Anatomical Characterization and Topographic Mapping of the Distal Ulnar Nerve and Its Peripheral Branches: A Cadaveric Analysis

Abstract

Background: Understanding peripheral ulnar nerve anatomy is necessary to refine surgical treatment of ulnar nerve injuries. This study topographically mapped the ulnar nerve and its distal branch points from a well-defined surgical landmark and assessed for variations in interfascicular motor arrangement and branch size. Methods: Fifty-four cadaveric upper extremities were dissected to expose the distal ulnar nerve and its branches (dorsal cutaneous (DCB), volar sensory (VSB), and motor branches). The motor branch underwent internal neurolysis to record the topographic orientation of abductor digiti minimi (ADM) and flexor pollicis brevis (FPB) fascicles and the combined intrinsic fascicle identified by its terminal branch (first dorsal interosseus (FDI)). Using a standardized grid system, the branch point location of each terminal branch was measured relative to the hook of the hamate. Diameters of VSB, DCB, and motor fascicles were also measured. Results: Mean branch point coordinates relative to the hook of the hamate for the FDI were 22.8 mm radial/32.1 mm distal, 13.6 mm radial/25.1 mm distal for FPB, 7.7 mm ulnar/5.2 mm proximal for ADM, and 15.7 mm ulnar/95.3 mm proximal for DCB. The diameters of the VSB, motor branch, and DCB had a mean of 2.3, 1.9, and 1.6 mm, respectively. Proximal to the hook of the hamate, the fascicular arrangement from radial-to-ulnar was VSB, FPB, FDI/intrinsics, ADM, and DCB. Conclusions: This study provides a complete characterization and mapping of the distal ulnar nerve and its branches to assist surgeons with treatment of ulnar nerve injuries, including nerve transfer.