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Swollen Knees - Overview

by Jaydee Vykoukal, PT, DPT May 02, 2018 0 Comments

ice pack on knee

Whether the onset comes on quickly or gradually, after an injury or without warning, swollen knees are very common. Often troublesome, a swollen knee might cause you stiffness and pain, making it difficult to go about your everyday life. If you notice swelling in your knees, don’t worry--there are plenty of swollen knee treatments that you can try at home to reduce symptoms quickly and get you back to feeling your best. In this article, you’ll find everything you need to know about swollen knees--what they are, what causes them, and how to prevent them.

More about Swollen Knees

A swollen knee is caused when fluid accumulates in or around the joint. This can be caused by swelling within the joint itself (intracapsular), around the kneecap, or in surrounding tissues such as the local muscles or ligaments.  A swollen knee is sometimes referred to as “water on the knee” or knee effusion. If your knee feels swollen, it usually means that there’s a problem inside or around the joint, either from an injury or chronic condition. Swollen knees can occur either rapidly or gradually, and can range from mild to severe depending on your overall health and other underlying issues.

Are Swollen Knees Common?

A swollen knee cap is a very common condition and can affect anyone, young and old. A swollen knee can come about very quickly due to an injury, or, it can occur gradually over time as the result of a chronic condition. As we age, the types of chronic conditions that might cause swelling in the knees become more common, causing the possibility of swollen knees to increase.

Understanding Swelling in the Knee

Why is my knee swollen? To understand why fluid accumulates in the knee joint, it’s important to understand the anatomy of a joint. The knee joint itself is an enclosed system of connective tissue, known as the joint capsule. These tissues provide stability to the joint and also keep fluid where it belongs within the joint, known as synovial fluid. The fluid works to keep the joint lubricated so that it can move smoothly.

A knee will most often become swollen when excess fluid builds up in the joint capsule. The two most common swollen knee causes are from bleeding in the joint or an over-accumulation of synovial fluid due to injury or chronic wear. Additionally, knee swelling can be found around the kneecap or in tissues outside of the joint capsule as well, such as the hamstrings, quadriceps, and ligaments (such as the medial collateral ligament and lateral collateral ligament).

Swollen Knee Causes

If you notice that your knee is swelling up but aren’t sure why, there are a few swollen knee causes that may be the issue. Whether it’s an injury to the knee, chronic condition, or infection, learn more about the most common factors below.

Injuries to the Knee

If you’re noticing a swollen knee after a fall or other injury, it’s likely that you’re experiencing hemarthrosis, or the accumulation of blood in the knee. This will usually cause swelling in the knee, tightness and soreness, as well as bruising. Additionally, injured tissue naturally recruits more cells to the area to promote stability and healing; resulting in increased fluid in the area.

  • Ligament Tear

    One of the most common causes of a swollen knee from an injury is a ligament tear. The most commonly torn ligament in the knee is the Anterior Cruciate Ligament, or ACL. With an ACL tear, the knee will usually start swelling and become painful immediately.

    If you’re experiencing a torn ACL, check out this list of the five best knee braces for a torn ACL.

  • Meniscus Tear

    A meniscus tear refers to a sprain or tear in the horseshoe shaped cartilage within the knee joint, which is the rubbery disk that cushions the knee. With this type of injury, the pain is usually less intense than a ligament tear, and the knee will begin to swell more slowly. However, swelling tends to be more chronic with a meniscus due to lack of blood flow to these areas.

    Meniscus Tear

  • Bone Fracture

    One of the most common types of bone fractures in the knee is a patellar fracture. The bottom of the thigh bone (distal femur) or top of the shin bone (proximal tibia) can also be fractured. Additionally, an avulsion fracture can happen with a sudden forceful muscle contraction near the knee joint too. A bone fracture will be very painful and will require immediate medical attention for appropriate stabilization to allow healing.


If you have arthritis, it’s possible that the cause of your swollen knee might be your arthritis, especially if it is caused by Rheumatoid Arthritis over Osteoarthritis. Because arthritis wears down the cartilage and bones in the body, it can cause the body to produce excess fluid in the knees secondary to chronic tissue irritation. Arthritic knee swelling tends to be gradual and worse with aggravating positions or activities. 

Learn More About Arthritis in the Knee


Infections in the knee can occur after surgery or from a wound, and in less-common cases, an infection elsewhere in the body can spread to the knees. It can be difficult for the body to fight an infection in a joint, thus surgery or fluid removal might be required for full recovery.


Gout refers to the presence of crystals that can form in the joints as the result of a buildup of uric acid. This is most often caused by dysfunction with the digestive process and poor diet. Although more common in the feet and hands, when these types of crystals build up in the knees, they can cause swelling and pain.


To reduce friction, there are small sacs that are filled with fluid, called bursa, that sit between bones and soft tissue. When there is excessive friction on the bursa, they tend to become inflamed. This condition is known as bursitis, and it can lead to swelling in the kneecap at four different primary locations or in the back of the knee as well.

About Knee Bursitis

Swollen Knee Symptoms

Feeling your joint(s) start to swell up, but not sure what to expect from a swollen knee? Here are a few common symptoms that you are likely to experience.


Because swollen knees are caused by an excess buildup of fluid, it is primarily characterized by the knee becoming visibly larger and puffy. Knee swelling can make the skin appear red, tight, or even shiny.


Your knee might also be swollen and stiff, which means that the extra fluid is keeping it from bending or straightening through full range of motion. Most often, you will notice more stiffness after spending a significant amount of time in one particular position. This is because the knee fluid shifts and adjusts to this position and then needs to readjust when you start to move again.


Depending on the cause, you might also experience swollen knee pain, which can affect your ability to bear weight on the leg. The added pressure on your local nerve endings can certainly make your knee more sensitive to touch and movement. However, other causes might result in a swollen knee without pain.

Recovering from Swollen Knees

Depending on the severity of your swollen knee pain and the underlying causes, you should see recovery changes and pain relief in your swelling in about one to three days. However, this can vary greatly with different types of injuries and can take several weeks to months with more serious issues.

For swollen knees, recovery options include injections, prescribed or over the counter medication (NSAIDS such as ibuprofen), braces, physical therapy, massage therapy and home remedies like rest, ice packs, compression and elevation.

How to Reduce Swelling in Knees

If the swelling doesn’t go down within a few days or if it begins to get worse, you should seek advice from an orthopaedic doctor or medical professional. 

Dealing with Swollen Knee Pain

Whether they are caused by a knee injury, overuse, or by a chronic condition, swollen knees are very common. Fortunately, with the right treatment, they won’t keep you off your feet or limping forever. If you find yourself suffering from the pain, stiffness, and other symptoms associated with swollen knees, utilize the home remedies in this Injury Guide and you should be walking again pain-free in no time.


Swollen Knees Products


Jaydee Vykoukal, PT, DPT
Jaydee Vykoukal, PT, DPT

JayDee Vykoukal is a Doctor of Physical Therapy, owner of the healthy habit platform Health Means Wealth, and freelance medical writer. She loves traveling and spending time with her family in nature. Her passion is helping others continue to participate in the activities they love through education and proper exercise.

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