In the wild chameleons have a much greater variety of insects to eat and those have access to a large variety of fresh vegetation. In captivity they only get what we provide. In most cases that is mass-produced crickets and mealworms.
A PCL tear resulting in back of the knee pain can be caused by a fall on the knees when they are bent, a blow to the front of the knee or a major twisting motion, such as during a skiing wipeout. Physical therapy and surgery are the usual PCL tear treatment methods, likely with use of a ligament tear knee brace.
Clicking in knees may also occur after knee surgeries, because the muscles surrounding the knee are not as strong as before due to bedrest. This difference in muscle strength may cause misalignment issues that cause knee clicking. Luckily, this typically goes away as knee strength returns.