GC got the right idea. Most of the time, X-Ray won't show anything wrong because the bone is fine and nothing broken. But, everything else in the knee could be wrong and that's why a MRI is needed.
A MRI is the best choice test to see what is the problem. It showed so much more than bone problem. They are way more expansive than a X-Ray too, but that's okay as they show way more things that can be wrong. Then, a professional doc will tell you what wrong and what you need to do.

