The document discusses the history and evolution of implant materials used in orthopaedics. It describes how early implants were made from materials like gold, silver and platinum but were found to be too soft. The development of stainless steel and other alloys allowed for stronger, more durable implants. The document outlines various metal working techniques used to produce implants and surface treatments like passivation that enhance corrosion resistance. Key implant materials discussed include stainless steel, titanium, and cobalt-chromium alloys.

1. SRI SIDDHARTHA MEDICAL COLLEGE
TUMKUR
DEPARTMENT OF ORTHOPAEDICS
TOPIC:- Implants In Orthopaedics - Metallurgy
CHAIRPERSON & MODERATOR :- PROF. & HOD Dr. Kiran Kalaiah
SPEAKER:- Dr. Baibhav Kumar Agarwal

2. EVOLUTION
▪ With the introduction of antiseptic surgery between 1860s and
1870s, by Lord Lister and anaesthesia by Morton (ether) and
Simpson (chloroform), the surgery developed rapidly.
▪ In the pre- Listerian days, many surgeons were using books, pins,
and wires made of various metals—gold, silver, platinum or iron
to manipulate and hold fractured fragments in position.
▪ Bell in 1804 used silver-coated steel pins and noted corrosion in
them.
▪ Lavert after many animal experiments found in 1829 that
platinum was the most inert metal.

3. ▪ However, platinum, gold as well as silver were found to
be too soft for clinical use.
▪ The real development of implant surgery for fracture
fixation started after the advent of aseptic surgery.
▪ Lister himself was one of the first to successfully wire a
fractured patella using a silver wire.
▪ Among the early exponents of plate and screw fixation
was Hansmann (1866).
▪ His implants were made of nickel-plated sheet steel.

4. ▪ Since the certainty of corrosion and break-up of the implant was well
known if left inside the body for an appreciable duration of time.
▪ Hansmann’s plates had one end bent at right angle, and it was
allowed to protrude through the wound.
▪ Likewise, the screws were also applied so that the heads were
outside the skin.
▪ The whole implant was removed by 6–8 weeks, when the fractured
fragments were expected to be gummy.

5. ▪ Sir Arbuthnot Lane devised plates and screws that were made of
“stout steel” a high carbon steel, of considerable hardness and
containing a fairly high percentage of carbon.
▪ Lambotte brothers Elie and Aldin used other metals, aluminium,
silver, brass, magnesium and copper plates as well as steel-coated
with gold or silver.
▪ Their plates were curved to fit the curvature of the bones.
▪ Von Bayer in 1908 introduced pins for fixation of “small fragments”
at the intra-articular level.

6. ▪ Sherman (1912), in USA, improved the design of the
Lane’s plate to make it stronger.
▪ His implants were also now made of “vanadium steel”,
an alloy containing much less carbon and 0.1–0.15% of
vanadium along with small amounts of chromium and
molybdenum.
▪ L Guillet of France who was the first to make alloy
systems close to what we now call stainless steel.

7. ▪ The 18-8 SMo was the first stainless steel to perform
satisfactorily as a surgical implant.
▪ Venable and Stuck (1926) introduced their own design of
plates (Venable plates) made from steel with a
composition of 18% chromium and 8% nickel in addition
to iron.
▪ In 1959, Bechtol, Fergusson and Laing described the
superior properties of type 316 stainless steel.Type 316
then became the popular material for implants.

8. ▪ Further work has been done which has developed an
even better material type 316L stainless steel.
▪ This material has an extra low carbon content of
0.03% maximum which insures against the occurrence
of carbide precipitates.
▪ Carbide precipitates “and delta ferrites” make
stainless steel susceptible to intergranular corrosion.
▪ This condition would reduce the body compatibility of
the metal.

9. ▪ Therefore, type 316L is now replacing type 316.
▪ Vitellium 4 or vinertia was developed in 1929 and used
experimentally byVenable and Stuck. It contains no
iron, being an alloy of cobalt, nickel and molybdenum
mainly.
▪ Titanium was another metal which has come into use
in the last 30 years.
▪ Titanium and vitallium are almost totally inert in the
body.

