Sciatic and common peroneal nerve

Question 1

Sciatic and common peroneal nerve anatomy

Answer 1

• L4–S3 nerve roots
• It emerges from the pelvis below the piriformis muscle, curving laterally and downward through the gluteal region. Initially it lies midway between the posterior superior iliac spine and ischial tuberosity. Lower down in the thigh it courses midway between the ischial tuberosity and greater trochanter
• The common peroneal nerve and tibial nerve are its two derivatives at the mid-thigh. The common peroneal nerve importantly winds forward around the neck of the fibula

Question 2

Sciatic and common peroneal nerve injury

Answer 2

• At the sciatic notch and the lateral aspect of the fibular neck respectively
• Both nerves are susceptible to stretch injuries from hyperflexion of the thighs in improper lithotomy positions
• The common peroneal nerve may be compressed at the fibular neck in lithotomy

Question 3

Sciatic and common peroneal nerve symptoms

Answer 3

• Sciatic nerve injury presents as sensory impairment below the knee and weakness of hip extension and knee flexion
• Foot drop is reported when the common peroneal nerve is injured, along with paraesthesia over the calf and dorsum of the foot