What is the diagnosis?

This patient has an avulsion fracture of the anterior inferior iliac spine (AIIS).   

Figure 2: Right AIIS avulsion fracture (arrow). On the contralateral side, the AIIS, the anterior superior iliac spine (ASIS) and iliac crest are labeled. Original image provided by Abiye Ibiebele, MD

What age group is most at risk for this injury?

Pelvic avulsion fractures are exclusively seen in the adolescent population [1]. This is an injury of the apophysis, which is a type of growth plate on which tendons insert [2]. These injuries occur between the ages of 13 and 15 when secondary ossification has occurred but the growth plates have not yet closed. [3,4]. 

• Pearl: The other type of growth plate is an epiphysis, which are at the end of long bones, and associated with joints. These are where Salter Harris injuries occur and these contribute to the overall length of a bone after growth, while apophyses do not [2].

• Pearl: Similar injuries can happen to the ASIS and iliac crest, but the AIIS is the most common. [1]. 

What is the mechanism of injury?

These injuries occur with sudden eccentric contraction of the rectus femoris at the hip. Usually with a flexed knee and extended hip. such as occurs when kicking a ball or sprinting [3]. Patients will commonly endorse hearing a pop at the time of injury.

What is the management in the ED? What is your disposition?

Patients should be treated conservatively with rest from sports, pain control and crutches for protected weight bearing [3]. They do not need to be seen by Orthopedics in the ED but follow-up should be established for all injuries. Fractures displaced more than 2 cm may require operative intervention and follow-up should be prompt [3].

• Pearl: Patients should be instructed to avoid stretching in the acute phase, as this may increase the risk of non-union [4].