10. ▪ Use of compression to bring about early fracture healing has
found increasing favors.
▪ Danis (1949) of Belgium was the first to write about the
biomechanics of fracture healing produced by a compression
force when using a special compression plate and screws.
▪ He was first to describe “primary healing” of fracture.
▪ Charnley introduced and popularized the compression
method of arthrodesis of joints especially the knee.

11. ▪ The Arbeitsgemeinschaft für Osteosynthesefragen
(AO) group was formed in Biel, Switzerland by 13
surgeons on November 6, 1958.
▪ A combination of high-powered technology,
metallurgical excellence and a high level of
technical skill in optimum operating conditions has
allowed a total change in the concept of treatment
of many fractures by combining the principles of
rigid fixation, compression and early mobility.

12. Stress & Strain
▪ Stress is defined as the
force acting on a surface
divided by the area over
which it acts.
▪ Strain is the change in the
height or length of the
object (displacement)
under load divided by its
original height or length.

13. Stiffness & Elastic modulus
▪ Stiffness is defined as
the slope of a force
versus displacement
graph.
▪ Elastic modulus is the
corresponding slope,
but of a stress versus
strain graph.

14. Strain vs Stress Graph
• Yield point defines the safe
maximum functional load before
the plate is permanently
deformed.
• The point at which elastic
behaviour changes to plastic is
termed the yield point.
• The area beneath the curve is the
toughness of the material, or the
amount of energy that a material
can absorb before failure.

15. FATIGUE
▪ Fatigue refers to a mode of failure that results from
repeated stress at magnitudes lower than that
required to cause failure in a single application
(ultimate stress).
▪ Load can be applied that remains below the yield
point of the construct, yet creates a crack that
progressively grows.
▪ This lowers the yield point of the material and the
local stresses will eventually exceed the yield point
and the construct will fail.
▪ Implant materials necessarily must have a high degree
of fatigue resistance to perform over the long term.

16. CREEP
▪ Progressive deformation with time under
constant stress.ie decay of strain under
constant stress
▪ Non-crystalline materials such as polymers, are
particularly prone to this time-dependent form
of deformation
▪ Minimized by using metal alloys having a high
melting point.

17. STRESS RELAXATION
▪ Stress relaxation is a time-dependent, decay of
applied stress under conditions of constant strain
(in contrast to creep, which is a time-dependent
strain under conditions of constant stress).
▪ Time-dependent reduction in applied
interfragmentary compression at a fracture site
that is fixed and compressed with a DCP.

18. Metal working methods
▪ Forging
▪ Casting
▪ Rolling & drawing
▪ Milling
▪ Cold working
▪ Annealing
▪ Case hardening
▪ Machining
▪ Broaching

19. FORGING
▪ Metal is heated and
hammered or squeezed
into shape
▪ Produces an orientation of
grain flow making the
metal stronger
▪ Drop forging- commonly
used

20. CASTING
▪ Casting consists of
heating the metal
to a molten state
and pouring it into
a mould

21. ROLLING AND DRAWING
▪ Rolled between rollers or
drawn through a hole in a
hardened plate
▪ Used to form bars and wires
▪ Material gets plastically
deformed and grains gets
elongated in the direction of
deformation
Undrawn bar
Drawn bar

22. MILLING
▪ A machining process in which
material is fed into a machine
with multiple cutting teeth.
▪ Removes materials at high rate
▪ Good surface finish

23. COLD WORKING
▪ Cold working is a finishing process employed after the
metal has been shaped by hot forging.
▪ Performed below the recrystallization temperature.
▪ The advantages of cold working are:-
- smoother surface finish
- higher tensile strength
- uniform grain
- structure and superior dimension control

25. ANNEALING
▪ Annealing is heating to about half the melting
point, followed by controlled cooling.
▪ The process reverses the effects of work
hardening and restores ductility and
toughness to the metal.
▪ Annealing (heat treatment) of a forged piece
reduces its internal stresses.

