The document discusses implant failure in orthopedic surgery. It covers various causes of implant failure including issues related to the implant materials, surgical technique, and patient factors. Some key causes mentioned are corrosion, fatigue failure, improper implantation leading to instability, and infection. The document emphasizes that implant failure is usually due to multiple interconnected factors rather than a single issue. Understanding biomechanical principles and limitations of implants is important for surgeons to prevent failure.

1. IMPLANT FAILURE
Presenter : Dr. Saumya Agarwal
Junior resident Dept of Orthopaedics
J.N.Medical College and Dr. Prabhakar
Kore Hospital and MRC, Belgaum

2. 1. Introduction
2. Methods Of Metal Working And Their Effects On
Implants
3. Terminologies in Biomechanics
4. Characteristics and behaviour of implant materials
5. Materials Used In Orthopaedic Implants

3. 6. Causes of implant failure
7. Corrosion
8. Screw failure
9. Implant failure in plating
10. Implant failure in IMIL nailing

4. INTRODUCTION
Implants:
Implant is an iatrogenic foreign body
deliberately induced by surgeon into human
body where it is intended to remain for a
significant period of time in order to perform a
specific function

5. • In orthopaedics, implants are used to
reconstruct a fractured bone
• screws
• plates
• nails
• wires
• components- external fixator
help orthopaedic surgeon

6. Implant Failure
An implant is said to have failed if it ceases to
perform the function for which it is inserted
may be due to :
• Deformation
• Fracture of implant
• Loosening of fixator
• If implant causes undesirable consequences like
pain, infection or toxicity leading to rejection

7. Saying”
the true cause of implant failure is not the
failure of device but infact the failure of surgeon to
understand the principles of fixation and limitations
of implant
It is essential for an orthopaedician to know the
biomechanical aspects of the tools of his trade

8. Defect in manufacturing is
also a major concern

9. Methods Of Metal Working And Their
Effects On Implants
• Forging
• Casting
• Rolling and drawing
• Milling
• Coldworking
• Case hardening
• Maching
• Broaching
• Polishing and passivation

10. Forging

11. Casting

12. Rolling and
drawing

13. Milling

14. Coldworking

15. Case hardening

16. Broaching

17. Polishing and Passivation

18. Terminologies in Biomechanics:
Force:
Is an action or influence, such as pull or push
which when applied to a free body tends to
accelerate or deform it

19. Load:
refer to an application of a force to an object
5 types-
1. Axial load
- tension – traction or pulling
- compression – pressing together
2. Bending load
- simple three point
- cantilever
3. Torsion twisting
4. Direct shear - II forces in opposite direction
5. Contact load

21. A body under load reacts in two ways ;
• It deforms – changes it shape strain
• It generates internal force stress

22. Deformation:
change of shape
represents a change in dimension

23. Strain :
a technical term used to express deformation
defined as :
change in linear dimensions of a body
resulting from application of a force or a load
strain = change in length/original length

24. 3 types :
1. Compressive strain :
represented by ↓ in length of straight
edge or a line drawn on a body
2. Tensile strain :
represented by ↑ in length of straight
edge or a line drawn on a body
3. Shear strain :
represented by change in angular
relationship of two lines drawn on the surface

26. Stress:
the internal forces resisting deformation
are called stress
defined as :
internal force generated within a
substance as a result of application of external
load
stress = load / area on which load acts

27. 3 types :
1. Compressive stress
acts perpendicular
. to a given plane
2. Tensile stress
3. Shear stress
acts parallel to given plane

28. Stress risers (stress concentrators)
a point at which stress is appreciably higher than
elsewhere due to geometry of the stressed object
is called a stress riser
Stress riser produces ↑ local stresses , which may
be several times higher than those in the bulk of
the material and may lead to local failure.

