Chromium Cr(VI), also known as hexavalent chromium, one of the alloys used in a prosthetic hip, has been blamed for causing lung cancer in chemical workers and in homeowners exposed to the metal in drinking water. Nevertheless, researchers report no increased cancer rates in people who have had a hip replacement when compared with cancer rates in the general population.
"There is always a concern with any type of implant in the body as to whether, in the long term, it may induce cancer," says study author Joseph McLaughlin, president of the International Epidemiology Institute in Rockville, Md. "And procedures like hip and knee implants have become increasingly common and are being implanted at younger ages as the technology improves."Hip implants consist of either a mixture of titanium or cobalt/chromium-based alloys, high-grade plastics, and polymers to create a highly functional, long-lasting prosthesis. They weigh roughly a pound.
McLaughlin says American researchers have developed a partnership with Swedish researchers interested in looking at the long-term impact of hip replacements. Earlier research on cancer risk and hip implantation had shown no increased cancer rates, "so we decided to update our earlier publications, since the one thing lacking in this field was long-term follow-up," McLaughlin explains.
The Swedish researchers studied almost 117,000 patients who had hip replacements between 1965 and 1994, identified how many had developed cancer and then classified the cancers. The incidence of those cancers was then compared to the incidence rate among Sweden's entire population.
Overall, McLaughlin says, the hip replacement patients' cancer rates were about the same as the general population. "With one caveat," he adds. Long-term implant patients had a higher incidence of multiple myeloma (about 1.8 times the risk) and bladder cancer (about 1.4 times the risk), he says. The risk for prostate cancer and melanoma were about the same as everyone else, while the incidence of stomach cancer was slightly lower.
"But these are chance results," McLaughlin cautions. "Since we know very little about the causes of multiple myeloma, this finding should be pursued with further research. The finding for bladder cancer, on the other hand, could be due to other issues, like cigarette smoking, occupational exposure or analgesic use."
The findings were published in the Sept. 19 issue of the Journal of National Cancer Institute.
The most common reason people have hip replacement surgery is the degradation of the hip joint that is caused by osteoarthritis. Other conditions, such as rheumatoid arthritis, loss of bone as a result of insufficient blood supply, injury, and bone tumors also may lead to breakdown of the hip joint and the need for hip replacement surgery. According to the National Center for Health Statistics, almost 310,000 full and partial hip replacements are performed each year in the United States. The majority of total hip replacement surgeries are performed on patients 65 years of age or older.
The materials used in the hip implant are long-lasting and well tested, says Dr. John Callaghan, a professor of orthopedics at theUniversity of Iowa and president of the American Association of Hip and Knee Surgeons in Iowa City. "Any metal can be carcinogenic, but chromium/cobalt alloy is the biggest concern," Callaghan explains. "But these materials are used because they have excellent wear characteristics and they have been tried and true for 30 years, without any large concern."
"The Swedish study does not hold any surprise here," Callaghan adds. "There have been a number of studies that have looked at the carcinogenesis of hip and knee implants, and they have always been [inconclusive]. This study is, therefore, welcome in that it shows no difference between patients and the general population."
What To Do: For more on hip implants and replacements, see the American Academy of Orthopaedic Surgeons or the National Institute of Arthritis and Musculoskeletal and Skin Diseases.