Derek McMinn discusses Metal Ions and Pseduotumors
Mr. Derek McMinn on Pseudotumors - May 2010 (taken from written interview)
A few centres have reported a phenomenon, which has been named ‘pseudotumors’ by a renowned orthopaedic hospital in Oxford. The term pseudotumor refers to a problem, whereby a hip resurfacing or a metal-on-metal hip replacement fails with a painful swelling or with collection of fluid around the hip joint. The word ‘pseudotumor’ has caused consternation among patients who were worried if this is some kind of a hidden cancer or a pre-cancerous condition. These need to be put into perspective.
First, let us be clear that these reactions have nothing to do with cancer. Second, there isn’t a single artificial hip system metal, ceramic or plastic, that does not generate wear debris and all types of wear debris have been associated with these pseudotumor-type adverse reactions. Third, it is now becoming apparent that in a majority of cases of pseudotumors, the primary reason for the development of these reactions is excessive material being worn out from the device because they had been fixed in a skewed fashion in the first place. No artificial hip device lasts long unless it is placed in an optimal position. The components that had been removed in Oxford were tested in a highly sophisticated laboratory. It was found that in every case with a pseudotumor, the wear pattern in the components suggested edge-loading i.e. the components had worn excessively in an unnatural manner because of their placement in an unfavourable position. In components which did not show edge-loading i.e. those components which had been placed in the correct position to start with, no one had developed a pseudotumor.
Most modern artificial devices whether metal, plastic or ceramic, do not tolerate surgical error in component positioning. They wear excessively if they are fixed incorrectly and in the case of ceramics or modern plastics they can also break. Excess wear leads to pain and failure. Hip resurfacing is a technically challenging operation and minor surgical error may occur, especially when performed by surgeons who are not highly experienced. The degree of difficulty is further increased if the patient is a woman because hips in some women may be shallow or the upper end of the thigh bone directed differently. Their bones are petite, leaving no margin for error. The design of some types of resurfacings has been shown to be even less tolerant to minor malpositioning. One Centre reported pseudotumors only with ASR resurfacings, while they did not see any with Birmingham Hip Resurfacings. Therefore an experienced surgeon and a well-proven device are the key to success with a resurfacing.
Furthermore some women are constantly exposed to metals like nickel in costume jewellery which may pre-sensitize them to the tiny amounts of nickel found in the resurfacing or replacement components. It is not yet clear if there is a very tiny group of patients who would react badly in the face of expected and regular amounts of wear. The percentage of patients who may react like that is believed to be very rare, of the order of 1 in a 1000 or less.
What symptoms do these patients develop?
Out of over 3000 resurfacings over the past 12 years, we had 10 patients who were treated for a local adverse reaction like this. In a majority of these there was only a collection of fluid around the hip joint nearly 10 years or more after their original operation. They complained of groin pain or discomfort. A few developed swelling of the foot or ankle because of the collection of fluid above. In many cases there were subtle X-ray changes, although not in all.
What is the solution if a person develops a pseudotumor several years after a hip resurfacing?
If a person presents with a history suggestive of a pseudotumor, he/she needs to be examined by an orthopaedic surgeon and undergo Xrays, a special multi-slice CT scan and some blood tests in order to establish the diagnosis. The CT scan must be able to reduce artefact from the metal in order to provide any useful information. In some cases it may be necessary to exclude infection by aspiration of the hip joint. If it is indeed a pseudotumor then a revision operation to convert the resurfacing into a total hip replacement with a non-metal-metal bearing will have to be performed.
How do patients recover after revision of a resurfacing to a hip replacement for a pseudotumor?
The ten patients described above have recovered as if they were recovering from any first hip replacement. Their hips are functioning well. The worst affected of these patients underwent the revision operation in January 2010 and needed bone grafting of the socket. She has seen the sensational reports in the newspaper and questions “What is all the fuss about? I have had 10 good years of my life restored to me. I had then been in my early 50s and now I am in my 60s. I noticed hip discomfort a few months before the 10th anniversary of my operation and I had to undergo a revision operation to convert my hip resurfacing into a hip replacement and I am now getting back to normal again.” She adds, “Ten years ago, had I known that I would need a revision at this stage I would not have changed one thing. I would have gone ahead with the resurfacing operation”. Two months after her revision operation, she kindly agreed to be filmed and you can follow her account on our website, www.mcminncentre.com under the section Case Studies – Other – Joan Lindh.