This document discusses bone grafts and their substitutes. It begins by introducing the need for bone grafts to replace lost musculoskeletal tissue. There are various types of natural and synthetic bone grafts described, including autogenous grafts, allografts, xenografts, bone morphogenetic proteins, growth factors, stem cells, ceramics, polymers and others. The mechanisms of bone formation and graft incorporation are also summarized.
2. INTRODUCTION
Need for replacement of musculoskeletal tissue due to losses occurred in
various situations - common problem in surgical practice
Search for the solutions lead to the usage of biological reconstruction
methods - Grafts
4. TERMINOLOGIES
Orthobiologics - clinical application of biologically derived materials
engineered to promote the repair or regeneration of musculoskeletal
tissue.
Tissue engineering – interdisciplinary field, which applies the principles
of engineering and the life sciences
To grow cells on biodegradable scaffolds (temporary supports) for
the cells to attach, proliferate and differentiate.
5. TERMINOLOGIES
Bone regeneration – intricate and well organised physiological process
of bone formation, seen in normal fracture healing and physiological
bone remodeling.
Acceleration of bone regeneration – fracture healing, filling bone
defects, atrophic non-unions, infection and osteoporosis.
6. MECHANISM OF BONE FORMATION
Osteoinduction – recruitment of immature cells and the stimulation of
these cells to develop into preosteoblasts, leading to de novo bone
formation in mesenchymal tissue.
Osteogenesis – new bone formation from osteocompetent cells in the
connective tissue of cartilage.
Osteoconduction – process of bone formation on a 3D implant or graft
through ingrowth of capillaries, mesenchymal tissue and
osteoprogenitor cells from the recipient host.
7. Autogenous bone grafts
“Gold standard” – other substitutes are compared to this in terms of
efficacy and outcome.
Provide osteoinduction, osteoconduction and osteogenesis
Drawbacks – Limited supply and donor site morbidity
Types:
Cancellous
Cortical
Free vascular transfers
8. Cancellous bone grafts
Works by all three principles of bone formation
Little initial structural support, but gains support quickly as bone is
formed
Graft donor site
Iliac crest (anterior or posterior) – most common
Metaphyseal bone – GT, distal femur, ends of tibia,
calcaneus, olecranon, distal radius, proximal humerus
9. Cortical bone grafts
Provides more structural support and less biologically active than
cancellous bone grafts
Used to fill defects
Prolonged time to revascularization as it has less porosity, surface area and
cellular matrix
Vascularized cortical grafts
Earlier incorporation – better structural support
Osteogenic and osteoinductive – graft includes periosteum
10. Bone graft harvesting
Harvesting of cancellous bone grafts
Cortical window using osteotomes, harvest with gouge or curette
Trephine instrument – percutaneous procedure
Harvesting of cortical bone grafts
Fibula (most common) – avoid distal fibula and head of the fibula
Iliac crest – cortical or tricortical pieces in shape to fill defects
11. Bone marrow aspirate
Osteogenic and osteoinductive – contains
osteoprogenitors and MSCs
Minimally invasive percutaneous procedure
Can be used as a stand alone procedure or can be
combined with an osteoconductive matrix
On an average, 1:50,000 nucleated marrow cells is a
stem cell
Augments bone regeneration but doesn’t reduce the
healing time
12. Bone marrow - RIA
Reamer – irrigator – aspirator system – surgical instrument that works
on MIS but provides large amount of osteogenic material
Provides concomitant irrigation and suction of IM contents
Less rise in IM temperature and pressures and a lesser magnitude of
adverse effect on immune system
13. Bone marrow - RIA
Reaming particles are centrifuged and
reused as an ideal autograft
Haematopoietic stem cells – all types of
blood cells
Bone marrow stem cells – osteogenic
properties
14. Allogenic bone grafts
Allografts – obtained from a living donor or human cadaver
Provides osteoconductive scaffold and structural support
No osteogenecity since they are devitalized due to processing
Plentiful in supply
Limited risk of infection – depends on the method of processing
Cancellous or cortical bone grafts
16. Allogenic bone grafts
Advantages:
Can be stored for long time (5 to 6years)
Cheaper than metallic implants
Easy to obtain and enormous availability of the graft
Decreased donor site morbidity
Biologic form of fixation
Immunologic response in very minimal
Soft tissue and ligament attachments are possible in tumor resection and
revision arthroplasty surgery
17. Allogenic bone grafts
Complications
Infection – Staph. epidermidis
Non-union
Graft fracture
Transmission of infectious diseases – Group A Strep, HIV, HCV, HBV,
Treponema pallidum
Graft resorption
Cartilage fragmentation
Implant failure
18. Demineralized bone matrix
Acid extraction of bone – leaves behind growth factors, non-collagenous
proteins and collagen
Osteoconductive and osteoinductive; devoid of antigenicity
Cannot provide structural support, but quickly revascularizes
Used to expand autologous CBG, with autologous bone marrow or with
synthetic bone graft substitutes
19. Demineralized bone matrix
Available in various forms
Gel, putty, paste, flexible sheet, pulverized granules, crushed chips or a fine
powder, and cortical chips within the matrix.
