The historical and latest advancements in the field of total hip arthroplasty related implants and materials

1. PRIMARY TOTAL HIP ARTHROPLASTY
IMPLANTS
Dr. Rohit Somani,
Junior Resident,
Department of Orthopedics,
Dr. Shankarrao Chavan
Government Medical College,
Nanded.

2. HISTORY OF EVOLUTION OF THR
•In 1912, Sir Robert Jones used Gold Foil as an inter positional layer, other
materials used were muscle, fascia, skin, oil, rubber, celluloid, pig bladder.
•In 1923, SMITH-PETERSON introduced the concept of mould
arthroplasty
•In 1933, PYREX GLASS was chosen as the material for the first
mould..
•In 1937, Venable and Stuck developed VITTALIUM (an alloy of Cobalt
65%, Chromium 30%, Molybdnium 5%). In 1950, JUDET and BROTHERS
used acrylic femoral head prosthesis made of methyl methacrylate.

3. •In 1952 AUSTIN MOORE and FRED THOMPSON independently
conceived the idea of fixing endoprosthesis.
•The 1950, WRIST, RING, Mc. KEE-FARRER and others designed the
metal on metal total hip arthroplasty but did not prove satisfactory
because friction and metal wear
•Delbet – 1st reported hemiarthoplasty.
•Giliberty and Bateman- prototype of current bipolar.

4. FATHER OF MODERN TOTAL HIP ARTHROPLASTY
SIR JOHN CHARNLEY
• Pioneering work in all aspect of THA, including the
concept of low frictional torque arthroplasty, surgical
alteration of hip biomechanics, lubrication, materials, design
and clear air operating room environment.
• LFA – low friction arthroplasty consisted of a metal femoral
stem which had a small head (22.225mm) to reduce the
wear on the bearing surface, a polyethylene acetabular
component and acrylic bone cement along with a
trochanteric osteotomy.
• To overcome the failures of the Teflon cups for acetabular
component, he used a high density polyethylene (HDPE),
which was later replaced by (Ultra high molecular weight
polyethylene)UHMWPE.

5. LEVER ARMS OF THE HIP JOINT
Whenever abductor
lever arm is increased,
it reduces forces on
the hip joint. This
lowers the friction and
frictional torque and
hence lessens the
chance of wear and
loosening of implants

6. TRIBOLOGY?
• Science of interactive surfaces in relative motion – fixed acetabulum and moving
femoral head.
• It is a study of
- friction
- Lubrication
- Wear

7. WHAT IS WEAR?
•It is defined as the loss of material from
surfaces as a result of motion between
those surfaces.
•Material is in the form of particulate
debris.
• THR – Adhseive wear
• TKR – Abrasive wear & fatigue wear
•Wear rate lesser in cemented compared
to uncemented.
FAILURE
WEAR
DEBRIS
OSTEOLYSIS
LOOSENING

8. Step 1: Wear and Osteolysis
• Motion between articulating surfaces
•Unintended impingement or motion
•Leads to formation of wear particles
Step 2: Macrophage activated osteoclastogenesis and osteolysis
 Macrophage activation and recruitment
 Osteolysis by cytokines
- TNF – alpha, TGF – beta
- oxide radicals, hydrogen peroxide
- acid phosphatase, prostaglandins
- Interleukins ( IL – 1, IL – 6 )
 Increase RANK and RANKL activation
 RANKL mediated bone resorption

9. Step 3: Prosthesis Micro-motion
•Osteolysis surrounding the prosthesis leads to micromotion
•Increase particle wear and further prosthesis loosening

10. NEW UNIQUE DISEASE CREATED BY HUMANS –
POLY PARTICLES & OSTEOLYSIS
IMMEDIATE POST OP 17 YEAR FOLLOW UP

11. STRESS TRANSFER TO BONE
•A major concern with THR is that adaptive bone remodeling arising from stress
shielding compromises implant support, produces loosening, and predisposes to
fracture of the femur or the implant itself.
•Cementless stems generally produce strains in the bone that are more
physiological than the strains caused by fully cemented stems
•Increasing the modulus of elasticity, the stem length, and the cross- sectional
area of the stem increases the stress in the stem, but decreases the stress in the
cement and proximal third of the femur

