Study Links Metal-on-Metal Hip Implants to Two-Year Failure

July 18, 2012 — Experts know that the main reasons why metal-on-metal hip implants fail is due to loosening of the implant, toxic metal reactions, non-cancerous pseudotumor growth, and seizing of the device components.

Now, a new study published in the journal Orthopedics suggests that the devices are most likely to fail within the first two years, the most common reason for failure is loosening of the acetabular cup, and the devices most often responsible for failure are the DePuy ASR and the Zimmer Durom acetabular cups.

The researchers reviewed records from 80 patients who were forced to undergo revision surgery due to problems with their metal-on-metal hip implant. The researchers found the following rate of complications:

• Aseptic acetabular loosening (56.25%)
• Infection (12.5%)
• Metal hypersensitivity (6.25%)
• Failed resurfacing (6.25%)
• Fracture (5%)
• Loose stem (3.75%)
• Seizing of device components (1.25%)
• Cup malposition (1.25%)
• Femoral stem fracture (1.25%)

More than half of the patients had a loosening of the acetabular cup, which is a complication that occurs when the round head of the femur does not pivot tightly inside the hip socket. Pain, decreased mobility, abnormal sounds (“clicking”) when walking are all common symptoms. Many people who have a loose hip will require revision surgery.

During the study, 45 patients required revision surgery for a loose acetabular cup. Of these, nearly 80% were due to Zimmer Durom cups, 10% were due to DePuy ASR cups, and the other 10% were Magnum, Biomet, Pinnacle, or Conserve devices.

Furthermore, the researchers found that the vast majority of the patients undergoing revision surgery had only been implanted with the devices for 2-3 years — 80% of patients had surgery in two years, and 92.5% had surgery in three years.

Another common complication was local tissue reactions, which were a problem in 13% of patients. Experts believe this complication occurs because metal debris accumulates as the metal-on-metal parts of the device grind together. Particles of chromium corrode, releasing genotoxic cobalt ions, which destroy DNA and are highly soluble in the body and bloodstream. This can cause metal poisoning (metallosis), tissue damage, tissue death (necrosis), non-cancerous pseudotumors, pain, swelling, inflammation, dislocation or loosening of the hip joint, bone loss, and other severe complications.

This study emphasizes that experts still do not fully understand the health risks and safety of metal-on-metal hip implants, and more studies are needed to better understand the long-term effect of a metal-on-metal hip implant.

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