Used in repair of large bone defects and complex fractures, provided the
fixation is stable
20. Xenografts
Tissue graft is obtained from a species other than human
Bovine or Porcine bone – can be freeze dried / demineralized /
deproteinized
Only distributed as a calcified matrix
Coral based xenografts – calcium carbonate form, better resorption
Can be transformed into hydroxyapatite through a hydrothermal process
Wood based xenograft (Italian scientists in 2010) – wood are pyrolized
in an inert atmosphere, the carbonaceous residue is saturated with
calcium salts and finally reheated to obtain higly porous crystallized
material
21. Xenografts in Orthopaedics
Scarce validation in Orthopaedics, but good results in Dentistry
Advantages –
Easy availability
Osteoconductivity
Good mechanical properties and low cost
Complications –
Zoonosis – Bovine spongiform encephalopathy (BSE) and Porcine
endogenous retroviruses (PERV)
22. Graft incorporation
Hematoma formation – release of cytokines and growth factors
Inflammation – development of fibrovascular tissue
Vascular ingrowth – often extends to Haversian canals
Focal osteoclastic resorption of the graft
Intramembranous and/or endochondral bone formation on graft surfaces
23. BONE BANKS
Where allografts are processed,
sterilized and stored for future use
Goals of Bone banking
Preserve the physical integrity of the
implant and its inductive property
Reduce immunogenicity
Ensure sterility
DIRECTOR
OFFICER IN-CHARGE
RESEARCH FELLOW
TECHNICIAN
LAB ASSISTANT
ADVISORY BOARD
Dean
Orthopaedic HOD
Microbiology HOD
Pathology HOD
Forensic medicine
HOD
Anaesthesia HOD
24. BONE BANKS – LEGAL ISSUES
Getting the consent
Organ retrieval in medico-legal cases
Organ retrieval in unclaimed cases
CONSENT
Prescribed pattern as in the Transplantation Of Human Organs Act, 1994
In broader way – for using in educational, research and transplantation
purposes
Death at home – consent from the family as well as police clearance
25. BONE BANKS – LEGAL ISSUES
Organ retrieval in ML cases
No objection certificate from police
Proper consent from the donor(if living) or from the donor’s family in case
of cadaveric retrieval
Process should be carried out in the presence of forensic expert
Organ retrieval in unclaimed bodies
Time duration to identify the relatives – 48hours
Police, in case of ML cases; hospital authorities, in case of non-ML cases
Consent – by the person in-charge of the management of the prison or
hospital
26. BONE BANKS – ETHICAL ISSUES
Ethical issues should be handled at every step of the procedure
Promote voluntary tissue donation
Right to donation should be respected
Support the equitable allocation of allografts – equally distribute without
regard of race, religion, sex, social or economical status, material origin
and sexual orientation
Distributed on a priority basis to patients who are in need of life saving
and reconstructive procedures
27. BONE BANKS – ETHICAL ISSUES
Maintain confidentiality
Promote standards of practice – to ensure safety and effectiveness
Share information whenever permissible, for growth and equality of
professional knowledge
Advertising services – should be truthful, provide accurate information
and avoid unethical and misleading statements, emphasize community
support
28. BONE MORPHOGENIC PROTEINS
Discovered by Urist in 1965
They are the growth factors belonging to TGF – beta superfamily
They are dimeric molecules with 2 polypeptide chains of over 400AA
linked by a single disulphide bond and a characteristic cysteine knot is
seen in X-ray crystallography
Till date, more than 40 BMPs have been identified
They play an important role during embryogenesis and postnatal tissue
repair
Selective for osteogenesis – works by osteoinduction mechanism
30. BONE MORPHOGENESIS CASCADE
BMP 2 and 4 are expressed from
primitive MSCs and through out the
cascade
BMP 2, 6 and 9 – early stage of
differentiation
BMP 7 – expressed by osteogenic cells
by day 7
BMP 2, 4, 6, 7 and 9 – increase
osteocalcin expression and ALP
expression in preosteoblasts, leading to
mineralization
BMP 3 – osteoinductive, but also
inhibitory in the presence of BMP 2 and 7
32. BMPs in Orthopaedics
Treatment of non-union – as effective as autograft CBG
Augmentation of healing in fresh fractures
Autograft substitute in spinal fusion surgery – rhBMP-2, higher fusion rates
Healing of segmental / critical sized defects in bone
Congenital pseudo-arthrosis of tibia – along with autograft
AVN of femoral head
Cartilage repair – chondrocyte differentiation and regulation of SOX
proteins
Degenerative intervertebral disc repair – BMP 7
BMP specific antagonists – noggin, gremlin
33. BMP CARRIERS
Proteins are soluble in biological fluids – require appropriate carriers
Requirements to be met are – relative insolubility in physiological
conditions, biodegradability, protection against proteolytic activities,
substrate for cell adhesion and proliferation, immunological inertness,
mechanical stability in bridging bone defects, slow release of BMPs.
