ABSTRACT
THE BONY PELVIS consists of the sacrum and coccyx at the back, which unite at each side with the hip bone at the sacroiliac joint (7.1); at the front the two hip bones are joined at the pubic symphysis. The pelvic brim is formed by the top edge of the sacrum (with the sacral promontory in the midline), the arcuate line of the ilium and the top of the pubic bone and pubic symphysis; it is the boundary between the true pelvis or pelvic cavity, below the brim, and the false pelvis which is the part above the brim and really belongs to the abdominal cavity. It is important to note that when the bony pelvis is correctly orientated, i.e. tilted forwards so that the anterior superior iliac spines and the top of the pubic symphysis are in the same vertical plane (as when holding the pelvis against a
wall with these bony points touching the wall), the pelvic cavity runs backwards almost at a right angle to the abdominal cavity. The pelvic muscles of each side are piriformis at the back and obturator internus at the side (these muscles also belong to the gluteal region of the lower limb), while coccygeus and levator ani form the highly important pelvic floor or pelvic diaphragm. The sacral plexus lies in front of the piriformis; most of its branches are examined in dissections of the gluteal region (8.5). The sacral parts of the sympathetic trunks lie medial to the anterior sacral foramina and S2-S4 nerves give off parasympathetic branches. The inter-
7.1. Radiograph of the female pelvis
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Sacrum
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Rim of acetabulum
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Head of femur
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Neck
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Greater trochanter
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Lesser trochanter
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Superior pubic ramus
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Ischial tuberosity
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Pubic tubercle
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Body of pubis
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Shadow of vulva
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Pubic symphysis
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Ischiopubic ramus
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Obturator foramen
• First piece of coccyx
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Ischial spine
• Sacroiliac joint
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Anterior superior iliac spine
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Ilium
The pelvic diaphragm must not be confused with the urogenital diaphragm (p. 155) whose main muscle is the external urethral sphincter.
