Avulsion of the Anterior Superior Iliac Spine

A pelvic radiograph demonstrates an avulsion fracture (arrows) of the right anterior superior iliac spine (ASIS) in a 14-year-old boy. 

Facts: Pelvic Avulsions

• Avulsion of pelvic bones usually found in young, skeletally immature athletes.
• Forceful contraction of the attached muscle while the athlete actively engages in kicking, running or jumping.
• Three major locations: ASIS (sartorius attachment), anterior inferior iliac spine (AIIS, rectus femoral attachment) and ischial tuberosity (hamstrings and adductor attachment).
• 50% of cases at ischial tuberosity, 23% ASIS, 22% AIIS (of all pelvic avulsions).
• Localized swelling and tenderness at the site of avulsion fracture. Limited motion from pain.

Imaging

• Plain radiography usually sufficient for diagnosis. 
• Comparison view helpful to ensure that abnormality is not a secondary center of ossification.
• Pitfalls: secondary ossification center, osseous mass seen as a delayed presentation mimicking neoplasm.

References

Davies AM, Johnson KJ, Whitehouse RW. Imaging of the hip & bony pelvis: techniques and applications. 

Beaty JH, Rockwood CA, Kasser R. Rockwood and Wilkins' fractures in children.