Medial Synovial Plica Irritation 

Updated: Jul 22, 2022
Author: Robert F LaPrade, MD, PhD; Chief Editor: Craig C Young, MD 


Practice Essentials

Medial synovial plicae are embryological structures that form within the knee. They are normal anatomical structures found within the joint capsule of the knee, appearing as thin, soft, and flexible structures that move with the knee during flexion and extension. (See the image below.) Impingement of the plicae during motion of the knee can cause inflammation, resulting in medial knee pain. The medial suprapatellar plica of the knee is an intra-articular synovial fold on the medial aspect of the knee. This plica is one of the most common sources of knee pain in patients; however, a proper rehabilitation program allows most patients to recover from the symptoms associated with irritation of this structure.[1]

Medial plica of left knee. Medial plica of left knee.


United States statistics

No exact numbers on the incidence of patients with an irritated synovial plica are available; however, it is estimated that approximately 50% of patients who present with knee pain to a physician's office have some irritation of their patellofemoral joint. In this group of patients, most of them have some amount of suprapatellar plical irritation. Medial plica syndrome is seen in both young and old patients with a wide variety of activity levels.

International statistics

In European population studies, the prevalence ranges from 3% to 30%. Most report a prevalence of about 10% based on arthroscopic studies.[2]

Functional Anatomy

The suprapatellar plica is an intra-articular synovial fold, which has its main component on the medial aspect of the knee. When the knee is in full extension, the suprapatellar plica commonly forms a shelf, which can be palpated by an examiner. Proximally, the plica is attached to the articularis genu muscle. Distally, it is attached to the anterior horn of the medial meniscus and the medial edge of the retropatellar fat pad. In some patients, this plical shelf can become fibrotic and may impinge on the medial edge of the medial femoral condyle. The distal synovial fold of the medial plicae is in close proximity with the tendon sheath of the gracilis, which could potentially explain gait abnormalities seen with plicae irritation.

Sport-Specific Biomechanics

The quadriceps muscles and the articularis genu muscle dynamically control the medial suprapatellar plica. Good quadriceps tone seems to result in normal motion of this plica, whereas patients with poor quadriceps tone or tight hamstring muscles (antagonists of the quadriceps) commonly have irritation of their synovial plica.


Irritation (eg, direct trauma, repetitive use) leading to an inflammatory process, which occurs within the joint, can cause the synovial tissue to swell and thicken. Eventually, the normal elastic tissues are replaced with fibrous tissues, leading to a scarred plica. This scarred plica can develop fibrotic bands that extend over the medial trochlea and partially or completely cover the anterior femoral condyle. As the knee flexes, the bands are stretched, causing a painful sensation. Common causes of irritation are listed below:

  • Any type of dysfunction of the patellofemoral joint may cause irritation of the medial synovial plica. This dysfunction can be due to overuse, injury, or abnormal mechanics.

  • Patients often have concurrent patellar subluxation or apprehension, and this should be assessed as part of the physical examination. In addition, these patients often have a component of tight hamstrings or concurrent irritation of the pes anserine bursa. Measuring the hamstring-popliteal angle allows the examiner to assess the patient's hamstring tightness, whereas direct palpation helps to assess irritation of the pes anserine bursa.

  • See also Pes Anserine Bursitis (in the Sports Medicine section) and Pes Anserinus Bursitis (in the Physical Medicine and Rehabilitation section).

  • Direct trauma to the knee can also result in irritation of the medial plica (eg, dashboard injuries, fall onto a flexed knee), as can twisting injuries and overuse without proper time for healing.

  • Other pathology in the knee joint, such as a meniscal tear or arthritis, may cause knee effusions or quadriceps atrophy, which could result in plical irritation. Anything that causes bleeding in the joint or synovitis can lead to plica irritation. See also Knee, Meniscal Tears (MRI).


Lino classified medial plicae into 4 types (A, B, C and D) based on their appearance.[3]  Type A plicae appear under the retinaculum as thin, cordlike elevations of the synovial wall. Type B plicae have a shelflike appearance of narrow synovium that does not cover the anterior medial femoral condyle. Type C plicae also have a shelflike appearance, but they are larger and cover part of the anterior medial femoral condyle. Type D medial plicae are fenestrated and have 2 origins within the synovium of the joint. A and B types of medial plicae tend to be smaller and are unlikely to cause symptoms. Types C and D tend to be larger, which increases the chance they can become trapped and be impinged within the patellofemoral joint.

A second classification system based on the work of Lyu and Hsu divides medial plicae into 3 categories (A, B, and C) based on femoral condyle coverage.[4]  Type A plicae have no coverage or contact with the medial femoral condyle. Type B plicae have direct contact with the condyle but do not cover more than half of the anterior surface. Type C plicae obscure greater than half of the medial femoral condyle.


