Replying to Knee problems

Basically one time last season I had a pretty bad fall and ended up really hurting my knee. It was swollen for a bit over a week, maybe 2, then was full of some kind of gooey liquid. I got an MRI but there was no visible damage so I waited for the swelling to go and eventually the goo went too. Problem solved I thought? Apparently not. Now pretty much after every ski session my knee is swollen, it's not particularly sore and I can move it fine but I'm guessing this isn't good for my knee. Basically what I'm wondering is, is this going to end up causing long term damage and should a knee brace be enough to stop it happening?