Induced Pseudomembrane Enrichment In Long Nerve Allograft Reconstruction
Omar Alexander Protzuk, MD1, Mariam Samuel, MSBA1, Kriston Seward, .1, Christopher Keshishian, BS1, Geetanjali S Bendale, PhD1 and Jonathan Isaacs, MD2, (1)Virginia Commonwealth University, Richmond, VA, (2)Department of Orthopaedics, Virginia Commonwealth University, Richmond, VA
Long nerve defects are typically reconstructed with autograft or processed acellular nerve allograft (PNA). PNA is convenient and avoids donor morbidity, but lacks the intense neurotrophic environment found in autograft, limiting their effective length. Extrapolating from the observation that pseudo-membranes induced around artificial implants like methyl-methacrylate have a rich trophic microenvironment, we recently demonstrated increased levels of neurotrophic factors in biological membranes induced around silicone rods implanted between rodent nerve ends. We hypothesize that this rich neurotrophic milieu would enhance nerve regeneration across PNA inset within the induced pseudo-membrane tunnel.
Lewis rats (n=24) underwent resection of a 15mm sciatic nerve segment. The defect was filled with a silicone tube or nerve ends were secured to muscle bed. After 4 weeks, for the experimental group, the silicone rod was replaced with appropriately sized PNA threaded within the pseudo-membrane tunnel. In both groups, the nerve stumps were freshly cut and PNA was used to reconstruct the nerve defect. At weekly intervals, ambulation videos were collected for neuromotor assessment with sciatic function index (SFI). The nerve reconstruction matured for 12 weeks at which point muscle recovery was assessed with motor testing. Nerve tissue samples were taken distal to the coaptation and stained for histologic analysis. Bilateral gastrocnemius muscles were harvested, weighed, and measured to assess motor reinnervation as muscle mass is an accepted surrogate for motor reinnervation. Statistical comparison was performed with two sample t-test with p<0.05.
Muscle weight and girth were statistically higher in the induced membrane subgroup compared to control rats. Values were calculated as percentages of the non-surgical limb. The induced membrane group average percentage muscle weight was 46.25% vs. control group average of 33.19% (p = 0.009). The induced membrane group average percentage muscle girth was 78.25% vs. control group of 60.73% (p = 0.012). We were unable to detect a significant difference between groups in axon counts and muscle force. At 12 weeks post-reconstruction, the induced membrane group had significantly higher SFI scores compared to controls (p = 0.023).
By insetting PNA within an induced pseudomembrane sheath, we were able to significantly enhance muscle reinnervation as demonstrated by increased muscle mass and girth as well as enhancement of motor recruitment demonstrated by SFI. However, we were unable to detect a significant analogous enhancement in motor force generation or axon counts. These are promising results for enhancement of allograft nerve reconstruction necessitating further investigation.
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