The overall prognosis for most patients with medial synovial plical irritation is good. Most patients will respond to a physical therapy program within the first 6-8 weeks, with most of the other patients responding over the next few months. Surgical intervention for a medial synovial plica should be reserved for those patients in whom all other modalities previously described in this article have failed (see Treatment, Acute Phase, Rehabilitation Program and Other Treatment).


Nonoperative complications include continued medial synovial plical irritation, which over time could potentially lead to a fibrotic plica. The most common complication, which is a poorer result than a complication, is increased pain after surgical debridement due to increased scar-tissue formation after surgery. The best way to avoid these complications is to make sure that the patient is enrolled in an appropriate physical therapy or home exercise program.

Patient Education

Most patients need to be instructed in a home exercise program to address their underlying quadriceps weakness and hamstring tightness. In addition, many of these patients may have a recurrence of some symptoms over time. Patients need to be informed of this possibility and be instructed to work on a home exercise program first, before consulting their physician's office, because they can frequently have an alleviation of symptoms with their home exercise program.




Medial suprapatellar plical irritation is a common finding in patients who present with complaints of anterior knee pain.

Symptoms include complaints of pain and stiffness over the anteromedial aspect of the knee upon arising from a prolonged sitting position, pain going up and/or down stairs, and pain with prolonged activity.

The symptoms often wax and wane over periods of time until the patient presents to a physician's office because of persistent irritation.

Prolonged flexion may increase the pain, and extension might relieve the pain.

Some patients may have had a previous arthroscopy for complaints of medial-sided knee pain without alleviation of their symptoms after the arthroscopy, regardless of whether they had some medial meniscus or medial compartment articular cartilage pathology addressed at the time of their arthroscopy. Such patients usually did not have physical therapy or participate in an exercise program either before or after this surgery.

Physical Examination

The examiner can palpate the plica by rolling one's fingers along the tissue between the medial epicondyle and the medial border of the patella. The plica is most commonly palpated about 1-2 fingerbreadths medial to the medial edge of the patella.

Patient pain and irritation upon the examiner rolling the medial suprapatellar plica under his or her fingers is a classic finding on physical examination. The examiner should ascertain whether the elicited pain is due to palpation of this well-innervated area of the synovium or whether the examiner is producing the type of pain that the patient experiences with activities.

Three diagnostic tests have been described for medial plica syndrome. The first is the active extension test during which a patient is asked to make a quick extension movement (eg, kicking). A positive test result occurs when pain (due to tension on the plica from the quadriceps muscles) is elicited with rapid extension. The second test relies on flexion. From full extension, the knee is rapidly flexed to between 30 º and 60 º of knee flexion. As before, the test result is positive when a painful sensation (due to the plica stretching with eccentric contraction of the quadriceps muscle) is elicited. The third test for medial plica syndrome is known as the mediopatellar plica (MPP) test. The patient is placed in a supine position with the affected knee extended. The examiner applies force to the inferomedial portion of the patellofemoral joint whileflexing the knee to 90 º. A positive test result occurs when the patient reports pain relief as the knee goes into flexion.





Imaging Studies

Plain radiographs should be ordered in most patients to rule out the differential diagnosis or concurrent possible pathology of a medial synovial plica. Routine radiographs should include a standing anteroposterior (AP), lateral view, and a 45° patellofemoral view. These radiographs help to demonstrate any evidence of medial compartment arthritis, osteochondritis dissecans, or patellofemoral joint pathology.

See the images below.

Medial plica of left knee. Medial plica of left knee.
Patella in a male patient, medial aspect. Patella in a male patient, medial aspect.

See also Knee Osteochondritis Dissecans, Medial Compartment Arthritis, and Osteochondritis Dissecans.

Magnetic resonance imaging (MRI) may also be useful to confirm the presence of a thickened plica (axial view) and to rule out other causes of medial-sided knee pain (eg, medial meniscus tear, bone bruise, osteochondritis dissecans). However, the plica can rest flat against the synovium and capsule, causing an MRI appearance of normal synovium. Large synovial effusions separate the plica from the synovial membrane and make diagnosis on MRI easier.

Studies that investigated the use of dynamic ultrasonography to diagnose symptomatic plicae in the knee have reported good sensitivity and specificity.[5]


Diagnostic intra-articular lidocaine injections can be useful in some patients in whom it is difficult to determine if the pathology is intra-articular or extra-articular. Continued pain after an intra-articular lidocaine injection would point to an extra-articular cause of a patient's pain.



