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. 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. 
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.
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.
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.
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