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Metal Hips: What Did Industry Know and When Did They Know It?


If you were attending the recent FDA gathering of expert scientists, orthopaedic device developers, and surgeons who implant total hip replacements (THR), you would leave believing that the issue of early failures and metal toxicity from artificial hips was a new development. But a closer look at science from the early 1990s shows the device makers knew or should have known they were manufacturing and marketing defective total hip replacement medical devices and they continued to do it anyway!

If a patient had read these studies prior to surgery, do you think any one of them would have chosen a metal-on-metal total hip replacement?

The first one comes from St. Luke’s Medical Center and Northwestern University’s division of Biological Materials and the Department of Biomedical Engineering published in the Journal of Biomedical Materials Research in 1993.

When 148 modular hip prostheses (hip replacements) made of titanium, aluminum and molybdenum (mixed-metal), and of a mixture of cobalt – chromium (similar metal) were removed, there was significant corrosion observed in both combinations.

An artificial hip is made up of a neck and head as well as a stem. The cobalt-chromium alloys are typically used in the head and neck of the component, while titanium and aluminum is preferred for the stem portion of the femoral component.

In this particular review, 35% of heads, 16% of necks (in mixed metal), 14% of necks and 23% of heads (similar metal) showed evidence of moderate corrosion.  The longer the medical prosthesis was implanted, the greater the amount of corrosion – indicating that the corrosive process progresses with time.

But even for hips implanted for as little as 2.5 to 11 months, corrosion could be seen and was, in some, severe enough to be noted.  The corrosion was determined with an electron microscope and x-ray analysis.

What type of corrosion?

Depending on the metal, scientists were able to find dissolution of cobalt, as well as pitting, and something called fretting or wear lines in the mixed metals. Couple this with the repeated stress put on a major joint and fractures were observed in the oxide film and in the taper, leaving the component vulnerable to more corrosion.  Both the corrosion and accumulation of metal particulates, it was theorized, would lead to a loss of mechanical integrity of the implant while creating metal particulates which could destroy the surrounding tissue.

One of the complicating factors may be the environment inside the body. Cobalt-chromium as well as stainless steel resists corrosion due to a protective film of chromium oxides in a saline solution. But that layer may break down due to chemical and mechanical assaults. All of this evidence points to early hip replacement failure, loosening, local reactions, and trace metal accumulation.

The average age of revision surgery in this study was 59 and the duration of the implant was about 29.5 months. They had been retrieved (removed) because of the pain associated with a loosening hip replacement, infection, a cup malpositioned, necrosis of the neck graft, fractures of the implant and the bone and wear of the polyethylene liner.

For 14 patients the reason for the hip removal was unknown.

Again, this study was released 19 years ago! However, we have uncovered another study even older..  (Continue to Part 2)

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