- 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.
- High dose radiation to polyethylene (10 Mrad) leads to higher cross-linking and decreased adhesive and abrasive wear. However, fatigue wear and creep (deformation without wear) increases when polyethylene is melted (to remove free radicals) during the cross-linking process.
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.
- 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.