What structures form the pelvic brim?

The pelvic brim, also known as the pelvic inlet, is formed by several key structures. Anteriorly, it is defined by the pubic symphysis and the upper border of the pubic bones. Laterally, it includes the arcuate line of the ilium and the iliac crest, while posteriorly, the sacral promontory and the sacral alae contribute to its formation. Together, these structures create a boundary between the false pelvis (greater pelvis) above and the true pelvis (lesser pelvis) below.