| Dr. Su’s Protocol for Metal Ion Testing
Metal Ion Testing The testing of metal ion levels after hip resurfacing is controversial,
to say the least. Because we are still learning about the metals used in
resurfacing, how they are released (and in what quantity), and how the body
reacts to these metals, there are no definitive guidelines for metal ion levels
in every patient.
There has been research done regarding the amount of metal ions that we
expect to be produced and remain in the body after hip resurfacing. However,
what we don’t know is: “At what level do these metals pose a problem?” It
seems that different patients will have different tolerances for the amount of
metal in their body – some react to the metals at a very low concentration,
while others have no symptoms, even if their metal ion levels are high. This is what makes it difficult, if not impossible, to produce
guidelines for metal ion testing. Many surgeons believe that metal ion testing will
only lead to more questions and concerns, since we don’t know exactly what to do
with this information. There is no cutoff value for metal ion levels; that is,
there is no level that would make a revision necessary, at this point. The
British Orthopaedic Association has made recommendations that cobalt and
chromium levels be below 7 parts per billion, per hip; however, there can be
patients who have levels above this threshold who do not have problems. The
United States FDA has not made specific recommendations regarding metal ion
testing; in their Safety Communication dated January 17, 2013, they state: “The
FDA does not believe there is a clear need to routinely check metal ion levels
in the blood if the orthopaedic surgeon feels the hip is functioning properly
and the patient is asymptomatic.; and “At this time, the FDA is not
recommending a specific metal ion level as a trigger for revision or other
medical intervention.”
I believe that metal ion testing gives information about what is happening in the joint with regard to wear. With conventional metal-on-polyethylene
bearings, we can measure wear on an x-ray; with metal-on-metal, this is not
possible, since the ball and socket are the same material. Therefore, I find the use of metal ion testing to be informative as to what is occurring
inside the joint. Perhaps if I identify metal ion levels elevated above a level that
I Believe to be normal, I can help guide a patient into modifying his/her
activity to reduce the amount of wear. In addition, I believe it provides a check
to make sure that a patient’s kidneys are functioning properly to filter the
body of excess metals.
My current protocol is to test the metal levels yearly, in all patients. Once I have gathered enough information that a joint is functioning well, then
Decrease the frequency to every 2 years.
|
