Cyclosporin A Enhances Callus Formation in Rabbit Tibia Fractures

Purpose: Drugs that modify the production of cytokines may affect fracture healing.The immunosuppressive drug cyclosporin A is widely used to modify the immune response in transplantations and in treatment of rheumatoid disorders.We wanted to analyze the effect of cyclosporin A on fracture healing and on the development of trauma induced osteopenia.Methods: Experimental tibia fractures were stabilised with intramedullary pins in 26 rabbits.The animals were given 5 mg/kg/day of cyclosporin A or placebo for 5 weeks.Bone mineral content, callus volume and biomechanical testing were performed on both tibias and femurs.Results: At 5 weeks cyclosporin A treatment resulted in increased bone mineral content and increased callus volume of the fractured bone.The femora on the operated side had significantly lower bone mineral content compared to the non-operated side.This trauma induced osteopenia was unaffected by cyclosporin A treatment.Failure torque and stiffness of the tibia and femora were similar in both groups.Interpretation: Cyclosporin A stimulates bone formation in fracture repair.The mechanism is unclear, but a direct or cytokine mediated effect on bone forming cells, or enhanced bone induction resulting in increased bone formation, is possible.