Review with your CBC, CRP(quantitative), ESR and S.uric Acid profile.

If there is no infection or stitch abscess you need not  worry too much. Yes some patients after arthroscopy take long time for the fluid to resorb. If fresh effusion or swelling which is not leaking around the knee and you can put weight and bend the knee to some extent usually there is no infection. However if you feel unwell,feverish get the knee fluid aspirated and sending it for infection testing will tell you what is going on by your doctor.get also your bloods tested for infective parameters from your doctor

Leaking water from knee to be tested for germs. Most probably joint infection. You need immediate attention from oruthi surgeon.

May be Low grade subclinical infection

You may be having low grade infection in your joint. The fluid from the joint needs to be removed and sent for the necessary tests.

It's Probably Subclinical infection with synovitis. You need to get Blood reports done for infection like CRP ESR CBC pro Calcitonin. And repeat MRI if required.you should not ignore it as it might damage your knee cartilage if not treated now.