26. CASE HARDENING
▪ Treating a product to cause the
outside surface of the rod to be
harder than the inner core.
▪ The advantage is that
- the harder outer surface
will resist indentation while
- the core is able to absorb
more energy.

27. MACHINING
▪ For geometric features like holes and grooves
▪ It work hardens the surface of the material
▪ Grain structure is unchanged

28. BROACHING
▪ Comparable to sawing except the cut is
performed in a single pass of the broach.
▪ The geometry of the broach is the inverse
geometry of the surface that is to be
machined and consists of cutting teeth that
run the full length of the tool.
▪ Generally broaches are used in the machining
of non-circular holes, slots, and other
recesses of geometry that may be difficult to
produce with other machining processes.

29. Surface treatment
▪ Implants are grinded & polished to a
specified roughness.
▪ Removes scratches, this could act as
local stress risers.
▪ Cleaned with special cleansing agents.
Polishing

30. PASSIVATION
▪ The passivation process produces a protective oxide layer.
▪ It involves immersion of the device in a strong nitric acid solution
for a specific time.
▪ The solution dissolves embedded iron particles left by the
machining operations and generates a thin, transparent but
dense oxide film on the surface of the alloy.
▪ This process is important in enhancing the corrosion resistance of
the implant.
▪ Stainless steel forms a chromium oxide.
▪ Titanium and its alloys form a dioxide.

31. ▪ The passivation can be damaged by cold working,
scratching, and other mechanical trauma.
▪ The protective layer is self-repairing to varying
degrees in the presence of oxygen, a phenomenon
called re-passivation.
▪ Cobalt-chromium alloys apparently do not form a
distinct passivating layer.

32. Nitriding
▪ It is allowing the surface to react with
ammonia or potassium cyanate.
▪ Used to harden the surface of titanium
implants.

33. Corrosion
▪ Corrosion is the gradual degradation of metals by electrochemical
attack, and is therefore a concern when a metallic implant is
placed in the electrolytic environment of the body.
▪ Initiation of corrosion depends on pH and oxygen tension at the
implantation site.
▪ Generally, tissue conditions (pH 7.4) are such that the protective
preformed oxide layer is stable but some tissue locations and
occasional transient conditions, such as the acid pH shift
associated with infection, may damage the oxide layer and
produce corrosion.

34. Galvanic corrosion
▪ Components of a galvanic cell (two different
electrically conducting solids, an electrically
conductive path between them and an
electrolyte solution containing free ions) are
required to set up the corrosion process.
▪ Galvanic corrosion may occur at the surface of
an implant in which an impurity was
accidentally included during manufacturing.

35. ▪ At a more intrinsic level, separation of metal granules in
different phases may start a corrosive process.
▪ At times, rubbing of implants and instruments (cold
welding) may transfer metal, leading to corrosion.
▪ A significant amount of metal may be transferred from
the screw driver to the screw head and from the drill bit to
the plate.
▪ Use of an instrument set made from a material matching
the composition of the implant eliminates this cause.

36. Crevice
corrosion
▪ Metals and alloys that depend on an oxide
film or passive layer for corrosion protection
are particularly susceptible to crevice
corrosion.
▪ In a narrow gap (crevice) between implants,
e.g. screw head and plate, high
concentrations of chloride or hydrogen ions
destroy this film and local corrosion
commences.
▪ Crevice corrosion can occur in a fatigue crack
and in defects such as a scratch or
macroscopic fissure, where oxygen tension
becomes low, causing a reactive area.
▪ Molybdenum tends to limit crevice corrosion.

37. Pitting
corrosion
▪ This is a localized reaction similar to
crevice corrosion.
▪ Starting as a defect in the passive surface
layer. corrosion proceeds into the metal,
setting up self-accelerating
concentration gradients.
▪ Chromium, nickel and molybdenum are
added to stainless steel to increase the
resistance to pitting corrosion.
▪ Titanium and its alloys can quickly re-
passivate to regain protection against
pitting corrosion.

