The healing process of fracture with bone scab

The process of fracture healing is the process of "stasis removal, newborn, bone union", which is the process of removing necrotic tissue on one side, and the process of newborn repair on the other side (completed by the endosteum and the cartilage endosteum***), and the whole process is continuous and gradual. The process of fracture healing is also the process of temporary emergency connection to permanent solid connection. Generally, fracture healing is divided into 3 stages, namely, hematoma mechanization period, primitive bone scab formation period and bone scab modification shaping period; also according to the histological and physiological characteristics of the fracture healing process is divided into the impact period, induction period, inflammation period, cartilage scab period, hard bone scab period and remodeling period of 6 different phases.

1. Hematoma mechanization period

After the fracture, because of the fracture itself and the adjacent soft tissues of the vascular rupture bleeding, in the fracture part of the formation of a hematoma, hematoma in the post-injury 6 ~ 8 hours that is, it began to coagulate into a blood clot, and the local necrotic tissues to cause aseptic inflammatory reaction. The broken end of the fracture is gradually necrotic due to the interruption of blood circulation and is about several millimeters long. With the exudation of fibrin, capillary proliferation, invasion of fibroblasts and phagocytes, the hematoma is gradually mechanized to form granulation tissue and then evolve into fibrous connective tissue, which initially connects the fracture ends together, known as the fibrous junction, which is completed in about 2 to 3 weeks after the fracture. At the same time, the osteoblasts in the periosteum near the fracture end are active and proliferate soon after the injury, and after one week, they start to form bone-like tissue parallel to the bone stem, and gradually extend and thicken toward the fracture site. The endosteum undergoes the same change at a later stage.

2. Primary bone crust formation period

Primary bone crust formation or endosteum and periosteum of osteoblasts proliferation, in the fracture end of the internal and external formation of bone tissue gradually ossification, the formation of new bone, known as intramembranous bone. With the continuous increase of new bone, close to the bone cortex within the treatment of fracture, these complications should be prevented, and if they have appeared then they should be diagnosed and properly treated in time, so that most of the complications can be avoided or cured. The outside gradually grows toward the fracture end and meets each other to form a pike, called the inner and outer bone crust. The fibrous tissue in the broken end of the fracture and the medullary cavity is also gradually transformed into cartilaginous tissue and ossified with the proliferation and calcification of chondrocytes, which is called cartilaginous endochondral ossification, while a ring-shaped bone scab and medullary cavity endochondral bone scab are formed at the fracture. After the two parts of the scab meet, these primitive scabs continue to calcify and gradually strengthened, when it reaches enough to resist muscle contraction and angulation, shear and rotational forces, then the fracture has reached clinical healing, which generally takes about 12 to 24 weeks in adults (the latest revision of the 8th edition of the textbook of human health edition of Surgery). At this time, there is a pike-shaped bone scab shadow around the fracture site, but the fracture line is still faintly visible on the radiograph. Any damage to the periosteum is detrimental to fracture healing.

3. Scab transformation plastic period

The original bone scab in the new trabeculae gradually increased, and gradually arranged regular and dense, fracture broken end by dead bone removal and new bone formation of crawling instead of resurrection, the fracture site to form a bony connection. This process usually takes about 1~2 years. With limb movement and weight bearing, the bone crust on the stress axis is strengthened, the bone crust outside the stress axis is gradually removed, and the bone marrow cavity is recommunicated, restoring the normal structure of the bone (Figures 9-12), and eventually the traces of the fracture disappear completely histologically and radiologically.

Recent studies have shown that a variety of bone growth factors are associated with fracture healing, and that they ****together stimulate osteoblast activity and regulate local osteogenesis. For example, insulin growth factor I and II (IGF-I and IGF-II), platelet-derived growth factor (PDGF), basic fibroblast factor (bFGF), and transforming growth factor B (TGF-B) further stimulate the aggregation of mesenchymal stromal cells, proliferation, and vascularization in the inflammatory phase. Bone morphogenetic protein (BMP) has strong cross-species osteogenic activity (i.e., inducing the differentiation of undifferentiated MSCs to form cartilage or bone) and bone damage repair, and its effect is not species-specific.