Materials in Hip Replacement

Common questions about hip replacements relate to the material used to replace the hip joint. There are differences depending on whether a cemented hip replacement is used or a cementless hip replacement. My preference is to use a cementless device. The way this works is that the metal hip prosthesis which is made of a titanium alloy which has a special coating on it and has a special surface texture. This allows bone to grow into the implant and firmly anchor it to the bone. The implant effectively becomes part of the skeleton. On the socket side, the process is similar with a titanium alloy hemispherical shell which also has the special coating on it to allow bone ingrowth. Into this shell will fit a special liner which will articulate with the ball applied to the metal stem.

The key factors in determining how long a hip replacement will last, relate to obtaining a good bond of the implant to the bone, and the material that will be used for the ball and the liner of the socket. These materials can be quite different. The commonest material would be a obalt chrome metal ball and this would articulate with a polyethylene plastic liner placed in the shell. Historically this plastic liner has been the weak link in hip replacements as it tends to wear out with time and the bigger issue being the small particles that are released as it wears and which can damage the surrounding bone making any re-do surgery more difficult. This plastic material has changed and improved overtime and current research on so-called highly cross-linked polyethylene indicates that it will last much better.

My preference is to use a ceramic on ceramic articulation. Ceramic is a very hard material and highly polished. The amount of wear overtime is incredibly small and a further significant advantage is that the small particles released do not cause a bad reaction in the soft tissues or bone surrounding the hip replacement. We don’t quite know how long hip replacements using ceramic as the bearing surface will last, but data in the literature show that out to 15 and 20 years one can’t see signs of wear on x-ray. I recently looked at my own results of ceramic on ceramic hips with between 10-14 years of follow-up and we don’t see any signs of loosening or wear of the bearing surface.  The really important point about these results is that the bone remains in perfect condition around the implant which means that should a re-do procedure become necessary at some point, then this will be relatively straightforward.