38. Fretting corrosion
▪ Fretting corrosion results from very
small oscillating movements,
vibrations or a slip between the
components of a device causing
abrasive damage to the passivating
layer and permitting initiation of the
reaction.
▪ A multicomponent weight-bearing
implant may be affected by fretting
corrosion.

39. Stress corrosion
▪ High mechanical stresses may alter
the activity of a metal and rupture a
protective passive surface layer
thereby increasing its susceptibility
to corrosion.
▪ Stress corrosion involves both
mechanical and chemical effects.
▪ Localized corrosion can enhance
stress concentration and premature
implant failure.

40. Intergranular corrosion
▪ If impurities aggregate between grains of relatively pure
alloy, a localized galvanic corrosion may exist between
the crystals and the alloy in the grain boundaries.
▪ For example carbon depletes intergranular chromium
concentration as it forms chromium carbide.
▪ A low chromium level may initiate intergranular
corrosion leading to cracks between metal granules.
▪ This is why a low level of carbon is desirable in surgical
stainless steel.

41. Ion release
▪ Implanted metal releases ions in the tissue.
▪ The tissue reaction to ion release decreases with
time, and since tissue reaction is not a major clinical
factor, internal fixation devices need not be removed
routinely for reasons of metal ion concentration.
▪ Occasionally, patients may be sensitive to chromium
or nickel found in stainless steel implants, requiring
removal.

42. Standard organizations
▪ ASTM: American Society forTesting and Materials
● Committee f-4, Surgical Implants
▪ ANSI: American National Standards Institute
▪ AISI: American Iron and Steel Institute
▪ BIS: Bureau of Indian Standards
▪ BSI: British Standards Institute
▪ DIN: Deutsche Industrie Norm
▪ ISO: InternationalOrganization for Standardization
● CommitteeTC-150, Surgical Implants

43. Metallic
Implants

44. Stainless Steel
▪ Stainless steel designated as ASTM F-55, -56 (grades
316 and 316L) is used extensively for fracture fixation
implants.
▪ Type 316L stainless steel is an iron-based alloy.
▪ Alloying with chromium generates a protective, self-
regenerating chromium oxide layer which provides a
major protection against corrosion.
▪ The addition of molybdenum decreases the rate of
slow, passive dissolution of the chromium oxide layer
by up to 1,000 times.
▪ Molybdenum further protects against pitting
corrosion.

45. ▪ Nickel imparts further corrosion resistance and
facilitates the production process.
▪ Limited quantities of manganese and silicon
are added to control some manufacturing
problems.
▪ The carbon component increases the strength,
but its presence in the alloy is undesirable.
▪ Under certain conditions created as a result of
improper heat treatment, the carbon
segregates from the major elements of the
alloy, taking with it a substantial amount of
chromium in the form of chromium carbide
precipitates.

46. ▪ Carbides form at grain boundaries, where corrosion
selectively occurs.
▪ Furthermore, the carbides degrade the mechanical
properties of the material.
▪ Mixing of small quantities of titanium or niobium
reduces the formation of intergranular carbides by
competing for carbon.
▪ Type 316L stainless steel has a very low permissible level
of carbon to minimize this problem.

47. ▪ Though it is a strong, stiff and biocompatible material,
316L stainless steel has a slow but finite corrosion rate.
▪ Stainless steel is best suited for short-term implantation
in the body as in fracture fixation.
▪ Stainless steel is frequently used because the base
materials are cheap, the alloy can be formed using
common techniques, and its mechanical properties can
be controlled over a wide range for strength and
ductility.
▪ The elastic modulus of stainless steel is approximately 12
times higher than the elastic modulus of cortical bone.

48. Cobalt-Chromium Alloys
▪ The cobalt-chromium-
tungsten-nickel alloy (ASTM
F-90) employed for the
manufacture of fracture
fixation implants is very
different from the F-75 alloy
used for a femoral prosthesis.
▪ It is quite ductile and strong.

