Frost s mechanostat a Bone adapts to keep average daily strains within a normal range. a Strains above range cause new bone formation (modeling to stimulate bones to get stronger Strains below range cause bone to be lost increased rates of remodeling) to stimulate bones to get weaker
Frost’s Frost’s Mechanostat Mechanostat Bone adapts to keep average daily strains within Bone adapts to keep average daily strains within a “normal” range. a “normal” range. Strains above range cause new bone formation Strains above range cause new bone formation— (modeling) to stimulate bones to get stronger. (modeling) to stimulate bones to get stronger. Strains below range cause bone to be lost Strains below range cause bone to be lost– (increased rates of remodeling) to stimulate (increased rates of remodeling) to stimulate bones to get weaker. bones to get weaker
Bone remodeling a Occurs mainly on internal bone surfaces throughout lif Rates are influenced by hormones and by skeletal loading a Increased loading suppresses remodeling z Decreased loading stimulates remodeling
Bone Remodeling Remodeling Occurs mainly on Occurs mainly on internal internal bone surfaces bone surfaces throughout life throughout life Rates are influenced by hormones and Rates are influenced by hormones and by skeletal loading by skeletal loading Increased loading Increased loading suppresses suppresses remodeling remodeling Decreased loading Decreased loading stimulates stimulates remodeling remodeling
Bone remodeling Skeletal loading is diminished in the elderly relative to when they were stronger and more active Space-flight removes skeletal loading from most of the body (except upper extremities a Expect remodeling on internal bone surfaces to be stimulated in both cases
Bone remodeling remodeling Skeletal loading is diminished in the Skeletal loading is diminished in the elderly relative to when they were stronger elderly relative to when they were stronger and more active and more active Space-flight removes skeletal loading from flight removes skeletal loading from most of the body (except upper extremities) most of the body (except upper extremities) Expect remodeling on internal bone Expect remodeling on internal bone surfaces to be stimulated in both cases surfaces to be stimulated in both cases
Remodeling in presence of load Mechanical Load a Bone is temporarily removed from internal surfaces Bending strains increase on external surfaces New bone is added to external surfaces(modeling) Bone diameter increases to compensate internal bone loss
Remodeling Remodeling in presence of load in presence of load Mechanical Mechanical Load Bone is temporarily removed Bone is temporarily removed from internal surfaces from internal surfaces Bending strains increase on Bending strains increase on external external surfaces surfaces New bone is added to external New bone is added to external surfaces (modeling) surfaces (modeling) Bone diameter increases to Bone diameter increases to compensate internal bone loss compensate internal bone loss
Effects of normal modeling on bone density Less bone needs to be added to external surface than removed from internal surface a Bone gets less dense because it is bigger in diameter and because less bone needed to maintain section modulus
Effects of normal modeling on bone density Effects of normal modeling on bone density Less bone needs to be added to external Less bone needs to be added to external surface than removed from internal surface surface than removed from internal surface Bone gets less dense because it is bigger in Bone gets less dense because it is bigger in diameter and because less bone needed to diameter and because less bone needed to maintain section modulus maintain section modulus