Tremor in the human hand following peripheral nerve transection and reinnervation

Slow movements and position holding by the digits are both characterised by 8-10 Hz tremor which appears to be centrally generated. Denervation and subsequent reinnervation lead to significant alterations in peripheral connectivity and reflex organisation. We have tested the hypothesis that 8-10 Hz tremor is present in the digits of subjects following a complete nerve lesion. The frequency content of abduction and adduction movements was recorded in 12 index fingers and nine little fingers reinnervated subsequent to a complete ulnar nerve transection. An optical position laser transducer was used to measure digital movements, minimising mechanical interference to the system. Concurrently, surface electromyograms (EMG) were also recorded from first dorsal interosseus muscles (1DI) and abductor digiti minimi brevis (ADMB) muscles for index and little fingers, respectively. The maximal voluntary contraction (MVC) of the reinnervated muscles varied from 5.9% to 100% of those of the unimpaired, contralateral hands. The subjects performed abduction-adduction movements of the index and little fingers and a position holding task. Significant peaks in PSD curves of acceleration and rectified integrated EMG traces were identified. Tremor in the 8-10 Hz range was evident in both the acceleration and EMG signals for the majority of digits during both the slow movement and position holding tasks. These findings demonstrate the robust nature of these 8-10 Hz oscillations, even following the significant changes in peripheral connectivity of muscle and nerve resulting from nerve transection and reinnervation.