The periosteum, endosteum, and Haversian canals are classified as the sources of pluripotent mesenchymal stem cells that initiate the formation from the healing tissues. The bridging callus noticed on radiographs generally arises from your periosteum. The whole process of healing is different with regards to the configuration of the fracture https://www.theorthopaedicandpainpractice.com/what-is-a-long-bone-fracture/