A Baker's cyst is a tense fluid-filled swelling at the back of the knee.

Baker's cyst forming a painful lump at the back of the knee baker's cyst or popliteal cyst

Bakerzyste2 MRT sag

The lump that the patient can feel is usually on the inner aspect at the back of the knee where the knee bands. The cyst may become tense and rupture, with the fluid tracking into the back of the calf, mimicking a deep vein thrombosis. Fluid in the Baker's cyst shows up in white in this MRI scan towards the right of the image. You can see its relationship to the gastrocnemius muscle which is just below it.


What causes a Baker's cyst?

A Baker's cyst can appear suddenly and be experienced as a painful lump on the inner aspect of the crease at the back of the knee. A weak area in the bursa (pocket) between the gastrocnemius and semimembranosus tendons of the muscles at the back of the knee can break down, allowing a valve-like flap that allows joint fluid to enter but not escape. It is often associated with damage inside the knee, such as a torn meniscus or osteoarthritis, where there is increased fluid pressure in the joint.

popliteal cyst
baker cyst

Short article about the anatomical factors that allow a Baker's cyst to develop.

An explanation by Dr Lars Blond as to why he uses keyhole surgery to remove a Baker's cyst.

Enclosing the articulating part of the knee joint is a water-tight capsule made of a strong fibrous material lined on the inside with a thin layer of secretory cells.

Pain in the back of the knee

A short eBook discussing those conditions that may cause pain at the back of the knee.

A short explanation of the very common problem of a painful lump at the back of the knee due to a Baker's cyst.

Pain in the back of the knee

An overview with illustrations.



Baker's Cyst. Demange MK., Rev Bras Ortop. 2011 Nov-Dec; 46(6): 630–633.

Popliteal cysts: a current review. Herman AM, Marzo JM. Orthopedics. 2014 Aug;37(8):e678-84

Baker's cyst simulating deep vein thrombosis. Chaudhuri R, Salari R. Clin Radiol. 1990 Jun;41(6):400-4.

Baker's Cyst Filled with Hematoma at the Lower Calf Yoo M-J, Yoo J-S, Jang H-S, Hwang C-H. Knee Surg Relat Res. 2014 Dec; 26(4): 253–256.

See also -

eBook - Pain in the back of the knee