Le rameau transverse de la branche dorsale du nerf ulnaire : anatomie et rapports avec les voies arthroscopiques du poignet

To our knowledge, there has been only one report specifically devoted to this transverse branch. Two other reports simply mention its existence. According to the literature, the transverse branch of the dorsal ulnar nerve occurs in 60-80% of the cases. We found two anatomic variations different than those described in the literature. Based on our findings and data reported previously, we propose a new classification, describing two main types. In Type 1, the transverse branch arises proximally to the ulnar styloid process;type 1A and type IB are described in relation to the direction of the branch. In Type II, the branch arises distally to the ulnar styloid process;type IIA and type IIB again being described in relation to the direction of the branch. On the tangential trajectory over the radiocarpal joint, the morphometric data show a zone of risk described by a rectangle measuring 10 mm wide (6 mm distal and 4 mm proximal to the ulnar styloid process) and covering 50% of the wrist width. The relations with arthroscopic portals describe a zone of risk corresponding to a 5-7 mm radius circle centered on the portals (4-5, 6R, 6U), which includes 83% of the transverse branches.