Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

Overview

• Sciatic nerve is the largest nerve in the body.
• Originates from the lumbosacral plexus (L4–S3 nerve roots).
• Formed by two components: tibial nerve and common peroneal (fibular) nerve.

Course of the Sciatic Nerve

• Leaves the pelvis through the greater sciatic foramen.
• Usually passes inferior to the piriformis muscle.
• Enters the posterior thigh between the greater trochanter and ischial tuberosity.
• Travels down the posterior thigh.
• Typically divides into tibial nerve and common peroneal nerve in the upper popliteal fossa.

Anatomical Variation

• In about 10% of individuals the sciatic nerve divides early at the greater sciatic foramen.

Branches

• Tibial nerve – medial division.
• Common peroneal (fibular) nerve – lateral division.

Clinical Relevance

• The common peroneal division is most commonly injured.
• Injury can occur during total hip replacement or posterior hip approach.
• Traction or excessive limb lengthening during surgery may stretch the nerve.

Surgical Precaution

• During traction on the lower limb keep the knee flexed and hip extended.
• This reduces tension on the sciatic nerve.

Nerve Injury Effects

• Injury to common peroneal nerve leads to foot drop.
• Results in weakness of ankle dorsiflexion.

Muscle Innervation

• Sciatic nerve supplies hamstring muscles before dividing.
• Short head of biceps femoris is innervated by the common peroneal division.
• Long head of biceps femoris is innervated by the tibial division.