BG SUBSTITUTES
Transcript of BG SUBSTITUTES
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Bone Graft and its substitutes
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Introduction
Need for bone grafting: To replace skeletal defects
To augment bony recontruction
Bridge joints in arthrodesis
To provide bone blocks to limit joint motion [arthroereisis]
Establish union in pseudoarthrosis
To promote union : in fresh #s, delayed unions, non
unions and osteotomies.
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Bone Graft Terminology
Based on anatomic placement: Orthotopic: Transplantation to similar anatomic site
Heterotopic: Grafting to anatomically dissimilar site
Based on tissue architecture: Cortical, cancellous,corticocancellous, Osteochondral
Based on source: Autograft: same individual,different sitea] non vascularised b]
vascularised
Allograft: same species but genetically different individual
Xenograft: different species
Isograft: monozygotic twin
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Bone Graft Function
Osteogenesis
Mechanical support
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Biology of Bone Grafts
Bone regeneration: Osteoinduction
Osteoconduction
Osteoprogenetor cells
Osteoinduction: stimulation of host bed to synthesise new bone.-Graft derived Low molecular wgt protiens stimulate mesenchymal stem cellsto differentiate into bone forming cells.
This induction of stem cells does not require viable graft cells because it is aproperty of bone matrix.
Osteoconduction:The Matrix/ scaffolding that permits cellinfiltration and ingrowth of new host bone, this process is reffered asosteoconduction. A three dimentional configuration for ingrowth into graft ofhost capillaries, perivascular tissues, and osteoproginator cells from therecepient. [creeping sunstitution]
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Incorporation of the graft
Haematoma formation Inflamatory response releaseof cytokines and growth factors.
Osteoinduction drives chemotaxis, mitosis, anddifferentiation of osteoproginetor cells
Day5
chondrocyts form
Day 10- osteoblasts
Host blood vessels infiltrate through harvesian andvolkmanns canals and bring with them osteoclasts forresorption.
Remodelling occurs along the lines of biomechanicalforces.
Hence succesful incorporation needs: good bloodsupply, osteogenesis, grafts response to load applied.
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Cancellous autografts
Larger surface area
Faster incorporation [ 4 weeks- healing 6 months complete remodelling]
Good osteoinductive, osteoconductive
and osteogenetic properties.
No ability to confer structural strength
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Cortical Autografts
Due to density- revascularisation andremodelling are slower
Unlike cancellous grafts these are
incorporated by appositional bone growthover a necrotic area.
Good structural support
Minimal osteogenetic, moderateosteoinductive and conductive properties
Types: Vascularised , non vascularised.
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Disadvantages of autografts
A separate donor site is required
Increased surgical time
Another potential site for infection created
Additional amount of blood loss Weaknening of normal structure
Local complications
Limited availability
relative paucity of osteogenic cells in the graft inolder individuals
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Vascularised auto graft
Incorporates independent of host bed andfunctions even in biologically defecient hostenvironment
Advantages: Compromised vascularity in the host bed causing poor osteogenic
cells, poor surrounding tissues
If infection at surgical site
poor soft tissue coverage
Systemic chemotherapy
Disadvantages: Time consuming
Technically very demanding
Limited donor sites [ proximal fibula, ribs]
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Allografts
Graft taken from two genetically different
individuals of the same species.
Mode of availability: Frozen
Freeze dried [morcellised]
Cancellous allografts: mainly to fill the
cavitory defects Cortical allografts: for structural support
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How are they Preserved
Freezing
Freeze drying
[ helps in better incorporation as it reducesimmunogenecity]
Decalcification and demineralisation
[ these grafts have not much mechanicalstrength]
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Sterilisation techniques
Irradiation : destroys osteoinductive
property
Chemosterilisation
Autolysed
Antigen extraction
[ last three has good osteoinduction but poormechanical strength]
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Advantages
Abundantly available in amount, shapesand sizes
No donor site morbidity
Good mechanical strength
Good Osteoconductive property
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Disadvantages
Immunogenic
Higher failure rate notes
Graft incorporation very much delayed
[ more than 2 yrs]
Risk of disease transmission
Low osteoinductive property If these grafts fracture unlikely to heal
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Bone Banking
Tissues recovered under sterile conditions fromyoung donors with strong bone after carefulscreening for neoplasm and infection
If cartilage present graft is first treated by
dimethylsulfoxide and later freezed to preservethe viability of chondrocytes
The muscular, teninous, and ligamentousattachments are preserved
After biplanar radiographs taken, specimens arecultured, rapidly frozen, and maintained at -80*cuntil they are used
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Factors for success of a bone
grafting Clean, well vascularised host bed is critical
Wide excision of scar tissue
Treatment of infection
Protection of blood supply Satisfactory soft tissue coverage
Appropriate selection of graft material as per thedesired clinical function
Firmly/ tight apposition of graft bone and hostbone
Stable fixation of the graft
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Bone Substitutes
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Types
Naturally Derived Substitutes: Demineralised Bone Matrix [DBM]
Bone Marrow and Bone Marrow Products
Synthetically derived substitutes Calcium sulphates
Tricalcium Phosphates
Calcium phosphate cements
Corralline based hydroxyapatites
Bone Morphogenetic Proteins
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Synthetically derived substitutes
Less chances of viral transmission
compared to natural derived substitutes
Less variability
They are tested rigorously for safety and
efficacy
It mainly provides a scaffold forosteoproginetor cells to proliferate and
differentiate.
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Calcium sulphates [POP]
First used in in 1892 complete healing of nine
cavitory lesions
Has no weight bearing ability
Resorbs very quickly [6 weeks] [i.e: dissappearsfrom implantation site whether bone formation
has taken place or not]
A promising carrier for antibiotics,DBMs,BMPs,or any other molecules being
delivered to defect site.
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Tricalcium Phosphates
TCPs Less crystalline
Two types: Alpha and beta
Alpha soluble and resorbs fast
Beta less soluble and resorbs by
osteoclastic activity only : hence it will
disappear only after new bone formation
Has only osteoconductive property
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Calcium Phosphate Cements
No weight bearing capability
Powder and solvent is mixed and the resultantceremic paste injected/ moulded into non weight
bearing defect. Setting time 10 to 30 minutes depending on
formulations
After curing they form a apatitic compound
similar to bone mineral These cements do not degrade during a patients
lifetime.
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Coral based hydroxyapatite
Calcium carbonate exoskeleton of reef buildingmarine corals processed to form calciumphosphates.
Corals of scleractinian genus used
Goniopora species- first used- its pores aresimilar to cancellous bone pores- 500 to600microm
Porites species similar to cortical bone pore
diameter- 200microm. Useful to fill defects after tumour excision with
wide defects.
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Collagen Based technology
Type 1 collagen extracted from animal
source, mostly from bovine source
Good osteoconductive property
Disadv:
Hypersensitivity to bovine collagen
Uses: Mainly as a carrier along with other
materials.
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Naturally Derived
Available clinically from 1990s.
Disadv:
High tissue variability
Viral transmission
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