A variant of Kaplan's accessory branch of the dorsal cutaneous branch of the ulnar nerve: a case report and review of the literature

Kaplan's accessory branch is an aberrant branch of the dorsal cutaneous branch of the ulnar nerve that arises proximal to the styloid process of the ulna and courses ulnar to the pisiform. Variations of this anomaly have been described as having an end point of connection to the sensory branch of the ulnar nerve, to the motor branch of the ulnar nerve (rare), to the digital nerve at the level of the midhypothenar eminence, or to the proximal interphalangeal joint of the small finger or as running as an independent branch to the volar aspect of the small finger. We report a variant of Kaplan's accessory branch that coursed through the insertion of the flexor carpi ulnaris, a groove on the ulnar aspect of the pisiform, and connected to the ulnar nerve trunk proximal to its bifurcation into its motor and sensory branch. Based on the findings of the case presented and a review of the literature we offer a classification system for this anomaly.