Bone Grafts

Bone Healing

 

Bone healing requires 3 things

- osteoconduction - scaffold / matrix

- osteoinduction - growth factors

- osteogenesis - cells  to produce osteoid

 

Osteoconduction

 

Definition

- property of a matrix that supports the attachment of bone forming cells for subsequent bone formation

 

Substances

1.  Autograft

2.  Allograft

3.  Calcium phosphate

 

Osteoinduction

 

Definition

- process that supports the mitogenesis of undifferentiated mesenchymal cells

- osteoprogenitor cells to become osteoblasts

 

Substances

 

1. Autograft

2. BMP

- part of transforming growth factor (TGF) familty

- at least 15 types

- stimulate differentiation of mesenchymal cells

 

Osteogenetic properties

 

Definition

- generation of bone from bone forming cells

- require presence of osteogenetic cells / osteoblasts

 

Substances

1.  Autograft

2.  Autologous bone marrow

 

Autograft

 

Sources

 

Cancellous

- iliac crest

- proximal tibia

- distal radius

- PSIS

 

Structural

- iliac crest

- fibular / vascularised graft

 

Properties

- osteoconduction

- osteoinductive

- osteogenic

 

Autologous Bone Marrow Aspirate

 

Properties

- osteogenesis

- osteoinductive factors

 

Results

 

Hernigou et al JBJS Am 2005

- injected 20 mls into non infected NU site

- union in 53 of 60

- positive correlation of volume of mineralised callous and concentration of colony forming units

 

Allograft

 

Structural

 

Options

 

A.  Fresh

- inadequate time for disease screening

- HIV / HCV / HBV testing mandatory on donors

 

B.  Frozen

- stored at -60o

 

Allograft Talus Fresh Frozen

 

C.  Freeze-drying

- destroys all osteogenic cells

- limited osteoinductive properties

 

D.  Irradiated

- for sterility

- gamma irradiation (affects mechanical properties)

- ethylene oxide (affects osteoinductive properties)

 

Femoral Head Allograft 1Femoral Head Allograft 2

 

Properties

 

Osteoconductive

 

Types

 

Cortical strut grafts

- used in periprosthetic THR fractures

- creeping substitution via intra-membranous bone formation

 

Cortical Strut Grafts

 

Cancellous allograft chips

- osteochondral ossification

 

Disadvantages

 

Osteointegration is invariably

- incomplete

- much slower than autograft

 

Results

 

Gibson et al Spine 2002

- RCT of fresh frozen morcellised allograft v autograft in PLF

- comparable results

 

2.  Demineralised Bone Matrix / DBM

 

Concept

 

Produced by acid extraction of allograft

- retention of collagen and growth factors

- no structural strength

- osteoinductive

- comes as putty or gel

- used in spinal surgery

 

Results

 

Lindsay et al Orthopedics 2006

- compared DMB + BM aspirate to autograft in long bone fractures

- comparable findings in regards to union

 

Vaccaro et al Orthopedics 2007

- prospective study of DMB v autograft in posterolateral spinal fusion

- comparable findings

 

Synthetic Grafts

 

Calcium Phosphate Synthetic Substitutes

 

Properties

- osteoconductive

- provide scaffold

- allow host osteogenic cells to create bone under the influence of host osteoinductive factors

 

Structure

 

Ceramics

- highly crystalline structures

- obtained by sintering (heating > 1000o)

- pore size and porosity important

- osteoid formation requires minimum pore size of 100 microns (preferably 300 – 500)

 

A.  Tricalcium phosphate / Chronos

- formed by treating coral with ammonium

- similar structure and porosity to cancellous bone

 

B.  Synthetic hydroxyapatite / Pro Osteon

- may have some osteoinduction properties

- slower in vivo resorption than tricalcium phosphate

- higher brittleness

 

C.  Cements/ Norian

 

Indications

 

Metaphyseal defects

- calcaneum

- tibial plateau

- distal radius

 

Resorption

 

80% at 10 weeks

- can continue for as long as 30 weeks

- dissolution + osteoclast resorption

 

Results

 

Russell et al JBJS Am 2008

- RCT of autograft v calcium phosphate cement in tibial plateau fractures

- significantly reduced rates of subsidence

 

Buckley et al J Trauma 2009

- RCT of autograft v calcium phosphate past in displaced IA calcaneal fractures

- significantly reduced rate of articular depression

 

Calcium Sulfate Synthetic Graft

 

Plaster of paris

- calcium sulfate + water

- forms dihydrate known as gypsum

 

Properties

- ? osteconductive

- may resorb too rapidly

- takes 4 – 12 weeks depending on size of defect

- low mechanical strength

 

Indications

- bone graft extender

 

Types

- MIG

- Osteoset

 

Results

 

Niu Spine 2009

- RCT of autograft + BMA v calcium sulphate + BMA in PLF

- significantly reduced rates of union in calcium sulphate group

 

BMP

 

Bone Morphogenic Protein

 

Background

 

Group of growth factors / cytokines

- 20 different types

- a type of transforming growth factor

- interact with receptors on the cell surface

 

Production

- initially extracted from demineralised bone graft by Urist in 1965

- demonstrated ability to stimulate bone growth in rabbits

- now produced by recombinant technologies

 

Types

 

Infuse (BMP-2)

OP1 (BMP-7)

 

Usually delivered on a collagen matrix

 

Uses

 

Spinal fusion

Non union long bones

 

Tibial Results

 

Friedlaender et al JBJS Am 2001

- As efficacious as autograft in established tibial non union

 

Govender et al JBJS Am 2002

- RCT of control v BMP in open tibial fractures

– less secondary interventions, accelerated time to union, reduced infection rates

 

Jones et al JBJS Am 2006

- RCT allograft + BMP2 v autograft in tibial diaphyseal cortical defects

- similar rates of healing, reduced blood loss in BMP group

 

Spine Results

 

Vaccaro et al Spine 2008

- RCT OP1 v autograft in PLF spine

- as least as efficious as autograft

 

Dimar et al Spine 2006

- RCT of iliac crest autograft v rhBMP2 on a collagen matrix

- reduced surgical time, bleeding and increased fusion rates with BMP