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What is the diagnosis?

Anterior Superior Iliac Spine (ASIS) Avulsion Fracture

Image 2.  Plain radiograph of the Pelvis (AP View) from above with annotation. Author’s own image and annotations.

• Pearl: ASIS avulsion fractures typically occur in young athletes during the transition from the ossification nucleus to a mature iliac spine [1].

What is the mechanism of injury?

Injury usually occurs due to an indirect mechanism involving a forceful contraction of the sartorius muscle and fibers of the tensor fascia lata, coupled with hip extension and knee flexion [2]. Common sports implicated include sprinting sports such as running, soccer, as well as ballet.

What physical exam findings are expected?

Patients may retain the ability to walk but often experience difficulty running. They frequently report pain with hip extension. Additionally, they may exhibit swelling and tenderness upon palpation over the area of the anterior-superior iliac spine. Delays in seeking medical attention for these symptoms may also be observed [3]. 

Which imaging modalities can be used?

X-ray of the pelvis; however, a CT pelvis can be considered to identify small avulsion fractures not visible on plain films [4].

• Pearl: Point of care ultrasound by a skilled sonographer can be utilized to identify these injuries as well [4].

Image 3: Ultrasound image of ASIS avulsion fracture in long axis. Image courtesy of Henry Knipe, Radiopaedia.org; rID: 60137

What is the management in the ED?

Initial management is conservative for non-displaced or minimally displaced fractures including dedicated rest, pain control, and rehabilitation [1]. Expected recovery can vary from 2 to 5 months [1].

Surgical management with open reduction and internal fixation is considered for the following: high functional demand of activity, >2cm of fragment avulsed, and absence of bone union [1].

• Pearl: Surgical interventions for the above scenarios can decrease the risk of complications compared to conservative management (chronic pain, absence of bone union, prolonged return to play, etc.) [1]. 

When do you consult Orthopedics?

Unless requirements are present for surgical management, outpatient follow-up with Orthopedics or Sports Medicine is recommended.