RISystem 1 article published in JoVE Medicine In Vivo Evaluation of Fracture Callus Development During Bone Healing in Mice Using an MRI-compatible Osteosynthesis Device for the Mouse Femur Melanie Haffner-Luntzer1, Fabian Müller-Graf1,4, Romano Matthys2, Alireza Abaei3, René Jonas1, Florian Gebhard4, Volker Rasche*3, Anita Ignatius*1 1Institute of Orthopedic Research and Biomechanics, University Medical Center Ulm, 2RISystem, 3Core Facility Small Animal MRI, University Medical Center Ulm, 4Department of Traumatology, Hand-, Plastic-, and Reconstructive Surgery, University Medical Center Ulm The evaluation of tissue development in the fracture callus during endochondral bone healing is essential to monitor the healing process. Here, we report the use of a magnetic resonance imaging (MRI)-compatible external fixator for the mouse femur to allow MRI scans during bone regeneration in mice.