1.
Bearing Surfaces in Total Hip
Arthroplasty

2.
History
Interpositional arthroplasty
1912- Sir Robert Jones- Gold foil

3.
Mould arthroplasty
1923-Smith Peterson
Restore congruous articular surfaces
Bleeding cancellous bone of femoral head and
acetabulum
Metaplasia of fibrin clot to fibrocartilage

4.
Glass
Pyrex – viscalloid - celluloid derivative
Bakelite
Fragility and foreign body reaction

5.
1937-Venable and Stuck- Vitallium- results
encouraging
Aufranc

6.
Judet brothers- heat curved acrylic femoral head
prosthesis-fragmentation of acrylic with wear- severe
tissue reaction-bone destruction
Thompson and Moore – metallic endoprosthesis with
medullary stems- erosion of bone on pelvic side

7.
Metal on metal
Urist, Ring and McKee Farrar
Friction metal wear
High incidence of loosening and pain.

8.
Sir John Charnley
-Low friction torque arthroplasty
-Surgical alteration of hip biomechanics
-Lubrication
-Material design
-Operating room environment
-PMMA

9.
1 st Charnley prosthesis
Moore prosthesis stainless steel femoral component
Thin polytetrafluroethylene shell for acetabulum

10.
Tribology
Surfaces interacting under an applied load and in
relative motion
Study of:
-Friction
-Lubrication
-Wear

11.
Wear
Types of wear:
1. Adhesive wear
2.Abrasive wear
3. Third body wear
4.Fatigue wear

12.
Adhesive wear
Adhesion during contact of opposing bearing
surfaces
Sliding breaks these contacts
Strength of adhesion exceeds strength of material
Particles are pulled from the material

13.
Abrasive wear
Hard projection on one surface cuts into the opposing
surface

14.
Third body wear
Hard particles such as bone or PMMA if trapped
between bearing surfaces cause abrasive damage

15.
Fatigue wear
Repetitive loading of the bearings during articulation

16.
Wear modes
Conditions under which the prosthesis was
functioning when the wear occurred

17.
Mode 1
Motion of 2 primary bearing surfaces against each
other

18.
Mode 2
Primary bearing surface moving against a secondary
surface that was not intended to come into contact
with the first

19.
Mode 3
Contaminant particles directly abrade one or both of
the primary bearing surfaces
Third body abrasion or wear

20.
Mode 4
2 secondary surfaces rubbing together
Backside wear

21.
Wear debris causes osteolysis
Compromise fixation
Complicate revision procedure.

22.
Wear threshold value
 0.1 mm/year

23.
Threshold is modified by
-Intracapsular pressure
-Bone interface access
-Patient reaction to debris

24.
Types of bearings
Hard
Soft

25.
Femoral Head material
Metallic alloys that can be used with UHMWPE liner:
-Stainless steel 316L
-Cobalt chromium alloy
-Titanium alloys

26.
Ceramics with UHMWPE
Alumina
Zirconia

27.
Conventional UHMWPE
Ram extrusion
Compression molding

28.
Sterilization
Ethylene oxide
Gas plasma
Gamma radiation in air (2.5 to 4 mrad)
Gamma radiation in inert atmosphere (nitrogen,
argon or vacuum)

29.
Gamma radiation
Cross-linking of polyethylene molecules
Interaction of free radicals formed during irradiation
Improved wear resistance

30.
Highly cross-linked UHMWPE
Higher doses of radiation
Heat

31.
Remelting: Heating above the melting range of
polyethylene
Annealing: Heating below the melting range

32.
UHMWPE-
Semi crystalline polymer
Mechanical behavior - crystalline morphology

33.
Benefits of cross linked
polyethylene
-High wear resistance
-No toxicity
-Relatively low cost
-Multiple liner options (elevated rim etc)

34.
Risks of cross-linked
polyethylene
-Reduction in other material properties -gross
material failure
-Increased bioactivity of wear particles

35.
Metal on metal bearings
Muller and Weber
Wear depends on:
1.Type of cobalt chromium alloy
2.Surface finish
3.Bearing clearance
4.Sphericity

36.
Fluid film lubrication
1. Bearing size
2. Clearance
3. Sphericity
4. Surface finish

37.
Benefits of Metal on metal
 Very high wear resistance
 Favors larger diameters (lowers wear)
 Long in vivo experience

38.
Risks of Metal on metal
Increased ion levels
Delayed type hypersensitivity
Carcinogenesis

39.
Ceramic on ceramic bearings
Alumina:
1. Hardness
2.High wear resistance
3. Chemical inertness

40.
Benefits of ceramic on ceramic
Highest wear resistance
No toxicity
Long in vivo experience

41.
Risks of ceramic on ceramic
1.Position sensitivity
2.Liner chipping
3.Fracture risk

42.
Material
properties
CoC MoM MoHCLUH
MWPE
HardnessM
Pa
2300 350 Low
# reported no +remelted

43.
Tribology
CoC MoM HCLUHM
WPE
Wear 1 25 100
Particle
size
<0.02and
>0.2
0.05 0.4
Metal ion Not
increased
increased Not
increased

44.
Biologic effectsCoC MoM MoHCLUH
WPE
Cell
toxicity
No Yes No
Local
tissue
reaction
Low Low Low
Chromo.
changes
NR R NR
Hypersensi
tivity
NR R NR
Carcin. NR * NR

45.
Coc MoM MoHCLUH
MWPE
Squeaking + + -
Clicking + + -
Seizing - + -

46.
Future
*IDEAL*

47.
Next generation polyethylenes
1. Sequential irradiation and annealing
2. Irradiation and solid state deformation by extrusion
below melting temperature
3. Vit E antioxidant containing polyethylene

48.
Metal on metal
Increase in femoral head size –greater sliding velocity
and increased probability of fluid film lubrication –
decrease in wear
Reduced risk of impingement and dislocation
32 mm and bigger

49.
Ceramic on metal
Alumina head
Cobalt chromium alloy cup
Reduced wear rate 100 fold
Clinical studies underway

50.
Ceramics
Alumina – Zirconia combination: for increasing
toughness of alumina
75 % alumina 24 % Zirconia 1 % chromium oxide
- Greater bending strength
- Lower wear rate
- Added manufacturing complexity
- Cost

51.
Take home message
 There is no 100 % ideal bearing surface
 Hard/hard and hard/soft
 Tribology –friction, lubrication and wear
 Wear causes osteolysis

52.
 Modern bearings: - all have low wear
 Young and active patients Hard/hard bearings will
produce less wear debris but noise remains a
problem

53.
 For hard on hard bearings cup placement is
important to reduce risk of impingement, excessive
wear and fracture.
 Metal on metal bearings release metal ions and
corrosion products and probably should not be
used for patients with impaired kidney function or
women of child bearing age.