A Discussion Of Compound Muscle Action Potential And Effect Of Carpal Tunnel Release

Carpal tunnel syndrome (CTS) is the most common nerve compression syndrome. The patients of CTS show paresthesia, pain, weakness and hand functional impairment of the median nerve. The electrophysiological study can be helpful in the diagnosis of CTS. The distal motor lantency(DML) and the amplitude of the compound muscle action potential (CMAP) recorded from abductor pollicis brevis(APB) acts an important part not only in the electrophysiologic diagnosis but also in the clinical evaluation. For those CTS patients who had serious clinical symptoms, carpal tunnel release(CTR) may be one of the effective treatment. During the surgery, we can evaluate the effectiveness of the operation by the intraoperative electrophysiology examination. Objective:To explore a sensitive electrophysiological index and juncture which evaluating the effect of CTR by investigating the changes of compound muscle action potential before and during the surgery. Methods:15 patients with carpal tunnel syndrome were involved in the study. After having released median nerve, electrophysiologic examination was carried out to record and the CMAP of abductor pollicis brevis muscle at following moments:①Before the surgery (after local anaesthesia),②Instantly post-op,③1 minute post-op,④3 minutes post-op,⑤5minutes post-op,⑥7 minutes post-op. A statistics analysis would be applied to compare these parameters to get meaningful results. Results:1. There were statistically significant changes during the 5 minutes after releasing the tourniquet of both amplitude and latency of the CMAP (p<0.05), while there were not much difference after 5 minutes; 2. After the surgery:Both the latencies and amplitude of CMAP were greatly reduced(p<0.05), while the improvements of amplitude had more statistical significance. (p<0.01). Conclusion:It might be more reliable at least 5 minutes after release the tourniquet for carrying out the electrophsiologic examination and it might be more directly for amplitude than latency to evaluate the effectiveness of media nerve decompression.