29. Stresses also concentrate around discontinuities
such as
• holes
• sharp angles
• notches
• grooves
• threads
in a structure all stress risers greatly
weaken a structure

30. Stress Protection or Shielding
used to describe the reaction of bone to unloading
when a fractured bone is fixed with plate , both bone
and plate share the limb load
bone is relieved of some of its original load by plate
results in reduced density of bone under plate
because of reduced functional stimulation

32. Characteristics and behaviour of
implant materials
Three properties:
1. Mechanical
controls functional
. characteristics of implants
2. Physical
3. Chemical
determine biocompatibility between
implant and environment of body

33. Stress - strain curve

34. Mechanical Properties
Four properties :
1. Elasticity
2. Plasticity
3. Viscosity
4. Strength

35. Elasticity :
is the ability of a material to recover its
original shape after deformation on removal
of the force or load

36. Plasticity :
is the ability of a material to be formed
to a new shape without fracture and retain
that shape after load removal

37. Viscosity :
exhibited by viscoelastic materials;
shows progressive deformation with time under
constant stresses

38. Strength :
ability of a material to resist an applied
force without rupture
Stress strain curve :
defines certain universal qualities of the
behaviour of materials under load

39. Elastic Limit :
is that point on the stress strain curve
beyond which removal of applied load does not
result in full recovery of deformation
Yield Point :
denotes end of the elastic region of curve

40. Ultimate Tensile Strength :
with application of load , a maximum stress
will be achieved; this maximum stress attained
during a single loading is called the ultimate
tensile strength.
Beyond this; the metal will break or rupture

41. Physical Properties
1. Radio Transparency :
opaque to x-rays – located and examined
2. Heat and Irradiation :
sterilization of implants

42. Chemical Properties
When a material is exposed to a water containing
solutions, one of the three conditions exist when
the system reaches the equilibrium
1 corrosion
2 immunity
3 passivation

43. Corrosion :
is destruction of the metallic structures
by action of surrounding medium
No. of metal atoms > 106 gm atoms/lit – a state
of corrosion exists

44. Immunity :
if no. of metal atoms < 106 gm atoms/lit
– metal is said to be immune
does not possess enough energy to initiate a
significant reaction

45. Passivation :
brief period of corrosion
that results in an intimate
layer of oxide or hydroxide
being formed on the surface
that mechanically separates
the metal from solution

46. Materials Used In Orthopaedic Implants
Three types
1. Metals and Alloys
2. Polymers
3. Ceramics

47. Metals and Alloys :
1. Iron based alloys
2. Cobalt based alloys
3. Titanium based alloys

48. Iron based alloys (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)

49. Cobalt based alloys (stelites)
a) Cast Co-Cr
- Chromium (27-30%)
- cobalt (60%)
- Molybdenum (5-7%)
- nickel (2.5%)
- Carbon (0.35%)
Highly abrasion resistant and gives reasonable
bearing properties
Used in two piece joint replacement

50. b) Wrought Co-Cr
- Chromium (19-21%)
- Cobalt (46-53%)
- Nickel (9-11%)
- Tungston (14-16%)
quite ductile and strong

51. Titanium based alloys :
recently introduced
Ti 6Al 4V ELI
lower modulus of elasticity,
good corrosion resistance,
lower tensile strength

52. Different Components- Different Properties
- Chromium : corrosion resistance and hardenability
- Nickel : easy fabricability and corrosion resistance
- Molybdenum : brittleness and corrosion resistance
- Carbon : generates oxide film – corrosion resistant
- Manganese and silica : controls problem of
manufacture

54. Was the design of implant adequate
or faulty?
Was the choice of materials
satisfactory with regard to
strength, hardness, corrosion
resistance, and ductility?
Were defects due to errors during
fabrication??
Was the clinical condition adverse?
Did surgeon apply proper
mechanical and surgical principles
in implantation?
During after-care, any mechanical
lapses?

