| Archive of failed joint replacements
provides tips to building a better hip replacementA study by Hospital for Special Surgery researchers has
provided the first comprehensive look at just how
metal-on-metal total hip replacements are failing in
patients around the country. Made possible by what is
thought to be the largest archive of failed joint
replacements, the research should help doctors develop a
better hip replacement for future patients. The study will
be reported at the upcoming annual meeting of the American
Academy of Orthopaedic Surgeons, Feb. 7-11, 2012.
“This paper is the first step in what is a path to try to
understand what the problems are with metal-on-metal
joints,” said Timothy Wright, Ph.D., Kirby Chair of
Orthopedic Biomechanics at Hospital for Special Surgery (HSS).
He said that information gleaned from the study should be
useful in improving metal-polyethylene implants, the most
common hip implant put in patients today.
“We still use metal implants. We may rub them against
polyethylene instead of against another metal, but anything
we can learn about these mechanisms of damage could be
important,” he said. He also pointed out that evidence
suggests that the physical structure of the implant might
play a role in the failed metal-on-metal implants and not
the metal itself. In recent years, advances in the materials
have allowed implants with bigger heads to be used, which
increases stability, but now evidence suggests this may
cause other problems.
“What we learn about the effect of head size and learn about
the effect of positioning these components, and certainly
what we learn about the biologic reaction to metallic debris
is going to help us understand problems in general with
total joint replacements,” said Dr. Wright. “It’s not enough
to say, because some metal-on-metal implants have adverse
reactions, it has got to be all about the metal and let’s
just condemn an entire technology. We need to understand, in
a systematic way, what is going on.”
Since 1977, whenever a patient has undergone a joint
revision surgery at Hospital for Special Surgery, doctors
have collected and saved the failed implants for research.
At the same time, they have created a web-based system to
file information on the implant, such as the manufacturer,
and on the patient, such as age, weight and activity level.
Doctors at HSS perform roughly 8,000 joint replacement
surgeries per year and roughly 10% are revision surgeries,
so this database is growing by about 800 specimens per year.
Many patients who have had their joint replacement surgeries
elsewhere come to Special Surgery to have revision surgery.
In the current study, HSS researchers, who did not have any
ties to hip implant manufacturers, examined 46 retrieved
metal-on-metal total hip replacements from 44 patients. The
most common revision diagnoses were wear-related clinical
concerns including osteolysis and adverse soft tissue
reactions (16), loosening (11), instability (8) and
infection (5). The researchers used scanning electron
microscopy to determine the ways the hips were damaged,
called damage modes. They found that 98 percent of the cups
of the implant and 93 percent of the heads showed moderate
to severe scratching. Moderate to severe pitting was found
in 43 percent of the cups and 67 percent of the heads. They
identified areas near the cups and heads that had completely
lost their sheen.
“This study represents one of the largest collections of
retrieved metal-on-metal implants,” said Douglas Padgett,
M.D., chief of the Adult Reconstruction and Joint
Replacement Division and chief of the Hip Service at
Hospital for Special Surgery. “There appears to be unique
damage patterns which to date have not been identified. A
follow-on analysis using high resolution laser profiling to
quantify damage is in process which may yield further
clues.”
The patterns and similarities of the damage modes will shed
light on the mechanisms behind the damage. “The goal with
these hard metal-on-metal bearings is to drag a fluid film
in between the two metal surfaces so that they never touch,
so the wear is theoretically zero,” explained Dr. Wright.
“The fact that we look at these surfaces and see scratches
and wear patches means that these surfaces are touching one
another. That is problematic because if you had the
clearances just right, they might never touch, just like the
cylinder in an engine block.”
He pointed out that the study could only be done at a
hospital with a large number of archived hips. Spotting
patterns and variations is easier if you look across a large
patient population.
Researchers will next focus on what is causing the damage
patterns. If it is a corrosive problem, is the solution to
change the metallurgy? If the location is always the same
and the damage is always near the edge of the implant, is
that because they are being installed incorrectly? Is there
a way to change the design? “What we see in the retrieved
implants will begin to give us a picture of what is causing
this problem,” Dr. Wright said.
The multidisciplinary team of HSS clinicians, biologists,
engineers and imaging researchers has further studies
planned to understand the problem more fully. The retrieval
archive and database will allow researchers to continue to
look for correlations between implants that fail and factors
such as patient characteristics, the physical shape and
quality of the hip replacement, surgical factors, and the
biological response from a body that has an implant.
The work for this study was conducted in the recently
established Mary and Fred Trump Institute for Implant
Analysis.
###
Other investigators involved in the study include Kirsten
Stoner, M.S. from HSS; Samantha Lee, B.S., from Perelman
School of Medicine at the University of Pennsylvania,
Philadelphia; and Stefan Kinkel, M.D., from Orthopaedic
University Clinic Heidelberg, Germany.
Retrieval Analysis Reveals Damage Modes for Metal-on-Metal
Total Hip Replacements (Paper 301)
Wednesday, Feb. 8, 4:00 p.m.—4:06 p.m. Moscone West, 2014
About Hospital for Special Surgery
Founded in 1863, Hospital for Special Surgery (HSS) is a
world leader in orthopedics, rheumatology and
rehabilitation. HSS is nationally ranked No. 1 in
orthopedics, No. 2 in rheumatology, No. 19 in neurology, and
No. 16 in geriatrics by U.S.News & World Report (2011-12),
and is the first hospital in New York State to receive
Magnet Recognition for Excellence in Nursing Service from
the American Nurses Credentialing Center three consecutive
times. HSS has one of the lowest infection rates in the
country. From 2007 to 2011, HSS has been a recipient of the
HealthGrades Joint Replacement Excellence Award. HSS is a
member of the NewYork-Presbyterian Healthcare System and an
affiliate of Weill Cornell Medical College and as such all
Hospital for Special Surgery medical staff are faculty of
Weill Cornell. The hospital’s research division is
internationally recognized as a leader in the investigation
of musculoskeletal and autoimmune diseases. Hospital for
Special Surgery is located in New York City and online at
www.hss.edu.
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