Anterior inferior iliac spine avulsion injury

Anterior inferior iliac spine (AIIS) avulsion injuries are one of the six main types of pelvic apophyseal avulsion fractures. Subacute or chronic avulsion injuries can be mistaken for a pseudotumor. 

Epidemiology

As with many pelvic avulsion injuries, they most often occur in adolescents (mostly between the ages 14-17). There is a slight male predilection and they tend to occur most often in sports involving kicking.

Pathology

The straight head of the rectus femoris muscle originates from the AIIS and forceful extension at the hip joint can lead to an avulsion injury at this point. The mechanism is one of forced hip extension with the knee in flexion ⁴.

Radiographic features

Plain radiograph

The avulsed bony fragment may not be as obvious on the AP projection. An oblique projection can be utilized to demonstrate the fragment in profile.

Treatment and prognosis

Almost all cases are managed conservatively.