Proper TKA technique eliminates gender, femoral implant sizing effect on outcomes

Gender-specific implants appear to offer no clinical advantage, study author says.

ORLANDO, Fla. — Gender and implant size have no significant effect on clinical outcomes when performing total knee arthroplasty in women, according to a surgeon speaking here.

Merrill A. Ritter, MD, of Mooresville, Indiana, now retired from surgery, and Robert E. Booth Jr., MD, director of the department of orthopedic surgery, Pennsylvania Hospital, Philadelphia, took part in a crossfire debate on the topic at the Current Concepts in Joint Replacement Winter 2006 Meeting.

Booth said that the many definable differences in women's vs. men's knee anatomy mean that most femoral components used today in total knee arthroplasty (TKA) are too big. That creates problems such as anterior overhang and stuffing that lead to suboptimal results for women, he said.

"There is no data to support that argument," Ritter countered, citing a study designed to quantify the effect of gender and implant size on patient outcomes and survivorship.

In that retrospective study of 4,496 primary TKAs performed between April 1987 and May 2004, Ritter and colleagues examined pre- and postoperative improvements in Knee Society Scores, function scores, pain scores, walking ability, flexion and survivorship, among other parameters.

"Clinical scores were lower in women in the pre- and postop period, but the percentage of improvement has been the same in men and women" in the study, Ritter noted.

Women saw no significant differences in all other variables, Ritter said, noting the study found no relationship between the size of the femoral components and any clinical outcomes. Women made up about 40% of the patients in the study, which had a minimum 2-years' radiographic follow-up.

Booth, an early proponent of a newly introduced gender-specific knee, cited what he called many discernable differences between men's and women's knees, including fat distribution, "legendary flexibility" (for women), shape, ratio of height to width, the Q angle, and anterior trochlear flange.

The bottom line, according to Ritter: Gender-specific implants appeared not to offer any clinical advantages in the study.

Booth said he had implanted over 300 of the new Gender Solutions total knee (Zimmer) implants with good results, albeit in the short term only. "Yes, it's too early to tell" what the results will be, Booth said. But he noted that 10 years ago, people did not use "handed" (left- or right-handed) implants for knees either, but most surgeons would use them today.

"I think we'll see a multitude of other gender-specific joints and other medical devices," Booth said, noting that studies in other medical specialties, such as cardiology, are uncovering subtle anatomical differences between men and women.

Added Ritter: "Please look at the data and not the marketing."

For more information:
Booth R. Men are from Mars, women are from Venus — Affirms. #2. Ritter M. — Opposes. #3. Presented at the 23rd Annual Current Concepts in Joint Replacement Winter 2006 Meeting. Dec. 13-16, 2006. Orlando, Fla.
Robert E. Booth, MD, has indicated to Orthopedics Today that he receives royalties from Zimmer.