The injury initiates an inflammatory response which is necessary for the healing to progress. Immediately following the trauma, a hematoma is generated and consists of cells from both peripheral and intramedullary blood, as well as bone marrow cells. To better understand new concepts and strategies to enhance the healing of fractures this review presents a basic summary of the current knowledge of the biology of fracture repair. 16 The use of animal models have made it possible to investigate fracture healing from all perspectives such as histology, biochemistry and biomechanics and has hence been a very important tool in understanding fracture biology.
Investigations in both humans and animal models have provided insight into the pathways that regulate the biologically optimized process of fracture healing and provide direction for further research to prevent its failure. However, despite the regenerative capacity of skeletal tissue, this biological process sometimes fails and fractures may heal in unfavorable anatomical positions, show a delay in healing or even develop pseudo-arthrosis or non-unions. As such, the process of fracture healing recapitulates bone development and can be considered a form of tissue regeneration. It is known that bone is one of few tissues that can heal without forming a fibrous scar. In this article we summarize the basic biology of fracture healing.ĭuring the last two decades, our understanding of fracture healing has rapidly evolved. This primary callus later undergoes revascularization and calcification, and is finally remodeled to fully restore a normal bone structure.
It involves an acute inflammatory response including the production and release of several important molecules, and the recruitment of mesenchymal stem cells in order to generate a primary cartilaginous callus. In all other non-stable conditions, bone healing follows a specific biological pathway. However, when such conditions are achieved, the direct healing cascade allows the bone structure to immediately regenerate anatomical lamellar bone and the Haversian systems without any remodeling steps necessary. The most common pathway is indirect healing, since direct bone healing requires an anatomical reduction and rigidly stable conditions, commonly only obtained by open reduction and internal fixation. Following the initial trauma, bone heals by either direct intramembranous or indirect fracture healing, which consists of both intramembranous and endochondral bone formation. These efforts have provided a general understanding of how fracture healing occurs.
Although there is still much to be learned to fully comprehend the pathways of bone regeneration, the over-all pathways of both the anatomical and biochemical events have been thoroughly investigated. The biology of fracture healing is a complex biological process that follows specific regenerative patterns and involves changes in the expression of several thousand genes.
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