Bearing Surfaces in Total Hip Arthroplasty
Replacement of the arthritic or damaged hip joint, with use of a total
hip arthroplasty consisting of a femoral and acetabular component continues
to enjoy unparalleled success as a means of alleviating pain and restoring
function. The coupling of these two components consists of a liner for
the acetabulum, and a femoral head for the femoral component. This coupling
creates a true bearing surface, designed for maximum conformity between
these two surfaces to decrease wear (go to our web site, www.jointsurgeons.com,
for a diagram). There are three major materials used to make these bearing
surfaces, either high molecular weight polyethylene, metal, or ceramic
for the acetabular liner, and metal or ceramic for the femoral head.
Recently there has been a rapid increase in our understanding of the
importance of the materials used for this coupling surface. As with many
advances in orthopaedics, this understanding did not come about in a
linear fashion, and is still in evolution. When Sir John Charnley in
England pioneered the concept of total hip arthroplasty, or “low
friction” arthroplasty, he used a metal femoral head and a polyethylene
liner as his couple or bearing surface. Both of the components (femur
and acetabulum) were fixed to the bone with cement. This was the first
type of hip replacement performed in the United States, and through the
1970’s appeared to work well. Implants then started to loosen,
or fail, and the common finding was of cement fracturing. The working
theory for these failures was that cement could not stand up to the rigors
of the human body, and this was termed “cement disease”.
To avoid this problem, implants designed to achieve fixation by bony
attachment were utilized, and were called “cementless” implants.
These implants were first used in the mid-1980’s, and in the early
1990’s the first loosenings were noted. As there was no cement
involved, it was unclear as to why this was occurring. When these implants
were removed, a soft tissue membrane was found in the femur. When this
membrane was analyzed, two disturbing findings were seen. One, the same
type of membrane was seen in the patients with failed cemented implants.
Two, both membranes had microscopic sized polyethylene particles in them.
Initially this finding was of unclear significance.
The finding of polyethylene particles in these membranes, how they got
there, and what they do, represents a major advance in the science of
total joint arthroplasty. Whereas from the initial days of joint replacement
with fixation with cement, to the findings of failure of fixation and
the use of “cementless” implants, the science of joint replacement
had concentrated on fixation. Now the race was on to establish why implants
lost fixation. The current understanding of this process is that particles
are “shed” or worn off of the bearing surfaces, typically
off the polyethylene liner. These particles, being microscopic in size,
are transported to bony regions surrounding the fixed implants. The body’s
immune system senses this material as being “foreign”, and
in a similar fashion to the removal of bacteria or viruses from the body,
the immune system, via the white blood cell, attempts to eliminate the
polyethylene. The white blood cell (macrophage) ingests (eats) the polyethylene
particle. The white blood cell cannot digest (eliminate) the polyethylene
particle, and in the process is killed. In the white blood cell exist
enzymes and proteins, used to digest foreign material. These enzymes
and proteins stimulate the removal of bone. This process, bony removal
or “osteolysis”, if extensive enough, leads to the loss of
the fixation of the implant, either via removal of bone surrounding the
cementless implant, or removal of bone around the cement. If the loss
of fixation is great enough, the implant loosens or fails.
We are now in an exciting time period in total joint arthroplasty, as
we attempt to end the process of bone removal or “osteolysis”.
The ultimate aim of the eradication of osteolysis is to give you, the
patient, a permanent total hip that will not loosen. The current concept
is that if we can stop the loss of particles from the bearing surface,
we can stop osteolysis. As mentioned above, there are three materials
used to manufacture these bearing surfaces, either high molecular weight
polyethylene, metal, or ceramic. These three materials all have advantages
and disadvantages.
High molecular weight polyethylene, used only for the liner, has been
the standard choice for a liner material. This material has performed
extremely well for years. Recently the material has been modified to
improve the mechanical properties of the material. This next generation
of polyethylene, called “highly cross-linked polyethylene”,
has been shown in laboratory models to have no discernible loss of microscopic
polyethylene particles at 20 million cycles of simulated wear (about
seven years of walking for someone under age sixty, 15-20 years of walking
for someone over sixty). If this material, coupled with a metal femoral
head, works as well in the human body as it does in the laboratory, this
may lead to the permanent total hip. This modification can cause the
polyethylene to be weaker in one respect. Time will tell if the laboratory
data is correct. At this time many surgeons, including myself and Dr.
Bargar, believe that this modification will be beneficial, and have been
using this. Even if the material is not as good as the laboratory data
would suggest, we believe that it is better than the “standard” polyethylene.
