Distal nerve transfer for thenar palsy: A cadaveric study

Introduction Severe proximal median nerve palsies often result in irreversible thenar atrophy and thumb abduction function loss. Tendon transfer involves substantial limitations and challenges; but, distal nerve transfer may provide an alternative treatment. Our goal was to validate the anatomical suitability of two distal ulnar nerve branches for thenar muscle reanimation. Materials and Methods We assessed nerve transfer to the recurrent branch of median nerve (RMN) in 16 embalmed cadaveric hands. The ulnar motor branch to the flexor digiti minimi brevis (FDMBn) and the ulnar motor branch to the third lumbrical (3rdLn) were assessed for transfer. Coaptation success was measured by the overlap of the nerve donor with the RMN and correspondence of nerve diameters. Results The mean transferable length and width of the RMN were 20.7 +/- 4.5 and 1.0 +/- 0.3 mm, respectively. We identified an average of three branches in the branching anatomy from the ulnar nerve to the hypothenar muscles. The maximal transferable lengths and widths of the FDMBn and the 3rdLn were 13.8 +/- 4.4 and 0.5 +/- 0.1 mm and 24.1 +/- 6.4 and 0.4 +/- 0.1 mm, respectively. The overlap with the RMN of the FDMBn and 3rdLn was 9.0 +/- 3.6 (2.0-15.3) and 17.8 +/- 6.0 (4.7-27.5) mm, respectively. Conclusions This anatomical study demonstrates the feasibility of distal nerve transfers between the ulnar and median nerves in the hand for reanimation of thenar muscles. Ulnar motor donors of the BrFDMBn and 3rdLn likely represent the least morbid donors with short distances for regeneration and a single coaptation repair.