Regarding GBPA, it was early believed that there was no possibility of recovery in the intrinsic muscles of the hand until Wang L’s report [11]: Five of 32 patients with GBPA who had CC7 transfer to the median nerve showed reinnervation of thenar muscle. The strength of APB with Grade M2 was found in four patients. The incomplete interference pattern in the APB was detected by EMG in two patients and the minority MUP was detected in other two patients. The strength of APB was M1 in one patient with EMG showing MUP. Subsequently, Yang X [16] reported fifty-three of 95 patients with GBPA exhibited MUP recovery of APB after CC7 nerve transfer. Otherwise, the conventional CC7 transfer uses the whole ulnar nerve in the affected limb to connect the CC7 with target nerves, which makes it unnecessary to reserve the affected ulnar nerve and loses the possibility of recovery in the intrinsic muscles innervated by the ulnar nerve.
Most of the intrinsic muscles are innervated by DBUN. If we reserve the DBUN and use dorsal and superficial branches of the ulnar nerve and another nerve to connect CC7 with DBUN as a bridge, there is a possibility of recovery in the intrinsic muscles. Which nerve could be selected to connect the proximal end of the ulnar nerve and DBUN? MACN is a good choice based on its location and length. Therefore, we designed a modified CC7 nerve transfer: CC7— dorsal and superficial branches of the ulnar nerve—median nerve + MACN—DBUN.
In the study, the modified CC7 transfer was compared with conventional CC7 transfer. The MUP of ADM and DIM innervated by DBUN appeared in 4 and 2 patients respectively in the modified group. However, there is no MUP present in ADM or DIM in any patient in the conventional group, because DUBN and superficial branches of the ulnar nerve, along with the dorsal branch were used as bridging nerves. This indicated that the modified CC7 transfer could regenerate the intrinsic muscles innervated by DBUN from an electrophysiological perspective. Due to the small quantity, effective statistical comparison could not be conducted. APB, FDPI and FCR are innervated by median nerve. Both of the CC7 transfers were used to repair median nerve. There were no statistical differences of MUP in APB and CMAP in FDPI and FCR between the two groups, which suggested compared with CC7 transfer to median nerve, CC7 transfer to both median and DBUN did not affect the recovery of median nerve. As for MRC result, four patients experienced a recovery in muscle strength of ADM in the modified group and no patients had recovery of ADM in the conventional group, which were consistent with the results of electromyography. The recoveries of APB were similar between the two groups. Due to the small quantity, effective statistical comparison of ADM and APB could not be conducted. There were no significant differences in effect rates of FDPI and FCR between the two groups, which also indicated the modified CC7 transfer didn’t influence the recovery of median nerve.
Compared to the conventional procedure, this modified procedure increased the exposure, separation and anastomosis of DBUN and MACN. DBUN could generally be non-invasively separated to about 8cm above the wrist. Although the distal end of MACN in the forearm was not constant, it was generally located in the upper one-third of the forearm. Therefore, DBUN required further invasive micro-separation towards the proximal end for suturing with MACN. Because MACN at the proximal end of the upper arm was close to the inverted ulnar nerve, it was easy to suture the inverted ulnar nerve to median nerve and MACN simultaneously. Hong GH [17] carried out an anatomy study. In 10 cadavers, the distances between the starting point of DBUN and the midpoint of the line between the medial and lateral epicondyles of the humerus were close to the distances between the branching point of the MACN and the midpoint of the line between the medial and lateral epicondyles of the humerus. Therefore, the distal end of MACN and the proximal end of DBUN were close to each other. The ratios of MACN to DBUN in axon numbers were 0.61:1 on the left side and 0.65:1 on the right side. The ratios of ulnar nerve to the sum of median and MACN in axon numbers were 0.94:1 on the left side and 0.93:1 on right side. According to the principle that the axon number in donor nerve should equal to at least 30% of that in the recipient nerve [17–19], it was feasible to suture MACN with DBUN, ulnar nerve with median nerve and MACN.
There are few clinical reports on the recovery of intrinsic muscles of the patients with GBPA after surgery. CC7 nerve root is the main donor nerve for the intrinsic muscle recovery. Besides Wang L’s and Yang X’s reports on the APB recoveries after CC7 nerve transfer, Wang SF [20] proposed a procedure of direct CC7 nerve transfer to the lower trunk in the affected limb through the prespinal route without a graft. Among 20 patients, ADM recovered muscle strength of M3 in one patient and M2 in one patient. APB recovered muscle strength of M3 in one patient. But this surgical procedure was more complicated and riskier for making the prespinal route and dissecting the lower trunk to peripheral nerves compared with our modified CC7 nerve transfer. In addition, eleven patients were performed the humeral shorten osteotomy for reducing nerve suture tension in his study. The modified CC7 nerve transfer to both of the median nerve and DBUN has not been reported before and is innovative.
This study had some limitations. The small sample size resulted in some statistical comparisons being unable to be conducted. In this study, we did not collect the actual information of patient’s postoperative rehabilitation, which might induce some potential bias. This study belonged to a single-center clinical study, so the results had certain regional limitations. The mean follow-up period was 2.5 year in each group, which was relatively short for the intrinsic muscle recovery, so this study was an early-stage clinical study. In the future study, we will conduct a long-term follow-up.