anti-inflammatory medication can be helpful. Seizure medication such as Gabapentin and Lyrica are often more effective because they reduce the electrical activity in the nerve. Physiotherapy, chiropractic treatment and massage therapy can provide some temporary relief but do not make the disc herniation heal any faster. Injections of cortisone into the spine called nerve root blocks or epidural blocks can provide pain relief or improvement by decreasing the amount of inflammation around the nerve. The natural history of the condition means that no matter what treatment the person receives, the pain is probably going to gradually get better and go away. Lifestyle modification means avoiding activities that make the pain worse and finding positions or activities that minimize the pain. People often worry that they are causing more damage by remaining active or continuing to work but that is usually not the case. If people experience damage to the nerve it usually occurs at the time of the disc herniation. It is uncommon to develop damage later on. We encourage people to remain as active as their pain allows.

The distribution of a person’s pain depends at which disc the herniation occurs. This determines which nerve root is compressed or irritated. The two most common levels are between the L5 vertebrae and the sacrum (L5S1) and between the 4th and 5th lumbar vertebrae (L4-5). In both cases the pain usually runs down the leg to the ankle or the foot. If pain does not go below the knee the disc herniation is often between the 2nd and 3rd (L2-3) or the 3rd and 4th (L3-4) discs. The diagram below shows the pattern of pain that people experience with disc herniations at different levels in the lower back (lumbar spine). For example, an L5S1 disc herniation usually affects the S1 nerve root which controls movement of the hamstring (posterior thigh) and calf muscles and provides sensation to the back of the thigh and calf and the side of the foot. Pain runs from the buttock to the calf and foot.