Optimal carrier – still remains to be found
Polymers – PLLA, PDLA, PGA and calcium phosphate materials
Gene therapy – at experimental stage
34. Other growth factors
Beta-FGF – powerful mitogenic factor and stimulates differentiation of
chondrocytes
VEGF – improved healing in large bone defects
IGF-1 and TGF-beta – modulate synthesis of the cartilage matrix
PDGF – stimulatory effect on fracture healing
PRP – rich in PDGF and TGF-beta mainly. Other growth factors and
cytokines are also involved
35. CELL BASED – STEM CELLS
Immature or undifferentiated cell which is capable of producing any
identical twin cell.
Source – somatic (adult) and embryonic stem cells
Somatic stem cells – hematopoietic, bone marrow stromal MSCs,
neural, dermal and several others
MSCs from bone marrow – hematopoietic stem cells and MSCs which
give rise to connective tissues
36. CELL BASED – STEM CELLS
Repair and regeneration of bone, cartilage, muscle, tendon and ligament
Still in the experimental stage – lack of studies into the biology of MSCs
in vivo in the fracture environment
High cost, time consuming, 2 stage surgery and risk of contamination
37. CELL BASED – COLLAGEN
Osteoconductive, without any structural support
ECM of bone has abundant collagen – mineral deposition, vascular
ingrowth and growth factor binding
Acts as carrier for growth and differentiation factors – only a delivery
system
Can be used along with other carriers like HA and TCP
Can be used as autograft extender
Enhances graft incorporation
38. CELL BASED – GENE THERAPY
A method of growth factor delivery
Genetic material is incorporated into the target cell (bone cells) –
promotes long lasting formation of factors required for bone
regeneration
Direct method – gene introduced directly into the non-union site
Indirect method – in vitro technique, safer as it is done under controlled
conditions
Biosafety, efficacy and cost are the major concerns
39. CERAMIC BASED
2/3rd of dry component of bone tissue – inorganic salts
Ca. phosphate, Ca. carbonate, Mg. phosphate and Ca. fluoride
Minerals exists as apatite crystals
Connection between HA and collagen fibers – decides hardness and
resistance of bone
40. CERAMIC BASED
Bone graft substitutes – Ca hydroxyapatite, TCP, Bioglass, Ca sulphate
Ideal pore size of a bioceramic material should be similar to that of
spongious bone
Size <10micron – allows body fluid circulation
Size >50micron – provides scaffold for bone-cell colonization
41. CALCIUM HYDROXYAPATITE
Synthetic HA is biocompatible form of natural HA
Osteoconductivity and biocompatibility is attributed to its chemical
similarity to the mineralized phase of bone
Useful as graft extender – excellent carrier for osteoconductive growth
factors and osteogenic cells
Brittle in nature, undergoes slow resorption – focus of mechanical stress
Can be combined with TCP / autogenous CBG for improved outcome and
faster resorption
42. TRICALCIUM PHOSPHATE
Similar to amorphous bone precursors
Stimulates osteoclastic resorption and osteoblastic new bone formation
within the resorbed implant
Surface layer ceramic enhances bonding with the adjacent bone of the
host
43. TRICALCIUM PHOSPHATE
HA and TCP are different in their biological response at the host site
TCP – better degradation; HA – more permanent
Two types – alpha TCP and beta TCP
Alpha TCP – made of porous granules, can replace bone and absorbed in
24months; soluble in body fluids
44. Beta TCP
Ultra porous, available in injectable formulation
Pores are interconnected, size varies from 1 to 1000microns
Imitates trabecular structure of cancellous bone
Facilitates activities of bone regeneration
Osteoconductive, microporous and has a homogenous ceramic sintered
structure
45. BIOACTIVE GLASS CERAMICS
Hard, non-porous materials – consists of calcium, phosphorous and
silicone dioxide
Various forms – soluble to non-resorbable; by varying the proportions of
its constituents
Surface bioactivity – enables the growth of osseous tissue
46. BIOACTIVE GLASS CERAMICS
Bone and bioactive glass forms mechanically strong bond between each
other through HA crystals
Brittle and prone to fracture with cyclic loading
SS fibers + bioglass – increased bending strength
47. CALCIUM SULPHATE
Osteoconductive bone-void filler
Biocompatible, bioactive and completely resorbable after 12weeks.
