cadera / hip - Active Congress.......

MARTES / TUESDAY
34
• Importance of these elevations not established
• ? Hypersensitivity 77
• Prevalence of dermal sensitivity in patients
with a total joint arthroplasty substantially
higher than general population
• Unclear if metal sensitivity is a contributing
factor to implant failure
• Currently no generally accepted test for
clinical determination of metal hypersensitivity
to implanted devices
• No clinical data beyond 10 years for second
generation metal on metal implants
• Implant costs
III. Ceramic on Ceramic Bearing Surfaces
A. History
• First ceramic on ceramic total hip performed
in France in 1970 by Boutin 21
• First ceramic on ceramic total hip implanted
in Germany in 1974 by Mittelmeier
and Walter 141,142
• The Autophor implant (Richards, Memphis,
TN), a Mittelmeier design, marketed
in the US but abandoned secondary to
unacceptable clinical results 38,123
• First generation implants had limited clinical
success (high fracture rate and aseptic
loosening) secondary to poor materials,
manufacturing, and component design;
not the bearing surface itself 46,74,82
• European scientists and clinicians lead
development of improved materials,
manufacturing, component design, and
implantation technique 142,165,202,207
• Simulator and retrieval studies demonstrate
ceramic on ceramic bearings have the lowest
wear volumes of all currently available
bearing couples 50,51,61,152,157,158,164,199,207,211
• New clinical studies on second and
third generation bearing surfaces ongoing
157,213
B. Design Issues
• First generation ceramic articulations:
Alumina (1970)
• Poor understanding of materials and
manufacturing 207,213
• Poor materials
- Large grain size
- Low density
• Poor manufacturing
- Large sphericity deviations
- Large mismatches (diametral clearance
and taper tolerance)
- Large pore size
• Second Generation Ceramic Articulations
• Alumina (1977)- Significant advances in
quality and manufacturing 37,85,182,207,215
• High purity: monophase material provides
long term stability
• High density: provides better surface
finish
• Small grain size: provides increased
strength
• Taper lock: improved tolerance matching
between mating parts
• Improved processing: clean room processing,
improved sintering techniques,
hot isostatic pressing, laser marking and
proof testing
• Low porosity
• Zirconia (1989)-Mixed clinical and in
vitro results 36
• 73% improved strength 34,54,65
• Improved fracture toughness (2X) 85,182
- Allows use of smaller diameter femoral
heads
• Strength and toughness at expense of
thermal stability 17,161
• 1/98 – 9/99: St Gobain Desmarquest
changes manufacturing process of
Zirconia femoral heads - ↑ fracture rate
and FDA recall
• Third Generation Ceramic Articulations
• Ceramic composites (i.e. Biolox forte
and delta)
• Wear and thermal stability of alumina
2,3
• Strength and toughness of zirconia 2,3
• Clinical and in vitro investigations ongoing
156,186