Term
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Definition
lCortical- 80% of skeleton
lLocated in diaphysis of long bones
lRemodels at 50% per year at age 2 yr
lRemodels at 2%-5% per year in elderly
lTrabecular- 20% of skeleton
lLocation:
lEnds of long bones
lVertebral bodies
lPelvis
lRemodels at 3X rate of cortical bone
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Term
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Definition
lOsteocalcin:
lmarker for osteoblast formation
l vitamin-K dependent
lGrowth Factors
lBone Morphogenic Proteins (BMPs)
lTransforming Growth Factor-beta (TGF-beta)
lBasic Fibroblastic Growth Factor (bFGF)
lInsulin Growth Factors (IGFs)
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Term
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Definition
lMature bone; remodeling of immature woven bone
lHighly organized
lStress-oriented collagen
lAnisotropic mechanical characteristics
lMechanical behavior depends on orientation of applied forces
lParallel to longitudinal axis
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Term
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Definition
lImmature and primitive
lEmbryo, newborn, fracture callus, metaphyseal region of growing bone
lTumors, osteogenesis imperfecta and pagetic bone
lCoarse fibers; no uniform orientation of collagen fibers
lMineral content varies
lCells are randomly arranged
lIsotropic mechanical characteristics
lMechanical behavior is similar regardless of orientation of applied forces
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Term
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Definition
lNutrient arteries arise from the major peripheral arteries and enter the diaphysis through foramina
lMetaphyseal complex arises from the geniculates and enters the metaphysis
lPeriosteal system enters through the cortex and quickly splits to capillaries, supplies the outer 20% of the cortical bone
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Term
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Definition
lNutrient arteries arise from the major peripheral arteries and enter the diaphysis through foramina
lMetaphyseal complex arises from the geniculates and enters the metaphysis
lPeriosteal system enters through the cortex and quickly splits to capillaries, supplies the outer 20% of the cortical bone
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Term
Physiology of Bone Growth |
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Definition
lLongitudinal growth due to endochondral ossification
lCircumferential growth due to subperiosteal new bone formation
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Term
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Definition
lOsteoblast encased in mineral matrix
lRegulates bone metabolism
lSecretes RANKL and OPG
lGap junction: communication between adjacent osteocytes and central canals of osteons
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Term
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Definition
lDerived from a progenitor cell
lLines the surface of bone
lFollows osteoclast in cutting zones
lProduces osteoid or bone matrix
lProduces Type I collagen
lProduces osteoprotegerin (OPG)
l
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Term
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Definition
lPotent inhibitor of bone resorption
lDecoy receptor
lBinds and inactivates OPG ligand
lOPG ligand essential for osteoclast differentiation
lOpposes bone resorptive activity
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Term
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Definition
lMajor resorptive cell of bone
lHematopoetic cell (bone marrow)
lMonocyte/macrophage lineage
lProduces tartrate-resistant acid phosphatase
lLie in pits called Howship’s lacunae
lKey Receptors
lMacrophage-colony stimulating factor (M-CSF)
lReceptor activator for nuclear factor kappa B ligand (RANKL)
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Term
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Definition
l1, 25 (OH)2 Vitamin D3, PTH and IL-1 stimulate RANKL expression on the osteoblast
lRANKL binds to cognate receptor RANK on the osteoclast
lInduction of osteoclast differentiation
lRANKL stimulates fusion and activation of osteoclasts
lOPG decoy receptor of RANKL
lInhibits RANKL processes
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Term
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Definition
lInflammation
lBegins immediately
lBone fracture disrupts blood vessels with resultant ischemia of local tissue, and combined with injured cells, triggers inflammatory cascade.
lHematoma around the fracture forms the basis for the callus
lIschemia induces blood vessels to proliferate (angiogenesis) into the hematoma.
lChondrocytes are deposited into the hematoma, with subsequent chondrogenesis, and transition to Soft Callus Stage
l
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Term
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Definition
lSoft Callus Stage
lTransition from stage to stage is variable, and can differ from one location in a particular callus to another.
lAs cartilage tissue consolidates, osteoblasts are deposited into the chondral framework, and bone begins to form within the cartilage-collagen mesh.
lAs cartilage becomes more ossified, callus becomes more firm, and progresses to Hard Callus Phase
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Term
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Definition
lHard Callus Stage
lWoven bone is formed on the cartilage-collagen mesh.
lCallus density on x-ray increases, and begins to approach that of adjacent bone, as fracture lines become less distinct
lAs callus density increases, mechanical properties of callus begin to approach that of mature bone, and motion at fracture decreases, leading to Remodeling Phase
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Term
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Definition
lPrimary Bone Healing
lSeen in rare situations without surgery
lCommon after rigid internal fixation of non-comminuted fractures
lOccurs by direct Haversion remodeling without callus formation
lCutting cones of osteoclasts cross the fracture site and trailing osteocytes lay down new bone across the fracture.
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Term
Fracture Healing (Remodeling Phase) |
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Definition
lRemodeling phase
lWoven bone is resorbed by osteoclasts and replaced by lamellar bone.
lMedullary canal is reconstituted
lRemodeling of skeletally immature bone can result in amazing improvement in overall bone shape, sometimes correcting gross deformity.
lAs skeletal maturity is approached, remodeling capacity decreases.
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Term
Factors Affecting Bone Healing |
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Definition
lFactors affecting bone injury
lForce
lQuantity
lDirection(s)
lDuration
lBone
lWhich bone
lMetaphysis, diaphysis…
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Term
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Definition
lWolff’s Law
lBone remodels by the application of stress. Bone cells are presumed to have mechanoreceptors.
lBone adapts to the application of force
lif you don’t use it you loose it.
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