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Evidence of preferential sensory reinnervation in man: a study of nine patients

We studied nine men aged 17 to 44 years with traumatic complete transection of the median (four), ulnar (three) or both nerves (two) at the wrist or forearm. Epineural repair was carried out in eight patients and fascicular repair in one patient. All surgeries were done within 48 hours after injury. The purpose of this study was to study growth of sensory axons after human nerve injury and repair, in particular, to look for evidence that nerves had regrown to their previously innervated skin areas. Fifteen experiments were undertaken at a mean of 12 months (range 4–67) after repair. Ethics approval and informed consent was obtained in keeping with the declaration of Helsinki. Tungsten microelectrodes were inserted percutaneously into individual fascicles within the repaired nerve above the elbow. The electrode was first used to electrically stimulate the fibres within the fascicle. This produced a cortical stimulus that evoked sensation that subjects were able to identify as being in the hand. The maximum area of induced sensation was taken to represent a fascicular projection territory (FPT). The FPT is a measure that can only be described by humans and therefore makes these findings unique. If the stimulation caused muscle twitching, the electrode was assumed to be within a motor fascicle and not further studied. The second part of the experiment was to stimulate the skin by gently stroking or scratching it and to record the multi-unit activity while the electrode was still positioned within the fascicle. The area from which neural activity could be induced was charted as the fascicular receptive field (FRF) (Figure 1). In all hands there was electrically recordable activity from the regrown nerves that matched the return of clinical sensitivity. This was confined to the palm in patients with follow up shorter than 12 months after repair (hands #2–5; Figure 2). For those patients studied 12 months after surgical repair, the FRFs incorporated the fingertip in eight out of nine hands (#1, 6–11, 13, 15). The skin area where nerve fibres from any one fascicle had regrown, represented here as the FRF, overlapped the area of projected sensation from the same fascicle. An identical distribution was observed, in terms Journal of Hand Surgery (European Volume) 2021, Vol. 46(7) 781–790 journals.sagepub.com/home/jhs