Invited Discussion

This article confirms the effectiveness of muscle-vein combined conduits in the repair of a short nerve defect. As often occurs in our field, the results of a surgical method are presented, and the explanation of why and how the results occur may come later.

The origin of the described method goes back to the early 1980's,[1] [2] when I began examining the possibility of using different conduits to overcome defects in the peripheral nerves. I first used artificial tubes (polylactic acid), which were discarded soon afterward, because of the then primitive preparation and the random formation of lateral chains of the acid; I then began to experiment with biologic tubes (autologous veins). I noted that nerve regeneration occurred with veins shorter than 1 cm, while it did not occur with longer conduits. I had the idea of putting fresh muscle inside the vein, with the double aim of supplying an isomorphic scaffold for axon progression, and also avoiding the collapse of the vein before regeneration occurred. Some of this work was done with one of the authors of the present article.

Even with an isomorphic muscle scaffold, the optimal conditions for axons to progress is the presence of Schwann cells that myelinate the axons as soon as they elongate. With this in mind, two different hypotheses are possible. The first is that inside the fresh muscle, some cells, presenting as “satellite” cells or “stem” cells, could differentiate into Schwann cells. The second hypothesis is that Schwann cells coming from the nerve migrate before and together with the axons, with the possibility that these Schwann cells continue to proliferate inside and among the muscle fibers.

This reported study, by examining the expression of NRG-1 and its receptors, demonstrates not only that Schwann cells migrate, but also that they proliferate “on the spot,” as demonstrated by PCNA. The only doubt left would be that some of the cells positive to PCNA are stem cells from the muscle; however, the double staining demonstrated in the figures appears to eliminate this doubt. In the second experiment, it was confirmed that the cells are effectively Schwann cells, as Erb B3 is specific for these cells. Thus, this research confirms the validity of muscle-vein combined grafts in bridging nerve defects, and eliminates the objection that only predegenerated muscle may support axon progression.

REFERENCES

• 1 Brunelli G A, Milanesi S, Fontana G, Bartolaminelli P. Invaginamento in sementi venosi di lesioni nervosa.  Palmero: Congress of the Italian Society for Surgical Research 1982
• 2 Brunelli G A, Fontana G, Jaeger C. Chemotactic arrangements of axons inside and distal to a venous graft.  J Reconstr Microsurgy . 1987;  3 87-89