Gender-Specific Knees – True Need or Hype

There has been a fair amount of marketing over the last six months regarding the need for a gender-specific total knee prosthesis. The company promoting this states that traditional total knee replacements do not fit the female anatomy as well as they do the male anatomy. At first blush, this seems as though a tremendous slight to the female patient. However, if we drill down and look at the data, we can see that they claims are not totally accurate.
 
There have been several studies looking at the average size front to back and side to side of both male and female knees in patients prior to knee replacement as well as at the time of knee replacement. In general, there is a difference between the size of the male and female knee with the male knee being slightly broader in the medial/lateral direction in comparison to the female knee for a given anterior/posterior measurement. When a chart is assembled of these various sizes, the larger sized implants do not appear to match well with the female anatomy. However, when we look at the actual implants used for the female, typically the smaller size range implants are implanted in females and the larger size implants are implanted in males. If we look at data from over 14,000 knee replacements performed at eight different centers in the United States, over 75% of females received the smallest three sizes of a particular implant line. Within these sizes, the fit for the female was ideal. Less then 25% of females had a larger sized implant in which case some overhang of the implant is possible. The company that promotes the gender-specific knee throughout all their sizes had wider implants then the average orthopedic company in the marketplace. Therefore, they recognize an error in their implant design and to correct this, added more implants. The reality is that most other implants fit the female knee quite well. Therefore, the need for a gender-specific knee with other implant companies is not present.
 
The goal of knee replacement is to resurface the arthritic bearings of a joint, restore normal anatomic alignment of the limb, place the implants in appropriate position with appropriate sizes and by doing so, ensure good motion and function of the knee replacement. The overwhelming majority of implant manufacturers have sizes that fit the female very appropriately as well as the male individual very appropriately. Evolution of implant design continues with improvements in function and motion. So rather then having specific knees for a male or female patient, the important issue is to have the appropriate size for the male and female patient.