Even in those few studies showing that there might potentially be an outcome difference in women undergoing TKA, Dr. Boettner says that many other factors in addition to the size differentials of the implant would have a greater impact on outcomes. To the extent that these outcome disparities may exist, differences in activity levels and ways that outcomes are measured may play a more significant role than those addressed with a GSK.
Indeed, Dr. Boettner notes that the advent of GSK may be related more to marketing than clinical need. “With women comprising 60% of the patient base of TKA and the GSK being sold for a higher price than traditional implants, it was a smart idea that made Zimmer a lot of money and added market share.”
Other surgeons, however, see usefulness in the GSK concept. The differences in the sizes of the prostheses allow the surgeon to select the artificial knee that best fits the patient, instead of having to shape the bone surfaces to better fit the prosthesis. “If you think about it, just about everything works better if it fits correctly,” says Dr. Kraay. “Whether it is slacks, golf clubs, or shoes, if they fit you, you would expect a better outcome. However, there hasn’t yet been scientific data to back this up.”
Dr. Boettner, however, questions the reasoning behind such precision. “Both the gender-specific and standard implants have the same shape of the articulating surfaces and therefore move exactly the same. Both designs alter the natural kinematics of the knee significantly and the knee no longer rolls back naturally,” he says. “In addition, most of the changes they made in the prosthesis design are really minor changes and it is hard to imagine they have an impact on function in a knee with an altered kinematics and change in joint line. One should also not forget that other current implants like the Genesis II made by Smith and Nephew have received the FDA clearance for gender-specificity product requirements.”
Match to Patient and Not Gender
Selection of the implant should not be solely based on matching the “gender” of the knee to the gender of the patient. Rather, the implant used is most often based on decisions made by the surgeon during the operation. In some cases, the anatomy of a male knee may suggest that the use of a “female” implant is appropriate.
“I don’t use this on every female I see,” says Dr. Sporer. “About 70% of the time, I’ll use the GSK on female patients. There are also some men whose knees are a better fit for the GSK. For me, the decision to use a specific implant is based on the individual patient’s anatomical geometry and using the one that more closely reproduces the patient’s original knee.”
