I have chronic clicking and clunking of the knee joint. what coul be the problem? what is the difference of a displacement of the root or meniscus?

Could be arthritis: The clicking and clunking can be arthritis or a cartilage tear. The meniscus is a piece of cartilage that acts like a shock on a car. It goes in between the two bones. But like shocks on a car, it can wear out and tear. The second part of your question is the same thing. They are describing the part of the meniscus -- i.e. The root of the meniscus -- which is where it attaches to.