Definition: Sciatica refers to the experience of pain in the distribution of the sciatic nerve. The pain usually radiates from the buttock down the leg to the foot. Sciatica is caused by the compression or irritation of a nerve root in the lumbar spine. The distribution of the pain depends on which nerve root is affected. It is rarely due to irritation of the sciatic nerve itself.
Signs and symptoms: The major symptom is pain which can be excruciating. The onset of pain is often sudden and may be related to a specific event such as bending and twisting of the spine. However in many cases there is no specific injury that can be attributed to the onset of the pain. In some cases there is a specific cause such as heavy lifting, a fall or a motor vehicle accident. The pain is intense and persistent. Patients often have trouble finding a position which will improve the pain. Pain killers are often prescribed but usually do not provide complete relief of the pain. Leg pain is the major symptom. Some people also experience back pain. In some people they experience back pain for hours or days before the onset of the leg pain. However the leg pain is usually much worse than the back pain. Straightening the affected leg will often make the pain worse. Lying down with the knees bent can improve the pain. Coughing, sneezing or straining while going to the bathroom often makes the pain worse. In addition to the leg pain, patients can experience numbness in part of the leg. If the nerve root is severely compressed people can also experience weakness in one or more muscles in the leg. However most people only experience pain with no or little numbness and no weakness. The distribution of the pain, numbness and weakness can help identify which nerve root is being irritated. In severe cases the bladder or bowel can also be affected. This is referred to as cauda equina syndrome and is considered a true emergency and requires immediate investigation and treatment.
The two most common nerve roots that are affected are the fifth lumbar (L5) and the first sacral (S1) roots. Each has a specific distribution of the pain, numbness and weakness. An L5 radiculopathy causes pain that radiates from the buttock down the leg to the outside of the ankle and into the top of the foot toward the big toe. People experience numbness on the outside of the ankle and top of the foot. Weakness in the muscle that bends the ankle backwards results in a footdrop. This can often be detected by a slapping of the foot that occurs with each step. People often trip over small elevations because they are unable to lift their foot when they walk. An S1 radiculopathy causes pain that runs from the buttock through the pack of the thigh and into the calf and outside of the foot. The numbness is usually experienced on the outside of the foot. The weakness, when present involves the hamstring muscle which bends the knee and the calf muscle which bends the foot downward. If the S1 nerve root is affected the person may also have an absent ankle reflex when tested by their doctor. The 4th lumbar nerve root (L4) is the 3rd most frequently affected nerve and results in pain that radiates through the lateral thigh and the inside of the lower leg. Numbness usually occurs on the outside of the thigh. The thigh muscle can be weak and the knee reflex can be decreased or absent.
Causes: The most common cause of sciatica is a disc herniation in the lumbar spine.
The most common levels in the spine where disc herniations occur, is between the 4th and 5th lumbar vertebrae (L4-5) or between the 5th vertebra and the sacrum (L5-S1). Herniations occur less often at higher levels in the lumbar spine. Other less common causes are synovial cysts that arise from the facet joints and if they protrude into the spinal canal can compress a nerve root. Infections and tumors are very uncommon causes of nerve root compression. Spondylolisthesis (link) refers to a shift between two vertebrae which can result in narrowing of the foramen, which is the opening between the vertebrae where the nerve roots exit from the spine, causing compression of the nerve root. Spinal stenosis can result in severe leg pain but more often causes pain that is produced by activity such as walking.
Natural history: In 80 to 90% of people the leg pain gradually gets better regardless of what a person does. It often takes 6 to 12 weeks for the pain to completely go away. In some people the pain goes away much sooner and in others it can take several months for the pain to resolve. In 10 to 20% of people the pain does not go away. If often improves to a certain degree and then remains the same. These people would potentially benefit from surgery to relieve the pressure on the nerve root. In some people activities associated with work, recreation or activities of daily living can aggravate the pain. In other people the pain remains the same regardless of their activity. Once the symptoms resolve they usually do not recur. The disc herniation can heal and recur in approximately 10 % of people. 90% of people do not have a recurrence and should be able to return to normal activity without developing pain.
Most disc herniations occur in people between 20 and 60 years of age. They can occur in teenagers but this is uncommon. After the age of 60 disc herniations are less common than lumbar spinal stenosis. In most people the discs become dehydrated as they age. This results in a decrease in the height of intervertebral discs which can lead to bulging of the outer annulus. This decease in disc height affects the associated lumbar facet joints and can lead to the progressive development of osteoarthritis. The occurrence of a disc herniation may accelerate this process.
Testing: CT scanning and MRI imaging are the two diagnostic procedures that are used to show the disc herniation or other cause of nerve root compression. This should be performed in people who would potentially benefit from surgery. Because most people get better without surgery, most people do not require any imaging studies. If the person has had previous lumbar spine surgery then MRI with contrast is the best test for identifying a new or recurrent disc herniation. EMG and NCS can identify which nerve is affected, especially if the person has any muscle weakness.
Treatment: Because most disc herniations heal without surgery, non-operative treatment should be the first line of treatment. Physiotherapy, massage therapy and chiropractic treatment can benefit some people. Lumbar traction can also improve the sciatic leg pain. However in some people these forms of treatment can also aggravate the persons pain. Spinal decompression is a machine that applies repeated traction to the lower back is a non-operative approach that can help some people with disc herniations. However this treatment is not supported by any good scientific studies. People should remain as active as their pain permits. Injection of steroid medication into the spinal epidural space can significantly improve a persons pain by decreasing the inflammation which results from the disc herniation. This procedure is usually performed by anesthesiologists. Remaining active and continuing to work does not cause more damage and may not aggravate the pain. Bed rest, which was the most common recommended treatment in the past, does not relieve the pain or hasten a persons recovery. Prolonged bed rest can lead to loss of conditioning and make it more difficult for the person to return to their normal activity level once the pain resolves.
In the 10 to 20% of people whose pain does not go away after 6 to 12 weeks, surgery can relieve the pain. The most common operation for lumbar disc herniations is a microdiscectomy.
This involves a small incision in the back at the level of the affected disc. The piece of disc which is putting pressure on the nerve is identified and removed. Micro refers to the use of a microscope which provides better visibility and allows the operation to be done through a very small incision. Other surgical procedures include endoscopic discectomy and percutaneous discectomy which involve even smaller incisions but are less common. None of these procedures result in the removal of the whole disc. Usually only the small herniated fragment of disc material that is compressing the nerve is removed.
Results of surgery: The success rate of microdiscectomy or similar surgical procedures is 80 to 90%. Most people have immediate relief of their leg pain. Numbness and weakness sometimes improve very quickly but sometimes take months to improve. In a small number of people the numbness and weakness may not improve even if the pain is relieved. In 5 – 10 % of people treated with surgery, which is approximately 1% of people who develop sciatica from disc herniations, pain can persist and become a chronic problem. This is due to damage to the nerve at the time of the original disc herniation. This is referred to as neuropathic pain and can be difficult to treat.
Possible complications of surgery: Infection, nerve injury, spinal fluid leak and instability are possible complications of the surgery. Most of them cause temporary symptoms but can lead to chronic back or leg pain.