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Plica syndrome

As with all joints, the knee joint is covered by a thin, smooth layer of skin. This so-called synovial membrane produces articular fluid, which prevents friction in the joint and supplies the joint cartilage with nutrients.

In embryonic development, this synovial membrane creates a membrane that divides the knee joint into two separate areas (this comes from the time we evolved from sea creatures and began to move on all fours. Horses, for example, still have a knee joint divided into two). Normally this membrane regresses completely at the end of childhood development to favour a greater freedom of movement in the knee joint. In around 50-70% of adults, however, small folds remain, called plica. These are usually found behind, above or on the medial side of the patella.

Many people who have a plica have no problems at all, however, if the plica is more prominent, this can lead to irritations. Above all, overstraining of the knee joint leads to irritation of the plica and therefore to so-called plica syndrome. Demanding activities in which the knee is repeatedly flexed and then extended again (such as running, cycling, or exercises on "steppers") are the most frequent causes.

The plica itself, as well as the tissue around it, swells as a result and becomes painful. This thickening then rubs on the cartilage inside the knee joint and can lead to damage to the joint cartilage or joint inflammation (= arthritis) if exertion is continued.

The most common symptoms of plica syndrome are

  • Pain on exertion, mostly on the medial or posterior side of the patella
  • "Crepitations" or "clicking" of the joint in a specific position whilst flexing it
  • A feeling of "blocking" during the extending movement
  • Stiffness in the joint after sitting for long periods
  • In some cases, the thickened plica is also palpable under the skin or there is swelling over the whole knee joint.




To diagnose plica syndrome, you first need to try to locate the pain exactly or determine whether thickening has occurred in the patellar region. You can often also feel the rubbing of the plica in the knee joint on movement. Pain when tensing the thigh musculature is typical, if the examiner presses the patella against the articular surface at the same time (= positive Zohlen test. This test, however, can also be positive in the case of retropatellar cartilage damage - and 50% of all patients generally find it very uncomfortable to be subjected to this test).

Image: The MRI examination shows a significantly pronounced plica (as a secondary finding in a patient with an unstable patella)

An MRI examination can also be helpful for diagnosis, however it does not always yield clear findings. In some patients, definite proof of plica syndrome is only found during arthroscopy.



Non-surgical treatment and treatment of the inflammatory plica irritation can be carried out as an initial attempt. Rest must be prescribed here, in combination with treatment with anti-inflammatory medication. Cooling with ice is also helpful and alleviates pain and swelling.

Image: The arthroscopy in this young athlete with constant pain behind the patella showed this pronounced plica. Following removal, the patient was completely free of symptoms and was able to start in an international Iron Man tournament six months later.

The problem with plica syndrome in athletic patients, however, is that the symptoms often do not improve because the inflammatory changed and hardened edge of the plica continues to rub on the cartilage, and destroys it. An operation (arthroscopy) should therefore be considered early on for athletic patients. The plica is removed and the symptoms usually improve after a very short time - unless significant cartilage damage has already occurred.

It should therefore be explained to the patient before the operation that they may still have pain after the operation (due to cartilage damage). The majority of patients, however, are really fortunate following the minor arthroscopic operation because the pain, which has often accompanied the problem for years, has suddenly completely disappeared.


Please note that medical indications and treatments change constantly. Sometimes these changes occur more rapidly than I am able to update on my homepage. Some information regarding dosage, prescription and compositions of medications may have changed in the meantime. Reading an internet page cannot replace visiting a doctor - it may be that during an examination and subsequent discussion with your doctor, other information is also communicated as a result of new scientific knowledge.