Bony Pelvis

Gross Anatomy - Bony Pelvis

A. Pelvis

• Is the basin-shaped ring of bone formed by the two hip bones , the sacrum , and the coccyx. (The hip or coxal bone consists of the ilium, ischium, and pubis.)
• Is divided by the pelvic brim or iliopectineal line into the pelvis major (false pelvis) above and the pelvis minor (true pelvis) below.
• Has an outlet that is closed by the coccygeus and levator ani muscles, which form the floor of the pelvis.
• Is normally tilted in anatomic position. Thus:

• The anterior-superior iliac spine and the pubic tubercles are in the same vertical plane.
• The coccyx is in the same horizontal plane as the upper margin of the pubic symphysis.
• The axis of the pelvic cavity running through the central point of the inlet and the outlet almost parallels the curvature of the sacrum.
  

B. Upper pelvic aperture (pelvic inlet or pelvic brim)

• Is the superior rim of the pelvic cavity; is bounded posteriorly by the promontory of the sacrum and the anterior border of the ala of the sacrum (sacral part) , laterally by the arcuate or iliopectineal line of the ilium (iliac part) , and anteriorly by the pectineal line, the pubic crest, and the superior margin of the pubic symphysis (pubic part).
• Is measured using transverse, oblique, and anteroposterior (conjugate) diameters.
• Is crossed by the ureter, gonadal vessels, middle sacral vessels, iliolumbar vessels, lumbosacral trunk, obturator nerve, spermatic cord, round ligament of the uterus, sympathetic trunk, suspensory ligament of the ovary, etc.

C. Lower pelvic aperture (pelvic outlet)

• Is a diamond-shaped aperture bounded posteriorly by the sacrum and coccyx; laterally by the ischial tuberosities and sacrotuberous ligaments; and anteriorly by the pubic symphysis, arcuate pubic ligament, and rami of the pubis and ischium.
• Is closed by the pelvic and urogenital diaphragms.

D. Pelvis major (false pelvis)

• Is the expanded portion of the bony pelvis above the pelvic brim.

E. Pelvis minor (true pelvis)

• Is the cavity of the pelvis below the pelvic brim (or superior aperture) and above the pelvic outlet (or inferior aperture).
• Has an outlet that is closed by the coccygeus and levator ani muscles and the perineal fascia, which form the floor of the pelvis.

F. Differences between the female and male pelvis

• The bones of the female pelvis are usually smaller , lighter, and thinner than those of the male.
• The inlet is transversely oval in the female and heart-shaped in the male.
• The outlet is larger in the female than in the male because of the everted ischial tuberosities in the female.
• The cavity is wider and shallower in the female than in the male.
• The subpubic angle or pubic arch is larger and the greater sciatic notch is wider in the female than in the male.
• The female sacrum is shorter and wider than the male sacrum.
• The obturator foramen is oval or triangular in the female and round in the male.
  

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