Metal-on-metal bearing surfaces have been used for years in Europe. Long
term studies of total hips performed with this material have shown an
extremely low wear rate for the metal. These low wear rates were not
always the case, as the machined tolerances between the head and the
liner were at times too tight, leading to high wear and loosening. As
these tolerances have improved, and the wear rates are impressively low,
many magnitudes less than the wear rate of standard polyethylene, this
material is being used in the United States. In addition to the advantage
of low wear rates, hopefully leading to less osteolysis and failure,
this material also has the ability to allow fabrication of femoral heads
in larger diameters, leading to lower dislocation rates. There is a potential
disadvantage. In studying the blood of patients with metal-on-metal bearing
surfaces in their total hips it has been shown that there are elevated
levels of chromium and cobalt ions. It is surmised that these levels
may be harmful.
Ceramic-on-ceramic bearing surfaces have as well been used for years
in Europe. Again, analogous to the experience with metal-on-metal surfaces,
this material has shown extremely low wear rates. As well the femoral
heads can be made in larger diameters. The particles, compared to metal
ions, are inert. However the disadvantage of ceramic appears to be the
brittleness, which can lead to fracturing. Currently two manufacturers
have FDA approval in the United States.
We now are at a point in joint replacement where a major emphasis is
being placed on which of the three bearing surfaces to use. In our office
at this time we favor the use of “highly cross-linked polyethylene” with
a metal femoral head, for we believe that the science would suggest that
it will perform better than the prior polyethylene. While we acknowledge
that the wear rates for this polyethylene may still exceed that of metal
or ceramic, we have chosen not to use these at this time for the following
reasons. In regards to metal, we are concerned about the issue of elevated
chromium and cobalt ions. With ceramics, although fracturing is a low
risk, these are not yet readily available. Trials are underway, and at
some point if these are available we may elect to change to this material.
The future of total hip arthroplasty is extremely bright. Although we
cannot guarantee you a “permanent” implant at this time,
that day is nearing. As our knowledge of these materials grows, perhaps
a clear favorite will emerge. As our knowledge grows, we may also find
other ways to stop the bone removal that leads to implant loosening.
New Web Site
Six years ago, Dr. Bargar started our website and managed to get a great
address. www.JointSurgeons.com is a perfect name for us and describes
what we do: we are “joint surgeons” in that we operate on “joints” (hip
and knee), we work “jointly” (Drs. Bargar and Blumenfeld),
and finally we may “join” with other orthopaedic surgeons
in the future. Up until now, our website was simply a way that patients
could access the same educational material that we handed out in our
office. With the re-launch of our upgraded site, you can now do many
more interesting and helpful things when you visit us on the web.
We have added animated descriptions of total hip and total knee procedures. We
now have a photographic tour of our office, directions with a map for getting
there, and we have added the ability to download the patient registration and
health history forms, so new patients can fill them out at home and bring them
in at the time of their first appointment. The background and publications of
our doctors have been expanded. The current, as well as all back copies of our
newsletter, The Joint Effort, are now on the site and can be searched by topic.
The patient education section has been expanded and upgraded with more information.
More links have been added to valuable sites with information you can trust.
Finally we have added an e-mail capability, so that patients or any interested
party can e-mail our office. E-mail is advantageous because it is “asynchronous
communication”. By this it is meant that the sending and receiving of e-mail,
although essentially instantaneous in transmission, can be done at the sender’s
and the recipient’s convenience. Anyone who has tried to communicate with
a doctor’s office (yes, even ours) by telephone or letter, understands
what a hassle it can be. With e-mail you can communicate your non-urgent question
or concern at your leisure and phrase it exactly as you like, being sure to convey
exactly what you want. This is much preferable to calling on the phone only during
certain hours, waiting on hold or sitting by the phone waiting for a callback.
It is also much more convenient for the doctors and staff. They can check their
mail and respond when they have time and not take time away from other important
tasks.
With this added convenience come some concerns. One is security. We all realize
that a computer is not truly secure. Any computer system, it seems, can be “hacked”.
Doctor-patient communications are supposed to be confidential. We will strive
to keep it that way, but we suggest that sensitive topics not be discussed by
e-mail. Our doctors will not review test results or give diagnoses by e-mail.
Some things are just better discussed in person or on the phone. Please be aware
that all communications by patients with our office are considered part of your
medical record. We plan to keep a hard copy of all patient e-mails in the patient’s
chart. Another concern about using e-mail to communicate with a doctor’s
office is that patients may want to tell us about a medical problem that requires
urgent or even emergent care. This is very unwise and can be dangerous. We plan
to give you an answer to your e-mails within 2 business days, depending on the
doctor’s schedule. This is much too long for urgent or emergent medical
problems. So please, if the problem is urgent, call our office. If it is emergent,
call 911 and get to the nearest emergency room.
