The word 'syndrome' means a group of clinical findings that tend to be associated with one another, and likely to have a common cause.

The plica syndrome is a group of clinical findings in the knee which appear to be related to damage to a rather enigmatic structure called the synovial plica.

The inner walls of the knee joint are lined with a special tissue called the synovium, the cells of which secrete the fluid that lubricates the joint. In many people, but not all, a thin sheet of synovium may stretch from the wall across to the more central structures and this would be called a synovial plica.

Although there are differences in the extent of these plicae (the plural of plica), they might be found in one of more of four anatomical areas -

Some people will not have a plica at all, some will have just a tiny one in one place, and other people may have more than one. Theories differ about what they are or do, and the most common is that they are 'left-overs' of the walls of the various compartments that made up the knee in the very early foetus before the compartments combined to form the definitive structure.

Mostly the plicae are thin and stretchy, and just move with the other tissues of the knee when the knee bends and straightens. Sometimes, however, they get traumatised and swell, and catch on the knee structures, or between structures and then then can be the cause of a lot of misery, such as local tenderness, snapping, clicking and the knee may catch or give way.

Here are several sites that go into more explanation -

  1. Plica Syndrome Of The Knee: Causes, Symptoms, Diagnosis, and Treatment

    In this paper the author points out that in a symptomatic patient the presence of a plica does not mean that it is the cause of the symptoms, as these structures are common and generally do not cause problems. Although the plica may be damaged and giving rise to the patient's symptoms, the doctor needs to investigate all the structures of the knee that might be contributing to the picture.

  2. Plica of the knee - the great mimic

    Article by Angus Strover

    Looking at thing from a different viewpoint, it is also important that the doctor understands that a damaged plica may mimic other common conditions, and so unless it is taken into consideration the patient may be given a different diagnosis and managed inappropriately. Probably the most important of the conditions it can mimic is a medial meniscal tear, and there have been many a surgeon who has gone into the knee to deal with a torn meniscus, only to be surprised to find that the meniscus is completely normal!

  3. Plica

    This is a video that explains how a medial plica may become problematic.

  4. Tests for plica syndrome -

    Watch the videos -

    (a) Stutter test -

    The stutter test is a test to confirm the presence of an impinging medial plica of the knee. The patient sits on the edge of the examination table with the legs dangling freely over the side. The examiner puts one finger on the patella. The patient is instructed to slowly straighten the knee and the let it return to the resting position. Between the angles of 60 and 45 degrees of flexion, the examiner with experience a 'stutter' of the patella, and it may be sufficient to throw his finger off the patella.

    (b) Hughston plica test -

  5. Medial Synovial Plica Irritation

    This paper discusses, in several pages, the concepts of management of an irritated medial plica. Because so many problems around the kneecap result from alignment problems and an imbalance of the musculature of the lower limb and hip, you will note that there is strong emphasis on trying a non-surgical rehabilitation program before resorting to surgery.

  6. Knee Arthroscopy Plica Excision - recovery 7days later

    A patient's perspective after surgical removal.