Anatomical relationships and branching patterns of the dorsal cutaneous branch of the ulnar nerve.

ABSTRACT

PURPOSE: To describe the variable branching patterns of the dorsal cutaneous branch of the ulnar nerve (DCBUN) relative to identifiable anatomical landmarks on the ulnar side of the wrist. METHODS: We dissected the ulnar nerve in 28 unmatched fresh-frozen cadavers to identify the DCBUN and its branches from its origin to the level of the metacarpophalangeal joints. The number and location of branches of the DCBUN were recorded relative to the distal ulnar articular surface. Relationships to the subcutaneous border of the ulna, the pisotriquetral joint, and the extensor carpi ulnaris tendon were defined in the pronated wrist. RESULTS: On average, 2 branches of the DCBUN were present at the level of the distal ulnar articular surface (range, 1-4). On average, 2.2 branches were present 2 cm distal to the ulnar articular surface (range, 1-4). At least 1 longitudinal branch crossed dorsal to the extensor carpi ulnaris tendon prior to its insertion at the base of the fifth metacarpal in 23 of 28 specimens (82%). In 27 of 28 specimens (96%), all longitudinal branches of the DCBUN coursed between the dorsal-volar midpoint of the subcutaneous border of the ulna and the pisotriquetral joint. In 20 of 28 specimens (71%), a transverse branch of the DCBUN to the distal radioulnar joint was present. CONCLUSIONS: During exposure of the dorsal and ulnar areas of the wrist, identification and protection of just a single branch of the DCBUN are unlikely to ensure safe dissection because multiple branches normally are present. The 6U, 6R, and ulnar midcarpal arthroscopy portals may place these branches at risk. In the pronated forearm, the area between the DCBUN and the pisotriquetral joint contained all longitudinal branches of the DCBUN in 96% of specimens. CLINICAL RELEVANCE During surgery involving the dorsal and ulnar areas of the wrist, multiple longitudinal branches and a transverse branch of the DCBUN are normally present and must be respected.