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Improving Outcomes of Large Gap Peripheral Nerve Repair Utilizing Photochemical Tissue Bonding (PTB) with Acellular Nerve Allograft (ANA)
Marek A. Hansdorfer, M.D.1,2, Jane M. Tsui, M.D.1, Marco Visaggio, M.D.1, Gem G. Runyan, B.S., M.S.1, William S. David, M.D., Ph.D.3, Reiner B. See, M.D.3, Ian L. Valerio, M.D., M.S., M.B.A.4, Mark A. Randolph, M.A.S.1, Jonathan M. Winograd, M.D.1 and Robert W. Redmond, Ph.D.5, (1)Plastic & Reconstructive Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, (2)Rush University Medical Center, Chicago, IL, (3)Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, (4)Department of Plastic Surgery, Ohio State University Wexner Medical Center, Columbus, OH, (5)Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA



INTRODUCTION:
Standard-of-care large nerve gap (>3cm) reconstruction requires donor autograft. Alternatives are sought in clinical scenarios where donor limb is unavailable (e.g. multiple extremity trauma) or donor site morbidity (e.g. painful neuroma formation, paresthesia) makes autograft use suboptimal. A variety of alternatives have been proposed (e.g. allografts, conduits). Photochemical tissue bonding (PTB) as an alternative to traditional suture neurorrhaphy has been extensively studied in the rodent sciatic nerve model. PTB reduces needle trauma, prevents axonal escape, and creates a water-tight seal. We report a non-human primate study which recapitulates human anatomy, allows for objective quantitative functional outcomes testing, and electromyography (EMG). The purpose of this study is to evaluate whether PTB can elevate the performance of acellular nerve allograft (ANA) to that of standard-of-care autograft/suture.

MATERIALS & METHODS:
Nineteen rhesus macaques underwent 4cm proximal radial nerve defect creation in the right upper extremity, the radial nerve transected proximally at the spiral groove, distally at the branch to brachioradialis. The radial nerve was selected as it performs an isolated function with no input from other nerves which may confound recovery data. Three repair techniques were evaluated: n=6 autograft/suture, n=6 ANA/suture, n=7 ANA photosealed with light-activated human amnion wraps (PTB). An objective functional outcome test was conceived using an apparatus that accurately measures degree of wrist extension longitudinally (monthly) [Figure 1A-B].

RESULTS:
Average loss of wrist extension was 95.0±9.4¡ after radial nerve defect creation [Figure 1C-D]. At 6 months, autograft group animals recovered 75.5¡ (n=1 failure), ANA/PTB=35.1¡ (n=3 failures), ANA/suture=15.1¡ (n=2 failures) [Figure 1E-F]. At 4 months percent recovery of baseline EMG amplitude: autograft=35.2%, PTB/ANA=26.7%, ANA/suture=0%, at 8 months: autograft=59.4%, PTB/ANA=66.8%, ANA/suture=24.3%. Muscle mass retention (ECRL/ECRB muscle complex) at euthanasia results to date: no significant difference between autograft (76.1±18.3%) and ANA/PTB (61.9±35.7%), p=0.51.

CONCLUSION:
This radial nerve defect model improves upon existing animal models by allowing for large nerve gap testing in a primate model more analogous to the clinical large nerve gap injury in humans.  As expected, there was variability in functional outcomes in the ANA groups. ANA/PTB resulted in earlier electromyographic reinnervation and functional recovery than ANA/suture. Muscle mass retention was similar with autograft/suture and ANA/PTB. In the ANA group animals demonstrating functional recovery, outcomes were similar to autograft group animals. This preliminary data confirms PTB as a promising technique to improve outcomes of large nerve gap reconstruction in combination with autograft (previously demonstrated) and with ANA.


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