Investigation of Biological Mechanisms Underlying Non-Union Fracture Formation in Domestic Ruminants in Resource-Limited Settings in North West Nigeria

Non-union fracture formation represents a complex pathological failure of normal bone healing characterized by cessation of the healing biological cascade and persistent mechanical instability, and its mechanisms in domestic ruminants under resource-limited clinical conditions in northern Nigeria remain poorly understood. This doctoral study investigates the biological, mechanical, nutritional, and management-related mechanisms contributing to non-union fracture formation in cattle, sheep, and goats at teaching hospital and government veterinary facilities across Sokoto, Kebbi, and Zamfara States in North West Nigeria between 2020 and 2024. A prospective cohort design enrolled 53 ruminants with radiographically confirmed fracture non-union, with matched healing fracture controls. Bone biopsy samples from non-union sites were evaluated by histopathology, immunohistochemistry for bone morphogenetic proteins, angiogenic markers, and inflammatory mediators. Nutritional assessments including serum calcium, phosphorus, and vitamin D metabolite measurements were performed. Poor stabilization technique resulting in excessive interfragmentary motion was the most common mechanistic pathway, identified in 62% of non-union cases. Hypertrophic non-unions with abundant callus but absent bridging constituted 57% of non-union types. Immunohistochemical analysis revealed significantly reduced vascular endothelial growth factor expression and impaired angiogenesis in atrophic non-union tissue. Hypocalcemia and vitamin D insufficiency were significantly more prevalent in non-union cases than healing fracture controls. These original biological findings provide the first mechanistic characterization of ruminant fracture non-union in North Western Nigeria, informing both surgical technique improvement and perioperative nutritional intervention protocols. Keywords: fracture non-union, ruminant orthopedics, bone healing mechanism, North West Nigeria, bone morphogenetic protein.