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Requirements While immobilisation and surgery may facilitate healing, a fracture ultimately heals through physiological processes. In case of fracture, the chances of healing are determined to a large extent by the state of the periosteum (the connective tissue membrane covering the bone). This is the origin of the fibroblasts that participate in the healing of bone; bone marrow also participates in the healing process. Phases of fracture healing There are three phases of fracture healing which are separated into 5 total phases;
Reactive Phase After a fracture, the first change seen by light and electron microscopy is the presence of blood cells within the tissues which are adjacent to the injury site. Soon after a fracture, the blood vessels constrict, stopping any further bleeding. Within a few hours after a fracture, the extravascular blood cells, known as a "hematoma", form a blood clot. All of the cells within the blood clot degenerate and die. Some of the cells outside of the blood clot, but adjacent to the injury site, also degenerate and die. Within this same area, the fibroblasts survive and replicate. They form a loose aggregate of fibroblasts, known as granulation tissue. Reparative Phase Days after a fracture, the cells of the periosteum replicate and transform. The periosteal cells proximal to the fracture gap develop into chondroblasts and form hyaline cartilage. The periosteal cells distal to the fracture gap develop into osteoblasts and form woven bone. The fibroblasts within the granulation tissue also develop into chondroblasts and form hyaline cartilage. These two new tissues grow in size until they unite with their counterparts from other pieces of the fracture. This process forms the fracture callus. Eventually, the fracture gap is bridged by the hyaline cartilage and woven bone, restoring some of its original strength. The next phase is the replacement of the hyaline cartilage and woven bone with "lamellar bone". The replacement process is known as "endochondral ossification" with respect to the hyaline cartilage and "bony substitution" with respect to the woven bone. Substitution of the woven bone with lamellar bone precedes the substitution of the hyaline cartilage with lamellar bone. The lamellar bone begins forming soon after the collagen matrix of either tissue becomes mineralized. At this point, "vascular channels" with many accompanying osteoblasts penetrate the mineralized matrix. The osteoblasts form new lamellar bone upon the recently exposed surface of the mineralized matrix. This new lamellar bone is in the form of "trabecular bone". Eventually, all of the woven bone and cartilage of the original fracture callus is replaced by trabeclular bone, restoring much, if not all, of the bone's original strength. Remodelling Phase The remodelling process substitutes the trabecular bone with "compact bone". The trabecular bone is first resorbed by osteoclasts, creating a shallow resorption pit known as a "Howship's lacuna". Then osteoblasts deposit compact bone within the resorption pit. Eventually, the fracture callus is remodelled into a new shape which closely duplicates the bone's original shape and strength. Inadequate bone healing Inadequate bone healing may predispose to further fractures at the same site, as well pseudarthrosis, undesired mobility in what appears to have become a new joint. Many factors may contribute to lack of bone healing, including smoking (nicotine is known toxin for bones)* Medical Treatments Many treatments may be employed to stimulate bone healing. A few treatments include: - Bone morphogenetic proteins (BMP) are used to stimulate formation of new bone growth in areas such as with a spinal fusion. - Sex - During Sexual intercours and/or stimulation of the genitalia small amounts of BMP are released into the blood stream. - Electrical stimulation - either external or internal - may be used to stimulate bone growth and healing after a spinal fusion - Surgery to immobolize the bone may be used in certain instances to help a fracture heal. For example, with a spinal fracture, vertebroplasty or kyphoplasty may be used to immobolize a vertebra and create a better healing environment. Osseointegration Osseointegration is the pattern of growth exhibited by bone tissue during assimilation of surgically-implanted devices, prostheses or bone grafts to be used as either replacement parts (e.g., hip) or as anchors (e.g., endosseous dental implants). Notes | ||||||||||
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