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Do gender-specific implants make a clinical difference?

By: Jennie McKee

By Jennie McKee

Experts discuss current data and implications for patient outcomes
Are women so anatomically different from men that they require gender-specific hip and knee implants? A panel of experts explored this question yesterday, during a media briefing moderated by Craig J. Della Valle, MD.

Women make up a high percentage of joint replacement patients. In 2005, 125,000 total hip replacements (THRs) were performed on women compared with 108,000 THRs on men. The numbers for total knee replacements (TKRs) were even more lopsided, with 335,000 TKRs on female patients and 176,000 on male patients.

Until recently, orthopaedic surgeons chose from an array of standard implants designed to fit both men and women. However, the statistics showing that more women require joint replacement surgery—coupled with recent advances in technology—led to the release of gender-specific knee implants that aim to offer women a “better fit.”

Anatomic differences
“We all know there are differences between men and women, some more obvious than others,” said Scott M. Sporer, MD, MS, assistant professor of orthopaedic surgery at Rush University Medical Center. “Men, in general, tend to be larger. As a result, their bone structure tends to be bigger.”

“Now that gender-specific implants are being manufactured by industry,” continued Dr. Sporer, “the question becomes, ‘Do these implants make any clinical difference?’ If you look carefully at the studies, there is not much difference overall in outcomes. When you look at several subscales, however, you find slight differences.”

“We need to have randomized, prospective studies that compare patients who have these implants to those who do not,” said Dr. Sporer. “We also need outcomes scales to measure the subtle differences in patient outcomes.”

More testing needed
The need for randomized, prospective, clinical trials was echoed by Timothy Brox, MD, staff orthopaedic surgeon at Fresno Kaiser Permanente Medical Center, who presented data collected between April 2001 and March 2006 by the Kaiser Permanente Joint Registry Project.

“Women improved 5.41 points postoperatively (on a 0 to 10 scale); men improved 5.05 points (P value <0.001). The clinical significance of this difference is unclear,” said Dr. Brox. At greater than 9 months follow-up, no range of motion difference was observed between genders, and patient satisfaction among men and women was similar.

Dr. Brox cautioned that when a new total knee implant comes on the market, patient outcome data should justify the need for the new implant. “Based on current data, I and most of my colleagues do not advocate use of the gender-specific knee implant,” said Dr. Brox.

A study that evaluated the survivorship and clinical outcomes of men and women who underwent a hip replacement with a regular, nongender-specific implant found little statistical difference in clinical outcome scores, reported Robert Barry Bourne, MD, FRCSC, of the University of Western Ontario. “This leads one to question the need for a gender implant,” said Dr. Bourne, adding that based on this study, contemporary implants, regardless of manufacturer, seem versatile enough to meet the needs of both genders.

Gender-specific implants: not such a new trend?
“There is a mean population that is well-served by currently available implants,” said Andrew H. Glassman, MD, MS, attending physician at Grant Medical Center and associate professor of orthopaedic surgery at Ohio State University College of Medicine. “However, I believe that in some instances, gender-specific implant designs are extremely useful.

“I would submit to you,” continued Dr. Glassman, “that even the most ardent opponents of gender-specific implants are already using them.”

To make his point, Dr. Glassman cited a common patient type—the large male with “a small canal, huge metaphysis, and an enormous offset.” Using the radiograph of a patient fitting this description who had implant surgery in the 1990s, Dr. Glassman pointed to the custom-made hip implant, which had an extra-extended offset stem.

“As more surgeons treated this type of anatomy and mechanics, the implant became commercially available,” noted Dr. Glassman. “But I’ve never put one in a female, even though I’ve implanted several hundred.”

A need for consensus
According to the panelists, further study is required for orthopaedic surgeons to reach agreement about the impact of gender-specific implants on clinical outcomes.

“The question is whether the anatomic differences that we’re aware of are causally related to the subtle differences in clinical outcomes, or whether they are due to the failure of surgeons to recognize the differences, and perform adequate preoperative planning and execution of the procedure,” said Dr. Glassman. “Perhaps, in some instances—in my view, at least—they are due to a lack of appropriate implants.”

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