Influence of Breaching the Connective Sheaths of the Donor Nerve on Its Myelinated Sensory Axons and on Their Sprouting into the End-to-Side Coapted Nerve in the Rat

Abstract

The influence of breaching the connective sheaths of the donor sural nerve on axonal sprouting into the end-to-side coapted peroneal nerve was examined in the rat. In parallel, the effect of these procedures on the donor nerve was assessed. The sheaths of the donor nerve at the coaptation site were either left completely intact (group A) or they were breached by epineurial sutures (group B), an epineurial window (group C), or a perineurial window (group D). In group A, the compound action potential (CAP) of sensory axons was detected in *10% and 40% of the recipient nerves at 4 and 8 weeks, respectively, which was significantly less frequently than in group D at both recovery periods. In addition, the number of myelinated axons in the recipient nerve was significantly larger in group D than in other groups at 4 weeks. At 8 weeks, the number of axons in group A was only *15% of the axon numbers in other groups ( p < 0.05). Focal subepineurial degenerative changes in the donor nerves were only seen after 4 weeks, but not later. The average CAP area and the total number of myelinated axons in the donor nerves were not different among the experimental groups. In conclusion, myelinated sensory axons are able to penetrate the epiperineurium of donor nerves after end-to-side nerve coaption; however, their ingrowth into recipient nerves is significantly enhanced by breaching the epiperineurial sheets at the coaptation site. Breaching does not cause permanent injury to the donor nerve.

Changes of the donor nerve in end‐to‐side neurorrhaphies with epineurial window and partial neurectomy: A long‐term evaluation in the rat model

“…13 Oyamatsu et al 12 reported that deliberate donor nerve injury after creation of a perineurial window with ETS repair following a partial crush injury or partial neurotomy, promoted axon regeneration of the donor nerves, compared to simple perineurial opening, 7 days after surgery in a rat model. In our study, no marked functional impairments of the tibial nerve and gastrocnemius muscle were noticed in the group of ETS neurorrhaphy with an epineurial window at all time points after surgery as assessed by electrophysiology, myelinated axon recovery, muscle force, musclular fiber area, and wet muscle weight.…”

“…11 Kovacic et al found that an epineurial window or a perineurial window does not affect the average compound action potential area or the total number of myelinated axons in the donor sural nerves which were repaired in an ETS fashion as measured in peroneal nerves after 8 weeks postoperatively. 13 Oyamatsu et al 12 reported that deliberate donor nerve injury after creation of a perineurial window with ETS repair following a partial crush injury or partial neurotomy, promoted axon regeneration of the donor nerves, compared to simple perineurial opening, 7 days after surgery in a rat model. In our study, no marked functional impairments of the tibial nerve and gastrocnemius muscle were noticed in the group of ETS neurorrhaphy with an epineurial window at all time points after surgery as assessed by electrophysiology, myelinated axon recovery, muscle force, musclular fiber area, and wet muscle weight.…”

“…12 Other studies found that neither epineurial window nor perineurial window affected the average compound muscle action potential (CMAP) area or the total number of myelinated axons in the donor nerves for ETS nerve repair. 13 However, investigations concerning donor system responses were mostly short term, with study periods no more than 3 months. 3,[12][13][14][15] A recent experimental study by Geuna's group has demonstrated that nerve fibers are not able to return spontaneously to their normal preinjury state.…”

“…13 However, investigations concerning donor system responses were mostly short term, with study periods no more than 3 months. 3,[12][13][14][15] A recent experimental study by Geuna's group has demonstrated that nerve fibers are not able to return spontaneously to their normal preinjury state. 16 The aim of the present study is to identify changes of the donor nerve and its innervated targets following ETS neurorrhaphy with the creation of an epineurial window or 40% donor nerve neurectomy at several time points up to 24 weeks postoperatively.…”

Dynamic Quantitative Assessment of Motor Axon Sprouting after Direct Facial–Hypoglossal End-To-Side Neurorrhaphy in Rats

“…Although regenerating axons are able to penetrate the epineurium and perineurium of the donor nerves, connective tissue sheath of the nerve does pose an obstacle to axon sprouting after ETS neurorrhaphy, 23 and research increasingly suggests that axonal damage in the donor nerve may provide a significant positive stimulus to axon sprouting. 11,21,[24][25][26] Therefore, it can reasonably be expected that ETS neurorrhaphy with deliberate injury in the donor hypoglossal nerve may result in larger numbers of regenerating fibers and better functional outcomes. It is worth mentioning that both the reconstruction techniques resulted in partial functional recovery at different levels, but no complete restoration of function was obtained.…”