When is a cyst not a cyst? When it’s a Baker’s cyst.
First described by, and named after Dr. William Baker in the 1800’s, a Baker’s cyst is not a true cyst, because it is not within a fully enclosed fluid sac. A Baker’s Cyst isn’t fully enclosed because it usually forms due to an excess of synovial fluid that ideally maintains a healthy environment within a joint cavity.
A Baker’s cyst is a bulging pocket, usually soft, that appears at the back of the knee. It is also known as a popliteal cyst because it tends to bulge out in the popliteal space at the back of the knee capsule.
In the case of a Baker’s cyst, something inside the knee joint gets irritated, increasing the production of synovial fluid as a protective measure. When enough fluid develops the cyst is formed pushing out from the back of the knee.
A Baker’s cyst doesn’t necessarily hurt, though depending on the size it can reduce range of motion and get irritated and unhappy depending on the position of the leg, with a bent leg often being the most painful environment.
Injury to the cartilage of the knee (meniscus) or other issues around swelling such as arthritis can lead to the formation of Baker’s cysts. These types of cysts aren’t usually treated in and of themselves. The underlying cause of inflammation needs to be addressed for the swelling that led to the formation of the Baker’s cyst to reduce.
If Baker’s cysts aren’t painful they are often left untreated and will usually go away when the main knee issue resolves. They can be drained of fluid but there is little reason to imagine that the fluid won’t return depending upon the situation with the knee in question.
In truth there isn’t much to be done with Baker’s cysts by themselves. In some cases steroidal injections are used to reduce the swelling, though this option isn’t always effective. If the fundamental cause of the Baker’s cyst cannot be remedied (such as in an arthritis that will be maintained rather than eliminated) surgery is an option if the cyst is painful, or if the size interferes with the basic functioning of the joint.