Angle-stable interlocking nailing in a canine critical-sized femoral defect model for bone regeneration studies: In pursuit of the principle of the 3R’s

Introduction: Critical-sized long bone defects represent a major therapeutic challenge and current treatment strategies are not without complication. Tissue engineering holds much promise for these debilitating injuries; however, these strategies often fail to successfully translate from rodent studies to the clinical setting. The dog represents a strong model for translational orthopedic studies, however such studies should be optimized in pursuit of the Principle of the 3R’s of animal research (replace, reduce, refine). The objective of this study was to refine a canine critical-sized femoral defect model using an angle-stable interlocking nail (AS-ILN) and reduce total animal numbers by performing imaging, biomechanics, and histology on the same cohort of dogs.

Methods: Six skeletally mature hounds underwent a 4 cm mid-diaphyseal femoral ostectomy followed by stabilization with an AS-ILN. Dogs were assigned to autograft (n = 3) or negative control (n = 3) treatment groups. At 6, 12, and 18 weeks, healing was quantified by ordinal radiographic scoring and quantified CT. After euthanasia, femurs from the autograft group were mechanically evaluated using an established torsional loading protocol. Femurs were subsequently assessed histologically.

Results: Surgery was performed without complication and the AS-ILN provided appropriate fixation for the duration of the study. Dogs assigned to the autograft group achieved radiographic union by 12 weeks, whereas the negative control group experienced non-union. At 18 weeks, median bone and soft tissue callus volume were 9,001 mm³ (range: 4,939–10,061) for the autograft group and 3,469 mm³ (range: 3,085–3,854) for the negative control group. Median torsional stiffness for the operated, autograft treatment group was 0.19 Nm/° (range: 0.19–1.67) and torque at failure was 12.0 Nm (range: 1.7–14.0). Histologically, callus formation and associated endochondral ossification were identified in the autograft treatment group, whereas fibrovascular tissue occupied the critical-sized defect in negative controls.

Conclusion: In a canine critical-sized defect model, the AS-ILN and described outcome measures allowed refinement and reduction consistent with the Principle of the 3R’s of ethical animal research. This model is well-suited for future canine translational bone tissue engineering studies.

De novo assembly and annotation of the North American bison (Bison bison) reference genome and subsequent variant identification

Genomic tools have improved the ability to manage bison populations and enhanced efforts to conserve this iconic species. These tools have been particularly useful for detecting introgression of cattle genome within bison herds but are limited by the need to use the cattle genome as a surrogate for mapping reads. This complicates efforts to distinguish the species of origin of chromosomal segments in individual bison at the genomic level. An assembly (Bison_UMD1.0) based on 75X genome coverage by Illumina and 454 reads was generated using the MaSuRCA assembler, generating a 2.81 Gigbases de novo reference genome from American bison. Comparison of bison and domestic cattle references identified 28 443 364 single nucleotide variants and 2 627 645 insertions/deletions distinguishing the species. Sequence alignment of an additional 12 modern bison samples and two historic bison samples to domestic cattle and bison references provides a dataset of genomic variants defining the different species and within-species variation. This first annotated draft assembly represents a resource for the management and conservation of bison, as well as a means to study the effects on the genome of interspecies hybridization. The comparisons of historical bison sequences with the new bison reference identified genomic differences between modern and pre-population bottleneck bison. The results support the application of genomics to enhance future research on disease, the establishment of satellite conservation herds and insight into bison and cattle speciation. The first genome assembly for bison and dataset provides a foundation that can be built upon as genetic technologies improve over the years.