![]() An adequate number of MSCs is recruited at the fracture site from the nearby tissues and the circulation. The hematoma clots and forms the temporary frame for subsequent healing. The blood vessels supplying the bone and periosteum are disrupted during the fracture, causing a hematoma to form at the fracture site, which is rich in hematopoietic cells. This forms the key step in fracture healing. Hematoma Formation: (Immediately after the fracture) ![]() Others involved include inflammatory cells, endothelial cells, fibroblasts, osteoblasts, and osteoclasts. They are delivered mainly by two major sources periosteum and endosteum. Principle cells and their secretions are involved in the healing process, in which the mesenchymal stem cells play a pivotal role. However, there is considerable overlap between these stages. įracture healing is complex, and it involves the following stages: hematoma formation, granulation tissue formation, callus formation, and bone remodeling. This is followed by a catabolic phase where cartilage resorption ensues, resulting in tissue and callus volume reduction. With further progression of chondrocyte differentiation, the extracellular matrix is mineralized, and the chondrocytes undergo apoptosis. Simultaneously with cartilaginous callus formation, the cells involved in angiogenesis are recruited and differentiated in the nearby muscle mass. A cartilaginous callus forms at the fracture site, whereas at the periphery of this callus, the periosteum swells, and the primary bone formation starts. įracture healing starts with an anabolic phase where there is recruitment and differentiation of stem cells with subsequent increases in the skeletal and vascular tissue volume. Bone healing can involve a combination of primary and secondary processes based on the stability throughout the construct.įailed or delayed healing can affect up to 10% of all fractures and can result from factors such as comminution, infection, tumor, and disrupted vascular supply. During this article, we will work through each of these steps in order and detail before touching on primary healing, factors affecting fracture healing, and methods of stimulation of fracture healing. ![]() And it occurs via endochondral bone healing. These fixation modalities achieve a mechanical strain between 2-10%. The other type is secondary bone healing which occurs in non-rigid fixation modalities such as braces, external fixation, plates in bridging mode, intramedullary nailing. It is an intramembranous bone healing that occurs through Haversian remodeling. There are two main modes of bone healing primary bone healing is dictated by absolute stability constructs that achieve a mechanical strain below 2%. ![]() In contrast, a strain >10% results in non-union or delayed union. Primary bone healing ensues with mechanical strain below 2%, whereas secondary bone healing ensues when the mechanical strain is between 2 and 10%. The amount of the involved strain dictates the biological behavior of the cells involved in the healing process and, consequently, the type of bone healing. An appropriate mechanical stimulation, such as strain, facilitates tissue formation at the bony ends. ![]() The type of fracture healing is governed by the achieved mechanical stability at the fracture site and, consequently, the strain. ![]()
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