metals used in orthopedic implants

1. DATE: 03.05.2017
PRESENTED BY : MODERATORS:
DR RAKSHITH KUMAR K DR RUDRAMUNI.A.K
P.G. in orthopaedics PROFESSOR AND UNIT HEAD
JJM MEDICAL COLLEGE
DAVANAGERE DR RAGHU KUMAR
Professor

2.  HISTORY
 INTRODUCTION
 BASIC CONCEPTS AND DEFINITIONS
 IDEAL METALS FOR IMPLANTS
 PROPERTIES OF IMPLANT MATERIAL
 COMMONLY USED METALS IN ORTHOPEDIC IMPLANTS
 PROBLEMS ENCOUNTERED IN METAL IMPLANTS
 CONCLUSION

3.  A variety of metals have been used in the past
for fracture fixation.
 Lane (1905) used bone plates made from
vanadium steel.
 Titanium was first used in bone surgery in
1950 s.
 Lapeyode and sicre (1775) used metal wires to
repair a fracture.
 von Langenbeck inserted a metal nail into a
fractures hip in 1840.

4.  The implants for fracture fixation are commonly
made of stainless steel and titanium
alloys.
 ALLOYS are materials composed of 2 or more
elements, one of which is a metal.
 A surgical implant may be defined as an
object made from a non-living material that is
inserted into a human body, where it is
intended to remain for a significant period of
time in order to perform a specific function.

5.  Implants are biomaterial devices.
A biomaterial is
 Any substance or combination of substances.
 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.

6.  In internal fixation, implant material of choice is
still metal, which offers high stiffness and
strength, good ductility and biologically well
tolerated.
 Today s metal, implants are made either of
stainless steel or titanium.
 Metals used for internal fixation must confirm
certain basic requirements like reliable
function and minimal side effects.

7.  SUCCESS OF AN IMPLANT IS DETERMINED BY
1.CONDITION OF THE PATIENT
2.SURGEON’S SKILL
3.BIOCOMPATIBILITY OF IMPLANT
4.MECHANICAL PROPERTIES
5.WEAR/CORROSION RESISTANCE

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

11.  STRAIN : it is defined as the change in linear
dimensions of the body resulting from the
application of a force or a load.
 Tensile strain is increase in length of a straight
edge or a line drawn on a body.
 Compression strain is decrease in length of
straight edge or a line drawn on a body.
 Shear strain is by a change in angular
relationship of two lines drawn on the surface

12.  DEFORMATION: Any force applied to a body
will change the shape of the body either
temporarily or permanently. Change of shape is
called deformation , represents change in
dimension.
 FORCE: is an action or influence, such as
push or pull, which when applied to a free body,
tends to accelerate or deform it.

13. LOAD: is a force sustained by a body. If no
acceleration results from the application of a load,
it follows that a force of equal magnitude and
opposite direction opposes it.
STRESS: it is defined as the internal resistance to
deformation or the internal force generated within
the substances as a result of application of
external load.
Stress = load/area on which load acts

14.  There are 3 types of stress –
1.compressive stress acts perpendicular to a
2.Tensile stress given plane
3.shear stress – acts in the direction parallel to
the given plane

15.  It s a measure to express the stiffness(ability to
resist deformation) or rigidity under normal
stress.
 Its calculated by dividing the load (stress) by
amount of deflection (strain).
 A high modulus of elasticity indicates that the
material is stiff.
 Bone has a lower modulus of elasticity than the
metal .

17. The yield point : or limit of proportionality
denotes the end of the elastic region of the
curve.
 It’s a point on the curve at which a marked
increase in strain occurs without significant
increase in stress or load or it’s the stress
beyond the elastic limit that results in
permanent bending or deformation.

18. ULTIMATE TENSILE STRENGTH(U.T.S)
The maximum amount of stress the material can withstand
before which fracture is imminent.
 With the application of a load, a maximum stress will be
achieved. This is the ultimate tensile strength.
 When exceeded, the metal will break.
 The U.T.S is linearly correlated to the hardness of the metal.
BRITTLENESS: A material is brittle if, when subjected to
stress, it breaks without significant plastic deformation.
 Brittle materials absorb relatively little energy prior to
fracture, even those of high strength.
 Breaking is often accompanied by a snapping sound.

