Your knee typically has an ounce of liquid inside of it. However, when you have an injury, arthritis, or another problem that irritates your knee, fluid accumulates to cushion and protect your joints.
Clinically, this is known as knee effusion, but most people call it water on the knee.
What Is Water on the Knee?
Water on the knee is a result of your body’s natural efforts to protect itself.
When you injure your knee joint causing irritation and inflammation, your body produces extra joint fluid to cushion and lubricate your joints.
The extra fluid causes:
You won’t be able to put pressure on your knee. Fluid on the knee can also limit your mobility and make it painful to go up and downstairs, kneel, or squat.
What Causes Water on the Knee?
Several factors can cause fluid to accumulate in your knee joint. Some of the most common injuries and health conditions include:
Osteoarthritis, rheumatoid arthritis, and gout are all types of arthritis that can cause the level of irritation in your knee that cause excess fluid to accumulate around the knee joint.
Osteoarthritis is the degenerative form of the disease that develops as the cartilage of a joint wears away.
Rheumatoid arthritis is an autoimmune disease that inflames the synovial lining of your joints.
Gout develops when uric acid crystals form in your joint and irritate the soft tissue that lines and protects your joints.
Ligament injuries like sprains and ACL tears can also trigger the condition.
Ligament tears and sprains are common sports injuries that occur when you forcefully twist or bend a joint in an abnormal direction.
You have liquid-filled sacs in your joints that absorb shock and help lubricate your joints.
Bursitis is a repetitive use injury that irritates and inflames the bursa, leading to a fluid-filled swollen knee.
A Baker’s cyst develops when the popliteal bursa at the back of the knee swells with excess liquid.
It causes knee swelling and stiffness and can lead to water on the knee.