55. Deformation
Fracture of implant
Loosening of fixator
or
Undesirable consequences like
Pain
Infections
Toxicity
leading to rejection of implant

56. Four principle modes of failure:
1. Excessive Deformation : most common
due to introduction of large, irrecoverable
strains following static or dynamic loading
2. Fracture
3. Abrasion or Erosion : repeated surface contact
4. Chemical attack : sudden failure by corrosion
fatigue

57. Willenegger
1. Instability :
a) Inadequate implant
b) Incorrect positioning of implant
c) Insufficient bone support
- inadequate interfragmentary compression
- inadequate reduction
- remaining defect
- absence of cancellous bone graft
- weak bone

58. d) Bone necrosis
e) Inadequate post operative treatment
2. Complications :
1. Local
a) Skin necrosis
b) Wound infection
2. General
thromboembolism

59. Black classified into
1. Functional failures
2. Material failures
3. Mechanical failures

60. Functional failure :
those in which desired effect is
not achieved, but no frank defect is observed
Causes :
a) Wrong device used
b) Incorrect application
c) Post-op infection
d) Inadequate post-op management

61. Material failure :
due to problems associated with
device; characterised by failure of materials in
device
May occur :
a) Secondary to corrosion
b) Tissue reaction to corrosion
c) hypersensitivity

62. Mechanical failure :
due to errors in implant design,
intra-op deformation of device
Three categories :
a) Ductile failure
b) Brittle failure
c) Fatigue failure

63. Ductile failure :
mechanical failure under static load
with excessive plastic deformation, long
before physical separation has occurred is
. ductile failure
Can be avoided by extension of design against
excessive plastic deformation

64. Brittle failure :
mechanical failure under static load without
plastic deformation
due to either defect in implant design or metallurgy
can be prevented by avoiding use of stress risers in
implant designing or by taking care not to damage
implant during insertion

66. Fatigue failure :
primary concern
results from cyclical loading on a device;
rhythmic nature of human
locomotion imposes such
cyclic stress on the bones and
soft tissues in the limbs and
thus on fracture fixation devices

67. When internal fixation device is implanted
fracture healing fatigue failure
of device

68. Mechanism of fatigue failure involves formation
of stress concentration points at superficial
irregularities
irregularities may consist of holes in the plate,
abrupt change in cross sectional area etc.
Small and round screw holes acts as stress
concentration points
can be avoided by using large screw holes

69. CORROSION
is the gradual degradation of metals by
electrochemical attack and is concern when a
metallic implant is placed in the electrolytic
environment of the body
initiation of corrosion depends on pH and O2
tension at the implantation site

70. Corrosion :
weakens implanted metal;
changes surface of metal;
releases metal ions into body fluids

71. Types of corrosion :
1.Galvanic
2.Crevice
3.Pitting
4.Fretting
5.Stress
6.Intergranular
7.Ion release

72. Galvanic corrosion :
mode of metallic deterioration in
which two dissimilar metals in content with
one another are immersed in solution
A battery is formed
Anode undergoes more rapid dissolution
Cathode undergoes less rapid dissolution

73. CAUSES :
1. use of stainless steel screw
in a cobalt chromium plate
2. when an impurity is
accidentally included during
manufacturing
3. rubbing of implants

74. Crevice corrosion :
in a narrow gap (crevice) between
implants e.g. screw head and plate;
high concentration of cl- or h+ ions destroy this
passive layers and local corrosion commences

75. Pitting corrosion :
localized reaction
Starts as a defect in the surface layer
Chromium, nickel and molybdenum are added
to stainless steal to the resistance to pitting
corrosion

76. Fretting corrosion :
results from very small oscillating
movements or vibrations
Causes abrasive damage to the passivating
layer
a multicomponent weight bearing implant
may be affected

77. Stress corrosion :
high mechanical stress may alter the
activity of metal and rupture a protective
passive surface layer, thereby increasing its
susceptibility to corrosion

78. Intergranular corrosion :
if impurities aggregate b/w grains of
relatively pure alloy a localized galvanic cell
may exist between crystals and alloy in the
grain boundaries

