Murine Aseptic Surgical Model of Femoral Atrophic Nonunion

Although bone repair is typically an efficient process, an inadequate healing response can occur, with approximately 5-20% of fractures developing nonunion. Even with improved healing strategies and external fixation devices, overall rate of nonunion has not been significantly reduced, particularly for atrophic nonunion. Atrophic nonunion is characterized by sparse or no callus formation and is difficult to treat clinically, resulting in long-term pain and functional limitation. Reliable preclinical models are needed to study the pathophysiology of atrophic nonunion to create better treatment options. The MouseNail kit (RISystem, Landquart, Switzerland) provides a highly standardized approach in which stabilized segmental bone defects are achieved through interlocked intramedullary nailing. However, reliably performing this surgery is technically challenging, particularly while maintaining strict asepsis. Skilled and aseptic surgical execution is important and necessary because it ensures optimal animal welfare and reproducibility. Therefore, the aim of this paper is to describe: • Novel modifications to the MouseNail kit that allow for: 1) a completely aseptic surgical environment, including description of a hanging limb orthopedic aseptic preparation and 2) a reduction in fracture gap size necessary for induction of atrophic nonunion. • Pre- to post-operative recommendations to facilitate successful performance of murine orthopedic survival surgery.