What is the Iliac Fossa?

The iliac fossa is a surface on the ilium bone in the pelvis to which the iliacus muscle attaches. One of three bones making up the coxal, or hip, bone, the ilium is recognizable for its large size and butterfly-wing shape. A concave surface on the interior side of the pelvis, the iliac fossa is found where the ilium flares up and out.

On the ilium, the interior side is that which is cupped inward around the cavity that houses the reproductive organs, as opposed to the exterior side of the bone, which faces backward and outward. Here in that cup is where the iliac fossa is located, bordered by the iliac crest, the bony ridge above it, and the arcuate line beneath it. The arcuate line is a smooth, narrow, bony surface, and it is a border separating the wing from the body of the ilium. It also transfers weight from the sacroiliac joint, where the spine meets the pelvis, to the hip joint, where the leg meets the hip.

The location of the iliac fossa can be approximated externally by placing the hands on the iliac crests, found on the front of the hips at the base of the abdomen, and then by pressing the fingers into the soft tissue just inside of the crests. This is the bone landmark that tells doctors where to palpate when diagnosing appendicitis. It is also where the iliacus muscle is located, arising from the bony surface of the iliac fossa beneath it.

Part of the iliopsoas or hip-flexor muscle complex, the iliacus is the only muscle that originates within the fossa. It is triangular and flat in shape, and its fibers converge from its broadest point within the iliac fossa to attach to the lesser trochanter of the femur, a small prominence on the back side of the leg bone just a few inches below where the femur inserts into the hip joint. Because it crosses the hip joint, the function of the iliacus is to flex the hip, whether by pulling upward on the leg or pulling downward on the trunk, as in performing a sit-up.

Fractures may occur at the iliac fossa, and because they involve the wing of the pelvic bone and not the weight-bearing body of the ilium or any of the structures surrounding the hip joint, they are considered to be mechanically stable injuries. Iliac fossa pain is also commonly diagnosed, but whether the pain occurs on the right or left side is significant to diagnosis. Pain felt on the right side is often consistent with appendicitis. Left side pain, on the other hand, can point to a variety of conditions, from gastrointestinal causes to gynecological causes to urological causes. In other words, pain in this region is typically a consequence of pathology of the organs contained within, and not of problems with the bone itself.