Experimental hyperextension supracondylar fractures in monkeys.

Discarded monkey autopsy specimens were used to investigate the mechanism of supracondylar hyperextension fracture. As the fracture progressed from mild angulation to complete lateral or medial displacement, the anterior periosteum first was detached from the bone and then stripped distally before tearing over the edge of the proximal fragment. Stability or reduction by acute elbow flexion and forearm pronation, owing to compressive forces, was transmitted through the elbow joint on the medial side of the fracture, and stability was not significantly influenced by a bridging periosteal hinge or forearm musculature. Forearm supination and elbow flexion of less than 90 degrees resulted in less stability. The influence of acute elbow flexion and forearm pronation was diminished when the fracture was distracted by traction. Interposition of the anterior periosteum in displacement fractures prevented anatomic reduction.