There are three distinct phases of fracture healing: 1) inflammation, 2) reparation, and 3) remodeling.
The first phase, inflammation, occurs immediately following the bone fracture. At that time, a hematoma or blood clot occurs at the fracture site. This hematoma provides two important factors important for fracture healing. First, the hematoma provides a small amount of mechanical stability to the fracture site. Second, and perhaps more importantly, the hematoma brings osteoblast, and chondrocyte precursors to the fracture site in large numbers that can begin to differentiate into osteoblasts and chondrocytes to begin producing matrix.
In addition, macrophages and osteoclasts come into the site to remove damaged and necrotic tissue. Also, since bone fracture usually involves disruption of the periosteum surrounding the bone, more precursor cells from the periosteum will be introduced into the fracture site. The will begin the process of making a fracture callus through the general process of osteogenesis, laying down bone on soft tissue. Both types of osteogenesis, intramembranous and endochondral ossification may be occuring at the fracture site. The resulting proliferation of woven bone tissue will produce a fracture callus, bridging the fracture gap.
The second step in the biology of fracture healing is he reparation phase. In this phase, the processes of osteogenesis continue and a fracture callus bridges the fracture site.
The bone again can be produced through intramembranous ossification, endochondral ossification or both. It is at this stage of fracture healing that external mechanical stimuli can have the greatest affect on fracture healing. This is because mechanical stability is crucial at this stage of fracture healing.
Although it is not necessary to completely immoblize the fracture, and there is some debate about the need for small motion at the fracture site, it is definitely clear that too much motion will lead to a non-union. A non-union is the healing of a fracture site with soft tissue instead of bone. The desire to prevent non-unions is the reason that different types of fracture fixation devices are used in clinical practice.
The healed bony callus is formed of woven bone and primary bone. At this point, it consists of a large bony bridge connecting the two bones. The base material of the callus typically will have lower strength and stiffness than mature lamellar bone. It is the large mass of bone in the callus that gives the construct its strength. To reduce the callus mass while maintaining mechanical integrity the callus must be remodeled to produce the lamellar bone. During the remodeling period, the large fracture callus is reduced to become the size of the bone at the fracture site. The woven/primary bone is replaced with secondary lamellar bone. This process may take months or even up to a year or more in adults.
The steps of fracture healing may be summarized as follows:
Phase I
1. Bleeding and fracture hematoma forms2. Inflammation3. Next 2-3 Days, granulation tissue formation4. Osteogenic Cells invade tissue and lay down osteoid
Phase II
5. At 3 weeks a soft callus forms consisting of osteoid and cartilage6. Hard tissue callus forms in 6 - 12 weeks7. Clinical union of bone ends occurs in 12 - 16 weeks
Phase III
8. Remodeling of united fracture
The first phase, inflammation, occurs immediately following the bone fracture. At that time, a hematoma or blood clot occurs at the fracture site. This hematoma provides two important factors important for fracture healing. First, the hematoma provides a small amount of mechanical stability to the fracture site. Second, and perhaps more importantly, the hematoma brings osteoblast, and chondrocyte precursors to the fracture site in large numbers that can begin to differentiate into osteoblasts and chondrocytes to begin producing matrix.
In addition, macrophages and osteoclasts come into the site to remove damaged and necrotic tissue. Also, since bone fracture usually involves disruption of the periosteum surrounding the bone, more precursor cells from the periosteum will be introduced into the fracture site. The will begin the process of making a fracture callus through the general process of osteogenesis, laying down bone on soft tissue. Both types of osteogenesis, intramembranous and endochondral ossification may be occuring at the fracture site. The resulting proliferation of woven bone tissue will produce a fracture callus, bridging the fracture gap.
The second step in the biology of fracture healing is he reparation phase. In this phase, the processes of osteogenesis continue and a fracture callus bridges the fracture site.
The bone again can be produced through intramembranous ossification, endochondral ossification or both. It is at this stage of fracture healing that external mechanical stimuli can have the greatest affect on fracture healing. This is because mechanical stability is crucial at this stage of fracture healing.
Although it is not necessary to completely immoblize the fracture, and there is some debate about the need for small motion at the fracture site, it is definitely clear that too much motion will lead to a non-union. A non-union is the healing of a fracture site with soft tissue instead of bone. The desire to prevent non-unions is the reason that different types of fracture fixation devices are used in clinical practice.
The healed bony callus is formed of woven bone and primary bone. At this point, it consists of a large bony bridge connecting the two bones. The base material of the callus typically will have lower strength and stiffness than mature lamellar bone. It is the large mass of bone in the callus that gives the construct its strength. To reduce the callus mass while maintaining mechanical integrity the callus must be remodeled to produce the lamellar bone. During the remodeling period, the large fracture callus is reduced to become the size of the bone at the fracture site. The woven/primary bone is replaced with secondary lamellar bone. This process may take months or even up to a year or more in adults.
The steps of fracture healing may be summarized as follows:
Phase I
1. Bleeding and fracture hematoma forms2. Inflammation3. Next 2-3 Days, granulation tissue formation4. Osteogenic Cells invade tissue and lay down osteoid
Phase II
5. At 3 weeks a soft callus forms consisting of osteoid and cartilage6. Hard tissue callus forms in 6 - 12 weeks7. Clinical union of bone ends occurs in 12 - 16 weeks
Phase III
8. Remodeling of united fracture
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