Age And Time Dependent Effects On The Functional Outcome After Median Nerve Injury And Repair
Thomas Hansson, MD, PhD
Department of Plastic Surgery, Hand Surgery and Burns, Faculty of Health Sciences, Linköping University, Linköping, Sweden
Object. To study age and time dependent effects on the functional outcome after median nerve injury and repair, and how such effects are related to changes in the pattern of cortical activation in response to tactile stimulation of the injured hand. Material. Eleven patients with complete unilateral median nerve injury at the wrist repaired with epineural suture were studied. In addition eight patients from a previous study 16 were included in the statistical analysis. Methods. Sensory perception was measured with static two-point discrimination test (2pd) and monofilaments. Functional magnetic resonance imaging (fMRI) was collected during tactile stimulation (brush strokes) of Digit II-III and IV-V of both hands, respectively. Results. The tactile sensation was diminished in the median territory in all patients. The strongest predictor of 2pd was age at injury (p<0.0048), and when this was accounted for in the regression analysis, the other age and time dependent predictors had no effect. The activation ratios (injured/healthy hand) for Digit II-III and Digit IV-V stimulation were positively correlated (rho 0.59, p<0.011). The activation ratio for Digit II-III stimulation correlated weakly to time after injury (p<0.041). Digit IV-V activation ratio correlated weakly to both 'age at injury' (p<0.048) and 'time after injury' (p<0.033), but no predictor reached the significance level in the regression model. The mean ratio of ipsilateral and contralateral hemisphere activation after stimulation of the injured hand was 0.55, which was not significantly different from the corresponding ratio of the healthy hand (0.66). Conclusion. The normal association between sensory input and cortical activation may be altered following a nerve injury due to an initial increase in the activated volume. This effect subsequently declines during the restoration phase. These dynamic changes seem to involve both median and ulnar nerve cortical representation. Our findings are in agreement with animal studies showing that cortical plasticity is an important mechanism for functional recovery after peripheral nerve injury and repair. Key words: median nerve, hand injury, neuronal plasticity, fMRI, human
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