A new cervical nerve root avulsion model using a posterior extra-vertebral approach in rats

Souichi Ohta,Shuichi Matsuda,Takashi Noguchi,Yukitoshi Kaizawa,Ryosuke Kakinoki

doi:10.1186/1749-7221-8-8

Souichi Ohta, Shuichi Matsuda + Show 3 more

Open Access

https://doi.org/10.1186/1749-7221-8-8

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Abstract

BackgroundThe nerve root avulsion injury causes decrease of motor neurons in the spinal ventral horn. To investigate the motoneuron death after avulsion injury in rats, the intradural root avulsion procedure is usually used, although it is technically demanding and associated with a risk of unexpected spinal cord damage. We have developed a new cervical nerve root avulsion procedure in rats and investigated the validity of our procedure.MethodsOur procedure is using a posterior approach and pulling the C6 nerve root outside the vertebral foramen without intradural procedures. The lateral third of the lateral mass is needed to be resected before pulling the nerve root. The accomplishment of our procedure is judged by confirmation of the bifurcated stump of the avulsed nerve root and the leakage of the spinal fluid from vertebral foramen. At first, four Sprague–Dawley (SD) rats were used for the examination of C6 motor neuron distribution in the normal spinal cord. Then, 40 SD rats were divided into following four groups and the survival rate of motor neuron was examined. (A) an intradural avulsion group, (B) an intradural rhizotomy group, (C) our extravertebral avulsion group, and (D) an extravertebral rupture group. Another 26 SD rats were used for the examination of histomorphorogic changes in the spinal cord after our extra-vertebral avulsion procedure.ResultsAt 28 days after injury, the percentage of surviving motor neurons in groups A (39.0 ± 2.1%) and C (47.5 ± 7.1%) were significantly lower than those in groups B (77.1 ± 12.3%) and D (98.9 ± 9.9%). Compared with other groups, our procedure was easier and associated with less unexpected spinal cord damage. Although the length of the distal stump of the extravertebrally avulsed ventral rootlets was varied between 1.5 and 3.2 mm, this difference did not affect motoneuron death. The extravertebral avulsion injury showed intraspinal bleeding along the motoneuron axons, glial reaction and macrophage infiltration in the lesioned side of the ventral horn.ConclusionsOur extravertebral avulsion procedure is simple and reproducible. It would become a useful tool for the study of cervical nerve root avulsion injury.

Highlights

The nerve root avulsion injury causes decrease of motor neurons in the spinal ventral horn
We have developed a less invasive procedure for cervical nerve root avulsion using a posterior extra-vertebral approach in rats and investigated the validity of this new procedure by histological examinations and examining the number of motor neurons remaining in the ventral horn of the spinal cord 28 days after the procedure along with previous reports [9,10,11]
Distribution of C6 motor neurons The C6 spinal segment was defined as the area between the lower edge of the C5 dorsal rootlets and the upper edge of the C7 dorsal rootlets (Figure 2A), as previously reported [9]

Summary

Introduction

The nerve root avulsion injury causes decrease of motor neurons in the spinal ventral horn. Carstedt et al were the first to report reimplantation surgery for avulsed roots in clinical cases [7]. This surgical procedure still has a number of unsolved shortcomings, limited functional recovery of the shoulder and elbow joints was seen in some cases. They suggested that one of the important factors for obtaining good functional outcomes in this repair was the survival of motor neurons within the pertinent spinal cord segment [8]

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