Swelling in the knee can result from banging your knee against something, an athletic injury, or overuse. This can lead to fluid in the knee, commonly called water on the knee. Pain in this condition can range from non-existent to extreme, and there may be a feeling of tension, stiffness or an inability to straighten the knee joint. Reducing fluid in the knee depends on the severity of the injury and the degree of swelling.
Stop or at least reduce any activity that causes pain. This may involve resting your knee and walking as little as possible. You might need to avoid driving if the affected knee reacts with pain when you push your foot down on pedals.
Apply ice wrapped in cloth on your knee, and keep it elevated as much as possible. Rest your leg on a chair, or if possible, lie down with your knee on a pillow. This allows fluid to drain away from the knee.
Wrap the knee with an elastic bandage to reduce swelling, pain and inflammation. Do not to wrap your knee so tightly that circulation is affected. Rewrap the bandage more loosely if your lower leg starts to feel tingly, numb or cold.
See a doctor if the swelling or pain is severe or does not lessen within a day or two. The doctor may decide to aspirate the fluid from your knee with a needle and syringe, which provides fast relief. If the fluid indicates an infection exists, take antibiotics.
See a physical therapist if the doctor refers you. A physical therapist can treat fluid and swelling in the knee with electrical stimulation and massage, and can teach you isometric exercises to reduce fluid and strengthen the surrounding muscles.