Synovitis is an inflammation of the joint lining (called the synovium).
In an active, healthy person, the most common cause is overuse of the joint.
However, synovitis is also a common symptom of some forms of inflammatory arthritis. In these patients, excessive growth of the synovium is part of an abnormal immune response, in which the body misidentifies cartilage as a foreign substance that must be attacked. Loss of cartilage eventually damages the joint surface and leads to the stiffness and pain characteristic of all types of arthritis. (Osteoarthritis, the more common form of the arthritis, does not involve this type of inflammatory response.)
Arthroscopic camera view of the inside of a knee joint, showing synovitis next to the femoral condyle (upper portion of the femur or thighbone). Image courtesy of Understand.com, LLC.
The chief symptom is arthralgia, which is Greek for “joint pain.” The pain of synovitis is usually more severe than expected based on the appearance of the joint. In other words, there may be no visible evidence of injury or swelling that is causing pain.
The symptoms are often short-lived and may be felt in different parts of the body at different times. However, when synovitis is caused by overuse of a joint, the pain usually remains in one spot.
A rheumatologist will aim to diagnose the cause of the patient’s pain by first determining whether it is inside the joint itself, meaning true synovitis, or if it is actually caused by an inflammation of the tendons, referred to as tendonitis. Imaging, such as an MRI or musculoskeletal ultrasound is often required to make a firm diagnosis.
Treatment for synovitis usually consists of rest and anti-inflammatory medications. Medications may include oral drugs known as DMARDs (disease-modifying anti-rheumatic drugs) and, in some cases, steroid injections. Patients who don’t respond to these treatments may be referred to an orthopedic surgeon to discuss a synovectomy, a procedure in which much of the synovium is removed. Learn more about synovitis treatments in the articles listed below.
Click on the image below to explore illustrated views of synovitis of the knee.