Knee Effusion: What It Is and How to Treat It

Key Takeaways: 

1. Knee effusion is often caused by injury, arthritis, or activities that put too much stress on the knee joint.

2. Gentle movement and staying active — even when your knee is swollen — can help reduce discomfort and support recovery.

3. Simple stretches and strengthening exercises can improve knee mobility and help relieve swelling (see videos below).

Hinge Health offers virtual physical therapy and more to help you manage knee issues. Learn more.

If you’ve ever had a swollen knee — maybe you banged it really hard or suffered an injury while playing sports — you know just how uncomfortable and limiting it can be. You may have trouble standing, walking, and going up and down stairs. Knee effusion, which is the technical term for knee swelling, occurs when too much fluid collects in the knee joint. All joints have a small amount of fluid in them to help promote smooth movement, but too much fluid can result in swelling and decreased range of motion and mobility.

While moving around may be difficult with knee effusion, staying active is actually one of the best ways to address swelling. Over time, the fluid — and the accompanying discomfort — should decrease, and you can return to your normal routine. 

Read on to learn more about what causes knee effusion, along with how to prevent and treat it — especially with exercises recommended by our Hinge Health physical therapists. 

What Is Knee Effusion? 

Effusion is a fancy word for joint swelling, says Mary Kimbrough, PT, DPT, a physical therapist at Hinge Health. Knee swelling occurs when fluid collects in the knee joint, often due to an injury or medical condition. 

While swelling can occur in any joint, Dr. Kimbrough says knee effusion can be particularly persistent due to the unique structure of the knee. “The knee joint has a capsule that wraps around it, and that capsule has pockets in it,” she says. “Fluid can collect in those pockets, causing swelling.”

Symptoms of Knee Effusion

By definition, the primary symptom of knee effusion is swelling in and around any part of the knee. Other symptoms depend on the underlying cause of the swelling. The most common symptoms of knee effusion include: 

• Knee pain or tenderness

• Visible redness or warmth on the swollen area

• One knee that looks puffier than the other

• Stiffness of the knee joint

• Bruising on the affected area

• Reduced range of motion 

• Difficulty bearing weight on the knee

Causes of Knee Effusion 

Several different underlying causes can lead to knee effusion, and some of the most common are: 

• Knee arthritis. As you age, it’s common to experience changes in your joints and cartilage. As a result, you may experience swelling during episodes of pain, explains Dr. Kimbrough. 

• Trauma or injury. A knee injury, such as a broken bone or a torn ligament, can lead to inflammation that causes swelling in the area. 

• Overuse. Typical overuse injuries, says Dr. Kimbrough, include knee bursitis and tendinitis (tendonitis). Tendinitis involves inflammation of the tendons that connect the kneecap to the shin bone — sometimes caused by repetitive jumping motions. Bursitis is inflammation of the fluid-filled sacs that help cushion the knee, and it can stem from repetitive crouching or kneeling on hard surfaces. 

• Infection. Swelling may accompany a bacterial infection anywhere around the knee. If infection of the knee joint is suspected, this can be a medical emergency, and prompt evaluation by a medical professional should be sought.

• Cysts. Baker’s cysts are nodules in the back of the knee that can lead to chronic swelling, or they may develop as a result of swelling from other conditions like arthritis.

Treatment Options for Knee Effusion

Most of the time, knee swelling can resolve on its own with time and conservative home interventions, including: 

• Ice. Applying ice to your knee will help manage inflammation, which in turn may reduce swelling and improve range of motion. Try icing your knee for 15 to 20 minutes every few hours as long as it’s swollen. 

• Elevation. Immediately following an injury, elevating your leg higher than your heart can help control swelling.

• Compression. A simple bandage or knee sleeve during high levels of swelling immediately after an injury can help promote healing. 

• Over-the-counter (OTC) medication. Pain relievers such as ibuprofen (Advil, Motrin), naproxen (Aleve), and acetaminophen (Tylenol) can be helpful for pain that results from knee effusion. It’s important to make sure that you are safely able to take these medications, based on your medical history. 

