Nerve Transfer for Wrist Extension Using Nerve to Flexor Digitorum Superficialis in Cervical 5, 6, and 7 Root Avulsions: Anatomic Study and Report of Two Cases

Abstract

To evaluate the feasibility of restoring wrist extension in patients with complete cervical root 5 (C5), 6, and 7 avulsion injuries by transferring the most proximal branch of the median nerve that innervates flexor digitorum superficialis (FDS) muscle (proximal FDS branch) to the branch of the radial nerve that innervates extensor carpi radialis brevis (ECRB) muscle (ECRB branch) in an anatomic study and 2 case reports. The study was performed on 10 fresh cadavers. The nerve branches of the median nerve and the radial nerve were measured for length, diameter, and sites of origin of their nerve branches. The nerve branches of the median nerve, the posterior interosseous nerve, and the ECRB branch of the radial nerve were processed for histomorphometric evaluation. Using image analysis software, we took all histomorphometric measurements of the nerve sections. Based on this anatomical study, the proximal FDS branch was transferred directly to the ECRB branch without nerve graft in 2 patients. The average distance from the origin of nerve branches to the interepicondylar line was 3.5 and 2.3 cm, respectively, for the proximal FDS and ECRB branches. The average length of the proximal FDS branch and ECRB branch was 2.8 and 3.3 cm, respectively. The average number of myelinated nerve fibers of the proximal FDS branch and ECRB branch was 983 and 2,797, respectively. At 2 years' follow-up, preliminary clinical results demonstrated that wrist extension had gained strength against resistance (grade M4). The arc of motion for wrist extension was 30 degrees in the first patient and 70 degrees in the second one. Useful functional recovery was achieved and classified as good result in both cases. The anatomic study and 2 reported results supports our hypothesis that transfer of the proximal FDS branch of median nerve to the ECRB branch of radial nerve could be an alternative method for reconstructiing wrist extension in C5, 6, and 7 avulsion injuries.