Metal-on-Metal Hip Implants Have Higher Fail Rates
Study: All-Metal Hip Replacements Fail Faster Than Other Types
Metal Implants vs. Non-Metal continued...
The new study, which is published in the Lancet, tracked more than 31,000 metal-on-metal replacement hips implanted in patients in the U.K. between 2003 and 2011.
The registry also includes information on more than 371,000 artificial hips made from other materials.
The study excluded the recalled ASR implants.
Compared to patients who got hips made with ceramic and plastic weight-bearing surfaces, patients who got all-metal hip replacements were significantly more likely to need revision surgery within the first few years of use.
The study shows 6.2% of all-metal implants required corrective surgery, usually to replace the implant, within five years.
“The [revision rate for] metal-on-metal in women is an order of three to four times higher, and in men, it’s an order of two to three times higher, depending on their [implant] head size and the age of the patient,” Blom says.
Blom says it’s not clear why women seem to be having more problems with metal implants, but there are some working theories.
“Women do seem to be more sensitive to the metal,” he says.
Anatomy might also be a factor.
“It might be that their implants might be implanted at slightly different angles,” creating more wear on the joint surfaces, says Blom. And because more women than men suffer from osteoporosis, they often start with weaker bones to support their new joints. That bone may break down more quickly if the new joints cause inflammation.
The problems also appear to be worse for patients who got all-metal implants made around 2004, when many manufacturers changed their implant designs to increase the size of the head. The head is the ball of the joint that fits into the hip socket.
Companies hoped larger heads would make the implants safer for patients since mechanical models showed they could reduce wear and make it less likely that the joints would dislocate. Dislocation is a major reason people need corrective surgeries.
Instead, however, the new study finds implants with the largest heads are failing faster than those that aren’t as big.
Researchers said they were particularly shocked by that finding. “The head-size effect, we weren’t expecting it to be going in almost the opposite direction as what was predicted,” says researcher Alison J. Smith, MSC, who works with Blom in the department of orthopedic surgery at the University of Bristol.