Anterior superior iliac spine avulsion
15-year-old track athlete complains of pain, weakness, and decreased range of motion of his hip after hurdling.
AP radiograph of left hip
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Single frontal radiograph of the left hip demonstrates a large crescent-shaped bone fragment adjacent to the anterior superior iliac spine compatible with avulsion fracture.
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An avulsion fracture of the anterior superior iliac spine (ASIS) presents with localized pain, weakness, and decreased range of motion at the tendon attachment site secondary to vigorous physical activity most commonly in adolescents.
Avulsion fractures occur when a tendon or ligament tears and breaks a piece of bone away from the attachment site. In the acute setting, these injuries most often result from forceful muscular contraction. In the chronic setting, these injuries result from repetitive overuse.1
Children and adolescents are prone to avulsion injuries secondary to skeletal immaturity. Avulsion injuries occur at tendon or ligament insertion sites known as apophyses. An apophysis is a secondary ossification center which fuses after skeletal maturation, normally occurring by the middle of the second decade.2 The cartilaginous growth plate of the apophysis is a point of weakness relative to the musculotendinous unit attached and is vulnerable to fracture secondary to sudden forceful muscle contraction.3 Since ligaments and tendons are able to withstand more force than bones in children and adolescents, these age groups are more susceptible to this injury.4
According to the data of Vandervliet et al1, ASIS avulsion fracture is the third most frequent pelvic avulsion fracture preceded by avulsion fracture of the ischial tuberosity and anterior inferior iliac spine, respectively. The ASIS serves as the attachment site for the sartorius muscle and the tensor muscle of the fascia lata. This injury commonly results from sudden extension of the hip often during sprinting, jumping, or kicking.1-5
Diagnosis is usually achieved with plain radiographs; however, CT and MRI are useful modalities in equivocal cases. MRI is also used to identify the extent of avulsion injuries and may yield important information regarding treatment strategies.5 Most ASIS avulsion fractures heal quickly with conservative treatment, including rest, slow return of activity, and pain management. However, surgical options are considered for avulsion fractures with more than 2 centimeters of displacement.5
- 1. Vandervliet EJ, Vanhoenacker FM, Snoeckx A et-al. Sports-related acute and chronic avulsion injuries in children and adolescents with special emphasis on tennis. Br J Sports Med. 2007;41 (11): 827-31. doi:10.1136/bjsm.2007.036921 - Free text at pubmed - Pubmed citation
- 2. Stevens MA, El-Khoury GY, Kathol MH et-al. Imaging features of avulsion injuries. Radiographics. 1999;19 (3): 655-72. Radiographics (full text) - Pubmed citation
- 3. Dhinsa BS, Jalgaonkar A, Mann B et-al. Avulsion fracture of the anterior superior iliac spine: misdiagnosis of a bone tumour. J Orthop Traumatol. 2011;12 (3): 173-6. doi:10.1007/s10195-011-0153-z - Free text at pubmed - Pubmed citation
- 4. Fernbach SK, Wilkinson RH. Avulsion injuries of the pelvis and proximal femur. AJR Am J Roentgenol. 1981;137 (3): 581-4. doi:10.2214/ajr.137.3.581 - Pubmed citation
- 5. Kjellin I, Stadnick ME, Awh MH. Orthopaedic magnetic resonance imaging challenge: apophyseal avulsions at the pelvis. Sports Health. 2010;2 (3): 247-51. doi:10.1177/1941738109347976 - Free text at pubmed - Pubmed citation