one thing you need to remeber here is any kind of 'free fliud' we have in our bodies thats not supposed to be there(this happens with larger bruises too) will just have a natural tendency becasue of the gravity to actually kind of 'pull downward" in us, espescially when in the knee area down to the ankle like yours is?
unfortunetly the only thing that any plain x ray would show is pretty much the harder more solid boney structures in any given area and not the soft tissue areas surrounding it or in any given joint or other areas either. trust me here when i say that you could actually have some very real underlying damage in that knee that would realistically just need an MRI to really see.
in most cases, the body actually would reabsorb any free fluid like you have going on right now. the only or one of the main reasons it still could be there is more could be added to it that you just are not really aware of? any inflammation within our bodies will generally create some level of fluid or real swelling. i think its time to just see at least your primary about this and see if they can try maybe a short course of a diuretic type med just to see if this actually clears? you should maybe also consider getting an MRI done on that knee too just to make certain what is generating this is not something more than what you were told based upon ONLY plain x ray. like i mentioned above, no real soft tissue structures would show, and those are what really need to be seen at this point. this is just one of those better safe than sorry things, ya know? i personally have had two seperate knee surgeries done on the same knee just for wear and tear type injuries and whats called a bakers cyst that formed inside after i somehow tore the inner synovial sac that surrounds the joint? i could still walk on all this so i really did not know just how bad the overall damage was in there til we did the MRI.
i would simply seek out your primary right now to get to the bottom of what just IS the main and true generator of this whole thing. ya never really know just what is going on within any area of your body til you just obtain that much deeper look inside, ya know? good luck with this and please let me know what you find out. FB