Path of the Sciatic Nerve

The sciatic nerve is the largest nerve in the human body, originating from the lumbosacral plexus and extending down the posterior aspect of the lower limb before dividing into its terminal branches. Here’s a detailed description of its path:

1. Origin

• The sciatic nerve arises from the lumbosacral plexus, specifically from the ventral rami of L4, L5, S1, S2, and S3.
• These nerve roots contribute to two major divisions:
  • Tibial division (L4-S3)
  • Common fibular (peroneal) division (L4-S2)

2. Pelvic Course

The nerve exits the pelvis through the greater sciatic foramen, passing inferior to the piriformis muscle (in most cases). It travels alongside the inferior gluteal artery and vein, posterior to the ischial spine.

3. Gluteal Region

The sciatic nerve runs deep to the gluteus maximus and superficial to the external rotators (e.g., gemelli muscles, obturator internus, quadratus femoris). It does not supply the gluteal muscles.

4. Posterior Thigh

The nerve descends along the posterior thigh, running deep to the biceps femoris. It provides motor branches to the hamstring muscles (except the short head of the biceps femoris, which is innervated by the common fibular nerve).

5. Division at the Popliteal Fossa

At the superior aspect of the popliteal fossa, usually near or just above the knee, the sciatic nerve bifurcates into:

• Tibial nerve – Continues down the posterior leg to supply the posterior compartment and plantar foot.
• Common fibular (peroneal) nerve – Wraps around the fibular head and divides into:
  • Superficial fibular nerve (lateral compartment of the leg)
  • Deep fibular nerve (anterior compartment of the leg and dorsum of the foot)

6. Termination

The sciatic nerve itself does not have a single termination point since it splits into the tibial and common fibular nerves. These two nerves continue their respective courses, innervating the leg and foot.

Clinical Relevance

• Sciatica: Compression of the sciatic nerve (e.g., from a herniated disc, piriformis syndrome, or spinal stenosis) can cause radiating pain down the posterior leg.
• Variations: In some individuals, the sciatic nerve may split within the pelvis, with part of it passing through or above the piriformis.