Status: Uncemented femoral

components in hip resurfacing

Uncemented resurfacing components are a new development. The acetabular components used routinely are uncemented, while the femoral components routinely have been cemented to bone.

There is virtually no published data on the use of an uncemented femoral component. I will need to gather data for at least three to four years before I will be able to provide any useful data on this subject. Fixation of total joint implants to bone can be accomplished by cement or by porous ingrowth technology. Cement fixation is immediate, while permanent fixation with uncemented components requires a six to twelve months of bone ingrowth before it is considered well fixed. Some total joint replacement components have had more success with cement fixation, while others have done better with uncemented technology.

In hip surface replacement at eight years, approximately 95% of implants are still working in young patients with cemented femoral fixation. Only rarely can these 5% failures be blamed on the cement fixation itself.

However, theoretically, cement is the weak link when long-term (> 10 years) fixation of the femoral component is contemplated. If uncemented femoral components can be shown to achieve reliably high rates of ingrowth in the short term, they will probably outperform cemented femoral components in the long-term. It is also possible that avoiding cement may decrease some of the early failure such as fractures or AVN of the femoral head. This is because cement heats up during its curing process and may traumatize the femoral head at the time of the original surgery. This may be part of the cause of the fractures or AVN seen in the few early failures of hip resurfacing.

At this point, I basically consider the cemented and uncemented versions equivalent. I believe that the uncemented femoral component will be superior but I do not know. Nobody knows! Added risk of the unknown is taken by the patient who wishes to try this new technology. If the uncemented femoral component fails, revision to a cemented component will not be an option; large bearing metal-on-metal total hip replacement will be the second operation to revise the failed femoral resurfacing component.

I worked with Biomet on an uncemented femoral component and the precision instrumentation required for this implant for the last five years. The Biomet component has a full coating or Titanium plasma spray under the entire under-surface of the femoral component. This is the best implant available to maximize the chance of bone ingrowth. To my knowledge, the only other femoral component available in the world currently is from Corin. There are some early experiments in Europe with this device. It is not available in the US even on a study basis. When I originally proposed an uncemented femoral component to Corin eight years ago, they were unable to manufacture it. When I started working with Biomet to develop an uncemented femoral component, Corin also started to work on one. They were able to bring it to market in Europe first; however, their component is only partially porous-coated (less than 50%) with Titanium (but it does have complete hydroxyl appetite coating. I personally do not believe this is good enough for long-term fixation (>10 years), but nobody knows for sure yet. Finally, this year, we have completed development of the uncemented Biomet femoral component and quality control tested implants have begun rolling off the assembly line in Warsaw, Indiana. In April 2007, I first started implanting the uncemented femoral components. Biomet is not yet able to produce enough for me to implant them in every patient. Hopefully, soon, production will be increased so that my needs can be met and other surgeons can also begin getting a supply of these implants. Much interest has been generated for these implants already.

My intention is to convert completely to uncemented femoral components, as they become available. If a patient still prefers the cemented version, I will be happy to use this in his/her case.

At the time of this writing, I have implanted approximately 60 uncemented femoral components without immediate problems, (but it is too early to say how they will work). I will not be providing continuing public updates on the use of an uncemented femoral component. Instead I plan to formally report my data after three to four years of use, when I have meaningful results to publish. I will be happy to take into account your personal preference at the time of surgery. If you are absolutely determined to have an uncemented device in the near future, I will have to take this into account when we schedule a surgery date for you, so that we can reserve an appropriate sized implant. However, please understand that before three to four years have rolled by, I will not be able to give you any better information about the uncemented femoral component. I will not be able to tell you if it is superior to the cemented component or not until at least three to four years have passed. Even at that time, it will be a very early judgment.

In summary:

• Uncemented femoral resurfacing components are now becoming available on a limited basis from Biomet.
• No other companies are yet selling these in the US
• Corin has had an uncemented femoral component available in Europe for several years.
• It is not clear, if uncemented technology on the femur will be better or worse then cemented femoral components at this point.
• Virtually all clinical data on hip surface replacement to date is based on an uncemented acetabular component and a cemented femoral component.
• I plan to use uncemented components whenever possible, unless the patient specifically requests the cemented femoral device.
• I am not sure when enough uncemented femoral components will be available that I can begin to implant these on every patient.

Sincerely.
Thomas P. Gross, MD
08/23/2007