To be sure that the e-mail sender is aware of these issues, we have arranged
for an automatic reply to be sent in response to all e-mails sent to the office.
This is a form letter that will not directly answer your query, but it will insure
that your message was received and that you are aware of the “rules of
the road” for e-mail correspondence with our office. Welcome to the future.
Are We Doing the New Minimally Invasive Surgery?
Yes, but...
We hate qualified yes answers. In this case, however, we feel it is justified.
Last year, we ran an article on this new “hot topic” in our
newsletter (Spring 2002, Issue #1).) entitled: “Minimally Invasive
Surgery: Hip or Hype”. In that article we differentiated between
what we felt was “minimally invasive” and “minimal
incision” surgery. In other words, we felt that a minimal incision
did not always mean that the surgery was less invasive, since under the
skin, the same degree of dissection may or may not be utilized. We stressed
that these were developing techniques, and that there were potential
risks due to the lack of visualization. More cases and longer follow-up
were felt to be required. We said we would begin using these techniques
when we felt they were safe.
In just one year this concept has exploded! The media and surgeon practice
marketing have created a tidal wave of patient demand for these “new
procedures”. Who wouldn’t want to have their surgery with
the least invasive technique and with the fastest, least painful recovery?
BUT, here comes the “but”: this assumes that these techniques
will result in the same high success rates that have been proven with
the more invasive traditional surgical technique. No one wants to trade
a higher risk of early failure or lesser quality long-term success for
a few weeks of faster recovery. There are still no published results
by the pioneers of these new techniques. The onus is on the surgeon to
insure that he or she can do the same high quality job through this less
invasive approach.
We now feel that we can do some of these procedures safely using a minimally
invasive approach. Most of our first-time hip replacements are now done
through a much smaller incision. The actual length of the incision depends
on the size and obesity of the patient. In thin patients we have gone
from the traditional 8-inch incision to a 4-inch one. New instruments
are coming that may allow reducing this to a 3-inch incision in thin
patients. We also have decreased some of the muscle dissection, so this
qualifies as being minimally invasive, not just minimal incision. We
plan to begin using the “two incision” approach (Newsletter
Spring 2002, Issue#1) on a limited basis in the next few months, but
this requires special training and at this time is appropriate only for
a specific brand of prosthesis.
We are also now doing minimally invasive knee surgery for the uni-compartmental
knee replacements. This is where only the affected medial or lateral
compartment of the knee is replaced. Again the size of the incision depends
upon the size and obesity of the patient. In patients with thin knees,
the incision is about 3-inches, as compared to the traditional 6-inches.
This again qualifies as being minimally invasive, since we have eliminated
the splitting of the quadriceps muscle. Although the indications for
uni-compartmental replacement are increasing, they still represent less
that 10% of knee replacements done in our practice. The rest require “total
knee” replacement, which as yet still requires the standard approach.
Another “but” to our affirmative answer is that we intend
to monitor and study the short-term as well as long term performance
of our patients in whom we use minimally invasive techniques. So far,
our patients seem to report less pain and may be going home a day or
two earlier. At their 6-week follow-up check they seem to be functioning
at a higher level. By 3 months, there is less of a difference and by
6 months, we doubt there will be any difference. Our post-op. x-rays
still show the same high quality job and we have not had any complications
that we can attribute to the change in technique.
New instruments to help with minimally invasive techniques are being
developed every day. New implants, that have been designed to be implanted
with these techniques, are on the horizon. Computer navigation techniques
are coming that may improve our ability to “see” using virtual
reality. Robotics (i.e. ROBODOC) will be adapted to insure the execution
of the surgical plan without the need for direct visualization.
The future looks promising for minimally invasive techniques in hip and
knee surgery, BUT we must do it safely, with no loss of quality and long-term
success.
Bio: Nicole Duarte
Nicole was born in Sacramento and has lived in the area all of her 22
years. She attends California State University of Sacramento full-time
where she studies history and plans to be a college instructor. Working
part-time for Drs’ Bargar & Blumenfeld, Nicole is in charge
of medical records, in addition to covering the front desk for Christina
when needed and a myriad of other tasks to help all the staff keep
on top of the mounds of paperwork that come into the office on a daily
basis. She is everyone’s best friend and we appreciate her pleasant
disposition in completing these sometimes very mundane chores.
