Humeral lesser tuberosity avulsion fractures - magnetic resonance imaging characteristics in the pediatric population.

Abstract

Avulsion fractures of the humeral lesser tuberosity are rare injuries in skeletally immature patients and can pose a diagnostic challenge that often leads to delayed identification. To describe the demographics, mechanism of injury and magnetic resonance imaging (MRI) findings of lesser tuberosity avulsion fractures in children. A retrospective search of children with lesser tuberosity avulsion fractures on MRI was done. Available radiographs were evaluated. Demographics, mechanism of injury, MRI characteristics and treatment were recorded. Thirteen children, all male, were included (median age: 13.8years, range: 12.5-16.8years). The most common mechanism was blunt, overhead or hyperextension traumatic injury related to sports. All patients were skeletally immature and 10/13 demonstrated isolated avulsion fractures at the footprint. Only one patient had associated osteochondral injury to the humeral head and labral tear. Two children demonstrated medial dislocation/subluxation of the biceps tendon. The median size of the avulsed fragment was 15mm (range: 5-29mm), median anteroposterior displacement was 3mm (range: 0-6mm) and medial displacement was 1mm (range: 0-20mm). There was no correlation between age and the size of the avulsed fragment (P=0.29). Common injury patterns were complete avulsion of the subscapularis footprint (6/13) and partial avulsion of inferior footprint (6/13). Two-thirds of the radiographs were initially reported as normal, but retrospectively showed two missed fractures. One of the initial radiographs raised concern for bone tumor. The best view for identifying an avulsion fragment was the axillary view. Seven patients of the 13 patients underwent internal fixation. Avulsion fractures of the lesser tuberosity are rare, challenging to diagnose and often radiographically occult. MRI can identify the injury at the subscapularis tendon footprint with variable size and displacement. The long head of the biceps tendon is usually normal in location. Although this entity is rare, radiologists should be aware of it to allow for correct and prompt diagnosis and prevent unnecessary biopsy or contrast administration.