49. ▪ It is available in a wide range of yield strength,
ultimate tensile strength and strain to failure.
▪ Its yield strength can be controlled by processing.
▪ In clinical practice it is used to make wire and
internal fixation devices including plates,
intramedullary rods, and screws.

50. Titanium Alloys
▪ Titanium is the ninth most abundant element in the earth’s
crust, where it forms oxidic minerals (rutile, ilmenite).
▪ The pure element is very reactive; it is the only element that
burns in nitrogen.
▪ However, the metal rapidly becomes coated with an oxide
layer, making it physiologically inert and resistant to most
chemicals.
▪ Titanium is used for making orthopaedic implants in two
forms: commercially pure and a variety of alloys.

51. ▪ Titanium-aluminum-vanadium alloy (ASTM
F-136) is commonly referred to asTi6AI4V.
▪ This alloy is widely used to manufacture
implants. Impurities such as oxygen,
hydrogen and nitrogen tend to make it
brittle, which explains why only minimal
amounts are acceptable in titanium alloys
used in surgical implants.
▪ ASTM F-136 limits the oxygen concentration
to an especially low level of 0.13%, known as
the extra low interstitial (ELI) grade.

52. ▪ Limiting the level of dissolved oxygen improves the
mechanical properties of the material, particularly
increasing its fatigue life.
▪ Aluminium stabilizes the alpha form of the material
while vanadium stabilizes the beta form.
▪ Combination of both components forms a two phase
alloy with good strength properties and one that can be
heat treated.
▪ Ti6Al4V ELI is frequently used for making orthopaedic
implants.

53. ▪ Titanium has an elastic modulus approximately half that of
the stainless steel and cobalt-chromium alloys.
▪ The lower stiffness of bone plate made of titanium reduces
the severity of stress shielding and cortical osteoporosis.
▪ Another advantage of lower stiffness is that a titanium plate
is less prone to fatigue failure than a stainless steel plate.
▪ The modulus of elasticity of titanium is still roughly six times
that of cortical bone.
▪ The ductility of titanium alloy is considerably lower than that
of most stainless steels.

54. ▪ Due to this difference a surgeon requires some adaptation
of his feel when determining the optimal amount of torque
to be applied to the screws.
▪ In the presence of unstable fixation, the titanium
components of an internal fixation system are subjected to
fretting conditions and produce metal debris.
▪ Such debris causes gray or black coloration of the
surrounding tissues.
▪ This discoloration, which is not a result of corrosion, is
harmless.
▪ Special surface treatment of the implant reduces such
discoloration.

55. Comparison of Stainless Steel and
Titanium for Fracture Fixation
▪ Stainless steel can be produced with a higher elastic
modulus and ductility than titanium alloys.
▪ Stainless steel implants are potentially cheaper.
▪ The more significant advantage of titanium alloy is
its corrosion resistance and the lack of potentially
toxic ions such as chromium and nickel which are
found in stainless steels.

56. ▪ Another advantage is that it does not cause
allergic reactions in individuals sensitive to
nickel and chromium.
▪ These properties make it possible to leave the
titanium implants in situ wherever there is no
mechanical hindrance to soft tissues.
▪ The mechanical properties of titanium are
closer to those of bone than those of steel.

57. Nickel-Titanium Alloy
▪ Nickel-titanium alloy, or nitinol, a shape memory alloy
(SMA) was discovered in 1965.
▪ The alloy contains nearly equal numbers of nickel and
titanium atoms, leading to its common compositional
representation as NiTi.
▪ Shape memory alloy can be “trained” to take on a
predetermined shape in response to a stimulus such
as a change in temperature.

58. ▪ Implant made from SMA has the ability to return to
its original shape after the environment
temperature rises to a certain level (e.g. 37°C).
▪ Its shape can be changed easily at low temperature
(e.g. 0–5°C).
▪ SMA can be bent, compressed, or deformed in
many other ways, but can then be made to recover
its original shape by heating.
▪ Compressive staples for fibula and scaphoid, clamp-
on bone plates, long bone fixator and patella fixator
are some of the clinical applications of SMA.