13. APPROACHES TO REDUCE WEAR AND OSTEOLYSIS
•Material combinations
• Cross linked polyethylene
• Ceramic on ceramic
• Metal on metal
•Component Geometry (diameter and clearance)
•Performance parameters to consider to reduce osteolysis
• Wear volume
• Particle shape and size
• Chemical and biological activity of the debris

14. MATERIALS IN THR
• Should be biocompatible – should evoke no more than a tolerable host reaction at
local, systemic and remote side effects, consistent with the intended function of the
device.
• It should also evoke responses such as adhesion and ingrowth and should be able to
tolerate cyclical physical loads consistently.
• Youngs modulus = Stress/Strain (Stress – force per unit area, Strain – change in
length from the original length)
• Approximate youngs modulus – 2(PMMA): 20 (bone): 100 (Titanium): 200 (Stainless
Steel & Cobalt alloys)

15. 1. COBALT BASED ALLOYS
• contain chromium, molybdenum, carbon and other elements like nickel, silicon
and iron.
• Primarily used in total joint replacements because of high strength and
resistance to corrosion.
• High strength, High Hardness (resistance to surface deformation)
• Used in making bearing surfaces and some cemented stems.

16. 2. TITANIUM AND TITANIUM BASED ALLOYS
• High strength and fatigue resistant
•Resistant to corrosion
•Has an oxide surface which is inert and helps in reforming after damage.
•Its low modulus of elasticity makes it favourable as it helps in transferring the
load to the bone and more so in uncemented implants
• Used in: Cementless Femoral stems, Acetabular shells
•Cannot be used in femoral heads due to wear (softer)

17. 3. STAINLESS STEEL
• Most common steel used in implants is the 316 steel
• inferior to both cobalt and titanium alloys when it comes to corrosion
resistance, biocompatibility and fatigue life
•Used in femoral components due to high strength, low cost and easy
workability

18. 4. ZIRCONIUM AND TANTALUM ALLOYS
• Zirconium is similar to titanium in some aspects.
• being tested for making femoral heads.
• Tantalum is used a bone ingrowth substrate for porous coated surfaces and
has excellent biocompatibility
• used in filling up bone defects in revision scenarios.

19. COMPONENTS OF THA
Acetabular component - consists of two components
Cup - usually made of titanium
Liner - can be plastic, metal or ceramic
Femoral components - consists of two components
Head - metal, ceramic
Neck & stem - metal

20. IMPLANT SELECTION IN THA
Bearing options
 Metal on Poly
 Ceramic on Poly
 Ceramic on ceramic
 Dual mobility systems
 Constrained liners
Fixation strategies
 Cemented systems
 Uncemented systems
 Hybrid options

21. FEMORAL COMPONENTS
• The primary function of the femoral component is the replacement of the
femoral head and neck after resection of the arthritic or necrotic
segment.
• The ideal femoral reconstruction reproduces the normal center of rotation
of femoral head, which can be determined by
-Vertical height (vertical offset)
-Medial head stem offset ( horizontal offset)
-Version of the femoral neck(anterior offset)

22. • Vertical offset- LT to center of the femoral
head. Restoration of this distance is
essential in correction of leg length.
• Medial head stem offset- distance from the
center of the femoral head to a line through
the axis of the distal part of stem.
Medial offset if inadequate, shortens the
moment arm – limp, increase, bony
impingement and dislocation.
Excessive medial offset –increase stress
on stem and cement which causes stress
fracture or loosening.
• Version of the femoral neck : important in
achieving stability of the prosthetic joint. The
normal femur has 10-15 degree of
anteversion.

