Repair of brachial plexus lower trunk injury by transferring brachialis muscle branch of musculocutaneous nerve: anatomic feasibility and clinical trials

BACKGROUND: There are few effective methods for treating injuries to the lower trunk of brachial plexus, and the curative effect is usually poor. The purpose of this study was to provide anatomic references for transferring the brachialis muscle branch of musculocutaneous nerve (BMBMCN) for selective neurotization of finger flexion in brachial plexus lower trunk injury, and to evaluate its clinical curative effects. METHODS: Microanatomy and measurement were done on 50 limbs from 25 adult human cadavers to observe the origin, branch, type of the BMBMCN and median nerve, as well as their adjacent structures. Internal topographic features of the fascicular groups of the median nerve at the level of the BMBMCN were observed. In addition, the technique of BMBMCN transfer for selective neurotization of finger flexion of the median nerve was designed and tested in 6 fresh adult human cadavers. Acetylcholinesterase (AchE) staining of the BMBMCN and median nerve was done to observe the features of the nerve fibers. This technique was clinically tried to restore digital flexion in 6 cases of adult brachial plexus lower trunk injury. These cases were followed up for 3, 6, 9 and 12 months postoperatively. Recovery of function, grip strength, nerve electrophysiology and muscle power of the affected limbs were observed and measured. RESULTS: The brachialis muscle was totally innervated by the musculocutaneous nerve (MCN). Based on the Hunter's line, the level of the origin of the BMBMCN was (13.18 +/- 2.77) cm. AchE histochemical staining indicated that the BMBMCN were totally made up of medullated nerve fibers. At the level of the BMBMCN, the median nerve consistently collected into three fascicular groups as shown by microanatomy in combination with AchE stain. The posterior fascicular group was mainly composed of anterior interosseous nerves and branches to the palmaris longus. The technique was tested in six fresh cadavers successfully, except that stoma split occurred in one case. Five of the six cases recovered digital flexion 12 months after operation, and at the same time grip strength, muscle power, and nerve electrophysiology also recovered markedly. CONCLUSIONS: The technique of transferring the BMBMCN for selective neurotization of finger flexion is anatomically safe and effective, with satisfactory clinical outcomes.