You may be referring to a supracondylar humeral fracture. Supracondylar humeral fractures occur most often in children. In fact, they are the most common type of pediatric elbow fractures. Children between the ages of five and seven are affected most often.
The child falls onto an outstretched hand with the elbow extended. The force of the impact causes a break in the humerus (upper arm bone) just above the elbow. The break doesn’t go all the way through the humerus. The anterior humerus (front part) is sliced open but the posterior (back) portion is still intact. This gives it the look of a hinge joint.
Boys are affected more often than girls but the incidence in girls is rising. This is likely the result of increased sports participation and athleticism among young girls. Treatment may be nonoperative with sling immobilization. Surgery may be needed to restore a normal position of the bone while it heals.