About 18 months ago I had total hip replacement, it is wonderful, but slightly behind the surgery site I have a lump that is fluid filled about the size of a small orange. It is filled with a yellow fluid. Have had an MRI and two CT scans with biopsy of hip, no fluid there, and biopsy of the lump itself. They drained it 75CC in one lump and about 45 in the other, the lump refilled within a day. Whats going on?