Knee Synovitis: Symptoms, Causes & Treatment

Knee synovitis is an inflammation of the synovial membrane, the tissue that lines the inside of the knee joint. It causes an increase in synovial fluid and can lead to symptoms such as pain, swelling, and difficulty walking or fully straightening the leg.

Knee synovitis can happen after direct trauma to the knee, such as a blow, fracture, or fall. It can also develop as a result of chronic health conditions such as rheumatoid arthritis, osteoarthritis, or gout.

Treatment for knee synovitis should be guided by an orthopedist. Depending on the cause and severity, treatment may include joint rest, physical therapy, medication, and in some cases exploratory surgery or arthroscopy.

Main symptoms

The main symptoms of knee synovitis are:

• Knee pain;

• Knee stiffness, especially in the morning;

• Difficulty walking or fully straightening the leg;

• Knee swelling;

• Redness of the knee;

• A feeling of warmth or increased temperature in the knee;

• Weakness in the thigh and leg muscles.

Symptoms of knee synovitis develop when too much synovial fluid builds up in the joint. Synovial fluid is a lubricating fluid that is normally present in the knee in small amounts, usually between 2 and 3.5 mL, but in cases of knee synovitis it may increase to about 20 to 100 mL.

If symptoms of knee synovitis appear, it is important to see an orthopedic surgeon so the condition can be diagnosed and the most appropriate treatment can be started.

Confirming a diagnosis

The diagnosis of knee synovitis is made by an orthopedic surgeon based on symptoms, medical history, and any recent trauma to the knee or leg, along with a physical exam of the knee.

The doctor may also perform a synovial fluid aspiration, removing part of the excess fluid from the knee and sending it for lab analysis to check for glucose or increased levels of proteins or antibodies in the fluid.

Other tests that may be ordered to diagnose knee synovitis include a knee MRI or ultrasound. These tests help show whether there is any injury to the bones, muscles, or ligaments that may be causing the fluid buildup.

Possible causes

The main causes of knee synovitis are:

• Direct trauma to the knee, such as blows, accidents, or falls;

• Injury to the knee ligaments or meniscus;

• Fractures or infections in the knee;

• Osteoarthritis, gout, or rheumatoid arthritis;

• Lupus or psoriasis;

• Synovial chondromatosis;

• Hemophilia;

• Cancer in the knee.

Knee synovitis can also develop because of overuse or repeated strain on the knee, such as in athletes or people who work in construction, auto repair, or nursing.

These conditions can cause inflammation of the synovial membrane, which is the tissue lining the inside of the knee joint capsule, leading to the symptoms described above.

Treatment options

Treatment for knee synovitis is managed by an orthopedic surgeon based on the person’s symptoms and the amount of fluid that has built up in the knee due to inflammation.

Some treatment options include:

1. Cold compresses

Applying a cold compress or ice to the knee is one of the most effective home treatments for knee synovitis.

It causes the blood vessels to constrict, which reduces blood flow and limits the arrival of inflammatory cells that contribute to fluid buildup. Cold also helps numb the superficial nerve endings, which can help relieve pain.

According to the American Academy of Orthopaedic Surgeons, cold therapy and elevation are commonly recommended to help reduce inflammation and swelling after soft-tissue injury.

2. Leg elevation

Keeping the leg elevated above heart level improves lymphatic circulation, which helps remove excess fluid and waste from the tissues.

This can help reduce swelling around the knee and relieve the pressure caused by joint effusion, although it does not replace the treatments recommended by a healthcare professional.

3. Medications

Treatment for knee synovitis usually starts with anti-inflammatory medications and corticosteroids, taken by mouth or given by injection, followed by physical therapy to help relieve knee pain and inflammation.

In some cases, the doctor may also remove excess fluid from the joint through aspiration.

4. Physical therapy

Physical therapy can help reduce knee swelling through exercises such as isometric activation. For this exercise, a towel or cushion should be placed under the knee with the leg extended, and the knee should be pressed gently against the surface for a few seconds.

The physical therapist may also use techniques such as pneumatic compression therapy, which helps promote fluid drainage.

5. Surgery

Surgery is recommended in cases of chronic synovitis, when knee pain lasts for more than 6 months due to rheumatoid arthritis or arthritis and does not improve with medication, physical therapy, or aspiration.

The surgery may be done as an open procedure or by arthroscopy and involves removing a large part of the synovial tissue. If the menisci are also affected, part of them may also be removed.

After surgery, the leg is typically wrapped and kept elevated for 48 hours to reduce swelling, and gentle foot movements are recommended to help prevent deep vein thrombosis, according to the American Academy of Orthopaedic Surgeons’ guidance on circulation exercises and blood clot prevention after orthopedic procedures.

About 72 hours after surgery, walking with crutches may begin, and isometric exercises can usually be started without moving the knee. As recovery improves, exercises that involve bending the knee and using light weights may be introduced, always under the guidance of a physical therapist.

Recovery time is about 6 to 8 weeks after open surgery and about 7 to 10 days after knee arthroscopy.