Bone grafts Flashcards
What are the features of bone grafts?
1) Osteoinduction
2) osteconduction
3) osteogenesis
4) osteopromotion
What are indications of bone grafts?
- enhancing fracture healing and stimulating healing of fracture gaps
- artrodesis
- treatment of comminuted fractures
- used in older animals or when delayed healing is percieved
What is osteoinduction?
- induced bone formation when placed into a site
- recruit mesenchymal cells to form osteoblasts/clasts
- related to presence of growth factors such as BMP, TGF, IGF
Osteoinduction is when non-osseus tissue becomes osteogenic.
What is osteoconduction?
- scaffold material for mesenchymal stem cells and progeny to migrate into
- three dimensional process of in-growth of capillaries, perivascular tissues, osteoprogenitor cells into structure of the graft
- may or may not be load bearing
- can be naturally occuring or synthetic
What is osteogenesis?
- new bone formation from transferred osteoblasts
- only about 10% of transferred cells survive
- autogenous calcellous bone grafts the best
- bone marrow is also osteogenic (lack scaffolt material to be efficacious on its own)
What is osteopromotion?
- enhanced regeneration of bone
- achieved by
1) introduction of substances that enhance bone regeneration
2) mechanical strategies that induce proliferation and differentation of stelm cells
–> e.g. Platelet rich plasma
Types of bone grafts?
1) Autografts
- cancellous
- cortico-cancellous
- cortical (vascularized, non-vascularized)
2) Allografts
- cancellous bone chips
- cortical grafts
- demineralized bone matrix
3) growth factors
- bone morphogenic protein
4) Synthetic
hydroxyapatite
Autograft?
From same animal
Allograft?
From different animal
Xenograft?
From different species
What type of bone grafts are considered gold standard?
Autogenous cancellous bone grafts
Where can you harvest autogenous cancellous bone grafts?
1) proximal lateral humerus (base of greater tubercle)
2) ilial wing (dorsal or lateral) - less risky
3) proximal lateral femur
4) distal femoral condyle
5) medial proximal tibia
Estimated viability of autogenous bone grafts?
3 hours after harvest the graft viability decrease to:
- 57% in blood soaked swabs
- 46% in saline
- 70-73% in ice and buffered solution
What are indications of bone grafts?
- enhancing fracture healing and stimulating healing of fracture gaps
- artrodesis
- treatment of comminuted fractures
- used in older animals or when delayed healing is percieved
- filling cavities (e.g. cysts)
Advantages of cancellous grafts?
- rapid stimulation of direct bone formation
- early osteoinduction
- early vascularization
What is the optimal size of a cancellous bone graft?
2-4mm
if <0,7mm will be swept away in granulomatous response
if >4mm may act as sequestrae
Complications of cancellous bone grafts?
pain
infection
fracture
Blood loss
Prolongation of anaesthetic time
increased discomfort to the patient
How to use bone grafts in delayed union?
- remove sclerotic tissue
- remove fibrous tissue
- stabilize fragments
- place graft around fracture site
Allogenous cancellous bone grafts?
- problematic availability
- provokes a strong rejection response
- osteogenesis less productive, re-vascularization very variable
- if cells removed prior to transplant the graft can still contribute to healing through its osteoconductive and osteoinducive powers
- particularly susceptible to infection
Advantages of cortical bone grafts?
- it has osteoconductive and osteoinductive properties
- supportive or weight bearing function
Indications for use of cortical bone grafts?
- treatment of multifragmented diaphyseal long-bone fractures
- limb lengthening procedures
- management of malunion or non-union fractures
- limb salvage procedures for primary bone tumours
- graft in vertebral fusion - wobblers
- arthrodesis
Properties of cortical bone ALLOgrafts?
- slow healing
- envoke inflammatory response
- resorption can take months or years
- do not supply cells
- if support is required need rigid internal fixation and compression
- limited stock (cadaver)
- aseptic removal, freezer (-70)
- no osteogenesis
- slow revascularization and incorporation
Complications: infection, implant loosening/breakage
Limitation of cortical autograft?
Limited amount of bone can be taken out
donor sites:
- rib
- ulna
- iliac wing
- medial tibial cortex
Types of cortical bone grafts?
- bone chips
- onlay bone graft
- tubular
- corticocancellous
- sliding onlay
Xenografts?
Lyophilized calf bone is generally used after it has been defatted and freeze dried
Used simply as a support
Vascularized grafts?
- not commonly used
- difficult, microvascular anastomosis
- expensive equipment
Synthetic grafts?
- ceramics, injectable calcium phosphate, bioactive glass and glass ionomer cements
Poor clinical results, unpredictable resportion rates and inflammatory reactions
Bone morphogenic proteins?
rhBMP-2
- promotes differentiation of mesenchymal stem cells
- applied on absorbable sponge
- expensive
