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| Phases of bone fracture healing |
First Phase reactive
I. Fracture and inflammatory phase
ii. Formation of granulation tissue
2. Reparative Phase
iii. Cartilage of callus formation
iv. Lamellar bone deposition
3. Remodeling phase
remodeling to original bone contour
Reactive
After a fracture, the first change seen by light and electron microscopy, the presence of blood cells in tissues adjacent to the site of injury. Shortly after the break, the constriction of blood vessels, stop the bleeding. In a few hours after the fracture, the extravascular blood forming a clot, known as a hematoma. All cells in the blood clotting degenerate and die.Some of the cells outside of coagulation, but next to the lesion, also degenerate and die.In the same area, the fibroblasts survive and proliferate. They form a loose collection of cells, interspersed with small blood vessels, called granulation tissue.
Reparative Phase
A few days after the fracture, the cells in the periosteum replicate and transform. Periosteal cells proximal to the fracture gap develop into chondroblasts that form the hyaline cartilage. The cells of the periosteum distal to the fracture gap develop into osteoblasts that form bone tissue. Fibroblasts of granulation tissue to develop into chondroblasts that form the hyaline cartilage.These two new tissues grow in size until they unite with their colleagues in other regions of the fracture. This process will lead to a new mass of heterogeneous tissue, known as the fracture callus.Ultimately, the gap is filled by a fracture of the hyaline cartilage and woven bone, restoring some of its original strength.
The next phase is the replacement of hyaline cartilage and bone tissue with lamellar bone. The replacement process is known as endochondral ossification of hyaline cartilage and bone replacement in relation to bone tissue. The replacement of bone tissue with lamellar bone precedes the substitution of the hyaline cartilage with lamellar bone. The lamellar bone begins forming soon after the collagen matrix or tissue is mineralized. At this point, the mineralized matrix is penetrated by channels, each with a number of osteoblasts and microvessels. Osteoblasts form new lamellar bone in the newly exposed surface of the mineralized matrix. This new lamellar bone is in the form of trabecular bone. Finally, all bone and cartilage of the original fracture callus is replaced by trabecular bone, restoring most of the initial resistance of the bone.
Remodeling
Re-training formulas trabecular bone with compact bone. Trabecular bone as the first resorbed by osteoclasts, creating a shallow pit resorption known as the "Howship the hole." Then osteoblasts deposit compact bone within the resorption pit. Eventually, the fracture callus is restored to the new format, which closely duplicates the bone to its original shape and strength. Remodeling phase takes 3-5 years depending on factors such as age or condition.
