Pelvic inlet

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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.

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.

[edit] Boundaries

It is formed as follows:

laterally: by the pectineal line (or iliopectineal line) and arcuate lines
in front: by the crests of the pubes (or pubic symphysis)
behind: by the anterior margin of the base of the sacrum (or the ala of sacrum) and sacrovertebral angle (or sacral promontory)

[edit] 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 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.