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1. Inflammation: Bleeding from fracture site and surrounding soft tissues creates a hematoma, which provides a source of hematopoietic cells capable of secreting growth factors. Subsequently fibroblasts, mesenchymal cells, and osteoprogenitor cells are present at the fracture site, and granulation tissue forms around the fracture ends. Osteoblasts, from surrounding osteogenic precursor cells, fibroblasts, or both proliferate.
2. Repair: Primary callus response occurs within 2 weeks. If the bone ends are not in continuity, bridging (soft) callus occurs. The soft callus later is replaced, via the process of enchondral ossification, by woven bone (hard callus). Another type of callus, medullary callus, supplements the bridging callus, although it forms more slowly and occurs later. The amount of callus formation is indirectly proportional to the amount of immobilization of fracture.
3. Remodeling: This process begins during the middle of the repair phase and continues long after the fracture has clinically healed (upto 7 years). Remodeling allows the bone to assume its normal configuration and shape based on the stresses to which it is exposed (Wolff's law). Throughout the process, woven bone formed during the repair phase is replaced with lamellar bone.
Text source: Miller Review of Orthopaedics
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http://www.youtube.com/watch?v=VZF3xicLtTwendofvid
1. Inflammation: Bleeding from fracture site and surrounding soft tissues creates a hematoma, which provides a source of hematopoietic cells capable of secreting growth factors. Subsequently fibroblasts, mesenchymal cells, and osteoprogenitor cells are present at the fracture site, and granulation tissue forms around the fracture ends. Osteoblasts, from surrounding osteogenic precursor cells, fibroblasts, or both proliferate.
2. Repair: Primary callus response occurs within 2 weeks. If the bone ends are not in continuity, bridging (soft) callus occurs. The soft callus later is replaced, via the process of enchondral ossification, by woven bone (hard callus). Another type of callus, medullary callus, supplements the bridging callus, although it forms more slowly and occurs later. The amount of callus formation is indirectly proportional to the amount of immobilization of fracture.
3. Remodeling: This process begins during the middle of the repair phase and continues long after the fracture has clinically healed (upto 7 years). Remodeling allows the bone to assume its normal configuration and shape based on the stresses to which it is exposed (Wolff's law). Throughout the process, woven bone formed during the repair phase is replaced with lamellar bone.
Text source: Miller Review of Orthopaedics
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