Causes / typical injury mechanism: Avulsion fractures from the anterior superior iliac spine (ASIS) are rare injuries seen almost exclusively in the adolescent population (aged 8-17 years).

Classic history and presentation: ASIS avulsion fractures present as pain, swelling, and weakness in the anterolateral hip at the groin line. Patients may have an antalgic gait secondary to pain. They may describe a pop or snap at the time of injury. Diagnosis is often based on history and physical examination in conjunction with radiographs.

Prevalence: The exact incidence of ASIS avulsion in the general population is unknown, but it is estimated to account for 1.4% of all injuries to the hip and pelvis. It is the second most common avulsion fracture (22%) in the pelvis, behind ischial tuberosity avulsions (54%).

• Age – Most commonly seen in patients aged 8-17 years.
• Sex / gender – Males are more commonly affected than females.

Risk factors: Risk factors include an open apophysis and participation in running / sprinting sports (eg, soccer, track and field) and sports involving sudden muscular contractions (eg, gymnastics, baseball, hockey, tennis).

Pathophysiology: In the adolescent, apophyses are centers of bony growth that contribute to the overall contour of bone but do not contribute to longitudinal growth. They also serve as muscular and tendinous attachments and are inherently weak until they completely fuse. Both the sartorius and the tensor fasciae latae (TFL) originate from the ASIS. The pathophysiology of ASIS avulsion is indirect trauma due to sudden and forceful eccentric contraction of the sartorius and TFL during hip extension, as can be seen during sprinting, jumping, or swinging a baseball bat.

Related topic: anterior inferior iliac spine avulsion fracture (AIIS)