Acute Phase

Rehabilitation Program

Physical Therapy

The first mode of treatment for suprapatellar plical irritation of the knee is nonoperative.[6] All patients should have a program of physical therapy established for them, which includes closed-chain quadriceps kinetic exercises and a hamstring-stretching program. A closed-chain quadriceps exercise program should include the use of an exercise bike, leg presses, straight-leg raises (with and without leg weights), and the performance of mini-squats or use of a squat rack machine.

An important consideration to recognize is that patients who participate in open-chain quadriceps exercises, especially those who work on knee-extension exercises on a weight machine, often have an increase in their suprapatellar plical irritation.

In addition, patients should recognize that a hamstring-stretching program must be performed several times daily to maximize improvement. Approximately 50% of patients notice a significant improvement with an exercise program in the initial 6 weeks, with a larger percentage of the remaining patients improving with an additional 6 weeks of rehabilitation.

Recreational Therapy

Patients who have medial synovial plical irritation should avoid those activities that cause irritation of their knees until they note improvement with a physical therapy or home exercise program. Such precluding activities may include avoidance of stairs, squatting activities, or long-distance jogging or running.

Medical Issues/Complications

The most common complication associated with medial synovial plical irritation is continued pain or increased pain after surgery.[6, 7] For this reason, it is important to have exhausted all nonoperative forms of treatment for patients before any attempts at surgery.

Surgical Intervention

In patients who have exhausted all other means of therapy, an arthroscopic evaluation of the knee may be indicated. Because a debrided synovial plica results in alleviation of symptoms in only about 60-70% of cases, with some of the remaining patients actually having more pain after surgery, it is recommended that the synovial plica be debrided only if significant scar tissue is present in the plica or if shelf erosion is noted on the medial femoral condyle from a fibrotic plica.

A study by Kan et al on 44 patients arthroscopically diagnosed with medial plica syndrome found that since the length of time from injury to surgery directly influenced the severity of cartilage damage, in order to reduce the potential for cartilage damage, surgical treatment should be an option when pain does not cease or when the medial synovial plica ruptures or covers part of the anterior aspect of the medial femoral condyle.[8]  In a study by Hufeland et al that included 35 young patients (mean age, 16 years), outcome, activity, and knee pain scores all improved significantly after arthroscopic resection of a symptomatic medial synovial plica.[9]

Some practitioners advocate resection of asymptomatic medial plicae in patients with a coexisting knee pathology that requires surgical intervention.[10] This is based on the idea that removing a medial plica helps to prevent future complications; however, this has been a source of debate in the orthopedic field.


Any patient in whom conservative and/or surgical treatment protocol fails should have consultation with a subspecialist fellowship-trained orthopedic surgeon who deals with knee pathology.

Other Treatment

In patients who have persistent pain after a rehabilitation or home therapy program for synovial plical irritation, consideration should be given for a possible combined local anesthetic and corticosteroid injection to try and decrease some of the inflammation.[11]

Patients who undergo this injection need to recognize that their underlying quadriceps dysfunction and hamstring tightness still need to be addressed. After the injection, these individuals should either be enrolled in a physical therapy program or have a well-instituted home therapy program to maximize their chances for a good outcome.

Maintenance Phase

Rehabilitation Program

Physical Therapy

Once a patient has recovered from medial synovial plical irritation, the individual needs to recognize that there is very likely a risk for the recurrence of symptoms if he or she does not participate in a maintenance rehabilitation program. Always recommend to these patients that they try to work on a routine exercise program indefinitely to minimize their chances of recurrence of their knee pain.

Return to Play

Patients/athletes may return to participation in sports based upon their symptoms. Athletes are recommended to start out slowly and observe how their knee reacts overnight, before advancing their workout/exercise regimen. This gradual progression is important to follow because plical irritation appears to involve some tissue inflammation, which may take hours to develop after activities. Usually, it is safe to say that if a patient does not have pain or swelling with an activity, that it is safe to continue or attempt to advance in that activity.


The best way to prevent continued medial synovial plical irritation is to avoid those activities that cause irritation and to address the problem that caused the plical irritation in the first place. Such prevention strategies would include surgery to address meniscal tears or cartilage flaps or enrollment in a proper physical therapy program for those with patellofemoral dysfunction.



Medication Summary

Any of the nonsteroidal anti-inflammatory drugs (NSAIDs) may be used to try to supplement the physical therapy program. Generally, it is recommended to start with over-the-counter (OTC) NSAIDs first. If these agents do not work, or if they work only in the maximum doses, prescription drugs may be utilized based upon the patient's previous success with these medications, drug allergies, or other medications.

Nonsteroidal anti-inflammatory agents

Class Summary

NSAIDs have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but these agents may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell membrane functions.

Ibuprofen (Motrin, Ibuprin)

An OTC NSAID that is useful to decrease pain and inflammation. DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.