What Causes Fluid on the Knee?

What Causes Fluid on the Knee?

Dimpled, chubby knees look cute on a toddler, but for adults, they spell trouble. If you've ever had fluid on your knee, you understand the physical pain not to mention the unsightly nature that accompanies this problem. Your knee will be stiff, and you will not be able to bend it completely. 

So, what causes fluid on the knee, and can you get rid of that fluid on your own? Fluid on the knee stems from any one of a range of possibilities from something as simple as an overuse injury to as scary as a tumor. Keep reading to learn about the causes for fluid on the knee and the ways you can both treat and prevent this problem. 

What Causes Fluid on the Knee? 

Doctors refer to fluid on the knee commonly as water on the knee or knee effusion. It means you have a swollen knee caused by fluid that has accumulated around the knee joint. 

Your knee will be swollen and difficult to move if you have fluid on your knee. You may have trouble walking or performing basic physical activities. In particular, you will struggle to kneel. 

Is This Fluid Water on the Knee?

While people may commonly refer to a swollen knee as "water on the knee," you may not have water on your knee. You could have one of three different types of fluid causing your knee to swell and ache. 

You may have blood. If you've had a recent injury near or on your knee, blood could pool around the joint. 

You could also have an excess over joint fluid. All functioning knees have some amount of joint fluid to keep the knee lubricated. Without joint fluid, your knee would hurt all the time. 

Some conditions can cause your body to produce an excess of joint fluid, and this would cause a swollen, stiff, and painful knee. Doctors refer to the excess of joint fluid as knee effusion

You could also have other body fluids present other than just blood or joint fluid. If you injure your body, your body reacts naturally by swelling with fluids that fight bacteria and help you heal more quickly. These fluids can cause your knee to swell. 

Causes of fluid on the knee will vary from something as simple as an injury to as serious as cancer. 

1. Knee Injury

Any sort of trauma to your knee can cause it to balloon up. If you injure the bone, tendons, meniscus, cartilage, ligaments, or virtually any combination of those things, fluid will accumulate. 

If you sustain a more traumatic injury, then blood will pool around the knee joint. This leads to a more swollen knee that is warm to the touch. When you see a bruised knee and experience significant stiffness, that is blood and not water around your knee joint. 

Blood around the knee is not the same as the water around the knee. Blood will be warm to the touch, and you need to seek medical care immediately. If you think you've broken a bone or if you cannot bear weight on the knee, find medical care immediately. 

2. Arthritis

When the cartilage around your knee breaks down, your body overproduces joint fluid. This causes your knee to swell. Doctors refer to this breakdown of cartilage as arthritis. 

Arthritis causes a swollen joint and significant pain. It just plain aches all the time. Doctors may refer to this condition more specifically as "knee osteoarthritis." 

Other types of arthritis can cause pain and swelling in the knee as well. 

Rheumatoid arthritis is an autoimmune disease that attacks the lining of joints. In particular, it causes knees to swell and stiffen up. A tender, red, painful knee can stem from rheumatoid arthritis. 

Typically RA affects hands, wrists, and feet, but knees are not immune to this horrible disease. 

Juvenile rheumatoid arthritis is another type of arthritis specific to children and teens. It causes a child to have achy, swollen joints, leaving the child to seem clumsy because their joints just don't work right. 

Often a fever or rash will accompany juvenile rheumatoid arthritis. When a child experiences a rash or fever along with swollen, stiff joints for a week or more, you should contact a doctor. 

Septic arthritis occurs when bacteria or microorganisms attack the lining of the knee joint. This bacteria can infect the knee joint, leading it to fill with pus. If your knee begins to swell suddenly or if you have intense knee pain accompanied by a fever, you could have septic arthritis. 

Sepsis is a serious condition. You cannot treat this problem at home, but you must seek immediate medical attention. 

Reactive arthritis is also known as Reiter's Syndrome. This illness occurs when a bacterial infection randomly stimulates an inflammatory immune response. Your immune system goes into overdrive, and your joints begin to swell and ache. 

When your joints begin to ache, seek an over-the-counter anti-inflammatory medication. Look for pain relievers specific to arthritis. If the condition worsens or persists, though, you need to seek a doctor. 

3. Bursitis

Your body has tiny, thin, fluid-filled sacs through it called a bursa. These bursae typically protect joints. If the bursa in your knee fills with excess fluid, your knee will swell, and you will have a water-on-the-knee condition. 

Doctors refer to an inflammation of the bursa as bursitis. 

Bursitis does not necessarily hurt that much, but it looks uncomfortable. The knee will feel squishy because of the fluid-filled sac. 

Bursitis can warrant medical care, though, if the bursa gets infected. When a microorganism infects the bursa, it fills with pus and flares up. It will redden and feel hot and hurt quite a bit.  

If you have a red, hot knee, seek a doctor. Doctors refer to an infected bursa as "septic bursitis," and this condition needs medical attention. You cannot fix it at home. 

4. Gout and Pseudogout

Gout occurs when microscopic uric acid crystals accumulate around a joint. When this happens around your knee, you end up with a swollen, painful, red, and warm knee. 

Gout just plain hurts. It typically affects the big toe, but doctors have reported incidents where gout has attacked knees, wrists, and fingers. 

The word "pseudo" means fake. So pseudogout is basically, a fake type of gout. with pseudogout, calcium pyrophosphate crystals accumulate instead of uric acid crystals. 

While pseudogout does not have the same type of crystals as gout, it hurts just as much. It also typically affects knees as opposed to big toes like regular gout does. 

