Effect of Collateral Sprouting on Donor Nerve Function After Nerve Coaptation: A Study of the Brachial Plexus

Abstract

BACKGROUND The aim of the present study was to evaluate the donor nerve from the C7 spinal nerve of the rabbit brachial plexus after a coaptation procedure. Assessment was performed of avulsion of the C5 and C6 spinal nerves treated by coaptation of these nerves to the C7 spinal nerve. MATERIAL AND METHODS After nerve injury, fourteen rabbits were treated by end-to-side coaptation (ETS), and fourteen animals were treated by side-to-side coaptation (STS) on the right brachial plexus. Electrophysiological and histomorphometric analyses and the skin pinch test were used to evaluate the outcomes. RESULTS There was no statistically significant difference in the G-ratio proximal and distal to the coaptation in the ETS group, but the differences in the axon, myelin sheath and fiber diameters were statistically significant. The comparison of the ETS and STS groups distal to the coaptation with the controls demonstrated statistically significant differences in the fiber, axon, and myelin sheath diameters. With respect to the G-ratio, the ETS group exhibited no significant differences relative to the control, whereas the G-ratio in the STS group and the controls differed significantly. In the electrophysiological study, the ETS and STS groups exhibited major changes in the biceps and subscapularis muscles. CONCLUSIONS The coaptation procedure affects the histological structure of the nerve donor, but it does not translate into changes in nerve conduction or the sensory function of the limb. The donor nerve lesion in the ETS group is transient and has minimal clinical relevance.

Figure 1

Macroscopic structure of the rabbit’s right brachial plexus. C5, C6, C7, C8, and T1 – ventral branches of the C5, C6, C7, C8, and T1 spinal nerves.

Figure 2

(A) An example of grade 0 (EMG triceps brachii, no. 8, ETS group); (B) An example of grade 1 (EMG teres major muscle, no. 10, STS group); (C) An example of grade 2 (EMG biceps brachii muscle, no. 6, ETS group); (D) An example of grade 3 (EMG subscapularis muscle, no. 2, STS group).

Figure 3

C5, C6, C7, C8, and T1 – ventral branches of the C5, C6, C7, C8, and T1 spinal nerves. The numbers 1, 2 and 3 indicate the collection site of the analyzed nerves. (A) End-to-side coaptation (ETS); (B) Side-to-side coaptation (STS); (C) Control group.

Figure 4

Bar graphs presenting histomorphometric analyses of the sampled nerves.

Figure 5

(A) Microscopic image of the sampled nerve before coaptation in the ETS group (toluidine blue staining); (B) Microscopic image of the sampled nerve 2 cm from the coaptation in the ETS group (toluidine blue staining); (C) Microscopic image of the sampled nerve in the control group (toluidine blue staining).

Figure 6

Distribution of pathological changes in the EMG. (A) ETS group, (B) STS group, (C) Degree of denervation of particular muscles in the ETS and STS groups.