Popliteal cyst, an accumulation of synovial fluid, is common. It 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 or sometimes surgical excision.
Popliteal cyst (also known as Baker's cyst) is the result of an accumulation of joint synovial fluid outside the knee joint; it forms behind the knee in the interval between the semimembranosus and the medial gastrocnemius. This occurs via increased intrasynovial pressure, and causes the synovial capsule to bulge at an area where there is a lack of external anatomical support. The most common underlying conditions that lead to overproduction of synovial fluid include arthritis and meniscal tears.
History and exam
Key diagnostic factors
- presence of risk factors
- popliteal bulge
- knee pain
- leg swelling
- calf tenderness
Other diagnostic factors
- calf ecchymosis
- lyme disease
- knee joint trauma
- underlying knee joint arthritis or synovitis
- underlying knee joint infection
- increasing age
1st investigations to order
- duplex ultrasound of the leg
Investigations to consider
- MRI of the leg
- CT scan of the leg
symptomatic: initial treatment
symptomatic: refractory to initial conservative treatment
John D. Kelly IV, MD
Professor of Clinical Orthopaedic Surgery
Director of Sports Shoulder Service
University of Pennsylvania
JK declares that he has no competing interests.
Dr John D. 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.
Brian Sabb, DO
Clinical Lecturer II
Department of Radiology
University of Michigan Medical Center
BS declares that he has no competing interests.
Hill Gaston, MA, PhD, BM BCh, FRCP, FMedSci
Professor of Rheumatology
University of Cambridge
West Anglia CLRN
HG declares that he has no competing interests.
Richard Wakefield, BM, MRCP, MD
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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