Incomplete avulsion fractures of the scapular spine caused by violent muscle contraction.

Two percent of scapular fractures occur as a result of indirect trauma caused by traction of the muscles and ligaments attached to the scapula. We present two cases involving adults with incomplete avulsion fractures of the scapular spine caused by violent voluntary contraction of the deltoid muscle. These cases are the first reported avulsion fractures confined to the scapular spine medial to the spinoglenoid notch. Although the fractures were incomplete, one patient had a typical symptom of scapular fracture - pseudo-rupture of the rotator cuff characterized by clinical signs of a complete rupture of the musculotendinous cuff. Although this symptom is generally thought to be caused by massive hemorrhaging under the rotator-cuff muscle bellies, it may develop from modest bleeding through the formation of an intramuscular hematoma and a resultant elevation in intramuscular pressure. Confirming the presence of tenderness on the scapular spine and performing appropriate imaging investigation constitute a clinically effective method for preventing misdiagnosis.