Auer Ch 77 Bone Grafts And Replacements

Front 1

How are biologic bone grafts distinguished from synthetic bone replacements?

Back 1

Biologic bone grafts come from different sources and require a variety of pre-treatments

Front 2

What is creep substitution?

Back 2

Graft replacement by host tissue

Front 3

How do grafts stimulate bone healing?

Back 3

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.

Front 4

What is a fresh biological bone graft?

Back 4

A bone graft transferred immediately from the donor to the implant site

Front 5

Examples of preserved grafts:

Back 5

decalcified bone, freeze-dried bone, irradiated bone, or sterilized bone

Front 6

Examples of synthetic bone replacements:

Back 6

ceramics, polymers, composites

Front 7

What is an orthotropic graft?

Back 7

Transferred tissue is applied in an anatomically similar location

Front 8

What is a heterotropic graft?

Back 8

Transferred tissue is applied in an anatomically dissimilar location

Front 9

What do free cortical grafts depend on for nutrition?

Back 9

Ingrowth of host vessels

Front 10

Examples of pre-treatments of preserved grafts:

Back 10

freezing, freeze-drying, radiation, sterilization, surface decalcification

Front 11

What does pre-treatment do for preserved grafts?

Back 11

Kills viable bone cells, reduces antigenicity, allows safer and sterile storage

Front 12

What are the functions of bone grafts?

Back 12

Osteoinduction and osteoconduction

Front 13

What is osteoinduction?

Back 13

Local triggering of osteogenesis

Front 14

What is osteoconduction?

Back 14

Graft acts as a scaffold into which MSC grow

Front 15

How does osteoinduction occur in fresh autogenous grafts?

Back 15

Partially by the activity of osteoblasts aligned on the surface of the graft

Front 16

What % of graft cells die after transfer?

Back 16

90%

Front 17

Which bone graft cells survive the best?

Back 17

Surface cells

Front 18

What are the most desireable bone grafts?

Back 18

Loosely arranged cancellous bone grafts

Front 19

What affects the number of cells surviving in a bone graft?

Back 19

# of surface cells, handling of the graft, dehydration of the graft, and compacting the graft

Front 20

How does the graft form new bone?

Back 20

Endochondral ossification which is later replaced by mature lamellar bone

Front 21

What growth factors are involved in fracture healing and graft incorporation?

Back 21

PDGF, FGF, IGF, TGF, BMP

Front 22

What family do BMP belong to?

Back 22

TGF beta

Front 23

What does successful incorporation of bone grafts depend on?

Back 23

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

Front 24

Which bone grafts have the greatest chance of acceptance?

Back 24

Cancellous and vascularized corticocancellous

Front 25

What is the relationship of the volume of bone to be grafted to the likelihood of complications?

Back 25

Larger volumes of graft take longer to be incorporated and remodeled which results in a greater likelihood of complications

Front 26

What decreases bone graft cell survivability during harvest?

Back 26

Exposure to air, saline soaked gauze, or antibiotics

Front 27

Why is the bone grafted not packed into the host bed?

Back 27

Loose packing encourages host tissues and fluids to ingress & nourish the graft

Front 28

What effect does fixation have on graft survival?

Back 28

Lack of rigid fixation results in mechanical damage to the graft

Front 29

Donor sites for cancellous bone grafts:

Back 29

tuber coxae, sternum, medial aspect of the tibia

Front 30

How is bone graft acquired from the tuber coxae?

Back 30

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

Front 31

How is bone graft acquired from the sternum?

Back 31

Incision made over sternum, through cartilage, cartilage lifted with periosteal elevator, cancellous graft taken from sternebra without incorporating hyaline cartilage

Front 32

How is bone graft acquired from the tibia?

Back 32

Incision made over medial aspect of proximal tibia, 5.5 drill bit used to penetrate the cortex, graft is harvested with a curette

Front 33

Examples of bone replacements:

Back 33

ceramics, polymers, gels, biomimetics

Front 34

Classes of ceramics:

Back 34

calcium sulfates, calcium phosphates

Front 35

Examples of calcium sulfate ceramics:

Back 35

alpha and beta CaSO4 (gypsum) with ½ H2O

Front 36

Examples of calcium phosphates ceramics:

Back 36

hydroxyapatite, beta tricalcium phosphate

Front 37

What does ceramic porosity relate to?

Back 37

Mechanical and biologic properties

Front 38

What are the pore types in ceramics?

Back 38

Micro and macro

Front 39

What are micropores?

Back 39

0.1-10 um

Front 40

What are macropores?

Back 40

50-2000 um

Front 41

What is the function of micropores?

Back 41

Prevent crack propagation

Front 42

What is the function of macropores?

Back 42

Enable blood vessel and cell ingrowth

Front 43

What factors affect the mechanical properties of ceramics?

Back 43

Porosity, chemistry, crystal and grain size

Front 44

What is the relationship of pore size to mechanical property of a ceramic?

Back 44

Increased pore size decreases mechanical property

Front 45

What are the forms of ceramics?

Back 45

Granules, macroporous blocks, hydraulic cements, putties

Front 46

How are polymers classified?

Back 46

First, 2nd or 3rd generation

Front 47

Examples of 1st generation polymers:

Back 47

silicone rubber, polyethylene, acrylic resin, polyurethanes, polypropylene, and polymethyl methacrylate

Front 48

What are the disadvantages of PMMA as a polymer?

Back 48

Toxic degradation products that provoke fat embolism, heat production during polymerization which can cause necrosis

Front 49

How do 1st generation and 2nd/ 3rd generation polymers differ?

Back 49

1st generation are nonbiodegradable and 2nd and 3rd have variable biodegradation

Front 50

What is a perfect biodegradable implant?

Back 50

Maintains mechanical properties until it is no longer needed then absorbed and excreted by the body without leaving a trace

Front 51

What are the criteria for an ideal polymer?

Back 51

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

Front 52

What are hydrogels?

Back 52

Network of polymer chains that have the capacity to hold up to 99% volume water

Front 53

What are natural hydrogels based on?

Back 53

Fibrin

Front 54

Examples of hydrogels used in horses:

Back 54

research on cartilage cell cultures, and wound healing

Front 55

What are biomimetics?

Back 55

Molecules known to enhance new tissue formation applied locally as proteins, peptides, or plasmids

Front 56

Example of biomimetic used in horses:

Back 56

PrP

Front 57

GF in PrP:

Back 57

PDGF, VEGF, TGF