Sciatica Health Article

Definition

Sciatica describes pain or discomfort in the distribution of the sciatic nerve or its components. This nerve runs from the lower part of the spinal cord, down the back of the leg, to the foot. Injury to, or pressure on, the sciatic nerve can cause the characteristic pain of sciatica—a sharp or burning pain that radiates from the lower back or hip, following the path of the sciatic nerve to the foot.

Description

The sciatic nerve is the largest and longest nerve in the body. It supplies sensation from the lower back to the foot. The nerve originates in the lumbar region of the spinal cord. As it branches off from the spinal cord, it passes between the bony vertebrae (the component bones of the spine) and runs through the pelvic girdle (hipbones). The nerve passes near the hip joint and continues down the back of the leg to the foot.

Sciatica is a fairly common disorder. Approximately 40% of the population suffers from it at some point in their lives; however, only about 1% experience any sensory or motor deficits. Sciatic pain has several root causes, and its treatment is directed to the underlying problem.

Of the identifiable causes of sciatic pain, lumbosacral (LS) radiculopathy and back strain are the most frequently suspected. The LS area is the lower part of the spine, and radiculopathy describes pain radiating from pressure on a spinal nerve roots. This area between the vertebrae (hard bones) is cushioned with a disk of shockabsorbing tissue. The spinal canal, comprising the spinal cord and other nerve roots, is hollow and lies in the middle of the spinal column. It is the disks between the vertebrae that enable the back to bend or flex.

A "ring" of cartilage, gristle-like in character, is found the outer edge of the disk (the annulus). The disk's center (nucleus) is a substance like gel. When a disk ruptures, or herniates, it does so because of wear-and-tear, excessive weight, poor posture, injury (perhaps due to improper lifting), or disease. The center nucleus pushes the outer edge of the disk into the spinal canal, putting pressure on the nerves. The spinal nerve root may become compressed by the shifted tissue or the vertebrae. This compression of the nerve root sends a pain signal to the brain. Although the injury is actually suffered by the nerve roots, the pain may be perceived as originating anywhere along the sciatic nerve. Further, if fragments of the disk lodge in the spinal canal, the nerves that control bowel and urinary functions may be damaged. Incontinence may result.

Sciatica is largely a symptom of a herniated disk. However, compression of the sciatic nerve can also present as muscle spasms in the lower back (back strain). In this case, pressure is placed on the sciatic nerve. In rare cases, infection, cancer, bone inflammation, or other diseases may cause pressure. Another possible cause of sciatica is piriformis syndrome.

As the sciatic nerve passes behind the hip joint, it shares the space with several muscles. One of these muscles, the piriformis muscle, is closely associated with the sciatic nerve. In some people, the nerve actually runs through the muscle. If this muscle is injured or has a spasm, it places pressure on the sciatic nerve, in effect, compressing it.

In many sciatica cases, the specific cause is never identified. About half of affected individuals recover from an episode within a month. Some cases persist and may require aggressive treatment. In other cases, the pain returns or becomes chronic.

Causes and symptoms

Patients with sciatica may experience low back pain, but the most common symptom is pain that radiates through one buttock and down the back of the leg. The most frequently identified cause of pain is compression or pressure on the sciatic nerve. The extent of the pain varies. Some patients describe pain that centers in the area of the hip; others feel discomfort all the way to the foot. The quality of the pain also varies; it may be described as tingling, burning, prickly, aching, or stabbing.

Onset of sciatica may be sudden, but it might also develop gradually. The pain may be intermittent or continuous. Certain activities (such as bending, coughing, sneezing, or sitting) can worsen the pain.

Sudden loss of bowel or bladder control, weakness in the legs, buttocks, or torso, as well as numbness that goes upwards from the toes or the feet, may indicate a sciatic condition.

Chronic pain may arise from more than simple compression of the nerve root. Discogenic pain, the result of injury to the innervated portions of the annulus fibrosus, is a common cause of sciatica. Pain is generally felt in the buttocks and in the posterior thigh.

According to some pain researchers, physical damage to a nerve is only half of the equation. A theory developed in 2001 proposes that some nerve injuries result when certain neurotransmitters and immune system chemicals that exacerbate and sustain a pain message. Even after the injury has healed or the damage has been repaired, the pain lingers. Effective management of this type of pain is difficult. Another theory that has been put forward is that back problems may be inherited. This theory presupposes that a genetic abnormality is responsible for a number of cases of spinal disk disease cases. This defect makes people susceptible to rupture when the back is strained. The investigators claimed that 25% of all cases of sciatica, lower back problems, and discomfort higher in the spine, might be attributable to this gene defect. When classic symptoms are absent, identification of the defect could enable diagnosis of disease, thereby facilitating the therapeutic process.