I Have Knee Pain And I don’t Know What It Could Be…An Introduction to Synovial Plica and Plica Syndrome

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When attempting to understand synovial plica in relation to plica syndrome, we must first understand the anatomical structures affected. Let’s start with learning about plicae.



Anatomy of Plica


Plica is a term used to describe a fold in the lining of the knee joint. Imagine the inner lining of the knee joint as nothing more than a sleeve of tissue. This sleeve of tissue is made up of synovial tissue, which is a thin, slippery material that lines all of the joints. This synovial tissue is important because it allows for movement of knee joint without restriction. 





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Four plica synovial folds are found in the knee, but only one seems to cause trouble. This structure is called the medial plica. The medial plica of the knee is a thin, well-vascularized intraarticular fold of the joint lining, or synovial tissue, over the medial aspect of the knee (Griffith & LaPrade, 2008). It is present in everyone, but can be more prominent in some people. Proximally, it is attached to the genu articularis muscle, while distally it courses over the far medial aspect of the medial femoral condyle to attach to the distomedial aspect of the intraarticular synovial lining of the knee. At this location, it basically blends into the medial patellotibial ligament on the medial aspect of the retropatellar fat pad (Griffith & LaPrade, 2008). The medial plica is composed of relatively elastic tissues which asymptomatically conform to the changes in shape and lengths of the plica folds as the knee flexes and extends. 



Causes of Plica Syndrome


A plica causes problems when it is irritated. This can occur over a long period of time, such as when the plica is irritated by certain exercises, repetitive motions, or kneeling. Activities that repeatedly bend and straighten the knee, such as running, biking, or use of a stair-climbing machine, can also irritate the medial plica and cause plica syndrome.


Injury to the plica can also happen suddenly, such as when the knee is struck in the area around the medial plica. This can occur from a fall or even from hitting the knee. This injury to the knee can cause the plica, and the synovial tissue around the plica, to swell and become painful. The initial injury may lead to scarring and thickening of the plica tissue later. The thickened, scarred plica fold may be more likely to cause problems later.


In some patients, particularly those who may have had injuries or multiple surgeries over the medial aspect of the knee, the medial synovial plica may become very thick and fibrotic and may catch over the medial aspect of the medial femoral condyle (Griffith & LaPrade, 2008).


In all patients, the medial synovial plica will glide over the anteromedial aspect of the medial femoral condyle with flexion and extension of the knee. In most patients, this gliding motion of the plica will occur without any symptoms, because of the high viscosity of the native synovial fluid of the knee. However, in patients with effusions, which decreases the viscosity of their synovial fluid, patients may either have crepitation or a catching of their medial synovial plica with flexion and extension of the knee (Griffith & LaPrade, 2008). This crepitation or catching can occur with patients while going up or down stairs, squatting and bending, and other types of activities. Since the medial synovial plica does have an attachment to the genu articularis muscle, and also an indirect attachment to the quadriceps musculature due to its attachment to the joint lining, it is dynamically controlled by the quadriceps muscles. Thus, medial plica irritation is more common in patients who have poor quadriceps tone or other problems with joint muscle balance around the knee (Griffith & LaPrade, 2008).



Symptoms of Plica Syndrome


The primary symptom caused by plica syndrome is pain. There may also be a snapping sensation along the inside of the knee as the knee is bent. This is due to the rubbing of the thickened plica over the medial aspect of the femoral condyle where it enters the joint. This usually causes the plica to be tender to the touch. In thin people, the tissue that forms the plica may be actually be felt as a tender band underneath the skin. In rare cases where the plica has become severely irritated, the knee may become swollen.



Diagnosis of Medial Plica Pathology


One of the most important points in diagnosing medial synovial plica pathology is obtaining an appropriate history from the patient. Patients usually describe pain which is dull, achy, and increases with activity. When asked to point to the area of their pain, they will commonly point to the proximomedial aspect of the knee, proximal to the medial joint line (Griffith & LaPrade, 2008). Most patients will complain of an achy type pain over the medial aspect of their knee, which is aggravated by activity and can be particularly bothersome at night. Their complaints of night pain over this area of the knee are due to the effects of inflammation, which can be particularly bothersome with activities. Patients most commonly complain of pain with activities which stress their patellofemoral joints, such as ascending and descending stairs, squatting and bending, and arising from a chair after sitting for an extended period of time. In addition, they may note difficulty with sitting still for long periods of time without having to move and stretch their knees. They also may complain of a catch over the anteromedial aspect of their knee upon arising from a chair following prolonged periods of sitting. In some patients, plica catching may present as a pseudo-locking event to their knee when they have been sitting down for an extended period of time and they first arise. Some patients may describe these pseudolocking events as instability or catching of their patella (Griffith & LaPrade, 2008). Clicking, giving way, and pseudo-locking have been reported in approximately 50% of all patients who present with medial plica irritation. Patients who might have problems with activity-related effusions may also complain of pain over the anterior aspect of their knee. While these activity-related effusions may not be directly caused by medial plica pathology, and are more commonly due to underlying quadriceps mechanism weakness, meniscal tears, and/or osteoarthritis, but they can cause secondary medial plica irritation. In addition, patients who have had postoperative or post-injury weakness of their affected extremity may develop pain over the anteromedial aspect of their knee in the region of the medial synovial plica. A definitive diagnosis of medial plica irritation is usually obtained by physical exam. A normal examination of the patellofemoral joint should always include an examination of the patient’s medial synovial plica fold to determine if they have any irritation of this structure (Griffith & LaPrade, 2008).




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Treatment of Plica Syndrome


The main treatment regimen for medial plica irritation is non-operative. For patients who have medial plica irritation as their main diagnosis without any underlying knee pathology contributing to their plica irritation, there is a very good chance that their symptoms will improve with a guided rehabilitation program (Griffith & LaPrade, 2008). The most successful rehabilitation programs focus on strengthening the quadriceps muscles, which are directly attached to the medial plica, and avoiding activities which cause medial plica irritation. These exercises can include quadriceps sets, straight leg raises, squat variations, and mini-squats, as well as, a walking program, the use of a recumbent or stationary bicycle, a swimming program, or possibly an elliptical machine (Griffith & LaPrade, 2008). Patients should work on gradually increasing strength over time to overcome any strength deficit in their quadriceps mechanism. Concurrent with this, patients should also work on a frequent hamstring stretching program throughout the day. As mentioned previously, tight hamstrings can increase the force needed to extend the knee, which can be an important source of medial plica irritation. Thus, it is important to make sure that the hamstrings are stretched frequently to diminish this extra stress on the anterior part of the knee (Griffith & LaPrade, 2008).







Griffith, C. J., & LaPrade, R. F. (2008). Medial plica irritation: diagnosis and treatment. Current reviews in musculoskeletal medicine, 1(1), 53-60.

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