Metal-on-metal hip implants risky: surgeon

A certain type of artificial hip, known as metal-on-metal hip replacements, are setting off alarm bells among some patients and surgeons north and south of the border.

Agrowing number of patients, some of them decades shy of their senior years, are experiencing problems withcertain implants, including inflammation, pain and loss of mobility, said Dr. Nizar Mahomed, an orthopedic surgeon at Toronto Western Hospital and the medical director of the Musculoskeletal Health and Arthritis Program.

These patients frequently areforced to have their hip replacements redone two to five years after their initial surgery, Mahomed told CBC News on Thursday.

The implants are sold under the names Durom (made by U.S.-based Zimmer Holdings) andDupuy Orthopaedics. According to the Times, British researchers last year found that 3.4 per cent of patients 17 of 660 patients studied who received a metal implant made by DePuy Orthopaedics, had an allergic reaction.The product had been used as a resurfacing system or for a conventional implant replacement.

And new research byfour orthopedic surgeonsat the University of British Columbia who recently received an award for their hip-replacement research, found that patients who underwent total hip replacement using large-diameter metal heads made by Zimmer had much higher levels of metal ions in their blood than patients who received resurfacing.

Conversely, the British study also found that an additional group of 155 patients who underwent surgery and received the Birmingham resurfacing system sold bymedical device giant Smith and Nephew, had no adverse reactions.

According to a report in the New York Times, the metal-on-metal hip replacement is often done in hip resurfacing procedures, a surgery in which the femur bone isreshaped and the artificial hip attached. The procedure conserves bone and is usually performed in patients who are younger and more active. Metal-on-metal is also used in conventional hip replacements, in which the entire joint is replaced with a prosthesis.

There have been reports in the U.S. that in some cases, small particles of the metal made of cobalt and chromium break off in the body and lead to theinflammation, pain, and death of tissue in the hip joint that some patients experience.

Many U.S. surgeons are severely curtailing the metal-on-metal surgery as a result, according to the report.

Mahomed estimates that anywhere from one per cent to 10 per cent of patients who have received the metal-on-metal implants have a reaction to the implant. There were 24,253 total hip replacements in Canada excluding Quebec, in 2007, a 52 per centincrease over 10 years, according to the Canadian Institute for Health Information.

"Every hip replacement, regardless of type, will create some particles," he said. "But I've seen patients very early after surgery develop ongoing pain and inflammation. Nobody can predict what person will be at risk of developing this reaction."

Other complications can develop

Mahomed says that in some cases, the muscles surrounding the hip joint will necrotize or die, an outcome that causes loss of mobility and for which there is no solution. "It can be a devastating problem," he said.

He also adds that the cobalt and chromium particles can enter the bloodstream and that testing has shown that in 10 to 20 per cent of people who've received the metal-on-metal implants, the levels of these metals can be high, leading to potential kidney failure or an increased risk of cancer long term.

Mahomed, who performs 350 hip replacements a year, says he already sees signs of a backlash against the metal-on-metal implants.

"The rate at which these are being put in will decrease significantly. I think a lot of surgeons are having potential concerns with metal-on-metal."

He says he never implants them, opting instead for the "gold standard." This is ametal-on-plastic hip replacement. While the device doesn't last as long as the metal-on-metal implant which has an average lifespan of 15 years, barring complications it has a high success rate.

"The metal-on-plastic implant has improved significantly,"Mahomed said, adding that the plastic particles do not cause an autoimmune response in a patient's body even though they break down over time.

As for those people who have received metal-on-metal implants, Mahomed suggests watching for any signs of pain, immobility or inflammation and recommends periodic follow-ups withan orthopedic surgeon.