Fluid on Knee Caused by Trauma

Updated November 21, 2016

Fluid on the knee, also called water on the knee, is a term used for the profuse swelling that can occur to the knee joint when it has been injured. In the case of trauma, it is a straightforward diagnosis, and no medical searching for a cause must be done. Whether in an accident, a sports-related activity, or other trauma, the knee has sustained an injury and reacts with copious amounts of swelling in the joint.

What It Is

Water on the knee is inflammation. It is the body's reaction to injury. When the injury is sustained, the body reacts with a super flood of platelets, blood, plasma and "cushioning" water to the affected area. In the case of the knee, where the joint is really only held together by a complex network of muscle, tendons and ligaments, the swelling can become quite extreme in a very short time.


Just as no two patients are the same, no two swellings are identical, and there are many different levels of water on the knee. In most cases, swelling makes the joint look puffy and feel swollen and stiff. There will be discomfort, but it can usually be alleviated with rest, compression, ice and elevation. If the injury is severe, as in the case of a torn ACL (anterior cruciate ligament) or a dislocated kneecap, the knee will react in shock and flood the joint with enough fluid that it can quickly become the size of a soccer ball. The more it swells, the stiffer it will become. If your knee becomes this swollen, you need to seek immediate medical attention.


The effects of water on the knee depend on the amount of fluid that has built up. If the swelling is minor, there will be some puffiness and tenderness in the swollen area. The knee may feel clumsy and thick. In the cases of more aggressive swelling, the knee is likely to feel numb and stiff, almost as if the joint had been given a shot of novocaine. Pain will be present, but it will mostly occur with movement and weight bearing. When still, the knee will feel "dead".


Treating water on the knee will vary by case. Most mild cases resolve themselves within a few days. More severe cases will need medical attention immediately to determine the damage. If you have mild to moderate swelling of the knee, stay off of it and elevate it above hip level. Apply an ice pack for at least 20 minutes and reapply every 30 minutes. Keep a compression bandage on it to encourage the fluids to be dispersed, and rest the knee. Do this for at least 24 hours and then reassess. For severe swelling, get to a medical professional as soon as possible, and do not put weight on the joint.


Severe swelling of the knee joint is a bad sign. There is something wrong. It may be a reaction to the trauma, but if it does not get significantly better within 24 hours after apply the above treatment, it is time to see a doctor. It may or may not reduce, but if it is a sign of impending infection or of a more serious injury--it will not go away but linger. In this cases, it is imperative to see a medical professional right away. Don't ignore it.

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