Humeral trochlear hypoplasia secondary to epiphyseal injury as a cause of ulnar nerve palsy.

Humeral trochlear hypoplasia (HTH) is a rare condition that occasionally results in ulnar nerve palsy. A 41-year-old man developed HTH secondary to an epiphyseal injury of the trochlea incurred 33 years earlier. This may be the first report of a case of HTH caused by injury. The ulnar nerve appeared compressed by the malposition of the HTH against the medial head of the triceps brachii when the joint was flexed. The close proximity of the olecranon to the HTH also allowed the triceps brachii muscle to compress the nerve by displacing medially and overriding the bone. The condition was resolved surgically and the patient returned to his former occupation as a coal miner.