At the 41st Annual Open Hip Society meeting in Chicago, Illinois 03/23/2013, several papers were presented on the evolving recommendations for patients with metal-on-metal hip replacement. Because of concerns about adverse tissue reaction due to wear products of metal-on-metal hips, the orthopedic community worldwide has been intently evaluating best practices for follow up of these patients. As it turns out there are several potential sources of metal wear debris including articulation between a metal ball and metal socket, corrosion between the metal ball and the stem, and or modular junctions between the metal neck and stem. All of these seem to contribute to the potential problem.
We have had modular junctions in hip replacement components for several decades, but the widespread use of metal-on-metal total hip replacements, which exceeds 1 million patients worldwide, has brought to the forefront some of the potential downsides of these articulations. There appear to be both mechanical problems, as well as chemical reactions that lead to the release of metal byproducts and ions. Currently, patients who have metal-on-metal hip replacements are recommended to see their orthopedic surgeon annually for a history, exam, and x-ray. If patients are having pain then it is recommended blood or serum cobalt and chromium levels be evaluated. If these are extremely low and the patient’s symptoms are otherwise minimal, continued followup is recommended. If patients are having significant pain and a limp or other mechanical factors then a special MARS MRI scan of the hip is recommended looking for fluid collection and/or significant soft tissue changes.
There are several factors that influence patient’s susceptibility to metal-on-metal wear debris and these include the patient themselves and their immune system, the particular implant utilized, and the surgical technique and implant positioning. All of these play a factor. It was concluded by experts worldwide that follow up is essential as recommendations keep evolving over the last 18 months.
—William P. Barrett, MD