I Have a Swollen Knee: What’s Wrong? (Video)

Swollen knees are a common concern. This swelling, also known as ‘water on the knee,’ can happen both inside and outside the joint itself. In this post, we’ll take a look at the symptoms and diagnoses related to swelling that occurs inside the knee joint.

About Swelling of the Knee

It’s normal to have some fluid in your knee. This fluid, called synovial fluid, is produced by the lining of your knee and is vital for a healthy, well-functioning joint. However, an excessive buildup of this fluid is a sign of a problem in your knee.

We use two terms to describe this buildup. If your knee is swollen as the result of a nontraumatic incident, then the fluid in your knee is referred to as an effusion. When the fluid in your knee is due to a traumatic event (like an injury or accident), the fluid will be called either an effusion or a hemarthrosis. Hemarthrosis means there is blood in your joint, which is never normal.

What Symptoms Accompany a Swollen Knee?

Small amounts of fluid in your knee often won’t cause any symptoms. However, if the amount of fluid becomes too great, symptoms can develop. These symptoms include a noticeable enlargement of your knee and loss of motion. These symptoms are frequently accompanied by pain, most often in the back of your knee or above the knee cap. This pain will be particularly noticeable when bending your knee.

The following video illustrates two simple ways to determine if you have a small amount of fluid in your knee:

What Can Cause a Swollen Knee?

Swelling in your knee is typically caused by one of three things. Your knee may have been damaged due to external trauma, or the swelling may be a result of a meniscal tear or cartilage issues. Each presents its own set of symptoms and requires a different treatment plan.


A male runner holds his painful knee with both hands.

Nearly any type of trauma can cause swelling in the knee. The most common injuries that cause knee pain and swelling are ligament injuries such as ACL tears, fractures (breaks in the bone), and bone bruises. Bone bruises can occur from an external force contacting a knee bone, or more commonly from two of your bones banging against one another, which is what happens when your knee cap dislocates.

If you experienced knee trauma, then your history, physical exam, and available imaging studies will help determine the correct diagnosis. Swelling from trauma often resolves in 4-6 weeks. The underlying problem, however, may continue to be an issue.

Meniscal Tears

The menisci are small c-shaped rubbery discs in your knee that rest between the end of your thighbone (femur) and upper shin bone (tibia). They help provide stability, cushioning, and normal functioning of your knee. At times, these can tear. Frequently, these tears will cause pain in your knee. They may also result in a swollen knee. Usually, meniscal tears cause lesser amounts of knee swelling. However, larger tears may cause greater amounts of fluid in your knee. This swelling will usually persist until the tear is treated.

Cartilage Issues

There are a number of cartilage issues that can cause a painful swollen knee. Osteoarthritis is by far the most common. Osteoarthritis (OA) is a degenerative process in our joints. It leads to a loss of cartilage, bone changes at the joint surfaces, and a release of inflammatory and degenerative mediators throughout the joint.

The common symptoms of osteoarthritis are pain, stiffness, weakness, clicking or catching, the knee giving way, and swelling. Cartilage issues, including OA, can cause greater degrees of swelling inside the knee than other sources of knee swelling. This swelling can occur from loose pieces of cartilage floating around the knee, exposed bone from the loss of cartilage overlying the joint surfaces, and those mediators mentioned above.

Additional cartilage issues that may also cause swelling are inflammatory forms of arthritis, such as rheumatoid arthritis and Lyme arthritis, as well as chondral defects (focal areas of cartilage loss).

Comprehensive Care for Knee Issues at Town Center Orthopaedics

A swollen knee can cause pain, stiffness, and tightness in the joint, and it is always a cause for concern. Swelling in the knee means something is wrong. An expert evaluation is required to make a diagnosis and develop a treatment plan.

The orthopedic experts at Town Center Orthopaedics specialize in knee care. Request an appointment here or call (571) 307-4985 to speak to one of our team members.

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