Summary
The Baker’s cyst (popliteal cyst) in the hollow of the knee is a fluid-filled sac in the hollow of the knee. It is an indirect sign of damage to the knee joint. The damage in the knee joint (the causes of this can be wear and tear, i.e. arthrosis, meniscus damage or an underlying inflammatory disease, such as rheumatism or rheumatoid arthritis) leads to increased water formation in the knee.
The knee joint tries to “lubricate” the knee better, but produces too much “joint lubricant” overall. Due to a permanently increased intra-articular pressure caused by increased synovial fluid, the surrounding connective tissue slackens and a fluid-filled cyst forms. The weakest point of the joint capsule, typically the inner hollow of the knee, gives way and forms an “overflow sack” between two muscles.
A Baker’s cyst is a disease of middle to old age (due to increasing wear and tear), although children can also be affected in isolated cases. Pain and a movement-dependent, frequently recurring swelling in the hollow of the knee and the upper calf muscles are the main features. If the cyst tears (rupture) occur, patients report severe sudden pain in the popliteal fossa.
If the cyst has a large volume, swelling in the area of the ankle joint can occur for a short time. In most cases, a new formation of the cyst can be detected after a rupture of the Baker cyst.
