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.