The effect of a gap concept on peripheral nerve recovery in modified epineurial neurorrhaphy: An experimental study in rats

Background: Several factors such as surgical approach that only consider topographic anatomy; inadequate fascicular alignment, extraepineurial sprouting in the repair zone; contact of axons with the suture area are the disadvantages of epineurial neurorrhaphy. Accordingly, axonal mismatch, neuroma, and unfavorable nerve recovery become inevitable. Neurotropism is the theory clarifying appropriate matching of the nerve fibers independently without needing surgical approach. The studies comparing the primary nerve repair with the nerve defects bridged in different ways demonstrated better outcomes of nerve recovery in the groups with a nerve gap. In this study, we aimed to demonstrate the effects of the gap concept in primary nerve repair bridged by own epineurium. We hypothesized that this technique will provide better results in terms of peripheral nerve recovery and will significantly eliminate the occurrence of a neuroma, which is quite possible in epineurial neurorrhaphy. Materials and Methods: A total of 35 Wistar female rats weighing 200 ~ 250 g were randomly divided into five groups each with seven rats. Sham controls constituted Group 1, while the rats with epineural neurorrhaphy were included in Group 2. The remaining three groups were the study groups. In Group 3, after the sciatic nerve transection, epineurium of the distal segment was sleeved and preserved. A 2-mm axonal segment was removed from the epineurium free distal ending and no any procedure was applied to the proximal ending of the transected sciatic nerve. Epineuriums of the both sides were approximated and repaired. In Group 4, a 2-mm axonal segment was removed from the proximal ending of the sciatic nerve after preservation of epineurium and no any procedure was applied to the distal part of sciatic nerve. Epineuriums of the both sides were approximated and repaired. In addition, in Group 5, after epineuriums were sleeved in the both distal and proximal stumps, a 1-mm nerve segment was removed from both endings and epineuriums were repaired in the middle bridging a 2-mm axonal gap again. After a 3 months follow-up period Sciatic Functional Index (SFI) was measured by walking track analysis; the area under the evoked compound muscle action potential (CMAP) and latency periods were calculated via electromyographic (EMG) analysis; and histopathological evaluation were performed to compare the parameters of edema, fibrosis, inflammation, vascularization, axonal degeneration, axonal density, myelination, disorganization, and neuroma occurrence. Vascular structures and nerve fibers were counted at ×200 magnification: +1, +2, and +3 indicated the presence of 0–15, 16–30, and >30 structures, respectively. For uncountable parameters (edema, disorganization, myelination, fibrosis, and inflammation): +1 indicated mild, +2 indicated moderate, and +3 indicated severe. Results: The differences between the groups with axonal gap repair and epineural neurorrhaphy were not significant regarding to SFI. The areas under CMAP were as follows: 27.9 ± 5.9 (Δ = 12.1%) in Group 1; 16.5 ± 5.5 (Δ = 6.3%) in Group 2; 14.1 ± 6.2 (Δ = 4.8%) in group 3; 13.8 ± 2.3 (Δ = 9.2%) in Group 4, and 22.5 ± 18.3 (Δ = 2.2%) in Group 5. Group 5 (1 mm gap in the distal +1 mm gap in the proximal segments) had a significantly better result in terms of the area under CMAP with the value of 22.5 ± 18.3 m/Mv (p =.031). Axonal density was 0.9 ± 0.6 (Δ = 2.2%) in Group 2, 2.4 ± 0.3 (Δ = 5.1%) in Group 3, 2.8 ± 0.1 (Δ = 7.7%) in Group 4, and 2.8 ± 0.2 (Δ = 4.8%) in Group 5. Myelination was 1.1 ± 0.5 (Δ = 3.4%) in group 2, 2.2 ± 0.2 (Δ = 6.7%) in group 3, 2.4 ± 0.4 (Δ = 6.0%) in Group 4, and 2.7 ± 0.3 (Δ = 4.6%) in Group 5. Disorganization was 2.3 ± 0.4 (Δ = 4.1%) in Group 2, 1.2 ± 0.2 (Δ = 7.7%) in Group 3, 1.3 ± 0.2 (Δ = 6.5%) in Group 4, and 1 ± 0.3 (Δ = 5.9%) in Group 5. And, neuroma occurrence was found 2.2 ± 0.6 (Δ = 2.8%) in Group 2 and 0.3 ± 0.2 (Δ = 0.1%) in Group 4 while neuroma was not encountered in Group 3 and Group 5. Comparison between the epineurial neurorrhaphy group and the groups with axonal defect revealed the statistically significant results in the factors of axonal density (p =.001), myelination (p =.028), disorganization (p =.016) and neuroma (p =.001). Conclusions: Creating axonal gap bridged by own epineurium showed favorable results comparing with epineurial neurorrhaphy. Resection of a 1 mm axonal segment from the proximal and distal stumps following the epineurial sleeve procedure and performing the epineurium- only repair can facilitate the nerve regeneration. The feasibility of the described technique has been demonstrated in a small rat model and must be further validated in larger animals before clinical testing.