Did you do your PT after surgery? I had surgery back in Mar 2012 for this. I had intense thearpy 2 x weekly for about 2 months.
I have my full range of motion BUT like you my knee cap
track & I have to jerk my knee
back in a quick motion or try to maunevere it until I can hear the pop. It is called an unstable knee cap
Look on line for knee
excersices you can do to strengthen your knee
muscles & ligaments & even the knee cap
You need thearpy, not pain management.