J.L. WEBB

Dr. Bryan Reuss

After almost three decades of fairly rigid thought, the latest equipment breakthrough in knee replacement surgery is bending the rules to accommodate women.

For the past 9 months, a relative handful of orthopedic surgeons in Florida have been using the Gender Solutions™ Knee to customize replacements that previously were designed exclusively for a man’s physique. By taking into account the anatomical differences between the sexes, physicians now are able to continue the slow, but logical, progress that has defined knee replacement surgery for a quarter-century.

Dr. Steven Lyons was on the roll-out team of this product, manufactured by Indiana-based Zimmer Corporation. Lyons is a partner in the Florida Orthopedic Institute in Tampa; he performs about 250 knee replacements each year, most at University Community Hospital in Carrollwood.

“The industry really has come about over the past 10 years or so. Twenty years ago we had only about three sizes of implants. Fifteen years ago we were able to match the tops and bottoms of knees a little better. Ten years ago we (distinguished between) lefts and rights. In 2007, gender specificity came into play,’’ said Lyons.

The Gender Solution™ Knee “really has taken over my product line,’’ Lyons said. He has done about 100 of these so far, and now “Every knee that I do is either a male or female version of this gender specific knee.’’

Gender Solutions™ “has taken our level of sophistication up a notch, and instead of putting in traditional mechanical replacements we are able to offer patients a more customized, form-fitting implant that is built just for them,’’ Lyons said.

The move toward gender-specific implants is long overdue, Lyons said.

“Two-thirds of all knee replacements are women. Yet, women are three times as likely to forego treatment,’’ he said. “Women are more stoic, perhaps because of their caregiver roles. They wait significantly longer to seek treatment … so, by the time women get to the point where they request knee replacement, their disability is much greater than (most) men,’’ Lyons said.

“We all know that women are built differently than men. Our sizes are different, our strengths are typically different. Our fat distribution, muscle tension and ligament laxity are different,’’ Lyons said. “But we also know there are measured functional differences. When you look at their actual strengths on Cybex machines, stair-climbing tests, 6-minute walks, quadriceps strengths and activation data, women are different. But we also have seen a disproportionate decline in function with women who have osteoarthritis. (Women’s) decline in function occurs at a tremendously more accelerated rate than in males,’’ he said.

Although the implants for women are slightly thinner than those for men, it is their contour that makes the most difference, said Dr. Bryan Reuss of the Orlando Orthopedic Center and a surgical staff member at Orlando Regional Medical Center.

“The big difference is the angle at which a woman’s knee is constructed,” said Reuss. “A woman has a wider hip, so the Valgus angle from the hip down to the knee is different than for men. That really impacts the way the kneecap tracts within the knee joint. … That’s called the Q angle … and a wider Q angle to accommodate women’s wider hips and the way the kneecap glides, that’s the main issue.’’

Lyons said surgeons are “trying to reduce the overhang that traditional implants would impinge or overhang the bone. We either downsized to the next lower size (male) implant and cut more bone off the front of the femur to make it fit better, or we flexed the cut,’’ he said. “Now we are not trying to fit the patient to the implant; we have an implant that fits the patient.’’

Although it is far too early to prove scientifically with studies, both Reuss and Lyons said they have noticed substantial differences in patient recovery.
“Based on what I have seen so far, my female patients are getting significantly more flexion at 2 and 6 weeks post-operatively,’’ Lyons said. “Knee and hip replacements (and revisions) are all I do, so I have a very big patient population. I have seen a difference in the immediate post-operative range of motion,’’ Lyons said.

Reuss concurred. “It’s early, and you need many years to get results, but what I see anecdotally is a better range of motion, especially for women.’’

That improved range of motion, which the Gender Solution™ Knee compensates for in the dissimilar trapezoidal shape of a woman’s femur, is slight but noteworthy.

“It has 3 degrees more lateral angulation of the kneecap joint,’’ Lyons said. It is 5 millimeters more narrow in the medial collateral width. And the kneecap itself is thinned out quite a bit more than the traditional male knee.’’

Still, not everyone needs a gender-specific knee implant, Lyons said. “There are still women who might need a male knee. Eighty-percent of females need an implant for women,’’ he said, “and (some) males will have this typical female anatomic attribute. That leaves 20 percent of the females who will need the male knee.’’ And, Lyons said, “almost all rheumatoids will have a smaller type of femur.’’

However, Reuss said he would “be wary about putting a female knee in a man because of the Q angle’’ and the way it tracks with the patella. Zimmer has a pretty wide range of (implant) sizes’’ that would be more appropriate, he said.
Still, using gender-specific implants does not affect the size of the incision, or the amount of bone or ligament that must be removed during surgery. “It’s just more (about) a customized fit,’’ Lyons said.

What’s the next breakthrough in total knee replacement surgery?

Reuss said it is improvements in the plastic components (Polyethylene) that may make the replacements even longer-lasting.

Lyons said “the next big thing on the horizon may very well be racial or ethnic variations.’’ Asians, in particular, have “a very small knee,’’ Lyons said, “and they typically need the smallest size knee (implant) we have.’’

Either vision of the future would appear to bode well for the orthopedic well-being of women.



May 2008