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. 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. When approaching the pelvis through a low midline incision, the surgeon gazes directly into the true pelvis.
[...] The linea alba is avascular and is a convenient point of access to the peritoneal and pelvic cavities. In its upper portion, the anterior rectus sheath is formed by the aponeurosis of the external oblique muscle and a portion of the internal oblique muscle. The posterior sheath is derived from the remaining internal oblique aponeurosis and the transversus abdominis aponeurosis. Two thirds of the distance from the pubis to the umbilicus, the arcuate line is formed, as all aponeurotic layers abruptly pass anterior to the rectus abdominis, leaving this muscle clothed only by transversalis fascia and peritoneum posteriorly. [...]
[...] This septum is the developmental remains of the rectogenital pouch of peritoneum that extended between the rectum and internal genitalia to the pelvic floor. The pelvic fasciae have been given a confusing array of appellations by anatomists and surgeons interested in female pelvic organ prolapse. To add to the confusion, the strength of pelvic fasciae can differ significantly between individuals and races, and these differences may predispose some individuals to pelvic prolapse. There are three important components of the pelvic fasciae: Anteriorly, the puboprostatic ligaments attach to the lower fifth of the pubis, lateral to the symphysis and to the junction of the prostate and external sphincter. [...]
[...] These fasciae can limit both the spread of infection in necrotizing fasciitis of the scrotum (Fourniers gangrene) and the extent of urinary extravasation in an anterior urethral injury. For instance, blood and urine can accumulate in the scrotum and penis deep to the dartos fascia after an anterior urethral injury. In the perineum, their spread is limited by the fusions of Colles fascia to the ischiopubic rami laterally and to the posterior edge of the perineal membrane; the resulting hematoma is therefore butterfly shaped. [...]
[...] Posterior to the ischial spine, the fascia fans out to either side of the rectum and attaches to the pelvic side wall as the lateral and posterior vesical ligaments. In the female, these are the strong cardinal and uterosacral ligaments. They are not true ligaments; rather, they are condensations of intermediate stratum around visceral neurovascular pedicles. The peritoneum over these ligaments forms discrete folds (rectovesical in the male and rectouterine in the female) that can be appreciated at cystectomy. Taken as a whole, the pelvic fasciae form a Y-shaped scaffolding for the pelvic viscera. [...]
[...] Fibers of the internal oblique and transversus abdominis arise from the iliopsoas fascia and inguinal ligament lateral to the internal ring and arch over the canal to form its roof. They fuse as the conjoint tendon, pass posterior to the cord, and insert into the rectus sheath and pubis. The conjoint tendon reinforces the posterior wall of the inguinal canal at the external ring. With contraction of the internal oblique and transversus muscles, the roof of the canal closes against the floor. [...]
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