Knee joint effusion occurs when the amount of fluid in the knee joint increases abnormally, causing restricted motion and potentially joint destruction. The condition has many causes, and if left untreated can lead to serious complications. Let’s explore the signs, causes and treatment methods in the article below. This article is written under the professional guidance of MSc, MD Nguyen Thi Oanh, Rheumatologist, Department of Internal Medicine – Vinmec Times City International General Hospital.