Nerve · Glutes

Sciatic nerve

Nervus ischiadicus

The sciatic nerve is the largest nerve in the body — about as thick as a thumb where it leaves the pelvis. It is really two nerves, tibial and common peroneal, bound in one sheath for the length of the thigh before they separate above the knee. Between them they supply the hamstrings and every muscle below the knee, and all the skin of the leg and foot except a strip on the inner side. It leaves the pelvis through the greater sciatic foramen, passes below piriformis, and runs down the back of the thigh midway between the sitting bone and the greater trochanter. One point is worth being precise about, because it is so often muddled: most true "sciatica" does not begin at the sciatic nerve at all, but at the nerve roots in the low back that feed it — so leg pain in a sciatic distribution is a signpost to look at the lumbar spine first, and at the buttock second. Where the nerve itself is the problem, the usual sites are the deep buttock, where it passes at or through piriformis, and the gap beneath the hamstring origin at the sitting bone, which typically gives pain on prolonged sitting and on driving.