The radiograph demonstrates a flexion type supracondylar humerus (SCH) fracture, in which the distal fragment is displaced anteriorly. In these fracture patterns, the ulnar nerve is the most likely to be injured, specifically by the sharp spike of the proximal fragment. Extension type SCH fractures are more common than flexion type and are commonly associated with injury to the anterior interosseous nerve (AIN). Weakness of the flexor digitorum profundus to the index finger and flexor pollicis longus would be associated with AIN palsy. Wrist drop would be associated with radial nerve palsy. Weakness of extensor pollicis longus correlates with posterior interosseous nerve palsy. Ulnar nerve palsy would cause hand intrinsic weakness and clawing.
Green, NE, Swiontkowski, MF (ed). Skeletal Trauma in Children. 4th ed, Philadelphia, PA, Saunders/Elsevier, 2009