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.
The development of
modern resurfacings was based on the secrets of success gleaned
from successful historic metal-metal hip replacements which
provide 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.
The hybrid fixed model turned out to be better than the others.
Review of the surviving hips amongst the early models reveals
that some of them are still going strong in spite of heavy usage
over the past 15 years. Hybrid fixation was used in all later
models and they were made even more reliable using more advanced
techniques.
The Birmingham Hip Resurfacing was released in 1997. In Mr.
McMinn's series of nearly 2700 BHRs to date, the failure rate
has been 1.2% at nearly 9 years. In the younger age group (under
55 years) with osteoarthritis, the failure rate of Mr. McMinn's
resurfacings is 0.2% (survival 99.8%) at 11 years follow-up. The
failure rate with a traditional hip replacement in this age
group by comparision is 19% at 10 years and 67% at 16 years
according to the Swedish Hip Arthoplasty Register.
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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