79. Ion release :
implanted metal releases ions into
tissues
occasionally patients may be sensitive to
chromium or nickel found in stainless steel
implants requiring removal

80. Implant failure is an interplay of multiple factors
and can be broadly classified into
1) implant related
2) patient related
3) technique related (surgeon related)

81. Implant related:
An ideal implant should be :
• Chemically inert
• Non-toxic to the body
• Great strength
• High fatigue resistance
• Low Elastic Modulus
• Absolutely corrosion-proof
• Good wear resistance
• Imaging compatible
• Inexpensive
So metallurgical problems contribute to implant failure

82. Patient related :
Osteoporosis
Comminuted fractures
Bone loss
Unstable fracture
Premature weight bearing in lower limb fractures
High velocity trauma with extensive injury to soft
tissues
Degenerative disease, alcohol intake, drug addiction,
over weight

83. Surgeon related :
wrong selection of patient
wrong selection of implant
wrong selection of operation and technique

84. Technique related :
1) Excessive stripping of soft tissues resulting in
wide spread devascularization
2) Inadequate interfragmentary compression
3) Inadequate purchase on fracture fragments
4) Early mobilization without adequate stability

85. 5) Application of plate on compression side
6) Inadequate bone support failure to use bone graft
7) Inadequate prebending of plate
8) Scratches on the implant
9) Improper placement of IM nail Improper
10) Dynamic locking of unstable fractures leads to
failure of intramedullary fixation device

86. Idiosyncratic failure:
originates from corrosion products
induced hypersensitisation phenomenon resulting
in implant rejection or loosening
~ 6% of population has existing hypersensitivities
to one or more constituents of stainless steel or
cobalt-chromium alloys, suggesting a need for
routine hypersensitivity screening prior to surgery.

88. SCREW FAILURE
Conical
1. Countersink
Hemispherical
Conical undersurface should be inserted centered & perpendicular to hole in plate
If set to any other angle
Undersurface does not adapt well to plate hole
Due to which Its wedge sharp create undesirable high forces and uneven contact
which predisposes to corrosion
Both factors weakens screw
Screw failure

89. 2.Run out :
screw may break at run out during
insertion if it is incorrectly centered over the
hole or is not perpendicular to the plate.

90. 3. screw may break :
during insertion; if applied torsional
load exceeds its torsional strength
Not tapped in hard bone
Due to lack of lubrication
High stress

91. Implant Failure In Plating
Plate failure occurs because of interference with
periosteal blood supply
Brittle and Plastic failure occur due to
- minor loads in small plates
- secondary major trauma in large plates
The most common failure of plate is fatigue failure

92. • The ends of plate act as stress riser leading to
a fresh fracture proximal or distal to the
original one
• Improper application of plates and poor
technique
• Fatigue failure of plate is inevitable if healing
fails to occur

93. Left. When a gap is left on the cortex opposite that to which the plate
is attached, bending of the plate at the fracture site can cause the
plate to fail rapidly in bending.
Right. Compressing the fracture surfaces not only allows the bone
cortices to resist bending loads, but the frictional contact and
interdigitation helps to resist torsion.
Breakage of
Fracture Fixation
Plates

94. The application of a plate on
the compressive as opposed
to the tensile side of a bone
subjected to bending causes a
gap to open on the opposite
side of the plate during
functional loading.

95. Plate Failure Through a Screw Hole
Placing the plate so that an empty screw hole is located over the fracture will
significantly increase the potential for fatigue fracture of the plate.
A second consideration---
The greater the span or distance of a beam is between its supports, the lower
its stiffness will be, and the more it will deform under load in bending and
torsion. For this reason, screws should be placed as close together across the
fracture site as possible.

