Pelvic Avulsion Fractures

Avulsion Iliac Apophysis	Avulsion Anterior Superior Iliac Spine (ASIS)	Avulsion Anterior Inferior Iliac Spine (AIIS)
Abdominal muscles Uncommon Log-distance runners	Sartorius Sprinters, hurdlers Pain below iliac crest	Rectus femoris muscle Less common than ASIS fractures Kicking in soccer or football
Avulsion Ischial Tuberosity	Avulsion Greater Trochanter	Avulsion Lesser Trochanter
Hamstring Most common avulsion Sprinters, cheerleaders, dancers Pain in buttock	Middle and least gluteal, internal obturator, gemellus, and piriform muscles Sudden directional changes	Iliopsoas Rare Very painful Runners

General Considerations

• Avulsion fractures result when the fracture fragment is pulled from its parent bone by forceful contraction of a tendon or ligament
• Avulsion fractures are most common in younger individuals engaging in athletic endeavors
• In the pelvis, the newly formed secondary centers of ossification, the apophyses, are the most likely portions of the bone to avulse
• Since the apophyses tend to form at the time of puberty, most of these pelvic avulsions occur at the time of puberty
• In general, they are uncommon injuries, seen almost exclusively in adolescent athletes with a 2:1 male to female preponderance
• They occur most often in track events like hurdling and sprinting, or games like soccer or tennis
• Most common to avulse is the ischial tuberosity followed by anterior inferior iliac spine (AIIS) and the anterior superior iliac spine (ASIS) about equally
• Prompt diagnosis will prevent development of chronic pain

Clinical findings

• Acutely, the athlete experiences sudden, shooting pain referred to the involved tuberosity
• They may lose muscular function
• Swelling and local tenderness may occur
• The clinical findings of the fracture are similar to those of soft tissue injuries to the muscles, tendons and ligaments and so may be initially missed
  • Most common site of a missed fracture is the ischial tuberosity

Imaging findings

• Since the apophyses occur in anatomically predictable locations, the findings are those of an avulsed bony fragment usually immediately adjacent to the parent bone
• Characteristic of these lesions is fracture healing with exuberant bony callus formation
  • Can be confused with a bone tumor but must not be as an osteosarcoma and a healing fracture may appear similar pathologically
• Conventional radiography is the study of first choice
• If negative, magnetic resonance imaging may be helpful in demonstrating soft tissue injury, such as a tear of the tendon of the hamstring muscles

Avulsion Fractures Around the Pelvis and the Attachments of Muscles

Imaging Features of Avulsion Injuries. MA Stevens, GY El-Khoury, MH Kathol, EA Brandser and S Chow. May 1999, Radiographics, 19, 655-672.