This document provides an overview of metallurgy in orthopedics. It discusses the timeline of metallic implant development, from early use of bone pegs and brass wire to modern alloys like titanium and cobalt chromium. Key topics covered include the ideal properties of implant materials, commonly used metals like stainless steel, titanium and cobalt alloys, and problems that can occur like corrosion, stress shielding and fatigue failure. The document aims to define important metallurgical concepts and provide context on the role and evolution of metals in orthopedic surgery.

1. Metallurgy in
Orthopaedics
Dr. Subhash Kumar Das
Resident
Department of Orthopaedics
SBH

2. Contents
• History
• Introduction
• Basic contents and definition
• Ideal Metal for Implant
• Properties of implant material
• Commonly Used Metals in Orthopaedic
Implants
• Problems Encountered in Orthopaedic Implant

3. Metals enjoy wide application in Orthopaedics,
as structural and load bearing devices for
fracture fixation and implants for joint
replacement.

4. TIMELINE
• Bone pegs -1500
• Brass wire -1775 (wire suture)
• Ivory rod -1890
• Steel plate (Lane) -1905 (Vanadium steel)
• Silver rod -1913
• Steel alloys -1926 (18-8 type SSMo)
• Vitalium (Stellite) -1929 (CC)
• Titanium - 1950s
• Ceramics -1970
• Biodegradable -1980

5. HISTORY
• Initially pure metals: corrosion
• Developments in metal refining and processing –
first half of the 20th century - wartime needs
• Led to - improved materials that were rapidly,
although empirically, adapted by surgeons for use
in fracture fixation.

6. Introduction
• 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.
• 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.

7. • An ideal implant material should be inert,
nontoxic to the body, and absolutely corrosion-
proof.
• It should be inexpensive, easily worked, and
mouldable in a variety of shapes without
expensive manufacturing techniques.

8. • It should have great strength and high
resistance to fatigue .
• Such a material is not available at present .

9. 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
Basic concept and definition

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

11. • STRAIN: it is defined as the change in linear
dimensions of the body resulting from the
application of a force or a load.
• Tensilestrain :is increase in length of astraight
edgeor a line drawn on abody.
• Compression strain :is decrease in length of
straight edgeor a line drawn on abody.
• Shearstrain : is bya change in angular
relationship of two lines drawn on the surface

12. Young’s Modulus of Elasticity
• It sa measure to expressthe stiffness(ability to
resist deformation) or rigidity under normal
stress.
• Its calculated by dividing the (stress) by
amount of deflection (strain).
• Ahigh modulus of elasticity indicates that
the material is stiff.
• Bone has a lower modulus of elasticity than
the metal .

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

15. • 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.

16. ULTIMATE TENSILE STRENGTH(U.T.S)
• Themaximum amount of stress the material canwithstand
before which fracture isimminent.
• The U.T.Sis linearly correlated to the hardness of the metal.
BRITTLENESS:
• Amaterial 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.

17. DUCTILITY:
• Theductility of an implant material
characterizes its ability to be deformed
under tensile stress and to be stretched
into wire without fracture.
• Determines the degree to which the plate, for
instance, canbe countered.
• Materials of high strength such as titanium alloys or
pure titanium offer less ductility than steel.

18. STRENGTH :
degreeof resistanceto 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: Theextent towhich
sensitivity of a material to fracture is increasedby
cracks or scratches.

19. TOUGHNESS: Amountof energyper unitvolume that a
material can absorb beforefailure
ROUGHNESS: Measurement of a surface finish of
a material
HOOKE’S LAW → when a material is loadedin
the elastic zone, the stress is proportional to the
strain
Stress α Strain

20. 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 LAW → Bone remodelling occurs along
the line of stress

21. • BIOCOMPATIBLE– NON-TOXIC, NON-CARCINOGENIC,
NON- IMMUNOGENIC
• BIOINERT– NOTELICIT ARESPONSE
• STRENGTH– COMPRESSIVE, TENSILE, TORSIONAL
• FATIGUERESISTANCE, CONTOURABILITY
• CORROSIONANDDEGRADATION RESISTANCE
• IMAGINGCOMPATIBLE– MRI, CTSCAN
• ECONOMICAL

22. 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

23. • PLATES,SCREWS,PINSANDRODS
CONTAINS:
- Iron(62.97%)
- Chromium (18%)
- Nickel (16%)
- Molybdenum (3%)
- Nitrogen (0.1%)
-Carbon (0.03%)
COMMONLYUSEDTYPESOFSTAINLESSSTEEL
ARE AISI 316 L,AISI 440 B.

24. Advantages:
1. Strong
2. Relatively ductile
3. Biocompatible
4. Relatively cheap
5. Reasonable corrosion resistance
Disadvantages :
-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.

26. Contains:
- Titanium (89%)
- Aluminium (6%)
- Vanadium (4%)
- Others (1%)
Most commonly orthopaedic titanium alloy is
TITANIUM64 (Ti-6Al-4v)

27. Advantages:
1. Corrosion resistant
2. Excellent biocompatibility
3. Ductile
4. Fatigue resistant
5 LowYoung’smodulus
6. MRI scan compatible
Disadvantages:
1. Notch sensitivity
2. poor wear characteristics
3. Systemic toxicity – vanadium
4. Relatively expensive
Useful in halos, plates, IM nails etc.

28. MAINLYHIPANDKNEEPROSTHESES
Contains primarily cobalt (30-60%)
•Chromium (20-30%) added to improve corrosion
resistance
•Minor amounts of carbon, nickel andmolybdenum added

29. Advantages:
1. Excellent resistance to corrosion
2. Excellent long-term biocompatibility
3. Strength (very strong)
Disadvantages:
1. Veryhigh Young’s modulus-Risk of stress
shielding
2. Expensive
3. Nickel sensitivity.
Used in making arthroplasty implants .

31. 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
NEWER METALS

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

33. Problems Encountered in
Metal Implants

34. EARLYINFECTIONS
Through skin,air or surgical instrumentation
Infection doesn’t subside bcoz revascularisation blocked by implant
LATEINFECTIONS
Hematogenous in origin
bacteria protected by glycocalyx present on the coating formed on the
surface of the foreign material
INFECTIONS

35. INFLAMMATION-METALLOSIS
OSTEOLYSISANDLOOSENING
STERILEABSCESS
NEOPLASIA

36. FATIGUE FAILURE

37. Fatigue Fractures
• 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.

38. • 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

39. Stress shielding
• Refers to reduction in bone density as a result of
removal of typical stress from the bone by an
implant (for instance , femoral component of hip
prosthesis).
• 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.
• This is because of Wolff’s law , bone in healthy
person remodels in response to the loads it is
placed under.

40. Gradual degradation of metals by electrochemical
attack ,and is therefore a concern when placed in
electrolytic environment of body.
Effects- tissue inflammation and
necrosis,weakening of implant
Corossion

41. 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
occurs where metals and alloys depends on oxide film for corrosion protection /
fretting
components have a relative movement against one another
Pit corrosion-
A local form of crevice corrosion due to abrasion produces a pit

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

43. References
• Theelements of fracture fixation; Anand JThakur
• Textbookof operative orthopedics;campbell
• Orthopedic trauma; GSKulkarni