A painful swelling below the back of the knee can be an indication of a Baker's cyst. This cystic sac, which can usually be felt as a sensitive, often spherical and elastic bulge in the hollow of the knee, should be examined and treated by a doctor so that the cause of the Baker's cyst can be determined and secondary diseases avoided.
The cyst was named after the English surgeon William Morrant Baker, who was the first to describe it in the 19th century, after whom he discovered this sagging in the back of the knee in some patients. Other terms for the Baker's cyst are known in medicine, for example, it is also referred to as a popliteal cyst, an internal knee disease, or a sagging of the knee joint capsule.
Unlike a normal cyst, which is a build-up of fluid within a cyst wall, a Baker's cyst collects fluid in the knee joint. Since the connective tissue in the hollow of the knee is weak, the Baker's cyst occurs in this area. People in middle and old age are particularly affected because, on the one hand, previous illnesses that cause a Baker's cyst occur more frequently, but also the connective tissue weakens in old age.
The Baker cyst can be felt as a bulge on the back of the knee joint. Little painful at first and hardly palpable, it develops into a plump and elastic ball that is not only felt in the hollow of the knee, but also visible. A clear movement of liquid can also be felt when scanning.
If the cyst becomes too large, the following symptoms may appear, such as:
- Numbness to paralysis in the underlying parts of the body,
- Water retention (edema) on the lower leg or
- Sudden pain if the Baker's cyst bursts, causing a rupture of the cyst wall.
Various pre-existing conditions can lead to a Baker's cyst, including:
- Arthrosis and rheumatic diseases,
- chronic damage to the meniscus,
- Injury to the cruciate ligaments or
- Cartilage damage in the knee.
The previous disease creates increased friction within the knee joint. The body responds to this with excessive synovial formation within the knee joint. Synovia is the synovial fluid that ensures that the joint is adequately lubricated. The body tries to protect the knee joint from friction by increasing the formation of this synovial fluid. If there is too much fluid in the knee joint, it will move back into the connective tissue of the hollow of the knee. This then leads to the joint effusion known as the Baker cyst.
Consequential damage to a Baker's cyst
With a longer-lasting and rapidly enlarging Baker's cyst, the cyst wall may crack (rupture), i.e. it bursts. There are many vessels between the fascia in the calf and therefore there is not much space there. A compartment syndrome can be triggered by the leaked synovial fluid, which means that vessels are pulled off and structures die off due to insufficient supply.
When treating a Baker's cyst, it is important that the underlying medical condition must be treated. At the same time, the Baker cyst has to be treated itself. It is often sufficient to protect the knee so that the swelling disappears. At the same time, taking anti-inflammatory drugs is helpful. If the Baker's cyst has grown too large, it must be removed surgically.
Healing through protection and correct movement
Protecting the affected knee in the early stages of a Baker's cyst may be sufficient for it to regress. Swimming, as a sport that is easy on the joints, also helps to break down the excess tissue fluid.
Nevertheless, a doctor should be consulted so that the cause that led to the formation of a Baker's cyst can be clarified and treated. (fp, ok)
Author and source information
This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.
Dipl. Geogr. Fabian Peters, Barbara Schindewolf-Lensch
- Ruchholtz, Steffen / Wirtz, Dieter Christian: Orthopedics and trauma surgery essentials: Intensive course for further training, Thieme, 3rd edition, 2019
- Walter de Gruyter GmbH: Baker's cyst (accessed: July 24, 2019), pschyrembel.de
- Mayo CLinic: Baker's cyst (accessed: 07/24/2019), mayoclinic.org
- UpToDate, Inc .: Popliteal (Baker's) cyst (accessed: July 24, 2019), uptodate.com
- National Health Service UK: Overview - Baker's cyst (accessed: 07/24/2019), nhs.uk
ICD codes for this disease: M71ICD codes are internationally valid encodings for medical diagnoses. You can find e.g. in doctor's letters or on disability certificates.