59. Non-metallic
Implants

60. Bioinert Ceramics
▪ They are incorporated in the bone in accordance
with pattern of contact osteogenesis
▪ There are two types viz. alumina ceramics (Al2O3)
and zirconia ceramics (ZrO2).
▪ Alumina ceramics contain entirely hexagonal crystals and hence are
stable in vivo as against zirconia ceramics consist of three
crystallographical phases viz. cubic, tetragonal and monoclinic and
transformation takes place under various change in temperature,
chemical mechanical stress and humidity.

61. ▪ Chemical stabilizers likeY2O3, CeO2 andAl2O3 are
added to form partially stabilized zirconia (PSZ).
▪ Alumina is chemically more stable than PSZ in vivo.
▪ While PSZ is mechanically stronger than alumina.
▪ Both of them exhibit much better wear resistant
characteristics compared to stainless steel or cobalt
chromium alloy when assessed in form of bearing
components of hip prostheses.

62. Bioactive Ceramics
▪ These have a characteristic of osteoconduction and the
capability of chemical bonding with living bone tissue in
accordance with the pattern of “bonding osteogenesis”.
▪ These include glasses, glass ceramics and ceramics that elicit a
specific biological response at the interface between the
material and the bone tissue which results in the formation of a
bond between them.
▪ Bioglass, apatite-wollastonite containing glass ceramics (AW-
GC) and synthetic hydroxyapatite (HA) are representative
materials currently used for clinical applications.

63. ▪ As the bending strength of HA is lower than
cortical bone, HA cannot be used to fabricate
weight bearing prosthesis, instead they are
used for filling bone voids, coating of
prostheses.
▪ Mechanically stronger bioactive material is
AW-GC which has significantly greater
bending and compressive strength than
cortical bone.
▪ AW-GC is used in various bone prostheses like
vertebral prosthesis, iliac crest prostheses,
intervertebral spacers, laminoplasty spacers.

64. Bioresorbable Ceramics
▪ These are gradually absorbed in vivo and replaced by
bone in the bone tissue.
▪ The pattern of their incorporation in the bone tissue is
considered similar to contact osteogenesis, although
the interface between bioresorbable ceramics and bone
is not stable as that observed with bioinert ceramics.
▪ Eg:Tricalcium phosphate [Ca3(PO4)2] and polylactic–
polyglycolic acid copolymers, Calcium oxide, calcium
carbonate.

65. Tissue Sealant

66. Fibrin
▪ The source is from plasma and produced by either pooled donor
or autologous donor.
▪ Variation between products arises from source of plasma, mode
of precipitation, mode of purification.
Each product has two components:
1. A lyophilized concentrate of pooled human fibrinogen/ factor
XIII which is reconstituted with an antifibrinolytic solution.
2. Bovine thrombin which is reconstituted with a solution of
calcium chloride.

67. ▪ The fibrinogen is converted by thrombin into
fibrin monomer.
▪ These assemble into fibrils which eventually
aggregate to form a three-dimensional gel.
▪ Factor XIII activated by thrombin in presence of
calcium induces covalent bond formation
between the assembled fibrin monomers.
▪ This increases its overall strength and stiffness.

68. ▪ The three-dimensional structure of fibrin gel may be modified
by changing concentration of fibrinogen, thrombin, or
calcium ionic strength, pH, temperature that leads to the
formation of fine gel (<2 μm) or coarse gel (>2 μm).
▪ Increase in thrombin concentration results in increase in
ultimate tensile strength.
▪ The fibrin sealant has more bonding strength than sutures up
to 4th postoperative day, after which no difference between
two groups was observed.

69. Albumin
▪ Cross-linkage of albumin results in excellent adhesiveness.
▪ It is also used as a vehicle for site specific delivery of growth
factors to accelerate tissue repair.
▪ Glutaraldehyde albumin microsphere complexes are used
as vehicle for delivery of proteins and polymers.
▪ Prosthetic device coating has also been used.

