Medial Synovial Plica Irritation

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