Synonyms
- Popular cyst
- Synovial cyst
- Sacculation of the joint capsule
- Popliteal cyst
Definition Baker cyst
A Baker’s cyst is caused by a knee joint disease with chronic knee joint effusion. This results in a bulging (bulge) of the posterior joint capsule, comparable to an overflow valve. Alternatively, mechanical irritation of the muscles that are located in the hollow of the knee can also cause ganglia (cavities filled with jelly) to form, which are deposited in the hollow of the knee. A Baker’s cyst occurs particularly frequently in older people due to wear and tear of the knee joint and in children (usually without a clear cause).
General information
The so-called Baker cyst is a bag-shaped fluid-filled sac in the central (medial) popliteal fossa. Its name comes from its first descriptor W. M. Baker an English surgeon of the 19th century from London. The Baker cyst always starts from the knee joint capsule.
From the joint capsule, it is connected to the main chamber by a narrow bridge or passage (stem-like connection). In a Baker’s cyst, which is typically located at a typical position, the connecting duct is pushed through the muscular structures of the gastrocnemius muscle (caput mediale) and the semimembranosus muscle (flexor muscles of the thigh). If a Baker’s cyst persists for a longer period of time, several cyst chambers can form, making puncture of the cyst particularly difficult.
Development of a Baker cyst
A Baker cyst is often the result of an internal knee disease. In the context of rheumatoid arthritis (rheumatism) or chronic meniscus damage, a permanent joint effusion (water in the knee joint) occurs. The associated chro- nical increase of the internal joint pressure causes an increasing fatigue and slackening of the joint capsule of the knee joint and can lead to a permanent bulging of the capsule and thus to the formation of a popliteal cyst = Baker cyst.
Due to its swelling nature, a Baker’s cyst can resemble a tumor of the back of the knee, so that a malignant disease must always be ruled out. However, this can easily be done with a sonographic examination of the popliteal fossa. If an increase in chamber pressure causes a rupture/tear of the cyst, i.e. a tear with leakage of fluid into the tissue, swelling in the affected area and pain that increases with pressure can be found.
This condition can easily be confused with deep vein thrombosis of the leg. If the cause is not eliminated, however, the Baker cyst reappears, with uterine chamber formation. (left patella, right popliteal fossa)
- Thigh (femur)
- Shin bone (tibia)
- Baker’s cyst (politeal cyst)
- Meniscus
Cause
The cause for the formation of a Baker’s cyst in the hollow of the knee is the increased production of synovial fluid in the knee joint. The cause of this in turn is usually damage to the knee joint, such as osteoarthritis, prolonged meniscus damage or an underlying inflammatory disease such as rheumatoid arthritis. In the majority of cases, however, the formation of a Baker cyst is caused by wear and tear, i.e. arthrosis or a torn meniscus.
The knee joint tries to improve the function of the knee joint again by increasing the production of “synovial fluid“. This leads to a permanent increase in the pressure inside the joint. The weakest point of the knee joint capsule gives and gives way and forms the Baker’s cyst.
This forms an “overflow sack”, which is connected to the knee joint via a stem-shaped connection. This stem almost always runs between the central (medial) head of the gastrocnemius muscle (calf muscle) and the insertion tendon plate of the flexor muscle luteus (semimembranosus muscle = thigh muscle). On palpation, a fluid-filled, sealed connective tissue capsule can be palpated in the posterior area of the popliteal fossa, which is particularly difficult in the case of small cysts. In such cases, ultrasound examination (sonography) is a pioneering method.
