What Causes Fluid Retention In Knees After A Knee Injury?

I FELL ON MY KNEE ALMOST 2 YEARS AGO. IT WAS DRAINED 4 TIME, THEN SURGERY TO REMOVE THE BURSA SAC, THAN 4 MORE DRAINS AS MORE FLUID COLLECTED ON MY KNEE,THEN ANOTHER SURGER THAT WAS SCRAPING THE INSIDE OF MY KNEE. I WORKED FOR 8 MONTHS AND NOW AFTER 2 MORE DRAINS MY KNEE FILLS UP IMMEDIATELY WITH FLUID. WHAT IS WRONG HERE.