Sleeve bridging of the rhesus monkey ulnar nerve with muscular branches of the pronator teres: multiple amplification of axonal regeneration

Abstract

Multiple-bud regeneration, i.e., multiple amplification, has been shown to exist in peripheral nerve regeneration. Multiple buds grow towards the distal nerve stump during proximal nerve fiber regeneration. Our previous studies have verified the limit and validity of multiple amplification of peripheral nerve regeneration using small gap sleeve bridging of small donor nerves to repair large receptor nerves in rodents. The present study sought to observe multiple amplification of myelinated nerve fiber regeneration in the primate peripheral nerve. Rhesus monkey models of distal ulnar nerve defects were established and repaired using muscular branches of the right forearm pronator teres. Proximal muscular branches of the pronator teres were sutured into the distal ulnar nerve using the small gap sleeve bridging method. At 6 months after suture, two-finger flexion and mild wrist flexion were restored in the ulnar-sided injured limbs of rhesus monkey. Neurophysiological examination showed that motor nerve conduction velocity reached 22.63 ± 6.34 m/s on the affected side of rhesus monkey. Osmium tetroxide staining demonstrated that the number of myelinated nerve fibers was 1,657 ± 652 in the branches of pronator teres of donor, and 2,661 ± 843 in the repaired ulnar nerve. The rate of multiple amplification of regenerating myelinated nerve fibers was 1.61. These data showed that when muscular branches of the pronator teres were used to repair ulnar nerve in primates, effective regeneration was observed in regenerating nerve fibers, and functions of the injured ulnar nerve were restored to a certain extent. Moreover, multiple amplification was subsequently detected in ulnar nerve axons.

Keywords: NSFC grants; multiple amplification; muscular branches of pronator teres; nerve regeneration; neural regeneration; peripheral nerve; rhesus monkey; sleeve bridging; small gap; ulnar nerve.

Figure 1

Preparation of rhesus monkey models of ulnar nerve injury. (A) Exposure of muscular branches of pronator teres and ulnar nerve; (B) dissociation of muscular branches of pronator teres and ulnar nerve (blue arrow shows ulnar nerve; green arrow shows muscular branches of pronator teres); (C) sleeve bridging of proximal muscular branches of the pronator teres and distal end of the ulnar nerve.

Figure 2

Shape of cone chitin biological conduit and position of peripheral nerve collection. (A) Shape of cone chitin biological conduit; (B) sleeve bridging proximal nerve (4 mm proximal to proximal suture point) and sleeve bridging distal nerve (4 mm distal to distal suture point).

Figure 3

Pattern of small gap sleeve bridging to repair peripheral nerve injury. (A) Trimming nerve stump; (B) the proximal nerve stump was inserted 2 mm into the conduit and sutured 1 mm from the proximal nerve stump. Two suture lines outside the conduit were knotted. (C) Distal and proximal nerve stumps were separately inserted 2 mm into the conduit, with a 2-mm-gap between the two stumps.

Figure 4

General appearance and myelinated nerve fibers of the injured nerve in the rhesus monkey after peripheral nerve repair based on multiple nerve amplification at 6 months after model establishment. (A) Proximal muscular branches of the pronator teres were connected to the distal end of the ulnar nerve (arrow). The biological conduit had been absorbed. No noticeable tissue adhesion appeared surrounding the nerve. No neuroma was visible in the suture site. (B) Donor nerve proximal to the ulnar nerve; (C) receptor nerve distal to the ulnar nerve. Osmium tetroxide staining. Scale bar: 10 μm.