This document provides an overview of implant materials used in orthopaedics. It defines key concepts like stress, strain, modulus of elasticity and discusses properties of common implant materials like metals, ceramics and polymers. Metals discussed include stainless steel, titanium alloys and cobalt chrome alloys. Ceramics and calcium phosphates are used for their biocompatibility. Polymers like PMMA and UHMWPE are also reviewed. General tissue responses and potential complications are summarized. Recent advances aim to better match mechanical properties to bone.

1. OVERVIEW OF IMPLANT MATERIALS
IN ORTHOPAEDICS
MUKESH SUNDARARAJAN

2. OUTLINE
• INTRODUCTION
• BASIC CONCEPTS/DEFINITIONS
• COMMON ORTHOPAEDIC IMPLANT MATERIALS
& CLINICAL APPLICATIONS
• GENERAL TISSUE-IMPLANT RESPONSES
• COMPLICATIONS ASSOCIATED WITH IMPLANTS
• RECENT ADVANCES
• CONCLUSION

3. INTRODUCTION
• Implants are biomaterial devices
• Essential in the practice of orthopaedics
• A biomaterial is any substance or combination
of substances (other than a drug), synthetic or
natural in origin, that can be used for any period
of time as a whole or part of a system that
treats, augments or replaces any tissue, organ or
function of the body

4. BASIC CONCEPTS &
DEFINITIONS
• STRESS: The force applied per unit cross-
sectional area of the body or a test piece
(N/mm²)
• STRAIN: The change in length (mm) as a fraction
of the original length (mm)
- relative measure of deformation of the body or
a test piece as a result of loading

5. STRESS-STRAIN CURVE

6. DEFINITIONS
• YOUNG’S MODULUS OF ELASTICITY: The stress
per unit strain in the linear elastic portion of the
curve (1N/m² = 1Pascal)
• DUCTILITY: The ability of the material to
undergo a large amount of plastic deformation
before failure e.g metals
• BRITTLENESS: The material displays elastic
behaviour right up to failure e.g ceramics

7. DEFINITIONS
• STRENGTH: The degree of resistance to
deformation of a material
- Strong if it has a high tensile strength
• FATIGUE FAILURE: The failure of a material with
repetitive loading at stress levels below the
ultimate tensile strength
• NOTCH SENSITIVITY: The extent to which
sensitivity of a material to fracture is increased
by cracks or scratches

8. DEFINITIONS
• ULTIMATE TENSILE STRESS: The maximum
amount of stress the material can withstand
before which fracture is imminent
• TOUGHNESS: Amount of energy per unit volume
that a material can absorb before failure
• ROUGHNESS: Measurement of a surface finish of
a material
• HOOKE’S LAW → Stress α Strain produced
- The material behaves like a spring

9. BONE BIOMECHANICS
• Bone is anisotropic:
-it’s elastic modulus depends on direction of
loading
-weakest in shear, then tension, then
compression
• Bone is also viscoelastic → the stress-strain
characteristics depend on the rate of loading
• Bone density changes with age, disease, use and
disuse
• WOLF’S LAW → Bone remodelling occurs along
the line of stress

10. IDEAL IMPLANT MATERIAL
• Chemically inert
• Non-toxic to the body
• Great strength
• High fatigue resistance
• Low Elastic Modulus
• Absolutely corrosion-proof
• Good wear resistance
• Inexpensive

11. CLINICAL APPLICATIONS OF
ORTHOPAEDIC IMPLANTS
• Osteosynthesis
• Joint replacements
• Nonconventional modular tumor implants
• Spine implants

12. COMMON IMPLANT MATERIALS IN
ORTHOPAEDICS
• Metal Alloys:
- stainless steel
- Titanium alloys
- Cobalt chrome alloys
• Nonmetals:
- Ceramics & Bioactive glasses
- Polymers (Bone cement, polyethylene)

13. STAINLESS STEEL
• Contains:
- Iron (62.97%)
- Chromium (18%)
- Nickel (16%)
- Molybdenum (3%)
- Carbon (0.03%)
• The form used commonly is 316L (3%
molybd, 16% nickel & L = Low carbon
content)

14. STAINLESS STEEL
• Advantages:
1. Strong
2. Relatively ductile
3. Biocompatible
4. Relatively cheap
5.Reasonable coorsion
resistance
• Used in plates, screws,
IM nails, ext fixators
• Disadvantages:
- Susceptibility to
crevice and stress
corrosion

15. TITANIUM ALLOYS
• Contains:
- Titanium (89%)
- Aluminium (6%)
- Vanadium (4%)
- Others (1%)
• Most commonly orthopaedic titanium alloy
is TITANIUM 64 (Ti-6Al-4v)

16. TITANIUM ALLOYS
• Advantages:
1. Corrosion resistant
2. Excellent
biocompatibility
3. Ductile
4. Fatigue resistant
 5 Low Young’s modulus
 6. MR scan compatible
• Useful in halos, plates,
IM nails etc.
• Disadvantages:
1. Notch sensitivity
2.poor wear
characteristics
3.Systemic toxicity –
vanadium
4. Relatively expensive

17. COBALT CHROME ALLOYS
• Contains primarily cobalt (30-60%)
• Chromium (20-30%) added to improve
corrosion resistance
• Minor amounts of carbon, nickel and
molybdenum added

18. COBALT CHROME ALLOYS
• Advantages:
1.Excellent resistance
to corrosion
2.Excellent long-term
biocompatibility
3.Strength (very
strong)
• Disadvantages:
1.Very high Young’s
modulus
- Risk of stress
shielding
2. Expensive

