An electrophysiologic study on the origination of brachialis branch of the musculocutaneous nerve

Objective To identify the origin of brachialis branch of musculocutaneous nerve (BBMCN)at root level using intraoperative electrophysiologic testing and provide theoretical basis for BBMCN transfer. Methods Thirty patients of brachial plexus injury who underwent eontralateral C7 transfer were involved in the study.Patients'age ranged from 16 to 50 years with an average of(28.9±7.7)years.After exposure of the heMthy side brachial plexus,C5 to T1 nerve roots were stimulated respectively to record compound muscle action potential (CMAP) in the brachialis muscle using Esaote 4 channel eleetrophysiologieal devise.Onset latency and amplitude of CMAPs were measured. Results Ample CMAP was recorded in the braehialis muscle in 29 cases upon C5 stimulation,in 30 cases upon C6 stimulation and in 28 cases upon C7 stimulation.Only subtle CMAP was recorded in the brachialis muscle of 6 cases while C8 and T1 were stimulated.The amplitude and latency of CAMAP were(4.87±4.43)mV and(6.32±1.50)ms for C5,(5.65±4.76)mV and(6.51±1.36)ms for C6,and(0.90±2.29)mV and(6.99 ±1.33)ms for C7.CMAP amplitude from C5 and C6 was significantly higher than that from C7,while there was no significant difference between C5 and C6 nerve root. Conclusion Analysis of CMAP suggested that BBMCN is mainly comprised of fibers from C5 and C6 nerve roots.Transfer of this muscle branch to the median nenre (anterior interosseous nerve)is a feasible and effeetive procedure.The technique proposed here was a more direct and functional method to trace the origin of a specific nerve or of the nerve fibers innervating a given muscle.