I was having right knee pain/ache which usually comes and goes. I experienced this 2/3 times since a year back. No morning stiffness, when i move after resting for something i experienced sharp pain and after walking few steps it was manageable. Similarly i had pain in January this year on 7th night it worsened and I couldn't straighten my knee nor put pressure. Esr was raised upto 40mm/hr . Attaching the mri and other blood test reports. Aso was negative and urine was normal too. What could be the exact reason? An autoimmune arthritis? Or pvns? Anything other than?