What to do if i am 22 yrs old and knee keeps clicking when extended, went to the hospital and got an x-ray and it came out negative?

Consult orthopod: Plain radiograph demonstrates mainly bony abnormalities and sometimes joint effusion. Should see orthopedic surgeon for consult and possible MR exam to assess ligaments, menisci, joint space, muscles etc.

Painful??: while I completely agreed with prior answer, I would point out that there is a difference, in general, to painful popping vs painless. Since we really do not KNOW what causes the popping, we generally feel that painless popping is not likely to be representative of a problem. The orthopaedist may not order an MRI if they feel there is no pathology