19. DUCTILITY :
 The ductility of an implant material
characterizes its tolerance to plastic
deformation.
 The ductility of a material determines the
degree to which the plate, for instance, can be
countered.
 Materials of high strength such as titanium
alloys or pure titanium offer less ductility than
steel.

20.  Relative values of Young's
modulus of elasticity
(numbers correspond to
numbers on illustration to
right)
1. 1.Ceramic (Al2O3)
2. 2.Alloy (Co-Cr-Mo)
3. 3.Stainless steel
4. 4.Titanium
5. 5.Cortical bone
6. 6.Matrix polymers
7. 7.PMMA
8. 8.Polyethylene
9. 9.Cancellous bone
10. 10.Tendon / ligament
11. 11.Cartilage

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

22.  TOUGHNESSTOUGHNESS: Amount of energy per unit volume
that a material can absorb before failure
 ROUGHNESS: Measurement of a surface finish
of a material
 HOOKE’S LAWHOOKE’S LAW → when a material is loaded in
the elastic zone, the stress is proportional to the
strain
Stress α Strain

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

24. Several organisation exist that have
developed standard for materials:
 A.S.T.M – American Society for Testing and Materials.
 A.N.S.I – American National Standard Institutes.
 A.I.S.I – American Iron and Steel Institute.
 I.O.S – International Organisation for
Standardisation.
 B.S.I – British Standard Institute.
 I.S.I – Indian standard Institute.
 B.I.S – Bureau of Indian Standards.

25. • BIOCOMPATIBLE – NON-TOXIC, NON-CARCINOGENIC, NON-
IMMUNOGENIC
• BIOINERT – NOT ELICIT A RESPONSE
• STRENGTH – COMPRESSIVE, TENSILE, TORSIONAL
• FATIGUE RESISTANCE, CONTOUR ABILITY
• CORROSION AND DEGRADATION RESISTANCE
• IMAGING COMPATIBLE – MRI, CT SCAN
• ECONOMICAL

26.  Any given material has three properties –
1.Mechanical
2.Physical
3.Chemical
 Mechanical and physical properties control
active functional characteristics of the implants
 Whereas chemical properties determine
biocompatibility between implant and
environment of the body.

27.  Elasticity - is the ability of a material to recover its original
shape after deformation on removal of the force or load.
 Plasticity – is the ability of a material to be formed to a new
shape without fracture and retain that shape after load
removal.
 Viscosity – this property is exhibited by viscoelastic
materials. A material that exhibits a stress-strain relationship
that is dependent on duration of applied load and the rate by
which the load is applied (strain rate)
 Strength – is the ability of a material to resist an applied
force without rupture.

28. 1.Radio transperancy – the implants should
be sufficiently opaque to x rays so that they can
be located and examined during and after
implantation.
 The factor which influences the absorbtion of x
rays is density and there is a logarithmic
increase in absorbtion with increase in density.
2.Heat and irradiation – these are related to
the methods of sterilization of the implant.

29.  Chemical properties determine the
biocompatibility between implantable materials
and the environment of the body.
1.Corrosion
2.Immunity
3.passivation

30.  MAJOR METALS USED
1.IRON BASED ALLOYS (STAINLESS STEEL)
2.COBALT BASED ALLOYS
3.TITANIUM BASED ALLOYS
 NEWER METALS
1.OXINIUM
2.TRABECULAR METAL
3.NITINOL-NICKEL TITANIUM ALLOYS

31.  PLATES,SCREWS,PINS AND RODS
 CONTAINS:
- Iron (62.97%)
- Chromium (18%)
- Nickel (16%)
- Molybdenum (3%)
- Nitrogen (0.1%)
- Carbon (0.03%)
 COMMONLY USED TYPES OF STAINLESS STEEL
ARE AISI 316 L,AISI 440 B.

