Sacral Plexus

The sacral plexus is located on the posterolateral wall of the lesser pelvis. The two main nerves arising from the sacral plexus, the sciatic and pudendal nerves, lie external to the parietal pelvic fascia. Most branches of the sacral plexus leave the pelvis through the greater sciatic foramen.

The sciatic nerve is the largest nerve in the body. It is formed as the large anterior rami of spinal nerves L₄-S₃ converge on the anterior surface of the piriformis. As it is formed, the sciatic nerve passes through the greater sciatic foramen, usually inferior to the piriformis, to enter the gluteal region. It then descends along the posterior aspect of the thigh to supply the posterior aspect of the thigh and the entire leg and foot.

The pudendal nerve is the main nerve of the perineum and the chief sensory nerve of the external genitalia. Accompanied by the internal pudendal artery, it leaves the pelvis through the greater sciatic foramen between the piriformis and coccygeus muscles. It then hooks around the ischial spine and sacrospinous ligament and enters the perineum through the lesser sciatic foramen.

The superior gluteal nerve leaves the pelvis through the greater sciatic foramen, superior to the piriformis to supply muscles in the gluteal region.

The inferior gluteal nerve leaves the pelvis through the greater sciatic foramen, inferior to the piriformis and superficial to the sciatic nerve, accompanying the inferior gluteal artery. Both break up into several branches that enter the deep surface of the overlying gluteus maximus muscle.