Reinnervation of mechanoreceptors in the human glabrous skin following peripheral nerve repair

The technique of percutaneous microneurography was used to record single unit activity from 65 reinnervated and 24 normally innervated mechanoreceptors in the glabrous skin of the human hand. The results were obtained from 20 patients and 5 control subjects. The patients had suffered complete traumatic transsection, with subsequent repair, of the median or ulnar nerves. Three types of mechanoreceptors (RA, SAI, SAII) and many unidentified units located in deep tissues were found to become reinnervated. No reinnervated PC units could be identified. Response thresholds, discharge characteristics and receptive field properties of reinnervated receptors were comparable to normal, with the exception that reinnervated SA I units had slower static discharge rates and smaller receptive fields. No evidence was found for multiple peripheral innervation by a single afferent fiber. The reinnervated mechanoreceptors were predominantly located in the palm and the proximal fingers with few in the finger tips, contrary to normal. The locations and frequency of occurrence of the different types of receptors could be correlated with the goodness of sensory recovery. It is suggested that these differences result from misguidance of regenerating fibers and from poor reinnervation, and that they account for reduced sensitivity and poor tactile discrimination in patients with peripheral nerve injuries.