Baker's Cyst (Popliteal Cyst)
Lump Behind the Knee
Fluid-filled cyst in the popliteal fossa arising from the gastrocnemius-semimembranosus bursa. Communicates with the knee joint via a one-way valve mechanism. Almost always SECONDARY to intra-articular pathology (meniscal tear, OA, RA, chondral injury) in adults. Primary (non-communicating) cysts occur in children and are self-limiting.
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