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Musculoskeletal Imaging

E2670. Avulsion Fractures: Why Do They Happen, When Do They Happen, and How to Recognize Them

Narayanasamy S,  Krishna S,  Sheikh A. University of Ottawa, Ottawa, Canada

Address correspondence to N. Sabarish (

Background Information: Avulsion injuries are common in participants of organized sports, especially young athletes. Adolescents are more predisposed to avulsion fractures because of the inherent weakness of their apophysis. When there is a clear clinical history of preceding trauma, these injuries are easy to diagnose. Sometimes there is no history of a preceding traumatic event and radiologic findings are confusing. This can lead to excessive and often unnecessary imaging and biopsies.

Educational Goals/Teaching Points: At the completion of this educational exhibit, the radiologist will be able to recognize and describe the radiographic imaging features in a variety of common and uncommon avulsion injuries, describe the relevant osseous and musculotendinous anatomy and mechanisms and patterns of each injury, and differentiate subacute and chronic avulsion injuries from other serious bony pathologies.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: We present classification of avulsion injuries based on clinical presentation into acute with a clear history of preceding trauma (avulsed bone fragment), subacute injury in varying stages of healing (mixed lytic and sclerotic areas),and chronic due to repetitive microtrauma or overuse (may show protuberant bone). A variety of both acute and chronic avulsion injuries of the pelvis (iliac tuberosity, anterior superior and inferior iliac spines, greater and lesser trochanter), knee (Segond fracture, posterior cruciate ligament avulsion, Osgood-Schlatter disease, tibial tuberosity, jumper’s knee), fibular head avulsion fracture, ankle (calcaneal avulsion fracture, peroneal retinacular avulsion), elbow (Little League elbow, olecranon fractures), foot (base of fifth metatarsal), fingers (volar plate) and vertebral transverse process avulsion fractures will be presented. The relevant osseous and musculotendinous anatomy are discussed in detail. Common mechanism and patterns of each injury are described with identification of at-risk groups. The key imaging findings of each injury and their common mimickers are discussed. Distinguishing features are discussed with attention to differentiating chronic or healing avulsion fractures from neoplastic and infectious pathologies.

Conclusion: Acute trauma in skeletally immature adolescents usually results in avulsion fractures. These fractures often have a subtle appearance on radiographs and advanced imaging modalities, in particular MRI, is needed to adequately define the extent of damage. Early recognition of these injuries will help to prevent the chronic morbidity associated with delayed treatment.