Tardy ulnar nerve palsy caused by cubitus varus deformity.

Clinical features and X-rays of thirty-four cases with cubitus varus deformity were analysed in order to explain the occurrence of tardy ulnar nerve palsy caused by cubitus varus deformity. Cubitus varus cases with tardy ulnar nerve palsy, compared to cases without it, were older at the first visit to the clinic for cubitus varus deformity. There were no other differences between the two groups in clinical features. Computed tomography showed that the olecranon moved to the ulnar side against the olecranon fossa. Operative findings showed that the medial head of triceps brachii shifted medially and covered the ulnar nerve. Both from computed tomography and operative findings we conjectured the possibility that tardy ulnar nerve palsy was caused because the ulnar nerve was compressed by the forward medial movement of the medial head of the triceps brachii caused by cubitus varus deformity.