Why Is My Knee Swollen?

swollen knee

Swelling in the joints can be traced to a number of injuries or chronic conditions. Here are some of the most common.

A swollen knee can be uncomfortable and debilitating. But what causes the joint to become stiff and painful?

When your knee suffers a sudden trauma or gradual deterioration due to a chronic condition, the joint may become inflamed. This swelling is caused by a build-up of synovial fluid, which normally serves to reduce friction and lubricate the joint. In the case of an injury or underlying disorder, the fluid can accumulate within the joint or in the surrounding soft tissue.

To ease the swelling and stiffness, your doctor will likely recommend rest and icing. In more severe cases, an orthopedic specialist may remove some of the built-up fluid. But in order to accurately treat a swollen knee, it’s important to identify its underlying cause.  


If your knee is swollen, your doctor may perform imaging scans ranging from an X-ray to an ultrasound and MRI. These exams can identify any ligament injuries, broken bones, or degenerative disorders like arthritis.

The presence of blood in the fluid provides further clues as to the root of the swelling. If blood is detected, it usually points toward a serious injury like a fracture or an ACL tear.

A sudden fall or accident can fracture the kneecap, or patella. A stable fracture will heal with a cast or splint placed around the knee. If the trauma shatters bits of the patella, a surgeon can stitch the pieces together and bind them with screws and pins. Whether surgical or non-surgical therapy is used to heal the bone, patients will undergo a rehabilitation program to strengthen the muscles and steadily increase the joint’s capacity to carry the body’s weight.

In the case of an ACL tear, the joint’s stabilizing anterior cruciate ligament ruptures, and the knee swells immediately. Depending upon the severity of the tear, some ACL injuries can heal without surgery, but most require arthroscopic surgery to repair.

Clear fluid with no blood likely means the knee has a sprain or a meniscus tear. Made of cartilage, the meniscus cushions the knee joint. Unlike an ACL tear, a meniscus tear may not cause swelling until hours or days after the initial injury. Treatment for a traumatic meniscus tear usually involves surgery.

The meniscus can progressively wear down and tear due to arthritis, as well. As we age, the cartilage in the knee frays under the pressure we put on the joint. Eventually, osteoarthritis may inflame the knee, forcing excess fluid into the joint.

Non-surgical options for treating knee arthritis include physical therapy to strengthen the muscles and ligaments around the knee, lubricating gel injections, or a knee brace to stabilize the joint. If the condition worsens, surgical intervention to remove damaged cartilage or replace the knee partially or entirely may be recommended.


If you’ve tried at-home remedies like icing and rest to bring down the swelling in your knee and found only temporary relief, you should see an orthopedic doctor specializing in knee disorders. The physicians at New York Bone & Joint Specialists are experts in a wide variety of knee and other joint injuries. They can accurately diagnose your condition, and create a recovery plan to get you back to your active lifestyle. Contact the office today to set up an appointment.

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