Ceramic on Ceramic
The bearing surface is all important. The frictional forces are dependent on the surface roughness and the chemical composition of the material. Lubrication reduces friction, which reduces wear and optimum ‘joint’ motion occurs when there is a fluid film between hard on hard bearings, in this case, ceramic on ceramic.
Ceramics are hydrophilic and permit better ‘wettability’ of the surface, which ensures that a fluid is uniformly distributed over the bearing surface.
Ceramics have an extremely low wear rate - near zero wear - compared with conventional polyethylene. Ceramic is second only to diamonds in hardness and is stable and chemically inert. It has twice the hardness of stainless steel and is resistant to scratching. However, it is brittle and fracture of the ceramic liner (in a metal shell) or ceramic head remains a possibility, however small. The overall fracture rate reported in the literature is around 0.004% (4 in 100,000), compared with the fracture rate of femoral stems, which is 0.27% (270 in 100,000).
Ceramics are available from a limited number of companies as the quality of this material is dependent on a rigorous manufacturing process. At present, there is also no choice of elevated liners, which may potentially increase the risk of dislocation.
Ceramic bearing surfaces were first utilised in hip replacements by Pierre Boutin Pau in France in 1970. New composite ceramics such as Biolox and now Delta are associated with less crack propagation and fracture potential. The head size can be increased (to 36mm) when articulating with an average sized socket.
The well-publicised problem of a noise - squeaking - emanating from the ‘hip joint’ with ceramic on ceramic bearings is well documented in the literature(although it appears to be mainly associated with one make of cup). However, squeaking is not exclusive to ceramic couples and can occur with all bearing surfaces. Squeaking has not been documented in any patients reviewed in Bristol since 2006 in whom the Exceed ABT with a ceramic on ceramic bearing has been used.
The next generation of composite ceramics has been developed and it is likely the surgeon will be able to use even bigger head sizes, thus further reducing the risk of dislocation.
Bio-compatibility of ceramics is better than metal on metal or metal on polyethylene bearing surfaces. No toxicity or hypersensitivity reactions have been demonstrated and there is minimal tissue reaction. Osteolysis has been documented, but no chromosomal aberrations or carcinogenic changes have been triggered by such bearing surfaces.
To make an appointment e–mail Sue Misir, secretary to Mr Evert Smith, or telephone:
- 0117 907 4228 (private)
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For an NHS appointment your GP will need to refer you. How?
Evert Smith is an Orthopaedic Surgeon in whom I have absolute faith and confidence.
Bob Gibbons, 2007.