Bearing Surface— It is the surface of a bone that comes in (normal) direct contact with the similar surface of another bone as part of a synovial joint; naturally formed by articular cartilage.
In total hip replacement, both the acetabular and femoral bearing surfaces are replaced with artificial bearing surfaces made up of metal, ceramic, polymeric components etc.
Ideal bearing surface:
The ideal bearing surface in THR prosthesis would have the following features:
Low coefficient of friction
Small volume of wear particle generation
Low tissue reaction to wear particles
High resistance to third body wear
Enough deformation of articular surfaces to permit adequate fluid film lubrication during the stance phase without increasing wear
Types of bearing surfaces:
- Hard-on-soft bearings– Soft Bearing always on acetabular component, e.g. UHMWPE (ultra high molecular weight polyethylene) & highly cross-linked UHMWPE. Hard bearings: options for the femoral head bearing couple include CoCr, Ceramic (Zirconia & Alumina), & ceramicized metal (oxidised Zirconium-OxZr: improved wear properties, increased surface hardness, smoothness, & wettability, but high cost),
♦Ceramic-on- crosslinked polyethylene
- Hard-on-hard bearings–
♦Metal-on-Metal bearings: as both stemmed THA & hip resurfacing devices.
– benefits- lower volumetric wear rates compared with conventional metal- on-polyethylene bearings, greater implant stability because of the larger femoral head sizes, & greater femoral bone conservation in hip resurfacing.–risk of metallosis & associated lymphocyte-driven adverse soft-tissue reactions, aseptic loosening
♦Ceramic-on-Ceramic bearings: advantage of low wear and low soft-tissue reactions but, risk of device-generated squeaking, & ball & liner fracture (overcome by use of mixed oxide ceramic materials with increased fracture
⇒Bearing surfaces in hip replacement – Evolution and likely future by Narinder Kumar, Col; Gen N.C. Arora, Maj;& Barun Datta, Col (PMC4223187)