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Acellular Biological Scaffold Repair Does Not Overcome the Pathobiology of Volumetric Muscle Loss Injury

Volumetric muscle loss (VML) resulting from extremity trauma presents chronic and persistent functional deficits, restricted joint range of motion, and fibrosis, which ultimately manifest disability. Currently, there is a clinical need for therapies aimed at addressing the debilitating outcomes due to VML injuries. Recent investigations have examined the use of commercially available biological scaffolds as a regenerative medicine approach for VML. However, there is a paucity of large animal data to advance clinical translation. We hypothesized that repair of VML injuries with an acellular biologic scaffold would improve function, specifically neuromuscular strength following injury. To test this hypothesis, female Yorkshire Cross pigs (n=10) were randomized to sham or an ~20% VML injury to the peroneous tertius muscle, and injuries were left non‐repaired, or surgically repaired with an acellular biologic scaffold derived from either porcine small intestinal submucosa (SIS) or urinary bladder matrix (UBM) using standard clinical surgical implantation procedures. Analysis of muscle volume using CT imaging and muscle function via peroneal nerve stimulation was conducted through 12 weeks post‐injury. At this terminal time‐point, full thickness biopsy samples were used for histological analysis and sequencing of RNA extracted from the injured muscle tissue. All studies were conducted in compliance with the Animal Welfare Act, the Implementing Animal Welfare Regulations and in accordance with the principles of the Guide for the Care and Use of Laboratory Animals. Unexpected adverse advents occurred in 80% of the VML injuries repaired with the SIS scaffold. Both the repair with SIS and UBM resulted in a significant fibrotic response and increased volume of the anterior compartment. However, this volume could not be attributed to increased muscle, as histologic analysis of the muscle indicated sub‐physiologic islands of muscle fibers (~50 fibers). To understand the quality of muscle, peak muscle torque was normalized to the CT‐derived volume of the anterior compartment at 10 weeks post‐injury. Collectively in the non‐ and ECM‐repaired limbs there was ~45% deficit compared to sham operated limbs. Additionally, in both the non‐ and ECM‐repaired limbs there was an ~30% deficit in absolute peak isometric torque through 12 weeks post‐injury. Tissue level RNA sequencing analysis of the non‐repaired and surgically repaired samples compared to Sham controls revealed increases in expression of sets of genes associated with inflammatory signaling and fibrogenesis and downregulation of myogenic repair gene sets. Quantitative comparison of the transcriptomes from surgically repaired samples against the non‐repaired samples indicated high degrees of correlation amongst the differentially expressed genes. These results indicate the gene expression programs induced from a VML insult are not appreciably augmented when treated with surgical repair of an acellular biologic scaffold. Collectively, these data indicate that VML results in extensive and continued disruption of the remaining musculature and that ECM repair does not ameliorate the resulting pathobiology.