Your knee is your largest joint. When you injure or irritate it — whether it’s from playing basketball or smacking it into the coffee table — it can be alarming to see how much it can swell up. But rest assured, swelling in the knee is very common. In many cases, knee swelling is due to an injury or simply doing more than your body is ready for at that time. As one Hinge Health member told us recently, their knee would swell up after a long day at work. “A routine of standing and walking for hours, along with going up and down stairs frequently, would have my left knee swollen and painful for hours,” they said.

But there are plenty of ways to manage knee swelling. One sure bet: doing exercise therapy to strengthen and support your knee and surrounding muscles. The Hinge Health member mentioned above, for example, shared that their knee is feeling better as they do more gentle knee stretches and strengthening exercises. “Now, my knee might ache a bit after getting home but it normally goes away quickly with no intervention. Overall the stretches seem to be working and my knees are feeling much better,” they said. 

Here, we’ll explain what causes knee swelling and pain and what you can do to relieve it and prevent having a swollen knee in the future.

What Is Knee Swelling?

Knee swelling, also known as knee effusion, simply means that there’s a buildup of fluid in your knee joint. Your knee joint is made up of three bones: the femur (thigh bone), the tibia (shin bone) and the patella (kneecap). Your knee normally contains 2-3 mL (about half a teaspoon) of synovial fluid, which helps to lubricate the joint. If it’s injured or inflamed, it can produce more. When this happens, your knee may feel stiff and tight. It may be hard to move around as well as you normally do. It may also hurt or feel warm to the touch.

Common Causes of a Swollen Knee

There are two main classifications of knee swelling, explains Justin Melson, PT, DPT, a physical therapist at Hinge Health: swelling from repeated stress and swelling from episodic stress. 

Repeated Stress 

Overuse. This type of knee swelling develops after you do more activity than your knee can presently handle. For example, increasing your running mileage rapidly (e.g., running 10 miles when you typically do three) or going on an hours-long hike on the weekend when you’ve been sedentary all week can put extra strain on your knee joint, leading to inflammation and swelling. 

Knee arthritis. When you have knee osteoarthritis, the cartilage on the ends of your knee bones changes over time. Everyone experiences changes in their cartilage over their lifetime. For some people, it wears down and reduces the amount of space between bones, which can lead to pain, stiffness, and swelling. Inflammatory forms of arthritis (like rheumatoid or psoriatic arthritis, where your immune system attacks your joints) are also known for causing knee swelling.

Bursitis. Bursae are small, jelly-like sacs that act as cushions to help reduce friction between your tendons and bones. If a bursa in your knee becomes irritated, often from muscle imbalances, says Dr. Melson, it causes them to overproduce fluid, which leads to knee swelling, (known as knee bursitis).

Episodic Stress 

Sprains. A knee sprain refers to an injury to one of the knee ligaments (strong bands of tissue that connect bones to each other). A sprain typically occurs when the ligament is stretched beyond its normal range, sometimes due to sudden twists, falls, or impact. The injury triggers an inflammatory response from the body as part of the healing process, which can lead to swelling along with other symptoms such as pain, bruising, instability, and reduced range of motion.

Tears. If you’ve ever skied or played basketball, you may have seen a teammate sidelined by an injury like an anterior cruciate ligament (ACL) tear. “These are more likely to occur if you play a sport where you have to cut or pivot a lot,” says Dr. Melson. You can also injure other knee ligaments, such as the posterior cruciate ligament (PCL) or the medial collateral ligament (MCL). “These sorts of injuries are pretty significant,” says Dr. Melson. If you have a recent history of trauma to your knee, notice your knee buckling, cannot bear weight through your knee, or suspect something more serious is going on with your knee, see a doctor. 

Note that in rare instances, knee swelling can be the result of an infection. Such causes of knee swelling can require urgent treatment (such as surgery). If you are concerned that the swelling might be associated with infection, you should see a medical provider right away.

Swollen Knee Treatment

Treatment for your swollen knee depends, in part, on what’s causing it. If the swelling is due to a serious injury or an infection, you should seek immediate medical attention. But for other causes of knee swelling, consider the following:

• Ice, ice baby. Apply a cold compress or ice packs wrapped in a thin towel to your knee a few times a day for 15 minutes at a time for as long as there is swelling. “Once the swelling goes down, heat may feel better, but ice is the best thing to help calm inflammation and get swelling down,” says Dr. Melson. 

• Elevate. Prop your knee and leg up above your heart as much as possible. This will help drain excess fluid from your knee joint, which can help healing and reduce swelling. 

• Consider a brace or knee sleeve. You can use braces and sleeves temporarily for additional compression and stability until the swelling resolves.

• Over-the-counter (OTC) medication. Non-steroidal anti-inflammatories (NSAIDs) such as ibuprofen (Advil, Motrin) and naproxen (Aleve) can help relieve knee swelling. Talk to your doctor before you use them, however, to make sure you can take them safely.

• Physical therapy. It’s a good idea to consider physical therapy to treat a swollen knee. A PT can address underlying causes of swelling, and work with you on a strengthening and stretching regimen to help prevent it from recurring. This is especially important if your swollen knee is from a tendon or ligament sprain or tear, notes Dr. Melson. “Many patients are afraid that if they use their knee, they’ll damage it even more,” he explains. “We work with them to get them moving safely in a way that works for them.” You can see a physical therapist in person or use a program like Hinge Health to access a PT via telehealth/video visit.

Afraid to Move or Exercise? Don’t Be

If you have a swollen knee, you may be worried about moving it, exercising, or even doing your usual daily activities. But moving is exactly what your physical therapist wants you to do. “The more you move it and use it, the more fluid you’ll push out and the more you’ll increase blood flow to the joint to encourage healing,” points out Dr. Melson.

These exercises recommended by Hinge Health physical therapists engage the muscles in your lower extremities, which helps pump fluid out of your knee and reduces swelling.