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

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 ampli- fication 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 ampli- fication 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 su- tured 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 veloc- ity 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.

Techniques in Hand &Upper Extremity Surgery

The use of tendon transfer to restore functions of extremities was initially recognised in the 19th century, and its advancement was further amplified by the polio epidemic towards the turn of that century. Tendon transfer surgery extended to the use for traumatic reconstructive surgery during World War I, with key surgical pioneers, including Mayer, Sterling Bunnell, Guy Pulvertaft and Joseph Boyes. In 1921, Robert Jones first described the transfer of pronator teres (PT) to the wrist extensors for irreparable radial nerve paralysis in infantile hemiplegia. Although, a detailed description of its indication and surgical outcomes were not published until 1959 and 1970 by Stelling and Meyer, and Keats, respectively. Pronator teres is often the tendon of choice for reconstructing wrist extensors, and used in a multiple of pathologies, including radial nerve palsy, cerebral palsy, and tetraplegia. Reconstruction of finger extensors are less straightforward and options include flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), and flexor digitorum superficialis (FDS). Our article describes the techniques and outcomes of 25 patients that undergone pronator teres transfer. A good understanding of the pronator teres anatomical location and potential variations, aids efficient harvesting and limits unnecessary tissue dissection. Pronator teres tendon harvest is best performed through a systematic and anatomic approach.