• Exercise. At first, it may feel uncomfortable to move your swollen knee, but Dr. Kimbrough emphasizes gentle movement is important for reducing swelling, and for preventing future knee pain or injuries. Any exercise that stretches and strengthens the knee can be helpful, but physical therapy exercises for knee pain and swelling can target movement most likely to help improve your symptoms. 

Your muscles have a “pump function” that can pump out swelling in your joints — so any exercise using your leg muscles can help reduce knee effusion. This active use of your body’s natural pump is more effective at reducing swelling than just waiting and resting. Physical therapy exercises for knee effusion typically target flexibility and stretching to help preserve range of motion, while also strengthening muscles that support your knees. The above exercises recommended by Hinge Health physical therapists are a great place to start. 

The information contained in these videos is intended to be used for educational purposes only and does not constitute medical advice or treatment for any specific condition. Hinge Health is not your healthcare provider and is not responsible for any injury sustained or exacerbated by your use of or participation in these exercises. Please consult with your healthcare provider with any questions you may have about your medical condition or treatment.

Knee Effusion Prevention

It’s not always possible to prevent knee swelling, since it’s often your body’s natural response to an injury or another medical condition. But you can take steps to reduce the likelihood of experiencing knee effusion, such as: 

• Staying active. According to Dr. Kimbrough, healthy habits such as moving your body regularly can help prevent swelling, including in your knees. 

• Listening to your body. Try not to overdo it when you’re playing sports or working out, as injuries can cause inflammation that results in swelling. If you’re looking to ramp up your intensity, do it in a gradual way so that your knees have time to prepare for the increased load. 

• Changing positions frequently. If your job or a hobby requires you to be on your knees or jump, Dr. Kimbrough encourages switching up your posture and movement to prevent an overuse injury. One way to do this is to regularly engage in short bursts of activity, which we call movement snacks, to avoid getting locked in any one position for too long. 

• Doing physical therapy. If you’ve injured your knee, starting physical therapy sooner than later can sometimes prevent excessive swelling. You can see a physical therapist in person or use a program like Hinge Health to access a PT via telehealth/video visit.

PT Tip: Know When to Use Heat and Ice

Both heat and ice can help manage pain that results from knee effusion and improve mobility, and you can use them to your benefit in different scenarios. “People are always asking me if they should do heat or ice,” says Dr. Kimbrough. “With an acute injury, I recommend ice over heat to reduce immediate swelling. Heat can be effective in calming down pain, but it can sometimes increase swelling to the joint.” 

How Hinge Health Can Help You 

If you have joint or muscle pain that makes it hard to move, you can get the relief you’ve been looking for with Hinge Health’s online exercise therapy program.

The best part: You don’t have to leave your home because our program is digital. That means you can easily get the care you need through our app, when and where it works for you.

Through our program, you’ll have access to therapeutic exercises and stretches for your condition. Additionally, you’ll have a personal care team to guide, support, and tailor our program to you.

See if you qualify for Hinge Health and confirm free coverage through your employer or benefit plan here.

This article and its contents are provided for educational and informational purposes only and do not constitute medical advice or professional services specific to you or your medical condition.

References

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3. Dubois, B., & Esculier, J.-F. (2019). Soft-tissue Injuries Simply Need PEACE and LOVE. British Journal of Sports Medicine, 54(2), 72-73. doi:10.1136/bjsports-2019-101253

4. Gerena, L. A., Mabrouk, A., & DeCastro, A. (2024). Knee Effusion. PubMed; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK532279 

5. Jones, B. Q., Covey, C. J., & Marvin H. Sineath, J. (2015). Nonsurgical Management of Knee Pain in Adults. American Family Physician, 92(10), 875–883. https://www.aafp.org/pubs/afp/issues/2015/1115/p875.html 

6. Zeng, C.-Y., Zhang, Z.-R., Tang, Z.-M., & Hua, F.-Z. (2021). Benefits and Mechanisms of Exercise Training for Knee Osteoarthritis. Frontiers in Physiology, 12(1). doi:10.3389/fphys.2021.794062