19. YOUNG’S MODULUS AND DENSITY OF
COMMON BIOMATERIALS
MATERIAL YOUNG’S MODULUS (GPa) DENSITY (g/cm³)
Cancellous bone 0.5-1.5 -
UHMWPE 1.2 -
PMMA bone cement 2.2 -
Cortical bone 7-30 2.0
Titanium alloy 110 4.4
Stainless steel 190 8.0
Cobalt chrome 210 8.5

20. COMPARISON OF METAL ALLOYS
ALLOY Young’s modulus
(GPa)
Yield strength
(MPa)
Ultimate tensile
strength (MPa)
Stainless Steel 316L 190 500 750
Titanium 64 110 800 900
Cobalt chrome
F562
230 1000 1200

22. CERAMICS
• Compounds of metallic elements e.g
Aluminium bound ionically or covalently with
nonmetallic elements
• Common ceramics include:
- Alumina (aluminium oxide)
- Silica (silicon oxide)
- Zirconia (Zirconium oxide)
- Hydroxyapatite (HA)

23. CERAMICS
• Advantages:
1.Chemically inert &
insoluble
2.Best
biocompatibility
3. Very strong
4. Osteoconductive
• Disadvantages:
1. Brittleness
2.Very difficult to
process – high
melting point
3. Very expensive

24. CERAMICS
• Used for femoral head component of THR
- Not suitable for stem because of its
brittleness
• Used as coating for metal implants to
increase biocompatibility e.g HA

25. POL
YMERS
• Consists of many repeating units of a basic
sequence (monomer)
• Used extensively in orthopaedics
• Most commonly used are:
-Polymethylmethacrylate (PMMA, Bone
cement)
-Ultrahigh Molecular Weight Polyethylene
(UHMWPE)

26. PMMA (BONE CEMENT)
• Mainly used to fix prosthesis in place
- can also be used as void fillers
• Available as liquid and powder
• The liquid contains:
→ The monomer N,N-dimethyltoluidine (the
accelerator)
→ Hydroquinone (the inhibitor)

27. PMMA
• The powder contains:
- PMMA copolymer
- Barium or Zirconium oxide (radio-opacifier)
- Benzoyl peroxide (catalyst)
• Clinically relevant stages of cement reaction:
1. Sandy stage
2. Mixture appears stringy
3. Cement is doughy
4. Cement is hard

28. UHMWPE
• A polymer of ethylene with MW of 2-6million
• Used for acetabular cups in THR prostheses
• Metal on polyethylene is gold standard
bearing surface in THR (high success rate)
• Osteolysis produced due to polyethylene
wear debris causes aseptic loosening

30. THR -IMPLANT BEARING SURFACES
• Metal-on-polyethylene • Metal-on-metal

31. BEARING SURFACES
• Ceramic-on- • Ceramic-on-ceramic
polyethylene

32. BIODEGRADABLE POLYMERS
• Ex; Polyglycolic acid, Polylactic acid,
copolymers
• As stiffness of polymer decreases, stiffness of
callus increases
• Hardware removal not necessary (reduces
morbidity and cost)
• Used in phalangeal fractures with good
results

33. GENERAL TISSUE-IMPLANT
RESPONSES
• All implant materials elicit some response from
the host
• The response occurs at tissue-implant interface
• Response depend on many factors;
- Type of tissue/organ;
- Mechanical load
- Amount of motion
- Composition of the implant
- Age of patient

34. TISSUE-IMPLANT RESPONSES
• There are 4 types of responses (Hench & Wilson,
1993)
1. Toxic response:
- Implant material releases chemicals that
kill cells and cause systemic damage
2. Biologically nearly inert:
- Most common tissue response
- Involves formation of nonadherent fibrous
capsule in an attempt to isolate the implant
- Implant may be surrounded by bone

35. TISSUE-IMPLANT RESPONSES
- Can lead to fibrous encapsulation
-Depend on whether implant has smooth
surface or porous/threaded surface
- Ex; metal alloys, polymers, ceramics
3. Dissolution of implant:
-Resorbable implant are degraded
gradually over time and are replaced by
host tissues
- Implant resorption rate need to match tissue -
repair rates of the body

36. TISSUE-IMPLANT RESPONSES
- Ex; Polylactic and polyglycolic acid polymers
which are metabolized to CO2 & water
4. Bioactive response:
-Implant forms a bond with bone via chemical
reactions at their interface
-Bond involves formation of hydroxyl-
carbonate apatite (HCA) on implant surface
creating what is similar to natural interfaces
between bones and tendons and ligaments
- Ex; hydroxyapatite-coating on implants

37. COMPLICATIONS
• Aseptic Loosening:
-Caused by osteolysis from body’s reaction to
wear debris
• Stress Shielding:
-Implant prevents bone from being properly
loaded
• Corrosion:
-Reaction of the implant with its environment
resulting in its degradation to oxides/hydroxides

38. COMPLICATIONS
• Infection:
- colonization of implant by bacteria and
subsequent systemic inflammatory response
• Metal hypersensitivity
• Manufacturing errors
• VARIOUS FACTORS CONTRIBUTE TO IMPLANT
FAILURE

39. RECENT ADVANCES
• Aim is to use materials with mechanical
properties that match those of the bone
• Modifications to existing materials to
minimize harmful effects
- Ex; nickel-free metal alloys
• Possibility of use of anti-cytokine in the
prevention of osteolysis around implants
• Antibacterial implant

40. CONCLUSION
• Adequate knowledge of implant materials is
an essential platform to making best choices
for the patient
• No completely satisfying results from use of
existing implant materials
• Advances in biomedical engineering will go a
long way in helping the orthopedic surgeon
• The search is on…

41. THANK YOU