Baker's cyst pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Pathophysiology
In adults, Baker's cysts usually arise from almost any form of knee arthritis and cartilage (particularly the meniscus) tear. Baker's cysts in children do not point to underlying joint disease. Baker's cysts arise between the tendons of the medial head of the gastrocnemius and the semimembranosus muscles. They are posterior to the medial femoral condyle.
The synovial sack of the knee joint can, under certain circumstances, produce a posterior bulge, into the popliteal space, the space behind the knee. When this bulge becomes large enough, it becomes palpable and cystic. Most Baker's cysts maintain this direct communication with the synovial cavity of the knee, but sometimes, the new cyst pinches off. A Baker's cyst can rupture and produce acute pain behind the knee and in the calf and swelling of the calf muscles.
As a summary:
- A popliteal cyst is fluid distention of a bursa between the gastrocnemius and semimembranosus tendons via a communication with the knee joint.
- Fluid within a Baker's cyst may communicate freely with the knee joint. However, the presence of a valvelike mechanism may allow joint fluid to communicate in only one direction.
- Popliteal cysts may be seen with many joint abnormalities, such as internal derangement, osteoarthrosis, or inflammatory arthritis; the most common associations include joint effusion, meniscal tear, and degenerative joint disease.