Hi there,
I may well be wrong but from what you've said I'm not yet convinced that it is cartilage damage behind the knee, I think that you have strained/torn the muscle jsut above the knee cap which is responsible for holding the knee cap in the correct position. I'm jsut not sure that you could damage the cartilage from a single squat. I think you need to work on the quads muscle, strenghtening as teh physio said but maybe also some soft tissue work to try and break-up the knots the "netting-texture" and see if the work on the muscle changes your knee cap symptoms (which I am hoping that it does!!!)
Thank you!