Purpose or Case Report: Humeral lesser tuberosity avulsion fractures (LTAF) are rare injuries in children. Limited information is available describing MRI characteristics. We aim to describe demographics, mechanism of injury, and MRI findings of LTAF.
Methods & Materials: We conducted a retrospective search of the last 10 years. All children with shoulder MRI and LTAF were included. If available, radiographs were evaluated. Age, gender, mechanism of injury, and treatment were recorded. MRI evaluated size of the avulsion fragment, displacement in the axial plane, percentage of the subscapularis tendon involved, dislocation of the long head of the biceps tendon, and additional injuries.
Results: We found 11 children, all male, median age 13.8 yrs (range 12.5-16.1 yrs). Most common mechanism of injury was sports-related blunt trauma or overhead throwing (9 children; 82%), particularly football and wrestling. All patients were skeletally immature, 9(82%) demonstrated isolated LTAF at the footprint of the subscapularis tendon. Only 1 patient had associated osteochondral injury to the humeral head and a labral tear. The long head of the biceps tendon was normal in 10 cases (91%) with only 1 child demonstrating medial dislocation.
Median size of the avulsed fragment was 16mm (range 5-23mm), with a median AP displacement of 3mm(range 0-7mm). Age did not correlate with size of avulsed fragment (p=0.79). All subscapularis tendons were intact with redundancy and edema in cases of retraction. Total avulsion of the subscapularis footprint was seen in 5(45%), partial avulsion involving >50% of the footprint in 4(36%) and partial avulsion involving <50% of the footprint in 2(19%).
Of those cases with available radiographs (9/11), two thirds (6/9) were initially reported as normal with retrospective evaluation showing an avulsion fragment in two cases (2/6). One of the initial radiographs raised concern for bone tumor. The best view for identification of an avulsion fragment was the axillary view.
Treatment was variable with 6 patients (55%) undergoing internal fixation.
Conclusions: Lesser tuberosity avulsion fractures are rare and can be radiographically occult. MRI was able to identify mostly isolated injuries to the subscapularis tendon insertion with variable size of the avulsed fragment and degree of tendon involvement. The long head of the biceps tendon is usually normal in signal and location. Although rare, radiologist should be aware of this entity for correct diagnosis and prevention of unnecessary biopsy or contrast administration.