Common accumulation of synovial fluid that is usually the result of a knee joint abnormality, such as arthritis or a cartilage tear.
May present with swelling or pain behind the knee, but most cases are asymptomatic.
May rupture, leading to severe pain and calf swelling.
Usually only conservative treatment is required.
Large symptomatic cysts that do not resolve may require drainage.
Popliteal cyst, also known as Baker cyst, is the result of an accumulation of joint synovial fluid outside the knee joint that forms behind the knee. This occurs via increased intrasynovial pressure and causes the synovial capsule to bulge at an area where there is a lack of external anatomic support.  The most common underlying conditions that lead to overproduction of synovial fluid include arthritis and meniscal tears.
Associate Professor of Clinical Orthopaedic Surgery
Director of Sports Shoulder Service
University of Pennsylvania
JK declares that he has no competing interests.
Dr John Kelly IV would like to gratefully acknowledge Dr Antonios P. Gasparis and Dr Nicos Labropoulos, previous contributors to this topic. APG declares that he has no competing interests. NL is the author of multiple references cited in this topic.
Clinical Lecturer II
Department of Radiology
University of Michigan Medical Center
BS declares that he has no competing interests.
Professor of Rheumatology
University of Cambridge
West Anglia CLRN
HG declares that he has no competing interests.
Senior Lecturer in Rheumatology
Academic Section of Musculoskeletal Disease
Leeds Institute of Molecular Medicine
Chapel Allerton Hospital
RW declares that he has no competing interests.
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