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pl. pelvespelvises [L. pelvis, basin]
1. A basin-shaped structure or cavity.
2. The bony compartment comprising the innominate bones, the sacrum, and the coccyx, joined at the symphysis pubis, sacroiliac, and sacrococcygeal articulations by a network of cartilage and ligaments. The structure supports the vertebral column and articulates with the lower limbs.
3. The cavity encompassed by the innominate bones, the sacrum, and the coccyx.
The pelvis is separated into a false or superior pelvis and a true or inferior pelvis by the iliopectineal line and the upper margin of the symphysis pubis. The circumference of this area constitutes the inlet of the true pelvis. The lower border of the true pelvis, termed the outlet, is formed by the coccyx, the protuberances of the ischia, the ascending rami of the ischia, and the descending rami of the ossa pubis and the sacrosciatic ligaments. The floor of the pelvis is formed by the perineal fascia, the levator ani, and the coccygeus muscles. All diameters normally are larger in the female than in the male.
Interspinous: The distance between the outer edges of the anterosuperior iliac spines, the diameter normally measuring 26 cm (101/4 in). Intercristal: The distance between the outer edges of the most prominent portion of the iliac crests, the diameter normally being 28 cm (11 in). Intertrochanteric: The distance between the most prominent points of the femoral trochanters, 32 cm (121/2 in). Oblique (right and left): The distance from one posterosuperior iliac spine to the opposite anterosuperior iliac spine, 22 cm (81/2 in), the right being slightly greater than the left. External conjugate: The distance from the undersurface of the spinous process of the last lumbar vertebra to the upper margin of the anterior surface of the symphysis pubis, 20 cm (77/8 in).
True conjugate: The anteroposterior diameter of the pelvic inlet, 11 cm (41/4 in), the most important single diameter of the pelvis. Diagonal conjugate: The distance between the promontory of the sacrum to the undersurface of the symphysis pubis, 13 cm (51/8 in). Two cm (3/4 in) are deducted for the height and inclination of the symphysis pubis to obtain the diameter of the conjugate. Transverse: The distance between the ischial tuberosities, 11 cm (41/4 in). Anteroposterior (of outlet): The distance between the lower border of the symphysis pubis and the tip of the sacrum, 11 cm (41/4 in). Anterior sagittal: The distance from the undersurface of the symphysis pubis to the center of the line between the ischial tuberosities, 7 cm (23/4 in). Posterior sagittal: The distance from the center of line between the ischial tuberosities to the tip of the sacrum, 10 cm (4 in).