What is sciatica?

2010-11-25 00:00

LAST month we looked at slipped discs which is one of the principle causes of sciatica.

The sciatic nerve is made up predominantly of three nerve roots located at the very base of the spine: the so-called L4, L5 and S1 nerve roots. Occasionally the S2 and S3 nerves may be affected. They travel together down the lower spine in what is called the horse’s tail and then escape via openings called foramena, before making their way as the sciatic nerve down the leg to the foot. It’s the longest nerve in the body, and as thick as your little finger.

Sciatica is a group of symptoms in your leg that may include any of the following: pain, numbness, tingling and weakness. Very occasionally it may affect the bladder. The pain can be very severe and treatment is the single most costly item for medical aids.

What is a foramen?

On each side of the spine, an inter-vertebral foramen is located at each spinal level between the vertebrae, strategically and vulnerably placed right between a facet joint and the disc joint. Problems in either joint can cause sciatica by interfering with the nerve roots. Usually the pain is felt in one leg only.

The principle causes of sciatica

• Chemical irritation of the sciatic nerve. Both the facets and the vertebral end-plates are lined with cartilage which has no direct blood supply of its own. This cartilage is supplied with nutrients and oxygen, and waste products are removed, by fluid in and around the joints. If either the disc joint or the facet joints are fixated, the fluids in the joints are not adequately refreshed, causing a build-up of waste products. This toxic soup is now known to be one of the causes of sciatica.

• Pinching of the sciatic nerve, such as in a slipped disc. A bulging disc can physically press on a nerve root causing sciatica.

• A chronically fixated facet joint is starved of oxygen and nutrients. Experiments on white mice show that degeneration of the cartilage (scientists call it immobilisation arthritis) begins within 13 hours of the joint becoming fixated. Gradually over the years the shape of the facet changes, sometimes allowing the vertebra to subluxate forwards (called an antero-lysthesis) which can pinch the nerve root located just in front of the facet.

• Fixations in the sacro-iliac joint.

• The Piriformis syndrome. The sciatic nerve emerges from the pelvis together with a muscle called the Piriformis. Fixations of the sacro-iliac joint can cause the Piriformis to spasm, affecting the sciatic nerve and causing pain and tingling in the leg. SLUMP TEST

To test for sciatica, sit in a kitchen chair and slowly straighten your good leg. Remember that normal feel in your thigh and calf: tight muscles. Now straighten the naughty leg. Is it much tighter? Painful? Then slowly flex your head onto your chest. Worse? You probably have sciatica.

• Next month: what is the sacroiliac joint?

 • Dr Barrie Lewis, BSc, DC can be reached at contact@Chiropractic Help.com You can read more about the chiropractic management of sciatica at www.chiropractic-help.com/Help-for-sciatica pain.html

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