Which Hip Replacement is the best?

This remains a difficult question to answer and depends on a number of individual circumstances. Increasingly the Orthopaedic community is gathering more and more information from registries from  around the world that tell us how certain implants are doing. There can be conflicting information because different countries have a slant towards different implants and it is difficult to rule out the effect of historical bias where certain implants may not have been successful and are no longer used.

Broadly hip replacements can be divided into those which are cemented and those that are uncemented. The cement is a grouting agent which holds the implant in the bone and was the earliest method of fixation of hip implants. Newer technology is able to produce a surface coating on a metal implant that allows the bone to grow into the metal device and anchor it firmly – it effectively become part of the bone. This occurs over about a 6 week period and for that to happen the implant needs to be fixed very tightly in the bone and there should be no significant movement between the implant and the bone during that period.

Both these types of devices are showing good longterm results. Cemented fixation is considered a safer option for older patients where the bone may not be so strong and so may not be able to have a device implanted firmly enough to allow the bone to grow in.

It looks as if in younger patients, data is building to suggest that uncemented hips are starting to look better – certainly on the socket side.

The other major issue is the choice of the ‘bearing surface’. This is the part of the hip replacement that moves – the ball head of the stem against the liner of the new hip socket.

Historically this has been a metal on specialized plastic articulation. Time has shown that the plastic (a special type of polyethylene) is the weak link and the small wear particles can damage the bone over time and subsequently make it much harder to perform a re-do (revision ) hip replacement.

Newer materials have improved these wear properties. The polyethylene has been improved to make this longer lasting. A ceramic articulation continues to show that this has the lowest wear rate and in my view, remains the best material to use for this part of the replacement particularly for younger patients.

The answer to which hip replacement is the best is that there are a number of devices that have been used for many years which show good longterm outcomes. The difficulty is working out which of these is likely to last 30 or 40 years. Registry data is less good at determining which implants are doing well in specific cohorts of patients and for this one has to look at individual studies where this detail is available. The studies relating to ceramic on ceramic articulations continue to look extremely promising, with reports at 20 years showing no signs of wear or damage to the surrounding bone from wear particles. This bodes well for the device continuing to last for many more years.