Sciatica - Causes of sciatica

Slipped (herniated) disc

A slipped (or herniated) disc is the most common identified cause of sciatica.

Your spine is made up of vertebrae, discs and nerves. Vertebrae are the blocks of bone that make up the structure of your spine and protect the nerves.

The vertebrae are supported and cushioned by discs. The discs are made from a tough, fibrous case thhat contains a softer gel-like substance. A slipped disc occurs when the outer part of the disc ruptures (splits), allowing the gel inside to bulge and protrude outwards between the vertebrae. When this presses against the sciatic nerve, it can cause sciatica.

As a person gets older the discs start to become harder, tougher and more brittle. Repeated strain on the back means there is a greater chance of a hardened disc splitting and rupturing.

See the Health A-Z topic on slipped disc for more information.

Spinal stenosis

Spinal stenosis is the narrowing of nerve passages in the spine. It occurs when the bones, ligaments or discs of the spine squash the nerves of the spine (usually the sciatic nerve) causing pain, usually in the lower back and legs. It usually affects people in late middle age and older.

Causes of spinal stenosis include:

• age-related changes in the spine
• changes in the ligaments of the spine
• diseases of the bone, such as Paget s disease

See the Health A-Z topic on lumbar decompressive surgery for more information on the treatment of spinal stenosis.

Other causes

Less commonly, sciatica may be caused by:

• infection
• injury
• a growth within the spine, such as a tumour