Animal bones have evolved to provide mechanical support for active life-styles. In the wild, bone fracture is a serious threat to an animal’s life. But it is not always “game over”, as evidenced by the existence of the mechanism of fracture healing. How fractures heal is a big field in orthopedic research, and microCT can help elucidate the 4D progression of architecture of the fracture callus as it remodels back to a normal mechanically competent shape.
Remember the universal “pipeline” of bone morphometric analysis discussed previously: scan, align, volume of interest, segment and analyze. This applies equally to analysis of bone fracture healing, as is described in detail in <MN116 Analysis of fracture callus and healing> on fracture callus analysis. The example is presented of a rat femur mid-diaphysis fracture imaged by microCT at 2, 4 and 6 week intervals following fracture. First the scan dataset of the fracture region is oriented so that the bone’s long axis aligns with the dataset Z axis.
In a second step a region of interest representing the callus outline is defined. Using advanced CTAn software functions it is possible to both “shrink-wrap” the callus region automatically and also exclude the intact cortical bone – included displaced fragments – from the callus VOI. After segmentation of the bone, the 3D analysis can be run. The data (included in the linked fracture callus method note) show that while callus volume declines steadily from 2 to 6 weeks post-fracture, the texture or architecture of the callus remains of similar complexity, as indicated by fractal dimension and connectivity density, out to 4 weeks before eventually declining as the callus remodels to cortical bone.
