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.

1. BONE GRAFTS
AND ITS
SUBSTITUTES
MODERATOR: DR. A. K. SIPANI
PROF & HOD, DEPT OF ORTHOPAEDICS, SMCH
PRESENTED BY: DR. SACHIN. M.
2ND YEAR PGT, DEPT OF ORTHOPAEDICS, SMCH

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

3. BONE GRAFT AND ITS SUBSTITUTES
NATURAL BONE GROWTH FACTOR CELL CERAMIC POLYMER
1. Autogenous
2. Bone marrow
3. Allogenic
4. Xenograft
1. BMPs
2. Beta – FGF
3. VEGF
4. IGF – 1
5. TGF – beta
6. PDGF
7. PRP
1. Stem cells
2. Collagen
3. Gene
therapy
1. Calcium hydroxy-
apatite
2. Tricalcium
phosphate
3. Bioactive glass
4. Calcium sulphate
5. Injectable ceramic
cements
1. Polylactic acid
2. Polyglycolic acid
3. Polydioxanone
CLASSIFICATION OF BONE 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

15. Allogenic bone grafts - Classification
ALLOGRAFTS
GRAFT ANATOMY GRAFT PROCESSING GRAFT STERILIZATION HANDLING
PROPERTIES
1. Cortical
2. Cancellous
3. Osteochondral
4. Soft tissue
1. Fresh frozen
2. Freeze dried
3. Demineralized
bone matrix
1. Sterile processed
2. Irradiated
3. Ethylene oxide
1. Powder
2. Particulate
3. Gel
4. Paste and putty
5. Chips
6. Strips and blocks
7. Massive

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

29. BMP SIGNALLING
PATHWAY
Two pathways
 Smad pathway
 MAP kinase pathway

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

31. APPLICATIONS OF VARIOUS BMPs

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