Dr Wally Pearson offers advice and exercises for managing Patellofemoral Tracking Syndrome which involves pain in the front of the knee as well as a feeling of popping, grinding, slipping, or catching in your kneecap when you bend or straighten your leg. It can also include the feeling that your knee is buckling or giving way, as though all of a sudden your knee can't support your weight.
Specialty Reference:
Hip & Knee