Plica syndrome is a condition caused by inflammation in the lining of the knee joint.
It results in achy knee pain which gets worse with activity, particularly up and down stairs, a feeling of instability in the knee and sometimes a catching or locking sensation.
Plicae are small folds in the synovial membrane, the thin structure that surrounds and lines the knee joint. Plica syndrome, aka plica synovialis, can develop in any of the four knee plica, the most common being in the medial plica.
Knee plica irritation occurs when the plica gets caught or pinched between the knee bones, usually due to a knee injury or from overuse.
Here we look at how plica synovialis develops, the causes and symptoms, and finally look at the different treatment options for knee plica syndrome.
Knee plica are normal folds in the synovial membrane of the knee, a thin, fluid-filled capsule that encases the joint, like a bag. The word “plica” is Latin for “fold”.
During the first trimester of fetal development, connective tissue divides the knee into three compartments. During the second trimester, this tissue begins to reduce in size as the fetus starts moving more and is gradually reabsorbed before birth, leaving only a thin sleeve which surrounds the knee joint, the synovial membrane.
However, in up to 90% of the population, the connective tissue isn’t fully absorbed leaving small inward folds in parts of the synovial membrane, known as knee plica. Synovial plica are pliable and thin.
These folds in the membrane, known as synovial knee plica, are elastic so do not usually restrict normal knee movement and vary in size between individuals. In most cases, synovial plica are completely asymptomatic and don’t cause any problems. However, if the knee plica becomes irritated or inflamed, typically from overuse or an injury, plica synovialis develops causing pain and instability in the knee.
Plica syndrome develops when the synovial folds are irritated and become inflamed. This may be due to direct knee trauma, overuse or repetitive activities, or an underlying knee problem that affects the pliability of the synovial membrane.
The knee plica may get trapped or pinched between the knee bones, or caught on the femur. When this happens, the knee plica in question becomes inflamed, gradually thickens and eventually, if left untreated, becomes hard.
Plica syndrome is typically caused by:
The symptoms of plica syndrome may develop suddenly with an injury, or gradually from overuse, in one or both knees. Typical symptoms of knee plica syndrome include:
People may have up to four knee plica located in different parts of the knee, the medial plica, suprapatellar plica, infrapatellar plica and the lateral plica.
Plica syndrome can develop in any of these unless you are one of the 10% of the population have no knee plica at all.
The medial plica is the most common place to develop symptomatic knee plica syndrome. It is found on the inner side of the knee joint, running parallel to the kneecap.
The medial plica runs from the bottom part of the knee cap on the medial side, over the medial femoral condyle and down to the synovial lining on the inner side of the tibia, where it blends with the ligamentum patellae and the infrapatellar fat pad. It is often referred to as being like a shelf.
The position of the medial plica makes it the most prone to getting caught in the knee joint resulting in medial plica syndrome, aka medial patellar plica syndrome, medial plica synovitis and plica synovialis mediopatellaris.
The suprapatellar plica is found in the suprapatellar pouch, an area behind the kneecap extending up behind the quadriceps tendon. The suprapatellar plica is typically a domed, crescent shape, sitting between the suprapatellar bursa and the knee joint, and may be connected to part of the medial plica.
In some cases of suprapatellar plica syndrome, the plica becomes tethered with adhesions forming between the plica, the kneecap and the femoral condyle which can limit knee movement.
Suprapatellar Plica Syndrome is also known as supramedial plica syndrome, superior plica and plica synovialis suprapatellaris
The infrapatellar plica, aka ligamentum mucosum, may be shaped like a cord or bell-shaped. It sits inside the middle of the knee joint, alongside the Anterior Cruciate Ligament, attaching to the infrapatellar fat pad.
Whilst the infrapatellar plica is the most prevalent of the four knee plica, it does not tend to get damaged making infrapatellar plica syndrome rare.
Infrapatellar plica syndrome is also known as plica synovialis infrapatellaris.
The lateral plica is the least common of the four knee plica and is in fact, quite rare.
The lateral plica sits on the outer side of the knee, running down the lateral patella, and attaches to the infrapatellar fat pad.
Lateral plica syndrome is also known as plica synovialis lateralis or lateral para-patellar plica.
Knee plica syndrome is hard to diagnose as the symptoms mimic many other knee problems.
Your doctor will take a history asking questions about your knee pain. Plica syndrome is often diagnosed by ruling out other knee issues such as a meniscus tear or tendonitis.
To diagnose plica syndrome your doctor may do:
Treatment for plica syndrome focuses on reducing the inflammation in the synovial folds. Most people with plica synovialis will get better in 6-8 weeks with a course of physical therapy and will not require surgery.
Treatment for knee plica syndrome normally involves a combination of:
If you are getting a lot of pain at night-time from plica synovialis, it can help to sleep with a pillow or duvet in between your knees.
If the symptoms of plica syndrome fail to settle after 3-6 months of non-surgical treatment, then your doctor may advise surgery.
Surgery for plica syndrome will be carried out arthroscopically – key hole surgery. Small incisions are made around the knee joint and a fibre-optic camera is inserted into the knee so the surgeon can fully evaluate the joint.
Small surgical tools are used to remove the inflamed plica, known as synovial plica resection. The surgeon will also inspect the integrity of the other structures in the joint and may also carry out a meniscectomy, if there is a tear in the cartilage, or a lateral release, if the lateral retinaculum is tight.
A course of physical therapy is recommended after synovial plica resection surgery to prevent scarring and ensure full recovery. Physical therapy will be very similar to that with non-surgical management aiming to improve knee strength, motion and function and reduce any swelling.
Recovery from plica syndrome will depend on a number of factors – the age of the patient, how long they’ve had symptoms, which plica is affected, compliance with physical therapy and whether there are other associated knee problems.
The best outcomes are usually achieved in younger patients who have only had symptoms of plica synovitis for a short time.
There are a number of other knee conditions that present in a similar way to knee plica syndrome:
If you have been treated for any of the conditions above and your symptoms have failed to improve, it may well be that knee plica syndrome is to blame.
Page Last Updated: 10/07/21
Next Review Due: 10/07/23
1. Synovial Plica Syndrome of the Knee: A Commonly Overlooked Cause of Anterior Knee Pain. By P. Feng Lee, A. Nixion and J. M. Murray. The Surgery Journal. February 2017
2. The Role of Complete Suprapatellar Plicae. By T. Mine, K. Chagawa, K. Ihara, H. Kawamura, R. Kuriyama & R. Date. Arthroscopy Techniques Journal. February 2016
3. MR Imaging of Infrapatellar Plica Injury. R. Cothran, P. McGuire, C. Helms, N. Major & D. Attarian. American Journal of Roentgenology. May 2003
4. Anatomy and MR Imaging Appearances of Synovial Plicae of the Knee. R. García-Valtuille, F. Abascal, L. Cerezal, A. García-Valtuille, T. Pereda, A. Canga & A. Cruz. Radiographics. July 2002