Location of Baker Cyst
A Baker cyst is located in the popliteal fossa (the back of the knee), specifically as a fluid accumulation in the bursa between the medial head of the gastrocnemius muscle and the semimembranosus tendon. 1
Anatomical Details
The cyst represents a distention of the gastrocnemio-semimembranosus bursa, which is unique among periarticular bursae because it communicates with the knee joint space through an opening in the joint capsule posterior to the medial femoral condyle. 2
Specific Anatomical Landmarks
The cyst appears as a comma-shaped extension when visualized on ultrasound in the posterior transverse scan between the medial head of gastrocnemius and semimembranosus tendon. 1, 3
This bursa is located in the popliteal fossa at the back of the knee, making it palpable as a fluctuant swelling in this region. 2, 4
The communication with the knee joint occurs via an opening in the posterior joint capsule near the medial femoral condyle. 2
Extension Patterns
Baker cysts are not confined to a single location and can extend significantly:
Cysts can extend far into thigh and calf muscles, which ultrasound allows precise definition of their shape and size. 1, 5
The fluid accumulation frequently communicates with the joint space, creating a valve-like mechanism that contributes to cyst formation. 1, 2
Clinical Examination Findings
The cyst presents as visible and palpable swelling in the popliteal fossa, especially with the knee extended. 5
Tenderness in the popliteal fossa is a common symptom on physical examination. 5
Important Clinical Pitfall
Not all popliteal masses are benign Baker cysts - clinicians must obtain imaging to exclude popliteal artery aneurysm, especially in patients with a history of other arterial aneurysms. 5, 6 A popliteal artery aneurysm can simulate a Baker cyst and has been reported in patients with rheumatoid arthritis. 6