Overview of pelvic viscera

Surgical surface anatomy

The inguinal skin crease marks the junction of the anterior thigh with the anterior abdominal wall. It lies approximately 7 cm distal to the inguinal ligament. The anterior superior iliac spine (ASIS) lies superior to the lateral end of the crease; the iliac crest is palpable along its entire length from the ASIS. A line (Tuffier's) joining the most superior aspects of the iliac crests almost always crosses either the body of L4 or the L4/L5 intervertebral disc. The iliac crest terminates posteriorly as the posterior superior iliac spine (PSIS), which is marked superficially by the gluteal dimples. Palpation places the PSIS in the range L5/S1 to the spinous process of S2, whereas radiographic assessment places it at the level of S2. The ischial tuberosity is covered by gluteus maximus and is palpable during hip flexion. The coccyx is palpable in the superior part of the intergluteal cleft, the deep vertical groove between the buttocks extending to the S3–4 bony sacral segments. The sacral hiatus sits superior to the tip of the coccyx and is flanked by the raised palpable sacral cornua, which serve as reliable landmarks. The hiatus can also be located at the apex of an inverted equilateral triangle whose base is measured between the PSIS on either side.

The perineum is an approximately diamond-shaped region that lies below levator ani, between the inner aspects of the thighs and anterior to the sacrum and coccyx. It is usually described as if from the position of an individual lying supine with the hip joints in abduction and partial flexion. The surface projection of the perineum and the form of the skin covering it vary considerably, depending on the position of the thighs, whereas the deep tissues themselves occupy relatively fixed positions. The perineum is bounded anteriorly by the pubic symphysis and its arcuate ligament, posteriorly by the coccyx, anterolaterally by the ischiopubic rami and ischial tuberosities, and posterolaterally by the sacrotuberous ligaments. The deep limit of the perineum is the inferior surface of the pelvic diaphragm, and its superficial limit is the skin that is continuous with that over the medial aspect of the thighs and the lower abdominal wall. An arbitrary line joining the ischial tuberosities divides the perineum into an anterior urogenital triangle facing downwards and forwards, and a posterior anal triangle facing downwards and backwards at an approximate angle of 120° from the plane of the urogenital triangle. The male urogenital triangle contains the bulb and attachments of the penis, and the female urogenital triangle contains the mons pubis, labia majora and minora, clitoris and vaginal and urethral orifices.

Clinical anatomy

Bony pelvis

The pelvis is divided anatomically into the false (greater) and true (lesser) pelvis. The true pelvis is a bowl-shaped structure formed by the sacrum, pubis, ilium, ischium, the ligaments that interconnect these bones, and the muscles that line their inner surfaces. It starts at the level of a plane passing through the promontory of the sacrum, the arcuate line on the ilium, the iliopectineal line and the posterior surface of the pubic crest. This plane, or ‘inlet’, lies at an angle of between 35° and 50° up from the horizontal. Above this plane, the bony structures are sometimes referred to as the false pelvis; they form part of the walls of the lower abdomen. The outlet of the true pelvis is formed by the lower aspect of the pubic symphysis anteriorly; the ischiopubic rami running laterally and posteriorly; the ischial tuberosities and sacrotuberous ligaments laterally; and the tip of the coccyx and sacrospinous ligament posteriorly ( Fig. 68.1 ).