Somatic Innervation The lumbosacral plexus and its branches provide motor and sensory somatic innervation to the lower abdominal wall, the pelvic and urogenital diaphragms, the perineum, and the hip and lower extremity (Fig. 5.8). The nerves originating from the muscles, the lumbosacral trunk, the anterior divisions of the upper four sacral nerves (sacral plexus), and the anterior division of the coccygeal nerve and fibers from the fourth and fifth sacral nerves (coccygeal plexus) are found on the anterior surface of the piriformis muscle and lateral to the coccyx, respectively, deep in the posterior pelvis. In Table 5.5 each major branch is listed by spinal segment and structures innervated. In addition to these branches, the lumbosacral plexus includes nerves that innervate
Figure 5.7 The lymphatic drainage of the female pelvis. The vulva and lower vagina drain to the superficial and deep inguinal nodes, sometimes directly to the iliac nodes (along the dorsal vein of the clitoris) and to the other side. The cervix and upper vagina drain laterally to the parametrial, obturator, and external iliac nodes and posteriorly along the uterosacral ligaments to the sacral nodes. Drainage from these primary lymph node groups is upward along the infundibulopelvic ligament, similar to drainage of the ovary and fallopian tubes to the para-aortic nodes. The lower uterine body drains in the same manner as the cervix. Rarely, drainage occurs along the round ligament to the inguinal nodes.
muscles of the lateral pelvic wall (obturator internus, piriformis), posterior hip muscles, and the pelvic diaphragm. A visceral component, the pelvic splanchnic nerve, is included.
Nerves supplying the cutaneous aspects of the anterior, medial, and lateral lower extremities, and the deep muscles of the anterior thigh, primarily leave the pelvis by passing beneath the inguinal ligament. Nerves supporting the posterior cutaneous and deep structures of the hip, thigh, and leg lie deep in the pelvis and should not be vulnerable to injury during pelvic surgery. The obturator nerve travels along the lateral pelvic wall to pass through the obturator foramen into the upper thigh, and it may be encountered in more radical dissections involving the lateral pelvic wall, in paravaginal repairs, or in trocar-based incontinence and prolapse procedures.
The pudendal nerve innervates the striated urethral and anal sphincters and the deep and superficial perineal muscles and provides sensory innervation to the external genitalia. This nerve originates from S2–S4, crosses over the piriformis to travel with the internal pudendal vessels into the ischiorectal fossa through the lesser sciatic foramen, and travels through the pudendal canal (Alcock’s canal) on the medial aspect of the obturator internus muscles, where
Table 5.4 Primary Lymph Node Groups Providing Drainage to Genital Structures
Inguinal Vulva, lower vagina; (rare: uterus, tube, ovary) it divides into its three terminal branches to provide the primary innervation to the perineum. Other nerves contribute to the cutaneous innervation of the perineum: 1. The anterior labial nerve branches of the ilioinguinal nerve—these nerves emerge from within the inguinal canal and through the superficial inguinal ring to the mons and upper labia majora.
Figure 5.8 The sacral plexus. (Modified from Kamina P. Anatomie gyn´ et obst´ Editeur, 1984:90, with permission.) etricale. Paris, France: Maloine Sa ´
Table 5.5 Lumbosacral Plexus 2.