Patient Outcomes Similar for Gender-Specific and Conventional Knees


Patients who received both a gender-specific and a conventional knee replacement had similar outcomes and reported no preference between the two, according to new data published in JBJS. The study paired Zimmer’s gender-specific NexGen LPS-Flex with their standard NexGen LPS-Flex, and while the gender-specific knee is designed with certain anatomical benefits in mind, participants demonstrated similar Knee Society knee, function and pain scores; Hospital for Special Surgery knee and pain scores; and WOMAC scores in both knees. The patients also had similar range of motion and radiographic outcomes.

Zimmer’s gender-specific knee is designed to address female patients’ less prominent anterior condyle, an increased quadriceps angle and a reduced mediolateral:anteroposterior aspect ratio. While prior published data has indicated that total joint arthroplasty outcomes are equal or better for women compared to men, suggesting there may be little clinical need for a gender-specific device, the authors note that earlier data did not evaluate patient satisfaction with the knees. This study determined the difference in satisfaction between the devices to be negligible.

While the short-term clinical benefit of gender-specific knees has not been demonstrated, continued demand for the devices can potentially be attributed to the success of direct-to-consumer advertising. The study’s authors also note that long-term data would be required to better determine the efficacy of gender-specific devices.

Are device companies DTC campaign successful at driving adoption of a certain prosthesis? It seems that might be the case for Zimmer and it’s gender specific design. I doubt J&J would say their rotating platform DTC campaign was a success. Smith and Nephew is having some early success (based on my own anecdotal *data*) with branding their Journey knee as a “30 year” knee.

Should DTC ads drive usage patterns by surgeons…. no. Total knee systems are very complex and require that the physician be very comfortable with all the nuances of the system in order to assure you the best chance at having a successful procedure. Each system has its own unique little tweaks and quirks, and it even takes an experienced surgeon quite a number of cases to become comfortable with a system.  An experienced surgeon can overcome a significant number of obstacles and still obtain an excellent result with a new system, or a new set of instruments … but does that surgeon want to learn 4 different knee systems?  Is that efficient use of their time?  What about hospital concerns, staff education, supply chain mgmt nightmares, etc.   It’s not a simple straightforward issue.  

The scientific literature shows that if a surgeon performs somewhere around 75 total knees a year then the complication rates they experience are significantly less that the number of complications associated with a surgeon who performs far fewer procedures. Not only are the more experienced surgeons *better* because of the techniques shared by all the systems, but because they know how to get out of a problem (poor balance, etc) using the tools their system has.

I would be very careful about insisting that a surgeon use one prosthesis versus another… when you do that, you may be introducing variables; with limited upside at best, and a potentially significant increase in downside risks.

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About the author:

Howard J. Luks, MD

Howard J. Luks, MD

A Board Certified Orthopedic Surgeon in Hawthorne, NY. Dr. Howard Luks specializes in the treatment of the shoulder, knee, elbow, and ankle. He has a very "social" patient centric approach and believes that the more you understand about your issue, the more informed your decisions will be. Ultimately your treatments and his recommendations will be based on proper communications, proper understanding, and shared decision-making principles – all geared to improve your quality of life.