The newly formed callus is still damageable by shear forces, whereas axial traction and pressure promote matrix formation. They produce an extracellular organic matrix of fibrous tissue and cartilage, wherein woven bone is deposited by osteoblasts. Progenitor cells within the granulation tissue proliferate and begin to differentiate into fibroblasts and chondroblasts. On radiographs, there may be increased lucency of the fracture during this stage due to bone resorption. Within 7-14 days, granulation tissue is formed between the fragments, leading to vascularisation of the haematoma. Within 48 hours, chemotactic signalling mechanisms attract the inflammatory cells necessary to promote the healing process. The fracture haematoma initiates the healing response. The bridging callus seen on radiographs mainly arises from the periosteum. The periosteum, endosteum, and Haversian canals are the sources of pluripotent mesenchymal stem cells that initiate the formation of the healing tissues. Though the healing process of a fracture can be divided into various phases, it should rather be understood as a biological continuum. This is the most common 'natural' healing process, whereby the fracture ends are placed close to each other (but not apposed), with intervening haematoma and variable displacement and/or angulation. spontaneous (indirect/secondary) healing.The process of healing is different depending on the configuration of the fracture fragments and can be divided into three main categories:
mechanical rest: this can be achieved by not moving and external immobilisation, e.g.For normal fracture healing to occur a number of requirements must be met:
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