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The Anterior Superior Iliac Spine (ASIS) is a section of the ilium bone, the large wing-shaped bone of the pelvis. Easy to feel just beneath the abdomen on the front of the hip, the ASIS is the forward-most point of the iliac crest, the topmost lateral curve of the hipbone. It serves as a point of attachment for several tissues, including the tensor fasciae latae (TFL) and sartorius muscles of the front of the thigh and the inguinal ligament of the pelvis. Since it is so easily located, this site also acts as a point of reference in placing other anatomical landmarks such as McBurney’s point, where the bottom of the appendix is found.
Situated on the ilium, the largest of the three pelvic bones, the anterior superior iliac spine is among the most visible and palpable extremities of the pelvis. It can be located by placing the hands on the tops of the hipbones on either side — this is the iliac crest — and following this bony shelf around to the front of the hips. Here is a forward-facing protrusion where the iliac crest ends and the border of the ilium curves downward, and this is the anterior superior iliac spine. In some individuals the ASIS visibly protrudes against the skin. The horizontal distance between the ASIS on each hipbone is also greater in women than in men, as the female pelvis is typically wider than the male pelvis.
As the anterior superior iliac spine is located on the front of the hip on either side, several structures on the anterior hip and thigh connect to it. Two muscles of the anterior compartment of the thigh originate on the ASIS. The tensor fasciae latae (TFL) muscle of the hip flexor group arises from the ASIS, runs a short distance down the anterolateral thigh, and ends in a long band of connective tissue known as the iliotibial (IT) band. It also gives rise to the body’s longest muscle, the sartorius, which crosses the front of the thigh like a strap and inserts along the upper tibia bone on the inside of the lower leg. Both muscles are responsible for lifting the leg forward, lifting the leg sideways, and rotating the hip, with the TFL turning the leg inward and the sartorius turning the leg outward.
A long ligament of the anterior pelvis known as the inguinal ligament also attaches to the anterior superior iliac spine. The inguinal ligament is a narrow band of connective tissue that extends obliquely from the ASIS to the pubic tubercle, a point on the lower pubic bone on the bottom of the pelvis near its center. It demarcates the line where the leg meets the pelvis and acts to hold in place the muscles, nerves, and blood vessels running between the pelvis and the leg.