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

Classic history and presentation: The condition presents as pain, swelling, and weakness in the anterolateral hip a few centimeters distal to 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 AIIS avulsion in the general population is unknown, but it is believed to be the third most common avulsion fracture (19%) in the pelvis behind ischial tuberosity (54%) and anterior superior iliac spine (ASIS) avulsions (22%).

• Age – Most commonly seen in patients 8-17 years of age.
• Sex / gender – Male predominance.

Risk factors: Risk factors include an open apophysis and participating in kicking sports (eg, soccer), running / sprinting sports, and sports involving sudden muscular contractions (eg, gymnastics, tennis).

Pathophysiology: In the pediatric and adolescent child, 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 or tendinous attachments sites. The direct head of the rectus femoris (RF) originates from the AIIS. The pathophysiology of AIIS avulsion is indirect trauma due to sudden and forceful eccentric contraction of the RF during hip extension and knee flexion, as can be seen during kicking and sprinting.