Cutaneous innervation of the hand: clinical testing in volunteers shows high intra- and inter-individual variability

Background: Many clinicians require a solid understanding of the anatomical areas supplied by specific peripheral nerves. Virtually all pertinent medical textbooks claim that the entire (palmar and dorsal) surface of the hand is supplied by three (median, radial, and ulnar) nerves and that each of these covers a well-defined area. This study was designed to evaluate the sensory-distribution pattern of peripheral nerves in the hand. Methods: Twelve volunteers were enrolled and randomly allocated to have median, ulnar, or radial nerve blocks to each hand on three successive days. All blocks were performed using ultrasound guidance. A neurologist carried out pinprick testing to define the sensory-distribution area of each procedure. The hand surface was then scanned, and the sensorydistribution area of the blocked nerve was traced, measured, and quantified in relation to the entire hand surface for descriptive and comparative statistical analyses. Results: The sensory-distribution areas of the three nerves revealed a high degree of inter-individual and intra-individual variabilities. Sizeable areas were not covered by any of the three nerves, again involving great variability. Conversely, 15 of the 24 hands showed areas of overlapping supply from more than one nerve. Conclusions: Our findings suggest that the anatomical areas supplied by peripheral nerves are characterised by much greater variability than is routinely claimed.