23. METHODS BY WHICH THE HORIZONTAL OFFSET CAN BE CHANGED
• Increasing the neck length
• Decreasing the neck shaft angle
• High offset implant (medialize the neck and concomitantly increase its length)
•Trochanteric osteotomy
•Acetabular component

24. HEAD SIZE
• Range of head sizes – 22, 26, 28, 32, 34
mm.
• Large size femoral heads improve the
range of motion and the fluid film
lubrication would reduce the wear rates.
• smaller size of head is associated with
increased rate of dislocation.
•AOM (Arc of motion) directly proportional
to Femoral head:neck ratio

25. • For a given neck diameter, the use of a larger femoral head increases the head-
neck ratio and the range of motion before the neck impinges on the rim of the
socket will be greater.
•When this impingement does occur, the femoral head is levered out of the socket.
•The “jump distance” is the distance the head must travel to escape the rim of the
socket and is generally approximated to be half the diameter of the head.

26. • The size of the femoral head, the ratio of head and neck
diameters, and the shape of the neck of the femoral component
have a substantial effect on the range of motion of the hip, the
degree of impingement between the neck and rim of the socket,
and the stability of the articulation.
•Neck geometry and arc of motion
•Trapezoidal and oval neck increases the arc of motion
•Circular neck decreases AOM
•The ideal configuration of the prosthetic head and neck segment
includes a trapezoidal neck and a larger diameter head without
a skirt

27. DORR CLASSIFICATION OF PROXIMAL FEMURS

28. CEMENTED FEMORAL STEM
1. Cobalt chromium alloy – high Elasticity, Reduce stress
2. Cross section – broad medial border, broader lateral border
3. Sharp edges avoided – Stress riser
4. Stem should cover 80 % of femoral canal.
Proximal cement mantle – 4 mm
Distal cement mantle – 2 mm
5. Smooth polished surface – less debris, less loosening, less wear tear
6. Stem length – 120 to 130 mm
Larger stem – varus malposition and anterior cortex perforation

31. CEMENTLESS FEMORAL STEM
• Designed to ensure intimate contact between the implant and the bone which
reduced the motion between the two.
•Based on the principle-bone ingrowth from the viable host bone into porous metal
surfaces of implant.
•Indications for cementless components
1. primarily active young patients
2. revisions of failed cemented components.
•The close contact between the implant and the host bone is the key. Ideal gap of
about 50 µm can be bridged. More than 100 µm decreases the chances of bony
incorporation.

32. • Coated by surfaces that promote bone formation
•Surface Coating – Proximal, Extensive, Fully coated
• Surface treatment with Sintered Beads, Titanium mesh with or without HA coating.
• Material of stem – Titanium , Chromium Cobalt alloy
• Shapes – Cylindrical, Tapered, Anatomical
1. Cylindrical Stems – symmetrical in cross section, allow contact in proximal
diaphysis
2. Tapered stems – wedge shaped with widening in the proximal half,
improved contact with metaphysis and therefore rotational stability
3. Anatomic stems – Proximal posterior bow and distal anterior bow

38. NON POROUS COATED FEMORAL STEMS
•Non-porous femoral implants have surface roughening
that provide a macrointerlock with bone
•No capacity for bone ingrowth but provides lasting
implant stability
•With the concerns about fatigue strength, ion release
and adverse femoral remodeling, these non porous
stems came into use over porous stems

39. •Smaller stems have also come in
because metaphyseal fit and ingrowth can
allow rotational and axial stability without
the need for diaphyseal support.
• This allow preserves proximal bone stock,
especially in young patients who may need
revision surgery

40. WHICH STEM TO CHOOSE?
Young active patient more demands
DORR TYPE A & B
NON CEMENTED STEM
PROXIMAL COATED
METAPHYSEAL ENGAGING STEMS
(TAPERED)
Old patient with <10 years life
expectancy and less demands
DORR TYPE B & C
CEMENTED STEM
SMOOTH FINISH
METAPHYSEAL ENGAGING

41. ACETABULAR COMPONENT
Optimum position for the prosthetic socket which should be inclined 45⁰ or less to
maximize stability of the joint (normal 55⁰).
Types :
1. Cemented acetabular components.
2. Cementless acetabular components.
3. Custom made acetabular components

42. CEMENTED ACETABULAR COMPONENT
• Original sockets-
•thick walled polyethylene cups. Vertical and horizontal
grooves on external surface to increase stability within the
cement mantle
•wire markers were embedded in plastic to allow better
assessment of position on postoperative roentgenograms.
• Recent designs-
•have a textured metal back which improves adhesion at the
prosthesis cemented interface. A flange at the rim improves
pressurization of the cement.
•used in elderly patients, tumour reconstruction and the
circumstances with less chances of bony ingrowth as in
revision THR.