Indications – filling of bone cysts, benign bone lesions, cavitary /
segmental bone defect, as graft extenders in spinal fusion, and for filling
of bone graft donor sites
48. CORALLINE HYDROXYAPATITE
Based on natural material derived from sea coral – produces structure
made of CP (coralline)
Pore diameters between 200 and 500 micron
Osteoconductive substitute for bone grafting
It is brittle with low tensile strength but has high strength against
compressive forces
Can be used as a carrier for BMP and other growth factors
49. POLYMERS
Large molecules made from amalgamation of smaller molecules called
monomers
Properties of polymers – chemical, physical structure and molecular
weight of monomers, isomerism and crystallinity.
50. POLYMERS
Terminologies to be understood are –
Biodegradables – macromolecular degradation but no proof of elimination
Bioresorbables – bulk degradation and eliminated through natural ways
Bioerodibles - surface degradation and elimination of by-products along
with further resorption in vivo
Bioabsorbables – dissolve in body fluids without any process of
degradation
51. POLYMERS
Glass – transition temperature is defined as the one below which a
polymer is firm and tough and above which it is yielding and rubbery
Polymers in biomedical use have a Tg above body temperature
Polymers in Orthopaedics are viscoelastic in nature
Higher the molecular weight, more the viscosity and more gradual the
biodegradation
Examples: Poly-lactic acid, poly-glycolic acid, Polydioxanone – they are
poly-esters or poly-(alpha-hydroxy) acids
52. POLYMERS
Polylactic acid – made of Lactic acid which 3C molecule, small in size
and hydrophobic
Has two forms: Poly-L-lactic and Poly-D-Lactic acid
L-from is highly crystalline, whereas D-form is more amorphous
Poly-glycolic acid – hydrophilic, stronger than other polymers, but
degenerates faster than PLA
Polydioxanone (PDS) – produced by polymerization of para-dioxanone
Colorless (but violet dye is added), crystalline
PDS sutures – inherently stiff, extensively used in arthroscopic repairs
53. POLYMERS
Polycaprolactone (PCL) – was being used in drug delivery devices
Easy to manufacture and manipulate PCL
Can last in the tissues for 2-4 years
Biocompatible without any immunogenic, carcinogenic and thrombogenic
effects
54. POLYMERS - Degradation
Occurs in anticipatable format
Rate depends on initial molecular weight, crystallinity, composition,
porosity of the implant, its loading conditions and local vascularity
Chemical breakdown followed by loss of biological activity
55. POLYMERS - Degradation
Occurs by hydrolysis – breaks monomeric molecular bonds, decreases
the molecular weight and hence the mechanical strength of the implant
Rapid degradation – marked foreign body reaction, synovitis
Complications – sterile sinus tract formation, hypertrophic fibrous
encapsulation and osteolysis
56. POLYMERS – Mechanical properties
More viscoelastic than SS – superior properties of creep and stress
relaxation
Rapid degradation – due to enzymatic actions, areas of high metabolism
and blood flow, implants under load due to microfracture
Occurs at different pace – bending strength followed by shear strength
Mechanical strength can be improved by reinforcing techniques
57. POLYMERS – Applications
Bioabsorbable implants in Orthopaedics
Plates, nails and screws for fracture fixation
Pins for paediatric fractures
Suture materials, especially in sports medicine