Thursday, February 3, 2011

Continuing Medical Education Panel sponsored by the American Orthopedics Association for Surgeons: Total hip Atheroplasty: Is there a MOM bearings controversy? (Part Four of Five)

Metal Ions:  What do we need to be aware of?
Josh Jacobs MD:  Professor and Chairman of Rush Medical Center Orthopedics

My notes. Part 4 of 5:

How Do we perform metal ion measurements and how do we use them clinically? 4 points:
(1)   It’s tricky (measuring metal ions)
(2)   It requires an extensive data base
(3)   It requires clinical validation
(4)   It is a challenge to recommend routine surveillance
Can we monitor both wear and toxicity with the implants?
Yes, there is a way to measure ware with serum ions.  There is a correlation between the metal levels and wear.  There is ONE test  in the literature conducted by the speaker with only 26 patients so it is somewhat of a leap to make a strong connection to clinical practice.
·         You can measure degradation through corrosion
·         Studies done show that the  highest chromium levels occur with metal on poly with a titanium stem (only metal on poly was studied though)
·        In autopsies conducted on patients with implants to determine how metal can be distributed systemically, they found that it is fairly common that the metal is distributed in remote organs (liver and spleen.)
o   88% in revision hip
o   27% in primary hip
o   30% in primary knee
The metals may not have resulted from surface wear.
·         They  measured the highest serum titanium levels ever seen in one patient: 1203 ng/ml
·         When you remove the device, the metal ion levels will go down.
·         Very concerned about using most labs for measuring the ion levels because they just don’t have the data so it leads to interpretation problems.
·         There is physiologic variability in 3 areas:
o   Renal function
o   Serum metal transport proteins
o   Remote tissue transport and deposition
·         There are many different ways that ion levels are measured and they each yield different results.  They range from measuring ion levels in the serum, to blood to plasma etc.  Different units are used with different specimen collection protocols.
·         You can get “wildly different levels” even using the same lab over a time.
·         Techniques between labs are not standardized so the interpretation of these tests is difficult at best.
Toxicity-Can we use metal ion levels to monitor this?  Yes but with caution.
·         There are now 6 case reports in the literature associated with metal toxicity and hip replacements:
o   4 of them had in common a fractured ceramic component (not MOM)
o   2  new cases were published in December that produced neurotoxicity and cardiac toxicity both with MOM bearings/ASR hip
§  Serum Cr Co levels in the first case were over 20
§  In the second case, they were over 100

o   Metal toxicity from the MOM hip is a rare complication

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