Total brachial plexus injury: contralateral C7 root transfer to the lower trunk versus the median nerve

Abstract

Contralateral C7 (cC7) root transfer to the healthy side is the main method for the treatment of brachial plexus root injury. A relatively new modification of this method involves cC7 root transfer to the lower trunk via the prespinal route. In the current study, we examined the effectiveness of this method using electrophysiological and histological analyses. To this end, we used a rat model of total brachial plexus injury, and cC7 root transfer was performed to either the lower trunk via the prespinal route or the median nerve via a subcutaneous tunnel to repair the injury. At 4, 8 and 12 weeks, the grasping test was used to measure the changes in grasp strength of the injured forepaw. Electrophysiological changes were examined in the flexor digitorum superficialis muscle. The change in the wet weight of the forearm flexor was also measured. Atrophy of the flexor digitorum superficialis muscle was assessed by hematoxylin-eosin staining. Toluidine blue staining was used to count the number of myelinated nerve fibers in the injured nerves. Compared with the traditional method, cC7 root transfer to the lower trunk via the prespinal route increased grasp strength of the injured forepaw, increased the compound muscle action potential maximum amplitude, shortened latency, substantially restored tetanic contraction of the forearm flexor muscles, increased the wet weight of the muscle, reduced atrophy of the flexor digitorum superficialis muscle, and increased the number of myelinated nerve fibers. These findings demonstrate that for finger flexion functional recovery in rats with total brachial plexus injury, transfer of the cC7 root to the lower trunk via the prespinal route is more effective than transfer to the median nerve via subcutaneous tunnel.

Keywords: contralateral C7 root; lower trunk; median nerve; nerve regeneration; nerve transfer; neural regeneration; total brachial plexus injury.

Figure 1

Schematic diagrams of contralateral C7 (cC7) root transfer to the lower trunk vs. the median nerve for the repair of total brachial plexus injury. (A) Modified cC7 root transfer to the lower trunk: the C7 nerve root was separated and cut off at the division-to-cord level. The prespinal route was made along the anterior vertebral body by bluntly dissecting the sternocleidomastoid muscle and carotid sheath along their medial margin and severing the right anterior scalene muscle. The cC7 root was passed through the tunnel to the injured side. The coaptation was made utilizing end-to-end neurorrhaphy. (B) Traditional cC7 root transfer to the median nerve: the left pedicular vascularized ulnar nerve grafts were dissected, and the distal end was severed at the wrist level, moved to the contralateral side through the ventral thoracic subcutaneous tunnel and connected to the proximal cC7 root. Four weeks later, the ulnar nerve graft and median nerve were dissected and cut off from an incision at the middle of the injured arm. The distal stump of the ulnar nerve graft was coapted to the distal end of the median nerve with end-to-end neurorrhaphy.

Figure 2

Morphology of the flexor digitorum superficialis muscle in the rat model of total brachial plexus injury with cC7 root transfer to the lower trunk or the median nerve (hematoxylin-eosin staining, 200× magnification) Group A: cC7 root transfer to the lower trunk via the prespinal route; Group B: cC7 root transfer to the median nerve via subcutaneous tunnel; Group C: sham operation. Significant atrophy of the flexor digitorum superficialis muscle was seen on the injured side in groups A and B at 4, 8 and 12 weeks after the surgery. cC7: Contralateral C7.

Figure 3

Neuromorphology of the median nerve in the rat model of total brachial plexus injury with cC7 root transfer to the lower trunk or the median nerve (toluidine blue staining, 400× magnification) Group A: cC7 root transfer to the lower trunk via the prespinal route; Group B: cC7 root transfer to the median nerve via subcutaneous tunnel; Group C: sham operation. The total number of myelinated fibers in the median nerve in both groups A and B increased with time postoperatively. cC7: Contralateral C7.