70. Cyanoacrylates
▪ N-butyl cyanoacrylates have proved to be
promising role in tissue adhesion.
▪ They can be used to embolize arteries
because of its thrombogenic effect.

71. Mucopolysaccharides
▪ The blue mussel producing mussel adhesive protein
(MAP) serves to affix mollusk to rocks.
▪ MAP has been used as basement membrane and
because of its adhesiveness it has been used for
fixation of chondrocytes and osteoblasts.
▪ This may be in clinical use in permanent adhesion
such as implant fixation in hard tissues.

72. Polymers

73. Silicones
▪ These are chemically inert, have good
biotolerance, and high hydrophobic capacity.
▪ They are used in plastic surgery or in Orthopedics
in the form of elastomer, rubbers for joint
prostheses of fingers.

74. Polyacrylics
▪ Polymethyl methacrylate (PMMA) is used as the polymer of choice in securing
implant to bone since its introduction in 1970s by Sir John Charnley.
▪ It is provided in two parts, liquid monomer which helps methacrylate powder
to polymerize.
▪ Radiopaque barium sulphate or zirconia helps its visualization on radiographs.
▪ The reaction is exothermic.
▪ Clinical studies show that thermal necrosis caused by the heat does not affect
overall performance.
▪ Antibiotics added can aid in prophylaxis or treatment of infection.

75. Polyolefins
▪ Ultrahigh molecular weight polyethylene (UHMWPE) is a
group of novel linear polymers with high surface wear
resistance and low coefficient of friction.
▪ These resilient properties have made it a vital component
in the weight bearing component like the acetabular and
tibial plateau surfaces in joint replacement surgeries.
▪ Ultrahigh molecular weight polyethylene is used for
making friction components of prostheses.

76. Bioabsorbable polymers
▪ Improvements in polymer science have led to more
frequent use of bioabsorbable implants in orthopaedic
surgical procedures for fracture fixation of as well as for
soft-tissue reattachment.
▪ The chief advantage of these implants is that initially there
is adequate stability for healing and then it is gradually
resorbed after biologic healing is achieved.
▪ These implants limit stress shielding of bone and as they
degrade, gradually transfer load to the healing tissue,
eliminate the need for hardware removal.

77. ▪ Most research on the clinical applications of
bioabsorbable materials has focused on the use
of polymers known as alphapolyesters or poly-
(alpha-hydroxy) acids.
▪ These include polylactic acid (PLA), polyglycolic
acid (PGA), and polydioxanone (PDS).
▪ Combinations of these materials allow
optimization of their biomechanical properties
for specific clinical uses.
▪ The overall crystallinity of a polymer affects its
biomechanical and degradation properties.

78. ▪ These properties are influenced by the manufacturing
technique, with elevated temperatures and a slow rate of
cooling allowing the polymeric chains to align themselves in an
ordered solid structure.
▪ The glass-transition temperature (Tg) is the temperature below
which the polymer is stiff and hard and above which it is soft
and rubbery.
▪ The rate of degradation is dependent on the polymer’s starting
molecular weight, its crystallinity, the composition, porosity of
the implant, its loading conditions and local vascularity.

79. ▪ Although bioabsorbable fracture fixation devices appear to
have obvious advantages over metal implants, concerns
about the initial fixation strength of these materials have
limited their widespread acceptance.
▪ These materials must have the initial fixation strength
necessary to maintain the reduction of bone fragments
during the healing process.
▪ Compared with metallic fixation, absorbable fixation has
shown a lower incidence of infection.

80. ▪ The use of bioabsorbable implants for paediatric fracture
fixation is particularly appealing because it obviates implant
removal.
▪ In experimental studies, the presence of an absorbable
implant does not seem to interfere with the growth plate any
more than an empty drill hole does.
▪ Biodegradable implants have shown satisfactory results,
except for supracondylar humerus fractures where the
displacement forces encountered overwhelm the mechanical
properties of the absorbable pins, resulting in displacement.

