I did some weight lifting like four years ago and I started again.When I do squats the patellar tendon of my left knee hurts a little bit. It does not moves the same way as the one in my right knee. When I play table tennis and I play many games it hurt a bit as well. My little brother had a similar problem and he bought two open patellar knee supports and he does not have any problems now. That is why I decided to buy one but I just remember Wang Hao and Zhang Jike used a knee support as well and decide to find out what brand it was and what was the purpose of using it.
This link has the information clear about this :
http://redsports.sg/2009/03/18/right-knee-support/
This might help some people to choose the right one and not just buy the one that the pros use.
I know which one I need and I am happy that it is the one that the pros use lol