32.  AdvantagesAdvantages:
1. Strong
2. Relatively ductile
3. Biocompatible
4. Relatively cheap
5. Reasonable corrosion resistance
 DisadvantagesDisadvantages:
- Susceptibility to stress corrosion
 Used in plates, screws, IM nails, ext fixators
The chromium forms an oxide layer when dipped in nitric
acid to reduce corrosion and the molybdenum increases
this protection when compared to other steels.

34.  ContainsContains:
- Titanium (89%)
- Aluminium (6%)
- Vanadium (4%)
- Others (1%)
 Most commonly orthopaedic titanium alloy is
TITANIUM 64 (Ti-6Al-4v)

35.  AdvantagesAdvantages:
1. Corrosion resistant
2. Excellent biocompatibility
3. Ductile
4. Fatigue resistant
5 Low Young’s modulus
6. MRI scan compatible
 Disadvantages:Disadvantages:
1. Notch sensitivity
2. poor wear characteristics
3. Systemic toxicity – vanadium
4. Relatively expensive
 Useful in halos, plates, IM nails etc.

37.  MAINLY HIP AND KNEE PROSTHESES
o Contains primarily cobalt (30-60%)
o Chromium (20-30%) added to improve corrosion
resistance
o Minor amounts of carbon, nickel and molybdenum
added

38.  AdvantagesAdvantages:
1. Excellent resistance to corrosion
2. Excellent long-term biocompatibility
3. Strength (very strong)
 DisadvantagesDisadvantages:
1. Very high Young’s modulus-Risk of stress
shielding
2. Expensive
3. Nickel sensitivity.
Used in making arthroplasty implants.

41.  OXINIUM
• OXIDIZED ZIRCONIUM IS
A METALLIC ALLOY WITH A CERAMIC SURFACE.
• ZIRCONIUM: A BIOCOMPATIBLE METALLIC
ELEMENT IN THE SAME FAMILY AS TITANIUM
• COMBINES THE BEST OF BOTH METAL AND
CERAMICS.
• EXCELLENT FRACTURE TOUGHNESS LIKE COBALT
CHROME.
• CERAMIC SURFACE THAT OFFERS OUTSTANDING
WEAR RESISTANCE

42. o Elemental tantalum metal
o Vapor deposition techniques that create a metallic
strut configuration similar to trabecular bone.
o Crystalline microtexture is conductive to direct bone
apposition.
o Interconnecting pores
• 80% porous
• 2-3 times greater bone ingrowth compared to
conventional porous coatings
• Double the interface shear strength

45.  EARLY INFECTIONS
THROUGH SKIN,AIR OR SURGICAL INSTRUMENTATION
INFECTION DOESN’T SUBSIDE BCOZ REVASCULARISATION BLOCKED
BY IMPLANT
 LATE INFECTIONS
HEMATOGENOUS IN ORIGIN
BACTERIA PROTECTED BY GLYCOCALYX PRESENT ON THE COATING FORMED
ON THE SURFACE OF THE FOREIGN MATERIAL

46.  Means well tolerated by body tissues.
 All modern alloys are well tolerated by body tissues in
bulk form.
 The best tolerated is titanium in pure form.
 For this extreme biocompatibility, pure titanium is used
as porous coating for surfaces of total hip prosthesis.
 In dust form, as wear particles, all these alloys even
pure titanium may trigger osteolysis if they land in the
tissues around total hip prosthesis.
 Metallic wear particles in the soft tissues paint the
tissues black. This is called METALLOSIS.

47.  INFLAMMATION-METALLOSIS
 OSTEOLYSIS AND LOOSENING
 STERILE ABSCESS
 NEOPLASIA

48.  BRITTLE FAILURE –
screw head with poor ductility.
 PLASTIC FAILURE –
load > endurance limit.
IMPLANT BENDS PERMANENTLY.
 FATIGUE FAILURE – Repititive cyclical
loading.
•The endurance limit, also known as fatigue limit, is a stress
level below which a material has an "infinite" life. Infinite life is
commonly considered to be 1 million cycles.

