The Baker's cyst
Often a swelling in the area of the hollow of the knee is a symptom for the Baker's cyst. It is a cystic (=vesicular) sagging of the joint capsule of the knee joint in the hollow of the knee filled with joint fluid.
The name of the Baker's cyst derives from the London surgeon M.W. Baker, who described it for the first time.
Baker's cysts mostly develop as a consequence of chronic damages of the meniscus or cartilage, but they can also appear within the scope of chronic-rheumatic knee diseases (chronic polyarthritis). Normally a weakening of the joint capsule exists (mostly in combination with a meniscus damage). At this place the joint capsule can position itself outwardly. If the body now reacts to the constant friction (due to the meniscus- or cartilage damage) in the knee joint with an increased production of joint fluid in order to decrease exactly this rubbing, this leads to an articular effusion and an increase of the pressure in the knee joint. Sometime the joint capsule cannot withstand the increased internal pressure and a cystic sagging of the joint capsule – the so-called Baker's cyst – develops.
The Baker's cyst occurs in the hollow of the knee as the tissue-related structures are developed most weakly there.