Causes of sciatica

Sciatica is pain that travels along the sciatic nerve, the longest nerve in the body. It starts in the lower back, runs through the buttock and down the back of the leg, sometimes to the foot. Sciatica is a symptom of irritation or pressure on the nerve roots, not a disease by itself.

Most common causes

• Slipped (herniated) disc: the soft centre of a spinal disc bulges out and presses on a nerve root. This is the most frequent cause, especially in people aged 30 to 50.
• Spinal stenosis: narrowing of the spinal canal from age-related changes, which squeezes nerves, usually in people over 60.
• Degenerative disc disease: wear of the discs over time.
• Spondylolisthesis: one vertebra slips forward over another.
• Piriformis syndrome: a tight muscle in the buttock presses on the sciatic nerve.
• Bone spurs and arthritis in the spine.

Less common causes

• Injury or fracture of the spine or pelvis.
• Tumours or infection in or near the spine.
• Diabetes, which makes nerves more vulnerable.
• Pregnancy, due to weight, posture and hormone changes.

Factors that raise the risk

• Age, with disc wear starting in middle age.
• Excess body weight.
• Long sitting, sedentary work and poor posture.