Sciatic nerve

Roots

L4–S3 — the lumbosacral plexus's great outflow.

Course

The thickest nerve in the body (thumb-sized): leaves the greater sciatic foramen below piriformis, descends between the ischial tuberosity and greater trochanter under the gluteus maximus, runs down the posterior thigh on the adductor magnus, and divides at the knee's back into tibial and common peroneal nerves.

Motor supply

The hamstrings and (via its divisions) every muscle below the knee.

Sensory supply

Via its terminal branches — the leg and foot's supply.

Clinical relevance

Sciatica — radiating leg pain, usually from a lumbar disc compressing an L4–S1 root — follows the root's dermatome; gluteal injections outside the upper outer quadrant can hit the nerve. Hip surgery's posterior approach and posterior hip dislocation threaten it with foot drop.

Related conditions

• Sciatica
• Peripheral neuropathy
• Guillain–Barré syndrome