Bone graft

Bone Void Fillers : Bone And Bone substitutes

Dr Sitanshu

Introduction

• 2nd most common graft• Gold standard – autogenous

cancellous bone• Drawbacks – Morbidity Availability Operative time

• Allograft – immune response disease transfer impaired

osteoconductivity reduced mechanical

property cost

• 1st phase – 4 weeks – mainly from cells of graft

• 2nd phase – host cells (endosteal cells, marrow cells, osteocytes)

Role of cancellous bone

• Scaffold where cells interact• Nutrition• Hematopoiesis, Myelogenesis, Platelet

formation• Source of pluripotent osteoprogenitor stem

cell• Local growth factors for differentiation• Same strength of cortical bone by 6-12

months

General characteristics of successful bone graft

Osteogenesis

Osteoinduction

Osteoconduction

Good handling characteristic

Non toxic

Biomechanical property similar to cancellous bone

Osteogenesis

Process of bone formation through cellular osteoblastic activity which depends on the

presence of osteoprogenitor stem cells.

Osteoinduction

Biologically mediated recruitment and differentiation of cell types essential for

bone formation.

Osteoconduction

Apposition of growing bone to three dimensional surface of a suitable scaffold

provided by the graft.

Potential use of natural and synthetic grafts

• Fusion – cervical fusion

lumbar onlay graft

lumbar interbody fusion

arthrodesis

• Bone void filler – collapsed vertebral body

autograft donor site repair

bony defects

Autograft - Pros

• Osteogenic

• Osteoinductive

• Osteoconductive

• No disease transmission

• No host rejection

Autograft - Con

• Viability is compromised

• Quality is not constant

• Second fascial incision

Minor complications

Superficial infection

Seroma

Hematoma

Temporary sensory loss

Transient pain

Major complications

• Infection• Prolonged wound

drainage• Hernia• Deep hematoma• Need for reoperation• Pain > 6 months• Profound sensory loss• Heterotopic bone

formation

• Vascular injury• Neurologic injury• Scars• Subluxation• Gait disturbance• SI destabilization• Enterocutaneous

fistula• Pelvic fracture

• 3cm – distance from donor site and ASIS / PSIS

• 3cm – maximum distance from dorsal ilium

Factors which can’t be avoided

• Increased operative time

• Blood loss

• Donor site – pain

• Cosmetic defect

Sites

• Iliac crest (Anterior or posterior iliac crest)

• Greater trochanter

• Gerdy's tubercle

• Distal part of the radius

• Distal part of the tibia

• Autogenous cancellous bone graft is an excellent choice

for nonunions with <5 to 6 cm of bone loss and that

do not require structural integrity from the graft. It can

also be used to fill bone cysts or bone voids after

reduction of depressed articular surfaces such as in a

tibial plateau fracture. Stable internal or external

fixation is also required, to provide the optimum

environment for graft consolidation and successful

fracture-healing.

Autogenous cortical graft

• Fibula

• Ribs

• Iliac crest

• With or without vascular pedicle

• Osteoconduction + Osteogenesis

• Non vascularized grafts become weaker in 6 weeks – resorption, revascularization

• Vascularized – stronger – remodelling similar to normal bone

• But by 6-12 months – no difference

• Fixation required

• Advantage• Defects > 5-6cm• Immediate structural

support

• Disadvantage• Subjective sense of

weakness and instability

• Big toe weakness• Need for reoperation

at donor site

Osteoconductive matrices

• No osteogenic or osteoinductive property

• Greater source availability

• Elimination of second operative site

• Tricalcium phosphate (alpha, beta)

• Hydroxyapatite

• Injectable calcium phosphate cement

Graft Material Osteogenesis Osteoinduction Osteoconduction

Autograft 2* 2 2

Allograft 0 1 2

Xenograft 0 0 2

α-TCP 0 0 1

β-TCP (porous) 0 0 2

Hydroxyapatite 0 0 1

Injectable calcium

phosphate cement

(e.g., Norian SRS†) 0 0 1

BMA 3 2 0

β-TCP plus BMA 3 2 2

DBM 0 2 1

Collagen 0 0 2

BMP 0 3 0

Hyaluronic acid 0 0 0

Bioactive glasses 0 0 1 Degradable polymer 0 0 1

Porous metals 0 0 1

Allograft

• Surge in popularity – increased availability

donor screening and tissue processing for safety

new forms has increased versatility

• Machine tooling to shape structural allograft

• Reduction of procurement morbidity

• Potential for immediate structural support

• Reasonable success (60-90%)

Allograft - ConA

• Results inferior to autograft

• Vary in initial bone quality

• Expensive

• Disease transmission

• Immunogenic reaction

• Processing – its disadvantage

• Slower resorption

• Not completely replaced by new bone

• Reduced structural integrity

• Poor results in lumbar fusion

• Donor to donor variation

• Low grade inflammatory reaction

• Animal studies – correlation between histocompatibility difference and allograft failure

• Reaction specific to donor antigen

• CD8+ reaction

• Fresh frozen• Retain BMP• Strong• Better incorporation• Immunogenic• Disease transmission

