Anterior superior iliac spine avulsion
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