Extension supracondylar fractures

Hyperextension forces. A) Most young children attempt to break their falls with the upper extremity extended. Because of the laxity of the ligaments, the elbow becomes locked into hyperextension. B) This converts the linear applied force (large arrow) to an anterior tension force. Posteriorly, the olecranon is forced into the depths of the olecranon fossa (small arrow). C) As the bending force continues, the distal humerus fails anteriorly in the supracondylar area. D) When the fracture is complete, the distal fragment becomes posteriorly displaced. The strong action of the triceps (large arrow) produces proximal displacement of the distal fragment.