During bone regeneration, mechanical loading is believed to be responsible for provoking bone formation, however previous investigations into tissue level loading have been limited to crosssectional\u3cbr/\u3estudies and relied upon idealized models for mechanics.\u3cbr/\u3eBy applying in vivo time-lapse micro-computed tomography (microCT) in concert with imaged based micro-finite element (microFE) analysis we have overcome these limitations and have identified an association between tissue loading and bone formation during fracture healing.\u3cbr/\u3eA femoral defect of 1.24[SD = 0.13] mm was created in five female mice (C57BL/6); the femur was first stabilized with an external fixator (MouseExFix, RISystem, Switzerland). Weekly scans were\u3cbr/\u3eperformed using microCT imaging (vivaCT 40, Scanco Medical, Switzerland) over a period of 6 weeks, resulting in a series of timelapsed images. We determined sites of mineralization by registering\u3cbr/\u3eand overlaying images from the second and third week. Combining this with microFE (Parosol) simulations based upon images of the second week, we separated strains in volumes where mineralization occurred, from volumes where no change occurred.\u3cbr/\u3eTo assess the efficacy of strain as a predictor of mineralization, receiver operating characteristic analysis was used. The optimum strain level correctly predicted 60[SD= 9] % of the mineralization which occurred,\u3cbr/\u3eand the final state for 86[SD= 4] % of the entire volume.\u3cbr/\u3eWe have for the first time, quantitatively demonstrated that an association exists between local tissue strain and bone formation during fracture healing. This could be used to determine the optimal\u3cbr/\u3estiffness for biomaterials intended to promote bone healing