Postcards By Mail
In an effort to maintain patient privacy, we are asking that if you object
to receiving recall or birthday post cards please notify our office in
writing.
Patient Confirmation
It is also office procedure for our office to call and confirm office
appointments the day prior to your scheduled visit. If you have not been
telephoned by 4:00 pm the day before, please contact our office to be
sure you are on the schedule and do not make a wasted trip to our practice.
Local Service
The Senior Connection (a local area non profit organization): A Northern
California provider of innovative health, housing and social services
for seniors since 1968 with phone assistance five days a week, and quarterly
classes on various issues. Their website is www.eskaton.org and to reach
them by phone 916-334-1074 or toll free 888-334-3490.
In a recent search
in December 2002 on the web we found an interesting site: Health Grades.
This is a report card methodology on hospitals and the report was very
positive. The search was a review (3 years ending 2001) of 11 local area
hospitals for primary total hip and total knee replacement. In both reviews
Sutter hospitals had a five star rating which is the top 30% of all hospitals
within the State. If you want to look at this website it is www.healthgrades.com
Some Total Joint Terminology Allograft: tissue (I our case, bone) from one individual transplanted
to another individual. Arthroplasty: surgical procedure to reconstruct a joint as in a total
hip or knee replacement. Aspiration: removal of fluid from a hip or knee joint. This fluid is
then sent to a laboratory for diagnostic studies. Autologous: the use of your own bone or blood during a surgical procedure. Homologous: the use of blood or bone obtained from a donor bank. NSAID: An acronym to describe non-steroidal anti-inflammatory drugs,
including aspirin and ibuprofen. There are several of these types of
drugs available over the counter, others require a physician’s
prescription. Osteotomy: surgical cutting of a bone to change the alignment or alter
the weight-bearing stresses.
Office Reminders and Suggestions
Dr. Blumenfeld sees patients on Mondays and Wednesdays and it is difficult
for MaryPat, his nurse, to take calls on these days.
Please leave a
voice mail message or whenever possible, save your call for a Tuesday
or Thursday.
Dr. Bargar and Brian Shontz, Physician’s Assistant, see patients
on Tuesdays and Thursday and Elizabeth is busy with patients. It is recommended
you contact her on Mondays or Friday mornings.
The days that the physicians are not in clinic, they are in surgery.
In The News
The following letter appeared on the July 18,
2002 New York Times editorial page in response to the article, “Arthritis
Surgery in Ailing Knees is Cited as Sham.”
“It is a mistake to use a research publication that is focused on osteoarthritis
or degenerative arthritis of the knee to suggest that knee arthroscopy is ineffective
for treating knee pain caused by torn cartilage or ligaments, conditions far
more likely to have arthroscopic treatment than is osteoarthritis.
“Over the past 25 years, thousands of clinical research publications have
confirmed the effectiveness of arthroscopic knee surgery in reliving knee pain
for millions of Americans.
“Osteoarthritis of the knee constitutes only a small segment of those who
have arthroscopic knee surgery, and for the much larger group with torn cartilage
and ligaments, arthroscopic surgery remains effective, less invasive and more
cost-effective treatment than was available during its advent.” The letter
was signed by Vernon T. Tolo, MD president of American Academy Orthopaedic Surgeons
and Peter Fowler, MD, president of the American Orthopaedic Society for Sports
Medicine.
Attention all HMO patients
A letter was mailed in late September notifying you that Dr. Thomas Blumenfeld
is no longer a Sutter medical group or Sutter independent physicians
(SIP/SMG) participating provider. We are requesting authorizations
for all those patients that had surgery by Dr. Blumenfeld for their
follow-up appointments. Otherwise your care may be redirected by your
primary care physician to a participating physician.
For all SIP/SMG PPO patients: this has affected our contracts with some
of the ppo plans. For example Interplan has dropped our contract due
to the dissolution of our SIP/SMG participation. They are requiring that
we sign an individual participation agreement with them or they will
terminate Dr. Blumenfeld’s contract effective March 1, 2003.
If you had surgery, we will continue to honor the PPO contracted rate,
if in fact your carrier concluded our contract was cancelled due to this
tie with Sutter Independent Physicians and Sutter Medical Group.Our statements
have a new look! Marisa is still working out the bugs so that they are
easier to read and understand. But right now you can now easily tear
off the top portion and provide any of the following: address changes,
insurance updates, choose a payment option (we accept Mastercard, Visa
and American Express) and return in the envelope provided.
JOINT SURGEONS 
