sciatica
Meaning of sciatica: A symptom rather than a diagnosis, and a word stretched loosely to cover almost any leg pain that seems to start in the back.
Definition of sciatica
Sciatica is pain that travels from the lower back or buttock down the back of one leg, following the path of the sciatic nerve. It is caused by irritation or compression of that nerve or of the roots that form it, most often by a bulging spinal disc. The pain is usually sharp, burning or electric, and often comes with numbness, tingling or weakness.
Where does the pain come from?
The sciatic nerve is the thickest in the body, roughly the width of a finger where it leaves the pelvis. It is assembled from several nerve roots emerging from the lower backbone and the sacrum, runs through the buttock and down the back of the thigh, and divides behind the knee. Pressure anywhere along that path is felt not where the problem sits but along the territory the nerve serves, which is why a disc in the lower back produces pain in the calf and foot. The usual culprit is the soft center of a spinal disc bulging backward onto a nerve root. Age-related narrowing of the bony canal, a slipped vertebra, a cyst and, far less often, a tumor or an infection compress the same structures.
What else causes pain down the leg?
The distinguishing features are how far down the leg the pain travels, whether it follows a single nerve path, and whether numbness, tingling or weakness travels with it. Pain reaching below the knee along a defined strip points to a nerve root far more strongly than aching confined to the buttock does.
| Condition | How it differs |
|---|---|
| Disc pressing on a nerve root | Follows one nerve path below the knee, worse on coughing |
| Narrowing of the spinal canal | Aching in both legs on walking, eased by leaning forward |
| Hip or sacroiliac joint | Groin or buttock pain that stops above the knee |
| Restless legs syndrome | An urge to move at rest in the evening, not pain along a nerve |
What makes it urgent?
Most sciatica settles over weeks as pressure on the nerve eases, and scans done early often show disc bulges in people with no pain at all. One pattern is different. Numbness in the saddle area between the legs, loss of bladder or bowel control, and weakness spreading into both legs describe cauda equina syndrome, compression of the whole bundle of nerve roots at the base of the spine. It is a surgical emergency, and delay is linked to permanent loss of bladder, bowel and sexual function. Fever, unexplained weight loss, a history of cancer, or pain that is worse lying flat likewise shift attention away from a simple disc. Nerve pain responds poorly to ordinary painkillers, so drugs such as duloxetine are used instead.
Also known as
Used in a sentence
Sciatica was reported down the right leg as far as the foot, worse on coughing.
Good to know
Saddle numbness, loss of bladder or bowel control, or weakness spreading into both legs alongside back pain describes cauda equina syndrome, compression of the nerve root bundle at the base of the spine, in which delay to surgery is linked to permanent loss of function.
Word origin
Where “sciatica” comes from
Sciatica comes through Latin from the Greek ischiadikos, meaning of the hip, from ischion, the hip joint.