What Does 'findings Of Joint Effusion' Mean?

Hi, My name is Tonya. can you please answere a couple of questions for me? I have a final report and it sais: right knee with one oblique. Findings: Osseous structures of the right knee are intact and aligned normally. The joint spaces appear well maintained. No retained radiopaque foreign body is identified. Increased density suprapatellar region is evidence of joint effusion. Impression: Findings of joint effusion. Otherwise unremarkable radiographs of the right knee. My email address is: YYYY@YYYY Thank You