A History Of Metal-on-metal Hip Implants
When Are Hip Implants Indicated?
When Are Hip Implants Indicated?
While the majority of the population will never need
hip replacements surgery, in some cases hip implants can be the best choice for eliminating chronic hip pain due to fracture or arthritis after other treatment methods have failed. Prior to recommending a hip implant procedure, the patients doctor will generally have performed a surgical treatment known as arthroscopy which involves a tiny camera inserted into the hip, then treatment of identifiable problems. The inside of the hip may be irrigated; loose debris removed, or damaged cartilage trimmed. If none of these remedies are successful in decreasing the chronic pain levels, total hip replacement may be recommended.
This medical route involves replacing the painful and damaged parts of the hip with artificial implants. Hip replacements typically have three parts: a socket, a ball and a stem, with the outer shell of the new socket most often being constructed of metal. The inner shell can be made of ceramic, metal or a type of polyethylene plastic. The stem, which fits into the thigh bone, is typically made of titanium. Globally, hundreds of thousands of these hip implant surgeries are performed annually. The implants which incorporate a metal-on-metal design, however, have come under fire in the past few years.
The Push for Metal-On-Metal Hip Implants
Back in the 1960s, the conventional hip replacement consisted of a metal head with a polyethylene cup. While the design worked relatively well, over time the plastic cup would be worn away as it rubbed against the hard metal head. While this was not a major concern among elderly patients, younger patients who required hip implant surgery were likely to require subsequent surgeries as the plastic cup wore out. The metal-on-metal option was briefly used in the 1970s then discarded as health concerns surfaced. In fact, a 1975 study detailed tissue reactions which resulted from the cobalt and chromium used in the metal-on-metal hip implant.
A Birmingham surgeon, Derek McMinn, believed he could create a metal-on-metal implant made of cobalt and chromium in which the surfaces did not touch therefore would not experience significant wear. The first metal-on-metal hip implant device was implanted in Birmingham in 1990 and by 1997 McMinns design hit the European market where it was an instant success as it was believed to preserve more bone, last a lifetime and virtually eliminate the risk of dislocation. This initial release was carefully monitored however more manufacturers soon jumped on the bandwagon to create their own versions of the MOM and grab their share of the profits. Although the use of metal-on-metal hip implants escalated in the early part of 2000, there were surgeons who reported the spread of metal ions released into the body among
metal-on-metal hip implant recipients and advised caution in the use of the MOM implant.
As with most inventions which have the potential to create financial wealth, competition for the metal-on-metal implant grew, and regulations were relaxed. Soon, these carefully crafted surgical innovations became the domain of powerful multinational corporations, and patient safety soon went by the wayside. In 2004 Derek McMinn, the original creator of the MOM implant urged that caution be exercised in its use until longer term results became available. At the same time DePuy received clearance from the FDA with a modified MOM design. The FDA stated there were no new issues of safety or effectiveness to consider, although an internal DePuy memo reflected concerns about the potential health risks of the new design. By 2007 the metal-on-metal hip implant accounted for 20% of the market total however the MHRA Committee on Safety of Devices recommended all patients be required to sign a consent form which clearly detailed the risks associated with MOM debris. Unfortunately this recommendation was not particularly taken note of. A 2008 study showed that one-fifth of all DePuy implant patients had metal ion levels significantly beyond the upper acceptable limit. By 2010 DePuy had recalled its ASR hip implant device yet were simultaneously promoting their MOM Pinnacle device as a safe alternative.
A November 2011 study which was published in the British Medical Journal suggested that the metal-on-metal hip implant devices were no more effective than the more traditional hip replacement implants and were likely to have higher revision rates. In fact, those patients who received an MOM implant were more than twice as likely to require revision surgery. This is primarily due to the cobalt and chromium ions released into the bloodstream which destroys surrounding muscle and bone, leaving some patients with long-term disabilities. The DePuy ASR XL Acetabular System has reported a failure rate as high as 49% of patients, requiring revision surgery after only six years. Data on more than 400,000 metal-on-metal hip implants found these devices need revision surgery more often than any other type and that the failure rate is even higher among women. The revision rate for ceramic-on-ceramic hip implants is much less, at 2.3% while the metal-on-plastic implants carry only a 1.7% revision rate.
by: Sullo and Sullo Staff Writer
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