We read with great interest the research article by Sharula et al. entitled “Repair of the Sciatic Nerve Defect with a Direct Gradual Lengthening of Proximal and Distal Nerve Stumps in Rabbits.”1 In the article, the authors describe a novel technique for repairing nerve substance defects of 20 mm in peripheral nerve in rabbit by nerve lengthening performed with an external device. Nerves were extended for 3 weeks at a rate of 1 mm/day followed by end-to-end coaptation. Nerve regeneration was then evaluated by electrophysiologic and histologic examination at 16 weeks. It is worth mentioning that for the lengthening process no anesthesia was necessary.
We ask why the distal nerve stump was distracted as well. Usually, after the lengthening time of 22 days, the distal stump undergoes Wallerian degeneration. The advantage of stretching both ends is not fully clear to us. When the axon is severed by nerve injury, the axon dies back 1 or 2 mm from the injury site and the distal segment degenerates, a feature known as Wallerian degeneration.2 The myelin debris is phagocytized by macrophages. Whereas the axon segment distal to the injury site degenerates, the Schwann cells proliferate, typically within the basal lamina, and form a column of Schwann cells within a basal lamina or band of Büngner. Does the distraction of the distal segment lengthen connective tissue and allow for greater Schwann cell proliferation?
Moreover, the study by Kroeber et al. showed neuroma formation after the duration of the distraction of the proximal nerve end.3 After a delay of 1 or 2 days, the proximal stump of the cut nerve gives rise to axonal sprouts that will extend either on the surface of Schwann cells or to the inner laminin-rich surface of the basal lamina of the Schwann cell columns (bands of Büngner). If the regenerating axon sprouts do not reach and elongate through the trophic distal Schwann cell tube, they will grow in a more random manner and can form a neuroma.4 This is often the case after traumatic peripheral nerve injury, including limb amputation. The axonal sprouts within the bulbous neuroma show increased mechanosensitivity and chemosensitivity. It would be interesting if stretching itself could prevent neuroma formation after peripheral nerve injury, and this observation should be highlighted in this interesting study.
Christine Radtke, M.D.
Peter M. Vogt, M.D., Ph.D.
Kerstin Reimers, Ph.D.
Department of Plastic, Hand, and Reconstructive Surgery
Hannover Medical School
1. Sharula, Hara Y, Nishiura Y, Saijilafu, Kubota S, Ochiai N. Repair of the sciatic nerve defect with a direct gradual lengthening of proximal and distal nerve stumps in rabbits. Plast Reconstr Surg
2. Waller A. Experiments on the glossopharyngeal and hypoglossal nerves of the frog and observations produced thereby in the structure of their primitive fibers. Phil Trans R Soc Lond.
3. Kroeber MW, Diao E, Hida S, Liebenberg E. Peripheral nerve lengthening by controlled isolated distraction: A new animal model. J Orthop Res
4. Ramon Y, Cajal S. Degeneration and Regeneration in the Nervous System
. London: Oxford University Press; 1928.
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