Left knee effusion with no structural or systemic issues

Anna, it sounds like you have done absolutely evey test that could be ordered to determine what you have bothering your knee. I do have a bias as to the inadequate training of some radiologists because of their omissions in my testing, but that aside, you knee is telling you that it does not like what is happening to it, hence the repeated swelling.

?Aside from doing reserach to find an experienced radiologist to do one more MRI to fully examine the soft tissue that Xrays can't see, from my perspective, having tried it, I would ask you if it is possible that just losing a couple of pounds would benefit your knee. I did that and I still have a seriously damaged knee, but I had to agree that even a tiny weight loss did let me walk more comfortably and swellings were lessened.

?I'm not  medically trained, just going through a lot of the stuff you will read about here. I wrote my radiologist  up for an award at our medical center when she determined what my problem was after years of suffering. She confided that she was good at diagnosing this particular rare tissue problem. I hope you will have good luck getting an answer.

?On more thng, I, too, tried the walking routine, but I found out that when I walked quickly, the swelling was sure to come.  If I strolled (not really an exercise, is it?), then the swelling did not appear. I'm just saying, for me, that was a clue.  But we are all different.

?Best wishes, let us know how you are doing.

It is troubling that you do not really have a good diagnosis, nor a treatment plan.  Chronic moderate synovitis is a general term and could be a result of bad arthritis, which is why maybe they didn't advise a TKR  for osteoarthritis, as ordinarlily one would expect trying more conservative measures, like shot of cortisone, or gels, or platelet replacement therapy , or even stem cell replacement.(My medical center will only do the cortisone shots now and send you for physical therapy,)  However.....there are more reasons for that swelling and synovitis.  Namely, rare reasons like lupus, rheumatoid arthritis, gout, and my disease PVNS.  If your doctor was an orthopedic surgeon, then he is only interested in surgery to correct bones' malformations, etc, or replace your joint.  I have been dismissed by 2 of those doctors who didn't want to pursue other reasons for my periodic major swellings. Fortunately, I had a good radiologist.  But did you?  A MRI can tell a lot about the soft tissue, but the fluid inside can tell a lot too. For instance, my young nephew had a badly swollen knee and I thought, oh no!!, is my disease inherited etc.  But it turned out on careful analysis of that fluid that he was in Stage 4 of Lyme disease.  Who could possibly have guessed that?  The doctor who has the blood tests to determine all of the above is a rheumatologist, not a sports doctor, nor a orthopedic surgeon, nor general practioner or consultant.  I don't know your country, nor health insurance plans, etc. so I would ask you to push forward in getting an accurate diagnosis, less you end up with years of suffering like myself.  When they cut out the platelet therapy at my medical center (because they weren't paid enough to justify the labor and timing of taking one's own blood and injecting it into your joint) it left me with almost monthly swelling instead of every 6 months and maybe never with the platelet therapy.  I am still fighting the system to get what I need to stay mobile.  I cannot take NSAIDS and other meds are becoming scarce due to the big crackdown in America on opioids.  We are now given Tramadol which is kind of a big joke to those of us that are not helped by it.  And of course, no serious pain killer will ever reduce swelling.  I carry Prednisone in my purse to take immediately when the quick swelling hits me.  This starts to draw out the excess fluids. You may want to consider that med.

?Go to rheumatology with all your previous tests results so that they will not have to be repeated and ask for an evaluation of your swellings. In US, we own ouur health records and can get a printout of everything including a CD of Xrays, MRI, Ct Scan, etc. just for the asking.  One must keep one's own health records ourselves  in order to stay on top of what is happening to us.  We need to be in charge, not an assortment of disconnected doctors.

?I know, I am old and cranky.  I would submit that mobility issues can make one that way. Sending a cyber hug.