Bearing Surfaces and Wear

Hip Bearing Couples

  • Metal on polyethylene
  • Ceramic on polyethylene
  • Ceramic on ceramic
  • Ceramic on metal and metal on metal are now rarely used

Wear Modes

  • Mode 1 is wear between the two intended bearing surfaces
  • Mode 2 is an intended surface against a nonintended one, such as a head against an exposed metal shell
  • Mode 3 is third body wear from cement, bone or metal debris
  • Mode 4 is two nonbearing surfaces, such as modular backside or taper fretting

Wear Mechanisms

  • Adhesive, abrasive, fatigue and corrosive wear
  • Particles of 0.1 to 1 micron are the most biologically active
  • Macrophage response to particles drives osteolysis and loosening
  • Linear wear of conventional polyethylene above about 0.1 mm per year is linked to osteolysis

Materials

  • Highly crosslinked polyethylene greatly reduces wear, and vitamin E stabilised variants limit oxidation
  • Alumina and zirconia toughened alumina ceramics have low wear but can fracture, chip or squeak
  • Early zirconia heads were withdrawn after fractures
  • Metal on metal bearings release ions and caused adverse reactions to metal debris, pseudotumour and the ASR recall
  • Larger heads reduce dislocation but increase volumetric wear and taper stress

Knee

  • Cobalt chrome femoral component on polyethylene is standard
  • Backside wear occurs with modular tibial trays
  • Mobile bearings show no consistent benefit over fixed bearings
  • Oxidised zirconium suits metal sensitivity

Registry Data

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 15 October 2026.