Hi,
It is good that xray and MRI of the knee and other tests showed good results. Was there blood test done? This will help rule out infection or presence of gout. Knee pain usually results from arthritis (rheumatoid, osteoarthritis, and gout), baker's cyst, bursitis, connective tissue disorders such as lupus, dislocation of the kneecap, iIliotibial band syndrome, infection or any trauma or abnormalities in the structures in the knee.