Popliteal cyst; Bulge-knee
Definition of Baker’s cyst
Baker’s cyst is a buildup of joint fluid (synovial fluid) that forms behind the knee.
Causes, incidence, and risk factors
A Baker’s cyst is caused by swelling in the knee. The swelling is due to an increase in synovial fluid – the fluid that lubricates the knee joint. When pressure builds up, fluid bulges into the back of the knee.
A large cyst may cause some discomfort or stiffness, but there are often no symptoms. There may be a painless or painful swelling behind the knee.
Signs and tests
During a physical exam, the doctor will look for a soft mass in the back of the knee. If the cyst is small, comparing the affected knee to the normal knee can be helpful. There may be limitation in range of motion caused by pain or by the size of the cyst. In some cases there will be signs and symptoms of a meniscal tear.
Often no treatment is needed. The health care provider can watch the cyst over time.
A Baker’s cyst will not cause any long-term harm, but it can be annoying and painful. The symptoms of Baker’s cysts usually come and go.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; and C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. – 6/13/2010