50.  THE EVERYDAY LIFE PUTS ASTOUNDING DEMANDS ON THE
MATERIALS OF THE TOTAL HIP JOINT.
 THE SHAFT OF THE MODERN TOTAL HIP PROSTHESIS WILL
SUSTAIN SUCH LARGE LOADS, IF THEY OCCUR OCCASIONALLY;
THE SHAFT MAY FAIL.
 HOWEVER, EVEN FOR LOWER LOADS, IF THEY OCCUR VERY
OFTEN, THE METAL ALLOY WILL SUCCUMB TO THE SO- CALLED
FATIGUE FAILURE AND BREAK.
 THERE IS A LIMIT, HOW MUCH REPETITIVE LOADS THE
PROSTHESIS WILL EVENTUALLY SUSTAIN. THIS LIMIT IS
SPECIFIC FOR EVERY FORM OF THE TOTAL HIP PROSTHESIS
AND FOR THE METAL ALLOY USED FOR MANUFACTURE.
 ABOVE THIS LIMIT, THE PROSTHETIC SHAFT WILL SUSTAIN THE
FATIGUE FRACTURE.

51.  STRESS SHIELDING - A TOO STIFF SHAFT.
 THE PROSTHETIC SHAFT TAKES OFF A PART OF THE STRESS
THAT WALKING AND OTHER EVERYDAY ACTIVITIES PUT ON
THE UPPER PART OF THE THIGH BONE HOLDING THE
PROSTHESIS.
 A TOO STIFF SHAFT OF A TOTAL HIP PROSTHESIS "STRESS
SHIELDS" THE UPPER PART OF THE THIGH BONE TOO
MUCH.
 THIS IS SO BECAUSE THE ALLOYS USED FOR FABRICATION OF
THE SHAFT ARE MUCH STIFFER THAN THE SKELETON OF THE
THIGH BONE.
 THE SHIELDED BONE DOES NOT THRIVE, LOSES ITS
SUBSTANCE, AND BECOMES WEAK.
 THE TOTAL HIP JOINT HAS WEAK ANCHORAGE IN A WEAK
SKELETON AND MAY FAIL .

52.  DAMAGE OF MATERIAL DUE TO ACTION OF THE
ENVIRONMENT
 EFFECTS- TISSUE INFLAMMATION AND
NECROSIS,WEAKENING OF IMPLANT

53. Stress corrosion-
The presence of a crack due to stress
Galvanic corrosion-
due to two different metals being used e.g.
stainless steel screws and titanium plate.
Crevice corrosion / fretting
occurs where components have a relative
movement against one another
Pit corrosion-
A local form of crevice corrosion due to
abrasion produces a pit

54.  PRECAUTIONS
1.Use of corossion resistant material.
2.Use of same material for different parts of
same implant.
3.Avoid damages during transportation.
4.Avoid instability of fixation.

55. • NICKEL – CYTOTOXIC AGENT & ALLERGEN
• TITANIUM
– INHIBIT OSTEOCLASTIC ACTIVITY AND
REDUCE OSTEOBLASTIC PROTEIN SYNTHESIS
(THOMPSON & PULEO 1996).
– CONTACT DERMATITIS (LAYOR ET AL. 1991).
• COBALT-CHROMIUM
– METALLOSIS, OSTEOLYSIS,
– FORMATION OF SOFT TISSUE MASSES,
– INFLUENCE PROLIFERATION AND FUNCTION
OF
HUMAN OSTEOBLASTS

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

57.  Adequate knowledge of implant materials is an
essential platform to making best choices for
the patient
 Most of the existing implant material falls short
of one or the other criteria to be an IDEAL
IMPLANT.
 Advances in biomedical engineering will go a
long way in helping the orthopedic surgeon
 The search is on…

58.  Textbook of operative orthopedics;campbell
 Orthopedic trauma; G S Kulkarni
 The elements of fracture fixation; Anand J Thakur
 Materials and orthopedic surgery ; Dana C Mears
 A primer of orthopedic biomechanics ; Cochran
 Journals and internet.

59. THANK
YOU