These are essentially a little pinch of the capsule that cushions your joint
-plus the fluid inside it-that has bulged out the back side of the knee
join. Can cause pain
,burning,swelling, or be symptomless, usually behind the knee, often also in the calf. The fluid inside the cyst is not supposed to roam freely in our bodies, so if it ruptures the response can be mild for a small cyst or wicked for a big one. I have seen a few docs drain off fluid, but not often.