Effect of Axonal Trauma on Nerve Regeneration in Side-to-side Neurorrhaphy: An Experimental Study

Abstract

Background: Side-to-side (STS) neurorrhaphy can be performed distally to ensure timely end-organ innervation. It leaves the distal end of the injured nerve intact for further reconstruction. Despite encouraging clinical results, only few experimental studies have been published to enhance the regeneration results of the procedure. We examined the influence of different size epineural windows and degree of axonal injury of STS repair on nerve regeneration and donor nerve morbidity.

Methods: Three clinically relevant repair techniques of the transected common peroneal nerve (CPN) were compared. Group A: 10-mm long epineural STS windows; group B: 2-mm long windows and partial axotomy to the donor tibial nerve; and group C: 2-mm long windows with axotomies to both nerves. Regeneration was followed by the walk track analysis, nerve morphometry, histology, and wet muscle mass calculations.

Results: The results of the walk track analysis were significantly better in groups B and C compared with group A. The nerve fiber count, total fiber area, fiber density, and percentage of the fiber area values of CPN of the group C were significantly higher when compared with group A. The wet mass ratio of the CPN-innervated anterior tibial muscle was significantly higher in group C compared with group A. The wet mass ratio of the tibial nerve-innervated gastrocnemial muscle was higher in group A compared with the other groups.

Conclusions: All three variations of the STS repair technique showed nerve regeneration. Deliberate donor nerve axotomy enhanced nerve regeneration. A larger epineural window did not compensate the effect of axonal trauma on nerve regeneration.

Fig. 1.

Schematic diagram of experimental groups. Side-to-side repair between the distal end of transected CPN and parallel TN was performed in 3 different ways. In group A, 10-mm long epineural window was performed to both nerves. In group B, 2-mm long epineural windows were performed with tibial nerve axotomy. In group C, 2-mm long epineural windows and axotomies to both nerves inside epineural windows were performed. Red marks show the biopsy sites for morphometry.

Fig. 2.

Results of the walk track analysis. At 12 weeks, groups B and C showed significantly better results than group A. All experimental groups had significantly better values than the unoperated controls. The unrepaired group was derived from our previous study. The data were analyzed with the analysis of covariance with Tukey–Kramer adjustment for multiple comparisons (*P < 0.05; error bar, ± 1 SD).

Fig. 3.

Morphometric results of the CPN. A, The nerve areas of the groups did not differ. B, The values of the nerve fiber count of groups B and C were significantly higher compared with group A (both P < 0.007). The total nerve fiber area (C), nerve fiber density (D), and percentage of the nerve fiber area values (E) of group C were significantly higher compared with group A. The nerve fiber count, nerve fiber density, and percentage of the nerve fiber area values were significantly higher in the CPN distal site compared with the distal stump in groups B and C. *P < 0.05, **P < 0.01, and ***P < 0.001. Error bar, ± 1 SD.

Fig. 4.

Regenerating axons of the CPN distal to the neurorrhaphy. STS repair with 10-mm epineural windows (A), STS repair with 2-mm epineural windows and donor nerve axotomy (B), STS repair with 2-mm epineural windows and axotomies to both nerves (C), and control specimen from the contralateral side (D). Axons, some of them well myelinated, can be seen in all STS groups: toluidine blue staining.

Fig. 5.

In the anterior tibial muscle (TA) specimens, the fiber size was slightly decreased in the experimental groups. Focal changes of mild atrophy are more clearly seen in group A than in groups B and C. In the gastrocnemial muscle (GC), the general appearance was normal in group A, whereas in groups B and C, there were focal areas of atrophy: toluidine blue staining.

Fig. 6.

Results of the muscle wet mass ratio calculations. A, The anterior tibial muscle (recipient CPN innervated) mass of group C was significantly higher compared with group A. B, The gastrocnemial muscle (donor TN innervated) mass of group A was significantly higher compared with groups B and C. The data were analyzed using Mann–Whitney test U test with Bonferroni adjustment for multiple comparisons. *P < 0.05 and **P < 0.01. Error bar, ± 1 SD.