Patients and prospective patients are always concerned about
the complications that could occur after a hip resurfacing surgery. The typical
problems include femur neck fractures, dislocations, loose acetabular cups,
improperly positioned acetabular cups, high metal ions, infections,
pseudotumors, ALVAL and metalosis.
There has been a lot of discussion among patients on
discussion groups about the high metal ion issue and pseudotumors. I am
not a doctor or medically trained. I am a Patient Advocate, Hip
Resurfacing Patient and Mechanical Engineer. I had the opportunity to
attend the Second Annual U.S. Comprehensive Course on Total Hip
Resurfacing Arthroplasty October 24–25, 2008 Los Angeles, CA. I listened
to discussions about the metal ion issues and pseudotumors. I am going to
explain what I learned in simple, non-medical terms since that is all I can
do.
As an observer, I learned that the high metal ion issue has
occurred in a small number of cases as a post op problem after a hip resurfacing.
One of the most likely reasons, according to the experienced surgeons and
presenters at the course, was the incorrect placement of the acetabular cup
which resulted in additional wear on the bearing surface between the acetabular
cup and the femur cap component. The hip resurfacing device is really a
metal bearing made of High Carbon Cobalt-Chromium alloys.
A bearing is designed to equally spread out the load over the load bearing
components. If the components are not aligned properly, then only part of
the bearing is loaded resulting in much more wear in that area possibly causing a high
metal ion level. It was also
explained that women seem to have more problems with high metal ions than men.
Perhaps, this is due to the fact that most women use smaller sized hip
resurfacing devices which causes more loading on the bearing surfaces than the
men's larger sized devices.
When there is an abnormally high metal ion release from
misplaced components, it seems to
cause the surrounding tissue and bone to react adversely. The surrounding
tissue and bone tends to become abnormal. Some doctors call the
tissue reaction pseudotumors, AVAL (aseptic lymphocyte dominated vasculitis associated
lesion), & others call it metalosis. Whatever name given to the
abnormal reaction, it is not good to have this happening around the hip device
since it could become loose, pain could result and possibly more severe
medical reactions could happen.
There is concern among the hip resurfacing community about
the reactions to the very high metal ion issue. At this time, to my
understanding, there is not a standardized blood test available. Different
labs use different methods and tests. There are not yet any specific
guidelines as to what levels are too high for metal ions. There is a lot
of research being done, but there are no standards yet.
This makes a surgeon's job to define and solve problems due
to high metal ions difficult. Some doctors feel that
patients with very high metal ions should have a revision of their hip
resurfacing to a ceramic on ceramic THR. They don't want to take chances
that even more serious problems could develop due to the high metal ions.
Normally, from what I understand, the high metal ions are probably due either to the
incorrect position of the acetabular cup causing very high wear on the hip
resurfacing bearing device or due to the use of a small hip resurfacing device
causing excessive loading on the bearing surfaces. So once again, the learning
curve and experience of hip resurfacing surgeons is very important to
prospective patients along with proper patient selection. It takes a great deal of experience to consistently
place the acetabular cups at the proper angle and to know which smaller patients
can successfully receive a hip resurfacing.
That is my layman's explanation of the high metal ion issue.
I am posting a number of abstracts below by surgeons attending the Second Annual
U.S. Comprehensive Course on Total Hip Resurfacing Arthroplasty October 24–25,
2008 Los Angeles, CA. Their articles will help explain more about the high metal
ion issue, the small device issue used in many women and the acetabular cup
placement issue.
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