Anatomy

The sacral plexus is formed by the lumbosacral trunk and the ventral rami of the first, second, third sacral nerves. The nerves forming the sacral plexus converge towards the greater sciatic notch and unite to form a large band located on the posterior wall of the pelvic cavity, in front of the piriformis muscle. Hypo gastric vessels, the ureter and the sigmoid colon are located in front of the plexus. Of note, gluteal vessels follow the same course as the sacral nerves [3], but in an anterior plane. The sacral plexus lies dorsally on the piriformis and ventrally on the fascia of this muscle. This fascia contributes to form the pelvic aponeurosis or fascia. This fascia, fibrous and resistant, is fixed medially on the anterior sacral foramina, where the sacral nerves emerge. Through this fascia, the sacral plexus lies near the rectum. Laterally, the sacral plexus lies close to the greater sciatic foramen sandwiched by the obturator internus muscle. The sacral plexus runs in a fascial plane limited by the pelvic fascia ventrally, the piriformis dorsally and medially and laterally by the obturator internus muscle. Hypogastric vessels are located near sacral plexus as well as the superior gluteal artery which passes between the lumbosacral trunk and the first sacral nerve. The inferior gluteal vessels run between the second and the third sacral nerves. The other important arteries are the lateral superior and inferior sacral arteries, the ischial arteries and the pudendal artery (figure below).

Collateral and terminal branches of the sacral plexus
  •Ventral collateral branches of the sacral plexus are the nerve to the obtura-
    tor internus muscle, the haemorrhoidal nerve, the pudendal nerve and
    nerves to the various pelvic structures. All these nerves form the pudendal
    plexus (ventral branch of S4, anastomized with the S2 and S3 branches of
    the sacral plexus). These nerves supply pelvic and perineal organs.
  •Dorsal collateral branches are the inferior and superior gluteal nerves, the
    nerves to the piriformis, gemelli and quadratus femoris muscles.
  •A single terminal branch.

The sacral plexus innervates the skin of the medial part of the gluteal and
posterior aspects of the thigh. It also innervates the hip joint and proximal
muscles of the thigh. More caudally, the plexus extends as the sciatic nerve.