Sciatica is a pain in the leg caused by compression and/or irritation of one of five nerve roots that are branches of the sciatic nerve. The pain is felt in the lower back, buttock, and/or various parts of the leg and foot. In addition to pain, there may be numbness, muscular weakness, and difficulty in moving or controlling the leg. Typically, the symptoms are only felt on one side of the body.

Although sciatica is a relatively common form of low back pain and leg pain, the true meaning of the term often is misunderstood. Sciatica is a set of symptoms rather than a diagnosis for what is irritating the root of the nerve, causing the pain. This point is important, because treatment for sciatica or sciatic symptoms often will be different, depending upon the underlying cause of the symptoms.

Causes of sciatica

Sciatica is generally caused by the compression of a lumbar spine nerve root L4 or L5 or sacral nerve roots S1, S2 or S3, or far less commonly, by compression of the sciatic nerve itself.

When sciatica is caused by compression of a lumbar nerve root it is considered a lumbar radiculopathy (or radiculitis when accompanied with an inflammatory response) from a spinal disc herniation (a herniated intervertebral disc in the spine), or from roughening, enlarging, and/or misaligning of the vertebrae (spondylolisthesis), or degenerated discs.

Sciatica may also be experienced in late pregnancy, primarily resulting from the uterus pressing on the sciatic nerve, and, secondarily, from the muscular tension and/or vertebral compression consequent to carrying the extra weight of the fetus, and the postural changes inherent to pregnancy.

"Pseudo-sciatica", which causes symptoms similar to spinal nerve root compression, is caused by the compression of peripheral sections of the nerve, usually from soft tissue tension in the piriformis or related muscles. One possible cause of this is the piriformis syndrome. In this condition, the piriformis muscle, located beneath the gluteal muscles, contracts spasmodically and strangles the sciatic nerve beneath the muscle. Another cause of sciatic symptoms is sacroiliac joint dysfunction. Unhealthy postural habits, such as excessive time sitting in chairs, and sleeping in the fetal position, along with insufficient stretching and exercise of the relevant myofascial areas, can lead to both the vertebral and soft tissue problems associated with sciatica.

Another source of sciatic symptoms is active trigger points of the lower back and the gluteus muscles. In this case, the referred pain is not consequent to compression of the sciatic nerve, though the pain distribution down the buttocks and leg is similar. Trigger points occur when muscles become ischaemic (low blood flow) due to injury or chronic muscular contraction. The most commonly associated muscles with trigger points triggering sciatic symptoms are: the quadratus lumborum, the gluteus medius, the gluteus minimus, and the deep hip rotators.

One cause of sciatica is a spinal disc herniation, pressing on one of the sciatic nerve roots. The spinal discs are composed of a spongiform cartilage with a liquid center. The discs separate the vertebrae, thereby allowing room for the nerve roots to properly exit through the spaces between the L4, L5, and sacral vertebrae. The discs cushion the spine from compressive forces, but are weak to pressure applied during rotational movements. That is why a person who bends to one side, at a bad angle, to pick up a piece of paper may more likely herniate a spinal disc than a person falling from a ladder and landing on his or her back. Herniation of a disc occurs when the liquid center of the disc bulges outwards, tearing the external ring of fibers, and compresses a nerve root against the lamina or pedicle of a vertebra, thus causing sciatica.

Other compressive spinal causes include Spinal Canal Stenosis, a condition wherein the spinal canal (the spaces through which the spinal cord runs) narrows and compresses the spinal cord. This narrowing can be caused by bone spurs, vertebral dislocation, or herniated disc which decreases available space for the spinal cord, thus pinching nerves in the spinal cord that travel to the sciatic nerve and irritating them with friction.

The sciatic nerve runs through the piriformis muscle in the buttocks region. When the muscle shortens or spasms due to trauma, it can compress the sciatic nerve. This cause of sciatic symptoms is piriformis syndrome, a major cause of sciatica. The approach to treating Sciatica is to reduce the compressive forces causing the pressure upon the sciatic nerve. This can be accomplished through traction and realignment therapeutic procedures in the case where the sciatica is spinal-related. Manual muscle stretching, massage, and mobilization techniques should be used when the sciatica is piriformis muscle-related. General therapeutic goals include helping the muscles loosen, thereby lessening pain, and to minimize inflammation.

Diagnosis and treatment

Because of the many conditions that can compress nerve roots and cause sciatica, treatment options often differ from patient to patient. Treatment of the underlying cause of the compression is often the most effective course. When the cause is due to a prolapsed or lumbar disc herniation, research has shown that, with supportive treatment to help relieve pain, 90% of disc prolapse will recover with no specific intervention. Genetics appear to influence the risk of developing disc herniation.

Imaging methods such as MR neurography may help diagnosis and treatment of sciatica. MR neurography has been shown to diagnose 95% of severe sciatica patients, while as few as 15% of sciatica sufferers in the general population are diagnosed with disc-related problems. MR neurography is a modified MRI technique using MRI software to provide better pictures of the spinal nerves and the effect of compression on these nerves. MR neurography may help diagnose piriformis syndrome which is another cause of sciatica that does not involve disc herniation.

Most cases of sciatica can be effectively treated by one or a combination of the following:

  • Physical therapy and exercise, which generally is best done in a controlled, progressive manner and will include some combination of stretching, strengthening and cardio conditioning
  • Massage therapy
  • Appropriate changes in behaviour, ergonomics and environment (for example cushioning, chair and desk height, sleeping position).
  • Anti-inflammatory medications (NSAIDs)
  • Pain medication (eg. paracetamol)
  • Epidural steroid injections to deliver local anti-inflammatory agents (and possibly a pain medication) directly to the affected area.
  • Alternative medicine treatments (chiropractic or osteopathic manipulation).
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