81. ▪ The application of bioabsorbable implants in musculoskeletal
procedures is gaining acceptance.
▪ Plates and screws for fixation of fractures of lower end of radius,
fractures of small bones of hand, ankle fractures and pins for
children’s fractures are now available.
▪ Bioabsorbable intramedullary inserts improve hold of a screw in
porotic bone.
▪ While most commonly utilized in the field of sports medicine for
soft-tissue fixation, these implants may have additional
applications in other aspects of Orthopedics like a protective
perforated membrane for bone grafts in a gap nonunion or as
carriers for osteogenic substance to enhance bone healing
without interference with imaging.

82. Clinical relevance

83. Metal failure
▪ Types of mechanical failure observed in clinical practice:
- Brittle failure
- plastic failure
- fatigue failures
▪ A screw head made of material with poor ductility may
demonstrate brittle failure when overloaded in torsion.
▪ In plastic deformation, the implant bends permanently because of
loading beyond the yield strength of the material, causing loss of
surgical alignment.

84. ▪ All metallic materials are subject to fatigue fracture under
cyclic loading, a process that is hastened by body fluids.
▪ Such a repetitive loading may be experienced by implants
used to fix a weight-bearing bone in the lower extremity.
▪ Fatigue fracture of an implant originates in the small flaws
within the material (Grain boundaries, voids, inclusions)
▪ Extrinsic defects, such as scratches, bends, and divots from
surgical clamps, act as stress risers and can decrease the
fatigue life of an implant.

85. ▪ The fracture fixation device such as a bone plate or
intramedullary nail is designed to share the load with the
fractured bone.
▪ The bone is expected to heal and to assume a larger share of
the load with the passage of time.
▪ This unloads the fracture fixation device and prolongs its
fatigue life.
▪ Failure does occur when the loads are excessive, such as
when the fracture is comminuted and the bone is unable to
partake in load bearing.

86. ▪ Fatigue failure also occurs when the period of
load bearing is longer than the device was
designed to endure.
▪ Fatigue life therefore can be important in cases
of delayed union or non-union.
▪ Most fracture stabilization devices are over
designed to minimize the occurrence of fatigue
failures

87. Metal removal
▪ Implant removal may be challenging and lead to
complications, such as neurovascular injury, re-fracture, or
recurrence of deformity.
▪ Because implants may biomechanically function as stress
risers, theoretically they may predispose a patient to peri-
implant fracture.
▪ There is no significant risk of peri-implant fracture when
hardware is left in place, even when the patient resumes
contact activity.
▪ Tension band wiring of olecranon and patella often require
removal due to persistent pain

88. ▪ Nail is often removed for persistent pain after fracture union in
femur and tibia.
▪ Pain relief after nail removal is unpredictable; this is more so for
femoral and tibial nails.
▪ In some instances pain has increased after removal.
▪ The incidence of sensitivity to chromium, nickel, and cobalt ions in
stainless steel is low (0.2%, 1.3%, and 1.8%, respectively).
▪ A patient with metal sensitivity or a nickel allergy may report non-
specific deep generalized pain over the area of injury and implant.

89. ▪ The carcinogenic risk between metallic implants and
tumours has been established in experimental animals.
▪ The metal-induced carcinogenesis may be due to metal-ion
binding to DNA or alteration of DNA and protein synthesis.
▪ Sarcomas related to implants tend to be high-grade and
occur many years after initial placement of the device.
▪ Implants in humans pose a significant low risk for local
tumour development, and does not warrant the routine
removal of hardware.

90. ▪ Implant removal in paediatric patients is common
for the reasons like difficulty in removing implants
later because of exuberant callus overlying the
implant, stress shielding, risk of corrosion, metal
allergy, and potential carcinogenesis.
▪ The removal is frequently as difficult as or more
difficult than implantation and requires larger
incisions.

91. THANK YOU