The pelvic inlet is the anatomical limit between the false pelvis superiorly and the true pelvis inferiorly. Therefore, it is a space that marks the junction between both parts of the pelvis. The pelvic inlet is also known as the superior pelvic aperture.

The pelvic inlet can be delineated using bony landmarks that form the pelvic brim and define its limit. The edges of the pelvic inlet can be defined using the term linea terminalis. The linea terminalis crosses three of four bones of the pelvic skeleton, including the sacrum and both hip bones.

Posteriorly, the linea terminalis starts at the promontory of the sacrum, then it goes in the inferior anterior direction and continues along the anterior margin of the sacral ala. Further, it continues to go laterally towards the ilium.

Once it crosses the sacroiliac joint, it matches the arcuate line, then crosses the iliopubic (iliopectineal) eminence and continues to go towards the pubic symphysis along the pecten pubis.

Close to the pubic symphysis, it passes along the superior-posterior edge of the body of the pubis and ends laterally to the pubic symphysis. The superior pubic ligament (Read more!) that stretches above the pubic symphysis unites both ends of the linea terminalis.

Overall, the pelvic inlet is an important landmark in obstetrics, as it marks the entrance to the birth canal. The measurements of the pelvic inlet determine the size and shape of the birth canal.

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Pelvic inlet