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Pelvic inlet

Bone: Pelvic inlet

Diameters of superior aperture of lesser pelvis (female).
Latin	apertura pelvis superior
Gray's	subject #58 239
Dorlands/Elsevier	a_51/12144724

The superior circumference of the lesser pelvis forms the brim of the pelvis, the included space being called the superior aperture or pelvic inlet.

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The superior aperture is somewhat heart-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum.

The edge of the inlet is known as the pelvic brim. Occasionally, the terms are used interchangeably.

Boundaries

It is formed as follows:

	in front by the pubic crest (or pubic symphysis)
laterally by the pectineal line (or iliopectineal line) and arcuate lines		(same as other side)
	behind by the anterior margin of the base of the sacrum (or the ala of sacrum) and sacrovertebral angle (or sacral promontory)

Diameters

It has three principal diameters: antero-posterior, transverse, and oblique.

Name	Description	Average measurement in female
anteroposterior or conjugate diameter	extends from the sacrovertebral angle (promontorium) to the symphysis pubis;	about 110 mm.
transverse diameter	extends across the greatest width of the superior aperture, from the middle of the brim on one side to the same point on the opposite;	about 135 mm.
oblique diameter	extends from the iliopectineal eminence of one side to the sacroiliac articulation of the opposite side;	about 125 mm.

Additional images

v • d • e Bones of pelvis/pelvic cavity
General	sacrum, coccyx, hip bone
Ilium	Body (Arcuate line) Wing: gluteal lines (Posterior, Anterior, Inferior) - Fossa - iliac spines (Anterior superior, Anterior inferior, Posterior superior, Posterior inferior) - Crest - Tuberosity
Ischium	Body (Ischial spine, Lesser sciatic notch) - Superior ramus (Tuberosity of the ischium) - Inferior ramus
Pubis	Body - Superior ramus (Pubic tubercle, Pubic crest, Obturator crest) - Inferior ramus (Pectineal line)
Compound	Acetabulum (Acetabular notch) - Iliopubic eminence/Iliopectineal line - Linea terminalis - Ischiopubic ramus/Pubic arch Obturator foramen - Greater sciatic foramen/Greater sciatic notch - Lesser sciatic foramen Lesser pelvis (Pelvic inlet, Pelvic brim, Pelvic outlet) - Greater pelvis