Hip replacements more likely to fail in women, says study

Hip replacements have been in the news because of ongoing litigation over whether a device-maker was negligent in selling metal-on-metal hip implants that had to be removed from lots of recipients, because of high failure rates.

Now, a new study of more than 35,000 people finds regardless of the type of hip replacement, women were almost 30 percent more likely than men to need a repeat surgery within the first three years.

The message for women considering hip replacement surgery remains unclear. It's not known which models of hip implants perform best in women, even though women make up the majority of the more than 400,000 Americans who have full or partial hip replacements each year to ease the pain and loss of mobility caused by arthritis or injuries.

Study co-author Dr. Art Sedrakyan, associate professor of public health at Weill Cornell Medical College in New York City, told CBSNews.com that the overall absolute risk remains low.

"It's really an exciting paper," said Sedrakyan. "What we've observed is regardless of size, women had higher rate of revision occurrence."

The research was published Feb. 18 in JAMA Internal Medicine, and was funded by the U.S. Food and Drug Administration.

"This is the first step in what has to be a much longer-term research strategy to figure out why women have worse experiences," said Diana Zuckerman, president of the nonprofit National Research Center for Women & Families, who wrote an accompanying editorial to this study in the same journal issue. "Research in this area could save billions of dollars" and prevent patients from experiencing the pain and inconvenience of surgeries to fix hip implants that go wrong.

For the study, Sedrakyan and his team looked at 35,140 surgeries at 46 hospitals in the Kaiser Permanente health system.

• How much should a hip replacement cost? Study raises more questions than answers
• Trial over metal hip replacements begins in LA
• FDA to scrutinize safety of metal-on-metal hip implants

After an average of three years, 2.3 percent of the women and 1.9 percent of the men had undergone revision surgery to fix a problem with the original hip replacement. Problems included instability, infection, broken bones and loosening.

Sedrakyan said the increased risk was only seen when the cause of rejection was aseptic, meaning not caused by infection, which suggests the problems were not related to issues during surgery. The most common problems that required another surgery were dislocation and wear of the product.

Then what explained the gender differences?

Women tend to have smaller joints and bones than men, and so they tend to need smaller artificial hips. Devices with smaller femoral heads -- the ball-shaped part of the ball-and-socket joint in an artificial hip -- are more likely to dislocate and require a surgical repair.

That explained some, but not all, of the difference between women and men in the study.

Doctors traditionally believed the larger the size of the implant, the more protective it was against failure, according to Sedrakyan.However, he said his study found regardless of size, women had a higher rate of revision occurrence, so some other factor besides the actual implants may be leading to this effect.

"I think there's something beyond the use of the implants that seems to be related to this second surgery recurrence," he said.

He thinks anatomy may play a role. Women have different pelvic and hip anatomy, he said and it's also possible that some other unknown activities specific to women make them more vulnerable to a dislocation or higher wear.

Co-author Dr. Monti Khatod, an orthopedic surgeon in Los Angeles, speculated that one factor may be a greater loss of bone density in women.

Sedrakyan said that it's premature to say women need different, more-specialized hip implants than men, because the overall risk remained low. He references past research on gender-specific knee implants, and how researchers learned they weren't any more helpful.

"We shouldn't jump to conclusions," he said. "We need to understand this better."

He adds that overall it's a very safe surgery, with 97 percent of implants surviving at five years. In general, he'd expect that rate to fall to about 85 percent after 10 years. However, he notes that metal-on-metal hips, which have been under recent scrutiny, are now rarely considered.

The failure of metal-on-metal hips was almost twice as high for women than in men, according to the study. The once-popular models were promoted by manufacturers as being more durable than standard plastic or ceramic joints, but several high-profile recalls have led to a decrease in their use in recent years.

In June 2012, a panel of experts advising the FDA concluded that there are few reasons to continue using metal-on-metal hip implants, amid growing evidence that the devices can break down early and expose patients to potentially toxic metal particles.

That followed similar findings out of the U.K., where researchers looked at national registries and found more people with MOM implants needed surgery to fix or remove the implants within five years, compared with those who had ceramic or plastic joints.

In January 2013, the first of what could be several trials kicked off against Johnson & Johnson, alleging the company knowingly marketed a faulty metal-on-metal hip implant that officials may have expected to fail in up to one-third of recipients within five years. A lawyer for 64-year-old Loren Kransky said if his client's implant was not removed, the former prison guard may have died.

A lawyer for the manufacturer, Johnson & Johnson's subsidiary DePuy Orthopedics Inc., countered that Kransky had preexisting medical conditions, and did not get worse from the implant nor better after it was removed.

Doctors had originally thought MOM implants could benefit active adults.

"Don't be fooled by hype about a new hip product," said Zuckerman, who wrote an accompanying commentary in the medical journal. "I would not choose the latest, greatest hip implant if I were a woman patient. ... At least if it's been for sale for a few years, there's more evidence for how well it's working."

The American Academy of Orthopaedic Surgeons has more information on hip replacements.