Metal Alloy Use in MOM Implants Threatened – Part One

The metals industry is rightly proud and producers understandably value the successful application of metal alloys in the medical implants industry. From high-purity refining through forging and casting operations, machining, coating and treating the use of titanium, cobalt, chrome and stainless steels in addition to a number of less common metals, this has been a source of considerable profit for the sector over recent decades.

So the current furor about metal-on-metal (MOM) hip implants has understandably stirred up a lot of debate and not a little media hype into the bargain.

Here in the UK, a recent BBC Newsnight program and British Medical Journal (BMJ) report have thrust the debate into the public domain and a flurry of articles have played up the potential risks — risks that could ultimately lead to a sharp decline in the use of metal alloy implants if subsequent research supports early fears.

The procedure of hip implants has been around since the 1970s, but over time the materials and designs have changed as lessons have been learned. Earlier problems with stainless steel and post-operative dislocations have encouraged a move to cobalt-chrome and titanium alloys for the femoral head (the ball-shaped section with a spike that fits in the femur or thigh bone) and gradually larger femoral heads to counter the tendency to dislocate.

To reduce wear rates found in earlier metal-to-plastic joints, metal-to-metal joints were developed by a number of producers, but notably Johnson & Johnson’s subsidiary DuPuy. As a result, possibly of the larger surface area resulting from larger heads, tests have revealed that minute metal particles worn from the metal-to-metal contact are finding their way into the surrounding tissue and bloodstream.

An article in the Independent says metal ions appear to break off from the implants and leak into the blood, causing local reactions that destroy muscle and bone, cause severe pain and even long-term disability. Studies have shown that the metal particles can seep into the bloodstream, spreading to the lymph nodes, spleen, liver and kidneys before being excreted in urine. There are also concerns about damage to chromosomes, leading to genetic changes that could increase the risk of cancers.

The BMJ report is probably the best source of impartial information on the topic, even giving measured toxicity levels for cobalt and chromium blood tests. The Telegraph recently reported that in the US, experts studied 46 MOM implants retrieved from 44 patients at the Hospital for Special Surgery, in New York, where all implants removed from patients are kept for study.

They found that 98 percent of the cups of the implant and 93 percent of the heads showed moderate to severe scratching. Moderate to severe pitting was found in 43 percent of the cups and 67 percent of the heads; and near the cups and heads, the implants had completely lost their sheen.

Continued later today in Part Two.

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