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Interposing Auto/isografts to Promote Axonal Regeneration Across Long Acellular Nerve Grafts
Ying Yan, MD, PhD; Daniel A. Hunter, RA; Lauren M. Schellhardt, BA; Xueping Ee, MD; Alison Snyder-Warwick, MD; Amy M. Moore, MD; Susan E. Mackinnon, MD; Matthew D. Wood, PhD
Washington University School of Medicine, Saint Louis, MO

Introduction: Nerve grafting is often necessary to repair large nerve gaps. Alternatives to autografts are desirable; however, the leading alternative, acellular nerve allografts (ANAs), fail to facilitate axonal regeneration across long gaps (>3cm), where the need is greatest. In an effort to extend the graft length limit of ANAs beyond 3cm, we evaluated the effect of interposing a short auto/isograft between short ANAs, used to generate a long hybrid graft, on axonal regeneration.
Materials & Methods: Rat sciatic nerve was transected and repaired with 6cm nerve grafts. Nerve grafts consisted of either isograft interposition (coaptation of 1cm isograft between two 2.5cm ANAs: Hybrid group) or ANA interposition control (coaptation of 1cm ANA between two 2.5cm ANAs: ANA group). At an endpoint of 20 weeks post surgery, EDL muscle force and mass was measured, and nerve was harvested for histomorphometry or staining for cellular senescence. Cellular senescence accumulation was quantified using senescence associated markers (SA--galactosidase, p16INK4A, p53).
Results: In our initial studies, a limited number of axons regenerated across the hybrid (ANA-isograft-ANA) group reaching the distal nerve. Additionally, the hybrid group contained an ~36% increase in myelinated axon numbers when axons reached the mid-graft (isograft) compared to the proximal graft (ANA; 11,200 vs 8,230, respectively). In contrast, the ANA (ANA-ANA-ANA) group failed to facilitate axonal regeneration across the long graft, and axons arrested within the first ANA graft region. Neither experimental group achieved measurable muscle force production. Additional animal studies are underway to further power the study and assess cellular senescence accumulation.
Conclusions: The interposition of auto/isografts enhanced axonal regeneration across a long nerve gap reconstructed with primarily ANA. Additionally, the isograft portion promoted increased myelinated axon numbers suggesting axonal sprouting due to native Schwann cells. While axonal regeneration across the long hybrid graft was achieved, the outcome was still considerably worse compared to a sole, long auto/isograft based on our historic data.

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