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) The linear applied force (dashed arrow) leads to an anterior tension force (curved arrow). Posteriorly the olecranon is forced into the depths of the olecranon fossa (thick arrow).

(C) As the bending force continues, the distal humerus fails anteriorly in the thin supracondylar area (thick arrow).

(D) When the fracture is complete, the proximal fragment can continue moving anteriorly and distally (curved arrow), potentially harming adjacent soft tissue structures such as the brachialis muscle, brachial artery, and median nerve. The distal fracture is displaced proximally (thick arrow).