• Freeze dried• No BMP• Weak• Weaker• Least immunogenic• No documented

disease transmission

Demineralized bone matrix

• Allograft bone that has had the inorganic mineral removed, leaving behind the organic collagen matrix

• More osteoinductive properties

• DBM + glycerol carrier – commonly used

• Available data – more as bone graft extender, not substitute

• Revascularizes quickly

Factors affecting DBM product

• Processing

• Time of demineralization

• Final particle size

• Terminal sterilization

• Carrier

• Donor viability

Carrier for DBM

• Glycerol

• Thermogelling chitosan

• Hyaluronic acid

• Recombinant BMP

• Albumin

• Carboxymethyl cellulose

Disadvantage

• Difficulty in handling

• Tendency to migrate from graft site

• Lack of stability

• Transmit disease

Xenograft

• From animals

• Impractical for clinical use on a wide scale

• Removal of protein and fat – processing

• Removes osteoinductive proteins

• Kiel bone, Oswestry, Bio Oss

Ceramics

• Stable compounds of metals with oxygen or other anions

• Non injectable ceramics – according to resorbing power

• Injectable ceramics

Non injectable ceramics

• Osteoconductive

• Hydroxyapatite, Tricalcium phosphate, Calcium sulphate dihydrate

• High quality synthetic material with no biologic hazards

• Alternative or as an addition to either cancellous autograft or allograft or as a cancellous bone void filler or bone graft extender or in sites where compression is the dominant mode of mechanical loading

• Safe and effective substitute for iliac graft autograft

• Cost

Rapidly resorbing ceramics

• Tricalcium phosphate (alpha 1200 degrees, beta at 800 degrees) – 39% Ca, 20% P

• Calcium sulfate

• Calcium phosphate – calcium phosphate rich microenvironments that stimulate osteoclastic resorption and then osteoblastic new bone formation, resulting in new bone formation

• Pore size - less porous formulations resorb before complete bone ingrowth

• Calcium sulfate - Osteoconductive but its rapid resorption rate creates doubt about its ability to maintain a three-dimensional framework to support Osteogenesis

Intermediate resorbing ceramic

• Beta tricalcium phosphate - In the process of being resorbed, it can enrich the local environment with osteogenic substrates that, in turn, can be used by activated osteoblasts

• Broad range of pore size (<1µm to 1000µm)

• Sponge-like interconnected microporosity endowed with excellent wicking and hydrophilic properties

Slow resorbing ceramic

• Hydroxyapatite

• Bone incorporation – pore size and pore interconnectivity

• Drawback - slow resorption, brittle

Injectable ceramics

• Calcium phosphate cement - paste of inorganic calcium and phosphate that hardens in situ with a low exothermic temperature

• Slowly transforms into bone over 3 to 4 years

• Adjunct to fixation in both femoral neck and intertrochanteric hip fractures

• Drawbacks – 1. slow resorption

2. low porosity

3. high cost

4. extravasation

5. intra articular extension

6. increased washout

7. low shear resistance

Collagen

• Animal-derived collagen with synthetic calcium phosphate

• Putty-like consistency

• Can be used as bone graft extenders to increase the volume of bone graft into a defect when a sufficient volume of autograft is not readily available

Non biologic Osteoconductive substrates

1. absolute control of the final structure 2. no immunogenicity

3. excellent biocompatibility

Degradable polymers - polylactides

Bioactive glasses

Porous metals - tantalum

Composite graft

• Any combination of materials that includes both an osteoconductive matrix and an osteogenic or osteoinductive material

1.Bone marrow aspirate

2.Osteoblastic progenitor stem cell

3.Blood

4.Platelet rich plasma

5.Growth factors

Bone marrow aspirate background

• Osteoblast progenitor cells – 1.periosteum of long bones 2.the peritrabecular connective tissue 3.the bone marrow

• All the critical cellular components that contribute to bone growth present

• Fibroblast, undifferentiated cells• Animal research suggests that precursor

cells in bone marrow proliferate and differentiate after transplantation

• Availability and the relative safety of its harvest

• Harvested by aspiration from patients, with limited dilution by peripheral blood

• Concentration

• Culture

Bone composite

• Used successfully to stimulate healing in tibial fractures

• Osteogenic potential was maintained as the cells were expanded in culture

• Facilitated greater bone formation and fusion success rates

• Xenograft bone and other bone substitutes could be rendered osteogenic

Synthetic composite

• Addition of BMA was essential for tricalcium phosphate and hydroxyapatite to achieve results comparable to those obtained with cancellous bone at 24 weeks

• β-TCP/BMA composite may be superior even to autograft, which suffers from anoxic cell death in the center of the graft because of the absence of vascularization

BMP and synthetic composite

• BMP 2, BMP 7 (rhOP 1)

• Carrier to maintain optimum regional concentration

• Hydroxyapatite

• DBM

• Hyaluronic acid

• Collagen

Bone graft

Health & Medicine

Transcript of Bone graft