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 [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.
Keep It in Perspective
Experts who were not involved in the study had mixed reactions to the results.
Joshua J. Jacobs, MD, chairman of the department of orthopedic surgery at Chicago’s Rush University, and a vice president of the American Academy of Orthopedic Surgeons, said the findings should be kept in perspective.
“This clearly is a higher [failure] rate in some metal-on-metal large head-hip replacements compared to other bearing combinations,” Jacobs says.
But, he says, the vast majority of patients still have good results with their metal implants after five years.
“It’s not like half of the implants are failing or even a quarter or even 10%. It’s in the area of 6%. That’s not what we as orthopedic surgeons want. We would like a 0% failure rate at five years. That’s what we strive for in our patients, and we know we can’t get that just because of the nature of the surgery,” says Jacobs, who has consulted for orthopedic manufacturers in the past. He says he hasn’t received any personal support from device manufacturers in more than a year.
But other studies have shown that failure rates for metal-on-metal implants rise the longer a patient has the joint.
Some studies have shown nearly twice as many patients with metal-on-metal implants need corrective surgeries as patients who get joints made from other materials.