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

Posted on 06 Mar 2011 20:58

By Ground Up Strength

Plica syndrome is a post-traumatic or post-inflammatory thickening, chronic inflammation (synovitis), and/or fibrosis of the synovial plicae of the knee. This means that the plica (PLI-kah) have been irritated by overuse or injury to the knee. Most commonly affecting the medial plica, the symptoms mimic those of other other knee problems, such as a torn meniscus, causing patella pain, snapping, clicking, and tenderness of the joint. There may be a sense of instability in the knee and a knee-locking sensation. 1,2

First described in 1918, the plica is a remnant band of synovial tissue that is left over from fetal development. Normally, as the fetus grows, it is thought that the knee is split into three separate compartments: the medial and lateral synovial compartments and the suprapatellar bursa. These compartments are separated by snynovial septa (a synovial membrane). At somewhere between two to three months of fetal development these plica resorb to form one large cavity called the synovial cavity. Sometimes they are not resorbed completely and their folds partially remain, becoming plica. This theory may not adequately explain all the plica remnants of the knee and and the many variations that are found but it is at least a partial explanation of their formation.

There are several possible plicae that are found in the knee: the suprapatellar plica, the mediopetellar (medial) plica, the infrapatellar plica, and the lateral patellar plica (rare). When they were first seen during arthroscopy and excised they were thought to be abnormal but they are now known to be normal leftovers of the embryonic development. Although all the plica of the knee do not occur at the same rate and in everyone they do occur in many people. Their incidence, however, is controversial. Just the presence of plicae does not indicate a problem. Normally the plicae are asymptomatic and problems are rare. They are simply viewed as vestigial tissues which have no real function but do not necessarily cause problems. 4,3

What Causes Plica Syndrome?

Plica syndrome is caused by chronic inflammation from trauma to the knee or other pathological knee conditions. Normally the plica synovial membranes are thin and elastic. When these membranes become inflamed over time they can lose their elasticity and become thickened and fibrotic. This causes the plica to interfere with the normal dynamic function of the knee, manifesting in symptoms that are similar to many other knee problems. Symptomatic plica, are, as stated, rare. The medial (mediopatellar) plica is the most widely reported to be symptomatic. Symptomatic suprapatella and lateral plicae have also been reported, but much more rarely.4

Medial Plica Syndrome

The most problematic of the plicae is the medial plicae, which arises from the medial retinaculum and inserts on the intrapatellar fat pad. It is located just to the inside of the patella, about the width of a finger away. Sources vary as to their incidence with estimates anywhere from 18% to 70% of the population but problems are rarely seen, ranging from 35 to 11% of all cases. The medial plica is in such a position to be at risk of impinging between the medial facet of the patella and the trochlea of the humerus. The plica can then become inflamed and enlarged leading to more problems. Or the impingement can stretch nerve endings to cause pain. The plica can also become inflamed from direct trauma to the knee or other inflammatory processes.3,4

Plica Syndrome Symptoms

Symptoms of plica syndrome include knee pain and swelling, a clicking sensation, and locking and weakness of the knee. Medial joint pain above the patella is often reported. Pain during knee flexion, from around 30 degrees to 60 degrees of flexion is also sometimes reported and there may be pain during extension. There may be a palpable tender and painful band or cord along the inside edge of the patella.3,2

Diagnosis of Plica Syndrome

Diagnosis of plica syndrome can be very challenging. Many other conditions that cause similar symptoms must be ruled out and then plica syndrome becomes a diagnosis of exclusion. Although the plica can be seen in MRI the mere presense of the plica does not mean it is causing a problem. The goal of imaging is to show fibrosis in the plica or hyperintense areas and to exclude other pathologic changes. Imaging is not always helpful in diagnosing the syndrome. The best way to diagnose plica syndrome is through arthroscopic surgery which "fixes the problem" by removing the offending plica and confirms the diagnoses at the same time. However, surgery is not the first line of treatment and conservative treatment is usually tried first.


The treatment for plica syndrome is usually conservative. Ice, activity modification, and NSAIDs such as ibuprofen are used to reduce inflammation of the plica and its thickening. Compression wrapping of the knee may also be ordered. Cortisone injection into the plica folds are sometimes used as well an these may help about half of those treated.

If conservative treatment fails to relieve symptoms within 3 months, the doctor may recommend arthroscopic or open surgery to remove the plicae. Arthoscopic surgery should be sought, if possible as this is a much simpler and less invasive surgery. But if symptoms can be managed conservative treatment should be continued.

1. Klippel, John H. "Chp. 3: Musculoskeletal Signs and Symptoms." Primer on the Rheumatic Diseases. New York, NY: Springer, 2008. 80. Print.
2. "Medial Plica (Shelf Plica) - Wheeless' Textbook of Orthopaedics." Welcome to Wheeless' Textbook of Orthopaedics - Wheeless' Textbook of Orthopaedics. Web. 06 Mar. 2011. <>.
3. Scuderi, Giles R., and Alfred J. Tria. "The Pediatic Knee." The Knee: a Comprehensive Review. New Jersey: World Scientific, 2010. 142-44. Print.
4. Sanchis-Alfonso, Vicente. Anterior Knee Pain and Patellar Instability. London: Springer, 2006. 239-53. Print.

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This page created 06 Mar 2011 20:58
Last updated 22 Feb 2015 17:48

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