As Orthopaedic Surgeons, we are asked on a daily basis how we know what size knee a patient is going to get. People are also quite curious as to whether or not they will be receiving a gender specific knee - meaning, do men and women get differently designed knees?
The answer is quite straight forward. Each company that makes knee replacements has measured thousands of knees using precise CT scan data. Over time, they are able to use these statistics to "predict" which sizes people will need. By knowing this data and the variability of the knee size with respect to the ratio of the height to width ratio, companies make knees based on the most likely sizes. Interestingly, female bones tend to be slightly narrower, so prosthesis companies have started to make the "narrow" version of the knee, more commonly referred to as the female knee. With that being said, the surgeon must have multiple implants available at your knee surgery in order to choose the size that fits you best. So that's pretty much it! Women tend to have narrower knees, knee companies identified that, and the birth of the gender specific knee was born!