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57 Cards in this Set
- Front
- Back
How are biologic bone grafts distinguished from synthetic bone replacements?
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Biologic bone grafts come from different sources and require a variety of pre-treatments
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What is creep substitution?
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Graft replacement by host tissue
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How do grafts stimulate bone healing?
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MSC or osteoprogenitor cells and capillaries from nearby bone marrow, periosteum, endosteum, or soft tissue grow into the porous structure of the graft. Cells differentiate into osteoblasts to produce new mineralized ostoid. Osteoclasts are recruited through the vasculature to facilitate remodeling of the graft bone into mature bone.
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What is a fresh biological bone graft?
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A bone graft transferred immediately from the donor to the implant site
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Examples of preserved grafts:
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decalcified bone, freeze-dried bone, irradiated bone, or sterilized bone
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Examples of synthetic bone replacements:
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ceramics, polymers, composites
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What is an orthotropic graft?
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Transferred tissue is applied in an anatomically similar location
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What is a heterotropic graft?
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Transferred tissue is applied in an anatomically dissimilar location
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What do free cortical grafts depend on for nutrition?
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Ingrowth of host vessels
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Examples of pre-treatments of preserved grafts:
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freezing, freeze-drying, radiation, sterilization, surface decalcification
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What does pre-treatment do for preserved grafts?
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Kills viable bone cells, reduces antigenicity, allows safer and sterile storage
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What are the functions of bone grafts?
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Osteoinduction and osteoconduction
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What is osteoinduction?
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Local triggering of osteogenesis
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What is osteoconduction?
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Graft acts as a scaffold into which MSC grow
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How does osteoinduction occur in fresh autogenous grafts?
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Partially by the activity of osteoblasts aligned on the surface of the graft
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What % of graft cells die after transfer?
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90%
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Which bone graft cells survive the best?
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Surface cells
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What are the most desireable bone grafts?
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Loosely arranged cancellous bone grafts
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What affects the number of cells surviving in a bone graft?
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# of surface cells, handling of the graft, dehydration of the graft, and compacting the graft
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How does the graft form new bone?
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Endochondral ossification which is later replaced by mature lamellar bone
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What growth factors are involved in fracture healing and graft incorporation?
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PDGF, FGF, IGF, TGF, BMP
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What family do BMP belong to?
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TGF beta
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What does successful incorporation of bone grafts depend on?
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The host bed, the viability of the bone graft, the volume of bone to be grafted, the GF activity in the host bed, metabolic activity index, and the homostructural function of the bone graft
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Which bone grafts have the greatest chance of acceptance?
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Cancellous and vascularized corticocancellous
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What is the relationship of the volume of bone to be grafted to the likelihood of complications?
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Larger volumes of graft take longer to be incorporated and remodeled which results in a greater likelihood of complications
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What decreases bone graft cell survivability during harvest?
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Exposure to air, saline soaked gauze, or antibiotics
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Why is the bone grafted not packed into the host bed?
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Loose packing encourages host tissues and fluids to ingress & nourish the graft
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What effect does fixation have on graft survival?
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Lack of rigid fixation results in mechanical damage to the graft
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Donor sites for cancellous bone grafts:
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tuber coxae, sternum, medial aspect of the tibia
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How is bone graft acquired from the tuber coxae?
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1” incision over TC, 5.5 drill used to create hole in thin cortex, graft obtained with curette or a bone graft harvest drill can be used to harvest 4mm diameter cancellous bone plugs
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How is bone graft acquired from the sternum?
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Incision made over sternum, through cartilage, cartilage lifted with periosteal elevator, cancellous graft taken from sternebra without incorporating hyaline cartilage
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How is bone graft acquired from the tibia?
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Incision made over medial aspect of proximal tibia, 5.5 drill bit used to penetrate the cortex, graft is harvested with a curette
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Examples of bone replacements:
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ceramics, polymers, gels, biomimetics
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Classes of ceramics:
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calcium sulfates, calcium phosphates
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Examples of calcium sulfate ceramics:
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alpha and beta CaSO4 (gypsum) with ½ H2O
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Examples of calcium phosphates ceramics:
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hydroxyapatite, beta tricalcium phosphate
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What does ceramic porosity relate to?
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Mechanical and biologic properties
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What are the pore types in ceramics?
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Micro and macro
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What are micropores?
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0.1-10 um
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What are macropores?
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50-2000 um
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What is the function of micropores?
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Prevent crack propagation
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What is the function of macropores?
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Enable blood vessel and cell ingrowth
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What factors affect the mechanical properties of ceramics?
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Porosity, chemistry, crystal and grain size
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What is the relationship of pore size to mechanical property of a ceramic?
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Increased pore size decreases mechanical property
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What are the forms of ceramics?
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Granules, macroporous blocks, hydraulic cements, putties
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How are polymers classified?
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First, 2nd or 3rd generation
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Examples of 1st generation polymers:
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silicone rubber, polyethylene, acrylic resin, polyurethanes, polypropylene, and polymethyl methacrylate
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What are the disadvantages of PMMA as a polymer?
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Toxic degradation products that provoke fat embolism, heat production during polymerization which can cause necrosis
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How do 1st generation and 2nd/ 3rd generation polymers differ?
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1st generation are nonbiodegradable and 2nd and 3rd have variable biodegradation
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What is a perfect biodegradable implant?
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Maintains mechanical properties until it is no longer needed then absorbed and excreted by the body without leaving a trace
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What are the criteria for an ideal polymer?
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Polymer does not evoke inflammatory or toxic response disproportionate to its benefits, metabolized in the body after fulfilling purpose and leaving no trace, easily processes into the final form, acceptable shelf life, easily sterilized
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What are hydrogels?
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Network of polymer chains that have the capacity to hold up to 99% volume water
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What are natural hydrogels based on?
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Fibrin
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Examples of hydrogels used in horses:
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research on cartilage cell cultures, and wound healing
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What are biomimetics?
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Molecules known to enhance new tissue formation applied locally as proteins, peptides, or plasmids
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Example of biomimetic used in horses:
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PrP
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GF in PrP:
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PDGF, VEGF, TGF
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