5. Baker's Cyst

Swelling at the back of the knee can indicate a Baker's cyst. The cyst may have no other symptoms or may be accompanied by pain and stiffness.

A Baker's cyst is a fluid-filled cyst that causes a bulge and a feeling of tightness behind your knee. The pain can get worse when you fully flex or extend your knee or when you're active.

Doctors will refer to a Baker's cyst a popliteal. The cyst results from arthritis or a cartilage tear most often. 

Doctors will typically treat the underlying problem of arthritis or cartilage tear rather than just draining the fluid from the knee. A Baker's cyst will worsen with more activity or a lengthy period of standing. 

When your knee produces an excess of fluid, it can build up in the back of your knee and create this cyst that makes bending your knee painful and difficult. If you suspect you have a Baker's cyst, you should seek a doctor. 

A Baker's cyst can burst. If this happens, fluid will leak into your calf area and cause the calf to swell and turn red. This redness and swelling will look much like if you have a blood clot, so you need to seek a doctor's attention immediately to determine the cause of the pain and redness. 

6. Osgood-Schlatter Disease

Teens and tweens are most likely to develop Osgood-Schlatter disease. This disease occurs when the patellar tendon on the knee flares up. Active, growing adolescents experience this most often.

When a teen or tween experiences a growth spurt, pain may ensue. The bone may be growing faster than the muscle, ligament, or tendon. As a result, the bone will pull on the tissue and cause pain, and Osgood-Schlatter results. 

Adolescents can treat this pain at home with rest, ice, compression, and elevation. They should not need a doctor's care unless they push through the pain and injure their knees. 

7. Tumor

Tumors are the most uncommon reason for a swollen knee, but they do occur. Both a benign and malignant tumor can cause a knee to swell.

Tumors have specific accompanying symptoms. You will have a sore knee, but you will notice the pain more at night. You will also experience night sweats, a fever, and weight loss. 

How Do You Treat Fluid on the Knee? 

The way you treat your fluid depends on your condition. If the knee is not warm to the touch or red, you can use a basic treatment at home. 

Basic arthritis home remedies and natural treatments can alleviate your pain and put you back on track for the everyday activities you love. 

Fluid on the knee home treatment begins with rest. Take time to rest your knee whenever pain and swelling appear. In particular, avoid any activities that require you to bear weight. 

If the swelling and pain persist, you may need to find a new activity. 

Seek out over-the-counter medication to help with your pain. Look in particular for pain relievers and anti-inflammatories specific to joint pain. If you suspect arthritis, look for arthritis-specific medication. 

Elevate your leg and put some ice on the sore knee regularly. Create a routine where you ice the knee for 15 to 20 minutes at a time. Do this every two to four hours throughout the day, especially if you have sustained an injury. 

Proper elevation means your knee will be higher than your heart. So stack up some pillows, break out a good book or magazine, and take care of your knee. Tools for cold therapy on the knee will make your care routine simpler. 

As your swelling subsides, work on rehabilitating your knee. Focus on building the muscles around your knee to stabilize it. Low-impact exercises like swimming and water aerobics help build those muscles without putting stress on the joint. 

At this point, you should look into getting a knee brace. With so many options on the market, you will want a doctor or physical therapist's opinion so you know exactly how much of a brace to purchase. A brace will help stabilize the joint as you build up the muscles around it. 

Plus, a brace can serve to compress the knee and keep fluid and swelling at bay.

Can I Prevent Fluid Around My Knee? 

Injuries and auto-immune diseases are unavoidable. But you can do a few things that lower your chances of having knee problems in the future. 

For one, maintain a healthy weight. Less weight on your joint means less wear and tear and less chance of overuse injuries. 

Focus on keeping the muscles surrounding your knee strong. Exercises that work quads, hamstrings, and calves will stabilize the joint and keep it in line. 

Protect your knees with knee pads if you are in any activities that could injure your knees. You can even wear knee pads when you're gardening or working on your floor. 

Take time to stretch every day. Tight muscles surrounding your knees can cause your knees to ache and swell. 

If you think you've injured your knee, seek a doctor. Do not hesitate to seek medical attention to prevent further injury. Even if you just strained your knee, then you'll know to not push yourself through the pain, which could cause further damage. 

When Do I Go to a Doctor for Fluid On My Knee? 

You do not necessarily have to call a physician to learn how to get rid of fluid on the knee. But there are times when the injury warrants a doctor's call. 

1. If your knee is hot and red, go to the doctor. This could indicate an infection. 

2. If you cannot bear weight on your joint after a basic ice and elevation routine, seek a physician. 

3. If your condition worsens even after treating the swollen knee at home, go see a doctor. 

Small injuries may just require some ice, elevation, and over-the-counter anti-inflammatory medication. But if this basic treatment does not lead to improvement, you need a doctor. They will give you a treatment for fluid on the knee specific to the condition causing swelling. 

Treat Fluid Carefully

Now you can say what causes fluid on the knee when your knee begins to swell. Seek medical treatment if you need to, but otherwise, treat your knee purposefully and carefully at home to see the swelling go down. 

We have an excellent supply of knee braces that can help you recover from a knee injury quickly. For all of your knee care needs, contact us


  • Linda Handy

    My knee is swollen an hurts at the back of my leg as well as the front

  • twana valley

    My knee hurts when I bend it and hurts when I walk please help me

  • Husseina Ahmed

    I have a fluid on my knees. Pls I need yr help.

Leave a comment

Please note, comments must be approved before they are published