Assessment of nerve regeneration and adaptation after median nerve reconnection and digital neurovascular flap transfer

Six patients with median nerve severance (five sutured) were studied after an interval of 18 to 35 years to assess residual neurologic deficit, misdirected axonal regrowth, and adaptation to faulty reinnervation. Mild motor impairment was confirmed by the smaller thenar muscle action potentials and isometric muscle twitches from supramaximal stimulation of the median nerve. Sensory impairment was supported by the increased thresholds of vibratory (p = 0.003) and touch-pressure (p = 0.004) detection thresholds of the pulp of index fingers and decreased amplitudes of sensory nerve action potentials. A tactile hemidigit localization test revealed that localization was not significantly different from that on the contralateral side but perceptual temtory was increased. This increase is best explained by misdirected axon regrowth without CNS adaptation. Longstanding faulty tactile digit localization in neurovascular skin flaps from finger to thumb also was demonstrated—further evidence that CNS adaptation is imperfect when sensory nerves to digits are relocated.