96. IMPLANT FAILURE IN INTERLOCKING
NAILING
associated with either insertion of a small dmt nail
or use of an interlocking nail for a very proximal or
distal shaft #
Plastic deformation (bending) of IM rod mainly
occurs with nails < 10 mm in dmt;
minimal nail diameters range
12-14 mm for women
13-15 mm for men

97. Bending of nail at # site usually occurs as an
early complication caused by premature wt
bearing, lack of adequate support, or deficient
material (nail) strength

98. Bent distal screws may result from early wt
bearing if screws are too close to # site
Weak part of nail is proximal of the 2 distal holes
Fractures located within 5 cm of this hole will be
stressed above endurance limit with ambulation
These fractures must have delayed wt bearing
until callus is present

99. Femoral Splitting Due to IM Rod Insertion
Mismatch of the curvature
between the IM rod and the
medullary canal results in bending
stresses that could cause splitting
of the femur during insertion

100. If the same force acts on IM rods
placed in femur with more proximal
(left) or more distal (right) fractures,
the moment arm of the force will be
longer in the case of the more distal
fracture, and therefore the moment,
acting at the fracture site, on the
implant, will be larger.
IM Rod and Locking Screw Breakage

101. Because the distal end of the femur flares
rapidly, the length of the locking screw
required to cross lock the rod can be quite
variable.
If the screw is not well supported by
trabecular bone but mainly by cortex, then
its stiffness and strength decrease with the
third power of its length between cortices.
If the screw length doubles, the
deformation of the screw under the same
load increases by a factor of eight.

102. A proposed mechanism for loosening external fixation
pins involves under- or oversizing the diameter of the
pin relative to the bone hole.
A. If the pin and bone hole are the same diameter,
micromotion can occur with bone resorption.
B. If the pin is more than 0.3 mm smaller in diameter
than the hole in bone, microfracture may occur during
insertion.
C. If the bone hole diameter is about 0.1 mm smaller
than the pin diameter, the bone is prestressed but does
not fracture, micromotion is eliminated, and pin stability
is maintained
Loosening of External Fixator Pins

103. To produce more rigidity in construction of an external fixator, the basic
principles that should be considered are that for pin-and-rod-type sidebars;
stiffness increases with the fourth power of the cross-sectional area (the moment
of inertia, and decreases with the third power of their span or unsupported length
. This explains why it is beneficial to decrease sidebar to bone distance, increase
pin diameter, place pins as close together across the fracture site as possible, and
use larger-diameter or multiple sidebars in frame construction

104. IMPLANT FAILURE IN ARTHROPLASTY

105. ASEPTIC LOOSENING :
The most important cause of aseptic loosening is an
inflammatory reaction to particles of wear debris.
Abrasive, adhesive, and fatigue wear of
polyethylene, metal and bone cement produces
debris particles that induce bone resorption and
implant loosening.
Particles can cause linear, geographic, or erosive
patterns of bone resorption (osteolysis), the
distributions of which are influenced by the implant
design.
Micromotion of implants that did not achieve adequate initial
fixation is another important mechanism of loosening.

106. What should we do ? ? ?

107. Surgeon encounters evidence of failure of an appliance
by
•Breakage
•Tissue reaction
•Or suspect failure
What he will do ?
He will plan to remove the implant and plan for another
operative procedure
BUT
Most important now is surgeon has to investigate and
analyze what caused the failure

108. 3. During removal of implant; surgeon should record his
operative findings carefully, and, in particular, the
orientation of the device or of its fragments with
respect to grossly visible tissue reaction-discoloration,
granulation tissue, hemorrhage, or pus formation.
1.Details of condition for which device was originally
inserted, including dates, place of operation, operative
procedure
2. Details of postop treatment and any episode of
premature weight-bearing or undue loading, which
directly preceded the failure.

109. 4. Should then obtain enough material for biopsy
and label it.
5.If there is a suspicion of infection bacteriological
cultures of suspicious material are mandatory.

110. Beautifulppt.com
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…
19-03-2016 110

111. Questions in exams ??
Long question :
What is implant failure ? Enumerate the causes for
the same and management.
Short questions :
1) Corrosion
2) Materials Used In Orthopaedic Implants