AIIS avulsion injuries occur usually in adolescents as a result of acute trauma. The AIIS apophysis fuses with the ilium between 16 and 18 years of age, so before that, it is the physeal plate - as the weakest part of the musculotendinous unit - that gets injured from trauma or chronic overuse. The mechanism of the injury is a pull of the straight head of the rectus femoris, which attaches to AIIS, with hip in extension (usually forceful) and knee in flexion (e.g. during kicking or running). Treatment is in most cases conservative.