Failed ulnar nerve surgery due to persistent unrecognized snapping triceps from cubitus varus due to a distal humeral malunion in an adult: illustrative case.

Background: Snapping triceps is a dynamic condition in which a portion of the medial head of the triceps dislocates over the medial epicondyle during flexion or extension. Pushed by the triceps, the ulnar nerve typically also dislocates over the medial epicondyle, causing neuropathy. Posttraumatic cubitus varus deformities resulting from pediatric supracondylar fractures have been associated with snapping triceps. This is the first case of snapping triceps associated with cubitus varus due to distal humeral malunion, which occurred in an adult.

Observations: A 23-year-old man sustained a left distal humeral fracture from arm wrestling, which was treated nonoperatively, healing in a varus malunion. Within several months, he developed ulnar neuropathy and snapping at the medial elbow, which was diagnosed as a dislocating ulnar nerve and was treated with ulnar nerve transposition. He presented 8 years later with continued ulnar neuritis symptoms and snapping and was found to have snapping medial triceps. He chose nonoperative treatment.

Lessons: Snapping triceps, presenting as snapping at the elbow with ulnar nerve symptoms, can be incorrectly diagnosed as isolated ulnar nerve dislocation. Unrecognized snapping triceps leads to persistent symptoms after ulnar nerve transposition. The patient in this case demonstrated that an altered triceps line of pull can cause snapping triceps regardless of how the cubitus varus originated. https://thejns.org/doi/10.3171/CASE24596.