What causes swelling in the knee? i had surgery over 1 year ago and my knee is still very swollen? i had plica removal and think i have atrophy? expla

Inflammation: In a 40+ year old patient with prior surgery for plica/chondroplasty the possible reasons for the swelling are: 1) infection, 2) cartilage damage, and 3) mechanical symptoms from a torn meniscus. It is difficult to get more specific without more information, a physical exam and testing as indicated; however, I do think you should be evaluated by an orthopedic surgeon.