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Hip Resurfacing News

We simply cannot predict how long the hip resurfacing implants will last for several reasons. First, wear of implants is a function of how they are used; NOT a function of time! In other words, durability is directly related to several factors including the patient’s activity level, quality of the femoral bone, implant design, the patient’s unique anatomy and the surgeon’s skill in performing the surgery. Secondly, it is difficult and inappropriate to prognosticate about a device’s performance and longevity without long term clinical data. In the absence of long term data, categorical statements regarding implant durability are purely speculative. As the JRI and other centers continue to monitor hip resurfacing patients post-operatively for longer periods of time (e.g., 5-10 years and beyond), greater quantities of data will have been compiled and analyzed. Researchers will then be able to present clinical performance outcomes data to surgeons, patients, health insurance payors and other interested parties with a greater degree of statistical confidence.
 

What is the expected life for the resurfacing hip as compared to THR?

I DON’T KNOW! It is only one of the possibilities to do longer than 10 years in young and active people! If you don’t get osteolysis (bone that is going away) or no measurable wear of the friction couple, metal-on-metal resurfacing can last very long. Just give me a crystal bal. There are large metal-on-metal articulations that stayed for more then 30 years. If activity will play a big part in the wear of the prosthesis, is today also questionable.

 

It depends on your age and activity level. The best reports on standard metal plastic hip replacement indicate that in patients with average age 70, 95% last 10-15 years. With these same implants, patients age 40-60, the implants survivorship drops to 70-80% over 8 years. Metal hip surface replacement shows 96% survivorship at 7 years in patients age 40-60. Studies of ceramic-ceramic, metal crosslinked polyethylene and small bearing total hip replacements show approximately 95-98% survivorship in young patients as well.
 

How long will the implant last?

The development of modern hip resurfacings was based on the secrets of success gleaned from successful historic metal-metal hip replacements which proved their wear resistance, durability and biocompatibility over
several decades. The era of modern metal-metal hip resurfacings started in 1991 when Mr McMinn pioneered them. The early models were prototypes that gave precious further information on the best design and material combinations that would make resurfacing successful. Review of the surviving hips amongst these early prototype models show that some of them are still functioning well, in spite of heavy usage over the past 18 years. The hybrid fixed model turned out to be better than the others. Hybrid fixation was therefore adopted in all later models. In 1997, the fixation was made even more reliable using an advanced porous fixation surface and the Birmingham Hip Resurfacing (BHR) was introduced. Mr McMinn has performed over 3000 BHRs since 1997 and nearly 100,000 BHRs have been performed worldwide.

Orthopaedic surgeons consider that an implant has failed if following the original surgery, the patient goes on to have another operation for revision of one or more of the components of the implant. Failure of the component could be either due to a fracture, loosening or any other cause leading to pain and loss of hip function. Nearly 12 years on following the introduction of the BHR, the failure rate in our group of over 3000 patients is 1.6%. Fracture of the femoral neck or a collapse of the femoral head due to pre-existing inherent weakness in the bone or due to premature excess activity early after the operation led to failure in 1.1%. Infection and some other very rare causes such as dislocation or metal allergy led to failure in 0.5%. All of these have then been converted to a total hip replacement and the patients are back to a normal lifestyle following their revision surgery.

Based on the trend of time to failure of an implant, statisticians calculate implant survival to denote what percentage in a given group of patients are likely to reach a certain time point, such as 10, 15 or 20 years after an operation, without the need for a revision. In the younger age group (under 55 years) with osteoarthritis, the implant survival in Mr McMinn's series of BHRs is 99.5% at 11 to 12-years follow-up. The comparative figures for implant survival with the conventional cemented Total Hip Replacement in this age group and diagnosis are 81% at 10 years and 33% at 16 years, according to the Swedish Hip Arthroplasty Register.

Longevity of Implant

The short term results (4-6 year follow-up) of hip resurfacing are encouraging. However, the early failures of hip resurfacing appear to be greater than for total hip replacement (2.2% vs 1.9%), with the majority of the early failures due to femoral neck fracture. Whether the newer forms of hip resurfacing will be successful long term is unknown. It may require 10 years or longer to determine whether this newer form of hip resurfacing is as good as total hip replacement at comparable time intervals.

 

Dr. Michael Jacobs of Good Samaritan Hospital in Baltimore, Md., says resurfacing devices did not have a smooth beginning when they were introduced several decades ago.

"The devices failed because the sockets were made of plastic, and the plastic turned out to be the wrong material. It couldn't take the stress of the resurfacing device," says Jacobs.

The new devices seem to be working. Eight years of investigational studies have shown that the metal is holding up, and the surgeries are successful. But over a lifetime, the results are unknown.

 

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