43. NON CEMENTED ACETABULAR COMPONENTS
•Most cementless acetabular components are porous
coated over their entire circumference for bone
ingrowth
•Fixation of the porous shell with transacetabular
screws
•Pegs and spikes driven into prepared recesses in the
bone provide some rotational stability but less than
that obtained with screws.

44. ZTT socket
Hemispherical , porous coated cup designed
with dome screw holes and transacetabular
screws for stability.
Six peripheral screw holes provide choice of
screw locations for additional stability and
also lock in the polyethylene insert.

45. LINER
•Liners have been proven to be another zone of failures in the cmeentless cups
•Focus being on the
• Material
• Locking mechanism to the acetabular shell
• With an improvement in locking mechanisms, the earlier problem of
“Backside Wear” has lessened.

46. BEARING OPTIONS
1. Metal on Poly
2. Ceramic on Polyethylene
3. Metal on Metal
4. Ceramic on Ceramic

47. POLYETHYLENE
• UHMWPE has been the bearing material of choice in THA for over 50 years now.
•PTFE (polytetrafluoroethylene) was the initial choice by charnley but it failed
miserably.
• The polyethylene liner must be fastened securely to the metal shell.
•Current mechanisms include plastic flanges and metal wire rings that lock behind
elevations or ridges in the metal shell, and peripherally placed screws
• in vivo dissociation of polyethylene liners from their metal backings has been
reported micromotion between the nonarticulating side of the liner and the interior
of the shell may be a source of polyethylene debris generation, or “backside wear.”

48. GOLD STANDARD
•The bearing to which all others
shoulder be compared – Chrome
cobalt on UHMWPE sterilized with
2.5 to 4 mrads in air
•This has an approx. linear wear rate
of 0.01 to 0.02 mm/year

50. CROSS LINKING
•Chemical nature of UHMWPE consists of long chain of polyethylene molecules in
parallel orientation
•Exposure of these to gamma radiations leads to free radical formations which help in
formation of cross links between adjacent polyethylene chains
•This cross linking highly improves the wear resistance.
•Degree of cross linking depends on
• Type of irradiation
• Amount of irradiation
• Duration
• Atmosphere in which the irradiation is carried out in.

51.  XPLE reduces wear by 85% compared to conventional poly
 XPLE wear particles are small and are more reactive
 Models predicts and 4 fold reduction in osteolytic potentital compared to
conventional polyethylene
 Concerns increased wear when XPLE is used in active patients with Larger
head
 Highly cross linked poly – newer development wherein high doses of
radiation more than 5 mrad are given
 Improved mechanical wear properties and also decreases the oxidation of
polyethylene which was seen in the previous generations

53. METAL ON METAL
 In 1988, second generation MOM bearings were
introduced
 These are carbide containing forged Co-Cr-Mo alloy
 Better implant design with optimal clearance resulted in
low wear rate and longer life and were used in younger
patients
 Recent studies show a perivascular inflammation with
prominent lymphocytic cuff – under scrutiny
 Increase levels of Co and chromium in blood and urine
which are not BIOINERT
 Not in use anymore

54. ALVAL LESION (ASEPTIC LYMPHOCYTIC
DOMINATED VASCULTIS ASSOCIATED LESION)
 Hypersensitivity type IV
 Groin pain
 Green gray coloured fluid
 Looking like an abscess/pseudotumour

55. CERAMIC
•FATHER OF CERAMIC – BUTIN 1970
•FIRST AND SECOND GEN OF CERAMICS
•Started in Europe and japan
•Monolithic acetabular component, fabricated from alumina ceramics (AI203)
•Modular acetabular component with metal backing with biological coating to
improved the fixation later on
•Failure due to
oFixation was the biggest problem initially
oMigration and tilting of the component
oEdge loading, accelerated wear and impingement
oFracture of the acetabular component

