The Anterior Superior Iliac Spine, or ASIS, is a distinct bony point located at the front of the pelvis. It is a significant anatomical landmark that serves as a reference point in various medical and anatomical assessments. This projection is part of the ilium, one of the three bones that fuse to form the pelvis.
Anatomical Location and Feel
The ASIS is positioned at the anterior aspect of the iliac crest, which forms the curved upper border of the hip bone. It is readily palpable on both sides of the body, near the hip joint and just beneath the skin. To find your own ASIS, place your hands on your hips and slide them forward and slightly downward until you feel a prominent bony lump on each side. This makes it a practical landmark for self-identification and physical examinations.
Role as a Key Anatomical Landmark
The ASIS holds importance as a landmark for several reasons beyond its palpability. Its position helps in assessing pelvic tilt and overall body posture. Healthcare professionals use the ASIS to evaluate pelvic alignment and symmetry, which is particularly relevant in physical therapy and clinical evaluations.
Several muscles and ligaments attach to the ASIS, influencing movement and stability in the hip and thigh. The sartorius muscle originates from the ASIS and plays a role in hip flexion, knee flexion, and lateral rotation of the thigh. The tensor fasciae latae (TFL) also attaches here, working with the iliotibial band (ITB) to stabilize the hip and knee during activities like walking and running. Additionally, the inguinal ligament connects the ASIS to the pubic tubercle, contributing to pelvic stability and lower abdomen support.
Healthcare professionals frequently use the ASIS for various clinical measurements. It serves as a proximal landmark for measuring true lower limb length, which is done by measuring from the ASIS to the medial malleolus. This measurement helps identify leg length discrepancies, as pelvic rotation can sometimes compensate for these differences. The ASIS is also used to localize other anatomical structures, such as the common femoral artery and the base of the vermiform appendix.
Common Conditions and Pain Around ASIS
Pain around the ASIS can arise from several common conditions. Muscle strains or tendinitis of the muscles attaching to the ASIS, such as the sartorius or tensor fasciae latae, are common. These injuries often result from forceful contractions or repetitive actions, particularly in athletes involved in activities like running or kicking. The inflammation or strain of these tendons can lead to localized pain and tenderness.
Avulsion fractures are another type of injury that can affect the ASIS, especially in adolescents and young adults. This occurs when a sudden, forceful muscle contraction pulls a piece of bone away from the main bone at the attachment site. Since the ASIS’s apophysis, a cartilaginous growth center, is not fully fused until around 20-25 years of age, it is more susceptible to these fractures. Sprint athletes, soccer players, and gymnasts are commonly affected due to the dynamic movements and sudden changes in direction required in their sports.
Iliac crest contusions, often referred to as “hip pointers,” involve bruising or injury to the general area of the iliac crest, including the ASIS. These injuries typically result from direct impact or trauma to the hip. Pain in the ASIS region can sometimes be referred from other areas, meaning the discomfort originates elsewhere in the body but is felt at the ASIS. Persistent pain in this area should be evaluated by a healthcare professional to determine the underlying cause and ensure appropriate management.