Fluid on the knee, or knee effusion, is a condition that results in excess fluid accumulation in or around the knee. While all joints have a small amount of fluid to lubricate and protect them from damage, noticeable swelling or fluid buildup around the knee is not normal. Common symptoms accompanying water on the knee include stiffness, swelling and pain. According to MayoClinic.com, the most common causes of water on the knee include injuries, infection and disease, and osteoarthritis.
Knee Injuries
Swelling resulting from injury or trauma to the knee often results from an accumulation of blood in and around the knee. According to MayoClinic.com, examples of injuries resulting in fluid buildup include broken bones, a meniscus tear, a ligament tear and overuse injuries. The University of Minnesota Sports Medicine Institute reports that the most common injury to the knee that results in fluid accumulation is a tear to the anterior cruciate ligament, or ACL; torn ACLs account for nearly 75 percent of these types of injuries.
Infections and Disease
Conditions that may cause the knee to swell with fluid include infections and diseases such as gout, bursitis and tumors. Infections associated with fungi, tuberculosis and Lyme disease often cause excess pus to form around the knee. Gout causes small crystals to develop in the knee, leading to irritation and swelling. Benign and malignant tumors in the knee often cause fluid to form around the knee. Swelling in the knee associated with tumors often results from a combination of excess fluid in the joint and the size of the tumor itself.
Osteoarthritis
Osteoarthritis is a degenerative disease that wears down the cartilage of the knee. The risk of developing osteoarthritis increases with age, obesity, joint injuries and professions that repetitively stress the knee. In addition to collecting fluid around the knee, signs of osteoarthritis include pain, stiffness, loss of flexibility and bone spurs.
