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Are Metal-on-Metal Hip Implants Tied to Increased Cancer Risk? Part Three: Specific Cancer Risks Post Metal-on-Metal Hip Implant.

Are Metal-on-Metal Hip Implants Tied to Increased Cancer Risk? Part Three: Specific Cancer Risks Post Metal-on-Metal Hip Implant

By Independent Staff Writer

Do MOM Implants Increase the Risk of Cancer?

The risks of a metal-on-metal hip implant are many, yet the question has arisen as to whether the MOM implant is responsible for an increased risk of cancer among recipients. The metal-on-metal implant accounts for as many as one-third of all hip replacement implants in the United States and approximately 15% in England and Wales.  A cohort study of patients who underwent MOM hip replacement surgery in England and Wales compared the relative rates of cancer between the different types of implants and examined specifically the risk of cancer in those with metal-on-metal implants.

The British researchers assessed cancer rates in over 40,000 patients with MOM implants and nearly 250,000 patients with alternative implants such as metal and polyethylene and ceramic. The biological effects of the MOM implants have been an ongoing concern due to certain research which indicated a higher incidence of cancer in those exposed to metal ions. Following hip revision surgery to remove metal-on-metal implants, metal particles were found to have invaded the marrow, blood, liver, kidneys and bladder of some patients. A study done in Finland of over 2000 patients found a positive correlation between MOM implants and higher cancer mortality rates as compared to metal-on-polyethylene implants during the first 20 years post-surgery. Mortality rates between the two groups were not significantly different after twenty years.

British Study Findings

The National Joint Registry of England and Wales was established in 2003 and is the largest database of joint surgeries in the world, recording all primary and revision hip surgeries. The study focused on five classes of cancer including all cancers, lymphoma or myeloma cancers, malignant melanoma, prostate cancer and renal cancer. The cumulative risk was assessed between the various types of implants as compared to the cancer risks in the general population. The groups were separated between those with metal-on-metal implants, those with another type of implant and those who had received resurfacing arthroplasty surgery. Approximately 40% of those in the study were male, with 60% of those males being between ages 65 and 84.

Approximately 20% of the patients were considered to be healthy and physically fit, while another 67% had some form of mild disease which did not limit their normal day-to-day activities. The average length of time patients were observed following their hip replacement surgery was three years, with over 80% being monitored for at least one year, and the remainder being observed for a period of five to eight years. Within this study, 1.25% of the study participants were diagnosed with some form of cancer within one year of the hip replacement surgery, a number which was lower than expected. This study found that there was no significantly increased risk of cancer of any type from a metal-on-metal hip implant. Older patients were shown to be at a higher risk of developing cancer, although it was not related to the MOM hip implant.  Men were found to have a higher risk of developing some form of cancer than women.

The final conclusions of this British study—although it had certain limitations—showed that the use of MOM implants was not associated with an increased risk of cancer at three years post-surgery, and that the rate of cancer at seven years post-surgery was not significantly higher when compared with those patients who received alternative implants.  In other words, the use of metal-on-metal hip implants, while carrying a wide array of risks, is not associated with a short-term increased risk of cancer. The limitations of the study were judged to be its observational design as well as the fact that the follow-up was not of significant length to provide definitive information regarding cancer risk.

Several researchers and doctors noted the necessity of a long follow up—one to two decades—to fully determine the risk of cancer from a MOM hip implant. Also, the fact that the study compared MOM patients with the normal population may render the study somewhat less than reliable since patients undergoing hip replacement surgery are thoroughly checked to ensure they are healthy enough for the surgery, while the “normal” group underwent no such checkups. Further, the British study regarding the increased risk of cancer among MOM recipients may not prove as relevant to patients in the United States since only about 14% of hip implants in England are MOM compared to 35% in the U.S. In any case, although there are other equally serious considerations, the use of MOM implants in hip replacement surgeries has not been associated with a short-term risk of developing cancer.

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