Implant sizes have been developed based on "average" measures of joint depth and width. There is a range of sizes available to help the surgeon match the implant to the patient. Measurements are often taken from cadaver knees. This allows for more accurate measurements from inside out.
Men tend to have broader ends on the bottom of the femur (thighbone) as it forms the upper half of the knee joint. Larger implant sizes are adjusted to match this feature in men.
Implants with a narrower width are better suited for many women. Some consideration has been given to matching the implant to the Q-angle of the knee. The Q-angle is formed by the position of the quadriceps muscle and connected patellar tendon as it inserts into the front of the knee. It is the angle of the quadricep muscle's pull on the kneecap.
The Q-angle tends to be larger in women compared with men. But many women who have osteoarthritis and need a total knee replacement are overweight. These women have a reduced Q-angle because of a large thigh. In these cases, one of the many implants already available work best.
At this point, the extra cost of developing a gender-specific implant may not be needed. Money aimed at improving women's health and fitness may be better spent. Such an approach may help prevent obesity, arthritis, and the need for joint replacement.