Sciatic Nerve

Published on 08/03/2015 by admin

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Last modified 08/03/2015

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Chapter 16 Sciatic Nerve

The Sciatic Nerve in the Pelvis

Anatomy

The Sciatic Nerve in the Buttock

Anatomy

The gluteus maximus (inferior gluteal nerve) has a dual insertion into the femur and, with the tensor fasciae latae (superior gluteal nerve), into the iliotibial tract. The superior border of the gluteus maximus is contiguous with the inferior border of the gluteus medius (superior gluteal nerve).

The plane deep to the gluteus maximus is relatively avascular, and the entire muscle can be lifted to display the underlying anatomy.

The piriformis originates from the front of the sacrum and is inserted into the femur. The points of insertion of both the piriformis and gluteus maximus into the femur should be clearly understood.

The sciatic nerve enters the gluteal region through the greater sciatic foramen below the piriformis and comes to lie on the ischium (Figure 16-3). The nerve to quadratus femoris is deep to the sciatic nerve, and the posterior cutaneous nerve of the thigh lies superficial to the sciatic nerve. The sciatic nerve descends between the greater trochanter and the ischial tuberosity, crossing posterior to the obturator internus and the gemelli.

The inferior gluteal nerve arises from L5, S1, and S2 ventral rami, and leaves the pelvis via the greater sciatic foramen, below the piriformis. The inferior gluteal nerve divides into branches that sink into the deep surface of the gluteus maximus (Figure 16-4).

The pudendal nerve is the chief nerve of the perineum and of the external genitalia. Only a small segment of this nerve is seen in the gluteal region (Figure 16-5). The pudendal nerve arises from the anterior surfaces of S2, S3, and S4 rami, passing back between the piriformis and coccygeus muscles, medial to the pudendal vessels. The pudendal nerve and its accompanying vessel exit the greater sciatic foramen to enter the pudendal canal through the lesser sciatic foramen, having passed over the ischial spine. The spine can be palpated per vaginam, and this serves as the guide for local anesthetic injection, even if the fetal head is low in the pelvis. The nerve runs forward into the ischiorectal fossa to lie in the lateral wall of the fossa.