56. MEDICAL GRADE CERAMIC
Composed of pure crystals of aluminum or zirconium oxides
•Most chemically inert
•Biologically inert
•Stiff
•Strong
•Hard
•Only substance harder than aluminum oxide is diamond

57. CERAMIC-ON-CERAMIC BEARING
MECHANICAL LAW:
Harder surfaces coupled together reduce the wear of
the coupling surfaces and produce very low rates of
wear particles.
CERAMIC MATERIAL:
Hardness which it gives can be polished to much
lower surface roughness with wear resistance and
scratch resistance

58. HYDROPHIILIC PROPERTY
•Improved wettability of ceramics contributes to lower
friction than CoCr when articulated against UHMWPE
under physiological loading and lubrication conditions
•It ensures that the synovial fluid film is uniformly
distributed over the whole bearing surface areas

59. SUBOPTIMAL POSITIONING OF THE CUP
•Hardness and wear are sensitive to design,
manufacturing and implant variables
•Rapid wear has been also observed, generally
associated with sub optimal positioning of the
implants
•Edge loading, increased wear, fractures etc.

60. DISADVANTAGE
•Cannot deform under stress
•When stresses acting on medical ceramic
components exceed a certain limit, the
ceramic material bursts.
•Revision is very difficult in these cases
•Modern third generation ceramics are
better and will not burst out but will chip
off during assembling with the metallic
backup

61. •The feared fracture of the ceramic components mainly the ball has notably
disappeared off late due to two main technological developments
1. Introduction of individual testing of every ceramic component before it is
shipped and sold to the surgeon (1993)
2. Hot isostatic pressing (HIP): So alumina ceramics are produced in very
dense fine grain alumina with very limited grain boundaries and inclusions

62. POSSIBLE CONCERNS WITH CERAMIC HIPS
• Squeaking noise, clicking noise
• Stripe wear
•Studies have demonstrated that
these noises from ceramic total hips
are associated with faulty position
of the ceramic cup(Walter 2007)

63. DELTA CERAMICS (BIOLOX DELTA)
•Zirconia toughened alumina (ZTA) ceramic
•Nano sized
•75% alumina and rest is zirconium, yttrium and chrome
•Superior strength and wear
•Helps to limit crack propogration

64. CERAMIC-ON-POLY
 Ceramic heads have better wear characteristics compared to
metal heads
 Decrease in osteolysis
 Wear rate is 0.25-0.75% of metal on poly articultaions
 DISADVANTAGE
 Highly taper tolerance sensitive – cannot revise with existing
taper
 Risk of ceramic head fracture
 IT IS THE INTERNATIONAL WORKHORSE IN THA

67. OXINIUM (OXIDIZED ZIRCONIUM)
•It is a zirconium metal alloy that is placed
through an oxidation process to yield an
implant with a zirconia ceramic surface.
•Weighs 20% lighter
•Useful in young active patients

68. DUAL MOBILITY CUPS
•Head articulates within a retentive polyethylene
•Poly is free to move in a metal shell in a NON
RETENTIVE WAY
•Increased stability
•INDICATIONS
1. Done in patients with weak or poor soft tissues
2. Neuromuscular issues
3. Complex primary stituations like ankylosed hips
4. Revision scenario (Dislocations)

69. CONSTRAINED ACETABULAR LINER
Mechanism: lock the prosthetic femoral head into
the polyethylene liner
Indications
 Insufficient soft tissues
 Deficient hip abduction
 Neuromuscular disease
 Hip with recurrent dislocations despite well positioned
implants
Longevity is around 7 or 8 years, used as final
salvage.

70. CONCLUSION
•Avoid metal heads more than 32 mm size to rule out the risk of trunionosis
•Ceramic on highly cross linked poly is the most common bearing used world
wide with oxinium being preferred at some centers
•Ceramic on ceramic reserved for younger patients
•Head size more than 36 mm is not desirable as it increase the risk of trunion
wear
•28,32, 36 are commonly used
•Cemented in older patients with less life expectancy
•Uncemented in younger population

71. THANK YOU