If you have not had surgery or if you are far past your surgery and your knee still clicks painfully, it's time to consult your physician. If your knee clicks and does not hurt, it's probably safe to continue with your exercises. There are many exercises to strengthen your leg muscles. Some strengthening exercises often cause more pain or degeneration in the knee than they're worth. Leg extensions, a gentle kicking motion, sometimes causes problems with the patellar tendon or behind the kneecap.
Lunges have a similar, adverse effect in the same area.
We recommend exercises that use contraction and coordination of several muscle groups during the same activity. Leg-press exercises and exercises with the foot planted on the ground are some of the better exercises for leg strengthening. The answer to this question is entirely an individual matter. It depends on the extent of the surgical procedure and the surgeon s recommendation for rehabilitation. Most people begin months ahead of that time, working on strength and agility drills.