Name of bone



The ilium is the uppermost and largest bone of the pelvis. It is divisible into two parts, the body and the ala. This separation is indicated on the top surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum.

The name comes from the Latin, meaning “groin” or “flank.”

Muscle and ligament attachments

Surface anatomy


The body of the ilium forms the upper boundary of the acetabulum, providing a little less than two-fifths of its structure. The external surface of the ilium is partly articular, partly non-articular: the articular segment forms part of the lunate surface of the acetabulum, the non-articular portion contributes to the acetabular fossa. The internal surface of the body is part of the wall of the lesser pelvis and gives origin to some fibers of the obturator internus. Below, it is continuous with the pelvic surfaces of the ischium and pubis, only a faint line indicating the place of union.


The wing of the ilium (or ala) is the large, expanded portion, which bounds the greater pelvis laterally. It an external and an internal surface, a crest, and anterior and posterior borders.

Figure 1. Anatomy of the pelvic bones


Physical examination

Biiliac width

Biiliac width is an anatomical term referring to the widest measure of the pelvis between the outer edges of the upper iliac bones. It is also known as pelvic bone width, biiliac breadth, intercristal breadth/width, bi-iliac breadth/width, and biiliocristal breadth/width.

In the average adult female, the biiliac width is 28 cm (11 inches). It is best measured by anthropometric calipers (pelvimeter). Attempting to measure the biiliac width with a tape measure along a curved surface will be inaccurate.

The biiliac width measure is helpful in obstetrics; a pelvis that is significantly too small or too large can cause obstetrical complications. For example, a large baby and/or a small pelvis often lead to a Caesarean section.

Anthropologists also use biiliac width to estimate body mass.





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