Handa 9781496386441 Full Sample Chap 1

18

SECTION I  Preparing for Surgery

I and posterior aspects of the adductor brevis muscle. The anterior branch supplies the adductors longus and brevis muscles. The posterior branch supplies the gracilis, adductors brevis and magnus, and obturator externus muscles. The hamstring head of the adductor magnus receives innervation from the tibial branch of the sciatic nerve. Notably, though the pectineus muscle is anatomically part of the medial thigh and may receive some innervation from the anterior branch of the obtu- rator nerve, it receives primary innervation from the femoral nerve. The obturator nerve was described ear- lier under lumbar plexus branches. Symptoms of obtu- rator nerve injury may include medial thigh or groin pain, weakness with thigh adduction, and sensory loss in the medial thigh of the affected side. THE PELVIC FLOOR When humans assumed the upright posture, the open- ing in the bony pelvis came to lie at the bottom of the abdominopelvic cavity. This required the evolution of a supportive system to prevent the pelvic organs from being pushed downward through this opening. In the woman, this system must withstand these downward forces but allow for the passage of the large and cra- nially dominant human fetus. The supportive system that has evolved to meet these needs consists of a fibro- muscular floor that forms a shelf spanning the pelvic outlet and that contains a cleft for the birth canal and excretory drainage. A series of visceral ligaments and fasciae tethers the organs and maintains their position over the closed portions of the pelvic diaphragm mus- cles (levators) and covering fasciae. The openings in the pelvic diaphragm and in the perineal membrane for parturition and elimination have required the develop- ment of ancillary fibrous elements that are concentrated

over open areas in the muscular floor to support the viscera in these weak areas. This section discusses the structures of the perineal portion of the pelvic floor; the fibrous supportive system is described in the section on the pelvic viscera and cleavage planes and fascia. Perineal Membrane The perineal membrane forms the inferior portion of the anterior pelvic floor below the levator muscles and covering fasciae. It is a triangular sheet of dense, fibromuscular tissue that spans the anterior half of the pelvic outlet, separating the superficial from the deep perineal pouch (see FIG. 1.13 ). It was previously called the urogenital diaphragm, and this change in name reflects the appreciation that it is not a two-layered structure with muscle in between, as was previously thought. It lies just caudal to the skeletal muscle of the striated urogenital sphincter (formerly the deep trans- verse perineal muscle). Because of the presence of the vagina, the perineal membrane cannot form a continu- ous sheet to close off the anterior pelvis in the woman, as it does in the man. It does provide support for the posterior vaginal wall by attaching the vagina and peri- neal body to the ischiopubic rami, thereby limiting their downward descent. This layer of the floor arises from the inner aspect of the inferior ischiopubic rami superior to the ischiocavernosus muscles and the crura of the cli- toris. The medial attachments of the perineal membrane are to the urethra, walls of the vagina (approximately at the level of hymenal ring), and perineal body. Just cephalad to the perineal membrane, in the deep pouch of anterior perineal triangle lie two arch-shaped striated muscles that begin posteriorly and pass anteriorly to arch over the urethra ( FIG. 1.18 ) These are the com- pressor urethrae and the sphincter urethrovaginalis mus- cles. They are a part of the striated urogenital sphincter

Sphincter urethrovaginalis m.

Compressor urethrae m.

Vaginal m.

Copyright © 2019 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited.

Smooth m.

Iliococcygeus m.

FIGURE 1.18  Structures visible within deep perineal pouch/compartment after removal of the superficial perineal muscles and perineal membrane.

Puborectalis m.

0004290808.INDD 18

4/3/2019 9:30:15 PM