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Orthopaedic Materials / Bearing Surfaces

 

synonyms:

Polyethylene

  • Low wear, lowest cost, high oxidative resistance
  • Highly cross-linked polyethylene wear rate <0.1mm/year.
  • Sterilization in air = oxidation = increased poly fracture and wear.

Metal on Metal Bearing Surfaces

  • Lower wear than metal on poly, high cost
  • Initial high wear stage last for @1yr followed by steady state wear of a few microns/year.
  • Metal ions are found in blood and urine at 5-10 times normal levels.
  • Theoretical cancer risk. 28yr Nordic follow-up demonstrated cancer incidence in Metal-on-metal patients to be consistent with general poplulation. (Visuri TI, Proc Inst Mech Eng [H] 2006;220:399).
  • Relative contraindications: female of childbearing age, kidney disorder, known metal allergy.

Ceramics

  • Lowest wear, higly biocompatible, high cost, potential squeaking and fracture
  • Alumina components subject to fracture risk due to brittleness.
  • Potential for stipe weah if improperly positioned.
  • Squeking 1-3%, etiology unknown. (Walter WL, J Arthroplasty 2007;22:496).
  • Zirconia = yttrium-stabilized zironia: theoretical increased toughness and lower wear, but clinical studies indicate increase osteolysis likely due to phase transition in vivo. (Hernigou P, JBJS 2003;85Br:504).
  • Future alternatives: Alumina (75%)-Zirconia(25%) composites, oxidized zirconium, ceramic on metal articulations.

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