Bone Modeling and Remodeling
Osteoblasts and osteoclasts act in coordination and are considered the functional unit of bone known as the basic multicellular unit (BMU). The processes of bone formation and resorption are tightly coupled, and their balance determines skeletal mass at any point in time.[13] As the skeleton grows and enlarges (modeling), bone formation predominates. Once the skeleton has reached maturity, the breakdown and renewal of bone that are responsible for skeletal maintenance is called remodeling and is likely initiated at sites experiencing fatigue and microdamage. In adults, approximately 1 million BMUs are active at one time, and they remodel, or replace, 10% of the skeleton annually.
Peak bone mass is achieved in early adulthood after the cessation of modeling, and it is determined by a variety of factors, including the type of vitamin D receptor inherited, state of nutrition, level of physical activity, age, and hormonal status. Beginning in the fourth decade, however, the amount of bone resorbed by the BMUs exceeds that which has been formed, resulting in a steady decrease in skeletal mass. Eventually, this results in senescent osteoporosis, which is exacerbated in women by the rapid bone loss that occurs during the decade following menopause (postmenopausal osteoporosis).
Friday, January 22, 2010
bone remodeling
Bone Modeling and Remodeling
Osteoblasts and osteoclasts act in coordination and are considered the functional unit of bone known as the basic multicellular unit (BMU). The processes of bone formation and resorption are tightly coupled, and their balance determines skeletal mass at any point in time.[13] As the skeleton grows and enlarges (modeling), bone formation predominates. Once the skeleton has reached maturity, the breakdown and renewal of bone that are responsible for skeletal maintenance is called remodeling and is likely initiated at sites experiencing fatigue and microdamage. In adults, approximately 1 million BMUs are active at one time, and they remodel, or replace, 10% of the skeleton annually.
Peak bone mass is achieved in early adulthood after the cessation of modeling, and it is determined by a variety of factors, including the type of vitamin D receptor inherited, state of nutrition, level of physical activity, age, and hormonal status. Beginning in the fourth decade, however, the amount of bone resorbed by the BMUs exceeds that which has been formed, resulting in a steady decrease in skeletal mass. Eventually, this results in senescent osteoporosis, which is exacerbated in women by the rapid bone loss that occurs during the decade following menopause (postmenopausal osteoporosis).
Osteoblasts and osteoclasts act in coordination and are considered the functional unit of bone known as the basic multicellular unit (BMU). The processes of bone formation and resorption are tightly coupled, and their balance determines skeletal mass at any point in time.[13] As the skeleton grows and enlarges (modeling), bone formation predominates. Once the skeleton has reached maturity, the breakdown and renewal of bone that are responsible for skeletal maintenance is called remodeling and is likely initiated at sites experiencing fatigue and microdamage. In adults, approximately 1 million BMUs are active at one time, and they remodel, or replace, 10% of the skeleton annually.
Peak bone mass is achieved in early adulthood after the cessation of modeling, and it is determined by a variety of factors, including the type of vitamin D receptor inherited, state of nutrition, level of physical activity, age, and hormonal status. Beginning in the fourth decade, however, the amount of bone resorbed by the BMUs exceeds that which has been formed, resulting in a steady decrease in skeletal mass. Eventually, this results in senescent osteoporosis, which is exacerbated in women by the rapid bone loss that occurs during the decade following menopause (postmenopausal osteoporosis).
Fractures
The sequence of events in the healing of a fracture can be easily impeded or even blocked. Displaced and comminuted fractures frequently result in some deformity. The devitalized fragments of splintered bone require resorption, and this delays healing, enlarges the callus, and requires extremely long periods of remodeling so that in essence there is a permanent abnormality. Inadequate immobilization permits constant movement at the fracture site so that the normal constituents of callus do not form. Consequently the callus may be composed mainly of fibrous tissue and cartilage, perpetuating the instability and resulting in delayed union and nonunion. If a nonunion allows for too much motion along the fracture gap, the central portion of the callus undergoes cystic degeneration, and the luminal surface can actually become lined by synovial-like cells, creating a false joint, or pseudoarthrosis. In the setting of a nonunion or pseudoarthrosis, the normal healing process can be re-instituted if the interposed soft tissues are removed and the fracture site stabilized. A serious obstacle to healing is infection of the fracture site, which is a risk in comminuted and open fractures. The infection must be eradicated before bony union can be achieved. Bone repair can also be derailed by inadequate levels of calcium or phosphorus, vitamin deficiencies, systemic infection, diabetes, and vascular insufficiency.
Generally, with children and young adults, in whom most fractures are uncomplicated, practically perfect reconstitution can be anticipated. In older age groups, in whom fractures tend to occur on a background of some other disease (e.g., osteoporosis and osteomalacia), repair is less optimal and often requires mechanical methods of immobilization to facilitate healing.
Generally, with children and young adults, in whom most fractures are uncomplicated, practically perfect reconstitution can be anticipated. In older age groups, in whom fractures tend to occur on a background of some other disease (e.g., osteoporosis and osteomalacia), repair is less optimal and often requires mechanical methods of immobilization to facilitate healing.
Subscribe to:
Comments (Atom)
