BONY PELVIS

This chapter provides a general anatomic framework for understanding diseases of the pelvis. The bony, ligamentous, and muscular framework of the pelvis is presented first. Next, the pelvic vessels and nerves and the genital, urinary, and gastrointestinal viscera are discussed. Finally, the perineum and external genitalia are reviewed.

BONY PELVIS

The pelvic bones are the sacrum (the termination of the axial skeleton) and the two innominate bones. The latter are formed by the fusion of the iliac, ischial, and pubic ossification centers at the acetabulum ( Fig. 2-1 ). The ischium and pubis also meet below, in the center of the inferior ramus, to form the obturator foramen. The weight of the upper body is transmitted from the axial skeleton to the innominate bones and lower extremities through the strong sacroiliac (SI) joints. As a whole, the pelvis is divided into a bowl-shaped false pelvis, formed by the iliac fossae and largely in contact with intraperitoneal contents, and the circular true pelvis wherein lie the urogenital organs. At the pelvic inlet, the true and false pelves are separated by the arcuate line, which extends from the sacral promontory to the pectineal line of the pubis. The lumbar lordosis that accompanies erect posture tilts the axis of the pelvic inlet so that it parallels the ground; the pelvic inlet faces anteriorly, and the inferior ischiopubic rami lie horizontal ( Fig. 2-2 ). When approaching the pelvis through a low midline incision, the surgeon gazes directly into the true pelvis.

Figure 2-1 The bones and ligaments of the pelvis. (From Hinman F Jr: Atlas of Urosurgical Anatomy. Philadelphia, WB Saunders, 1993, p 196.)

Figure 2-2 Pelvis in standing position. The axis of the pelvic cavity is horizontal because of lumbar lordosis. (From Zacharin RF: Pelvic Floor Anatomy and the Surgery of Pulsion Enterocele. New York, Springer-Verlag, 1985, p 15.)

The anterior and posterior iliac spines, the iliac crests, the pubic tubercles, and the ischial tuberosities are palpable landmarks that orient the pelvic surgeon (see Fig. 2-1 ). Cooper's (pectineal) ligament overlies the pectineal line and offers a sure hold for sutures in hernia repairs and urethral suspension procedures (see Fig. 2-7 ). The ischial spine is palpable transvaginally and attaches to the pelvic diaphragm and the sacrospinous ligament. The sacrospinous ligament separates the greater and lesser sciatic foramina. Together with the sacrotuberous ligament, it stabilizes the SI joint by preventing downward rotation of the sacral promontory. The SI joint, synovial in type, gains additional strength from anterior and posterior ligaments. In pelvic trauma, fractures virtually never involve this joint but they occur adjacent to it. The pubes, the thinnest of the pelvic bones, are nearly always fractured, and their fragments may injure the adjacent bladder, urethra, and vagina. Resection or congenital nonunion of the pubes (e.g., bladder exstrophy) does not affect ambulation because of the strength of the SI joint ( Waterhouse et al, 1973 ; Golimbu et al, 1990 ).

Figure 2-7 Topography (A,) and posterior wall (B,) of the left inguinal canal, viewed from the preperitoneal space. The location of three types of inguinal hernia is demonstrated. (From Schlegel PN, Walsh PC: Simultaneous preperitoneal hernia repair during radical pelvic surgery. J Urol 1987; 137:1180-1183.)