“It’s really an exciting paper,” said study co-author Dr. Art Sedrakyan, associate professor of public health at Weill Cornell Medical College in New York City. “What we’ve observed is regardless of size, women had a higher rate of revision occurrence.”
“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.
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 for repeat hip implant surgery 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 explains the gender differences for repeat hip implant surgery?
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 repeat hip implant surgery, 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.”
The research was published Feb. 18 in JAMA Internal Medicine, and was funded by the U.S. Food and Drug Administration.
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