The embryologic work of Ogata and Uhthoff (, 5) showed that the mediopatellar plica is not a remnant of a septum of a distinct compartment during the development stage. This theory would explain the presence of suprapatellar and infrapatellar plicae however, it does not explain the presence of a mediopatellar or lateral plica because at no time does a membrane separate the patellofemoral joint into two cavities along a coro-nal plane (, 6). The motion of the fetal knee joint in utero may contribute to both the resorption of plicae and the development of the joint cavity. These plicae are remnants of the synovial septa that occupy the space between the distal femoral and proximal tibial epiphyses in the 8-week-old embryo during embryologic development of the knee (, 4,, 5). The incomplete resorption of these septa would leave well-developed plicae. We also discuss the pathophysiologic features, clinical manifestations, and treatment of plica syndrome.Īlthough there is no consensus, it is widely believed that the knee joint is originally composed of three compartments-medial, lateral, and suprapatellar-that are partitioned by synovial septa. In this article, we discuss and illustrate the embryologic development and MR imaging features of synovial plicae of the knee. The exact prevalence of medial plica syndrome is a subject of debate, as are the criteria that allow recognition of a clinically significant plica. The mediopatellar plica is considered the one most likely to cause problems when it becomes thickened, fibrotic, or bowstrung (, 3). With motion of the knee, the thickened fibrotic plicae can irritate the synovium of the condylar margins, leading to inflammatory synovitis and articular cartilage wear. Chronic inflammation secondary to direct trauma, repetitive sports activities, or other pathologic knee conditions affects the pliability of the synovial folds and can become symptomatic. The most commonly encountered plicae of the knee (in descending order) are the infrapatellar plica (ligamentum mucosum) (, Fig 1), the suprapatellar plica, and the mediopatellar plica (, 1,, 2).Īsymptomatic synovial plicae may be found normally within the knee. Some authors have suggested that the synovial plicae may act like eyelids, aiding in lubrication of the joint. The synovial plicae are normal structures that represent remnants of synovial membranes from the embryologic development of the knee. Plicae manifest at magnetic resonance (MR) imaging as linear low-signal-intensity structures, sometimes delineated by joint fluid. These folds are quite filmy, thin, and vascularized and have no known function. Failure of the patient to improve with conservative treatment leaves arthroscopic excision of the pathologic plica as the treatment of choice.Ī plica is a fold of synovial tissue found in the lining of a joint. Once the diagnosis has been made, nonsurgical treatment is preferable initially. A diffusely thickened synovial plica, perhaps associated with synovitis or erosion of the articular cartilage of the patella or femoral condyle, in a patient with no other significant MR imaging findings suggests the diagnosis of plica syndrome. Plica syndrome, the painful impairment of knee function in which the only finding that helps explain the symptoms is the presence of a thickened and fibrotic plica, should be included in the differential diagnosis of internal derangement of the knee. Gradient-echo T2-weighted and fat-suppressed T2-weighted or proton density–weighted MR images are optimal for the evaluation of plicae. At MR imaging, synovial plicae appear as bands of low signal intensity within the high-signal-intensity joint fluid. Magnetic resonance (MR) imaging and MR arthrography are useful tools in the evaluation of synovial plicae and allow differentiation of these entities from other causes of knee pain.

Synovial plicae are normal anatomic structures of the knee that sometimes become symptomatic.

Pica syndrome radiopaedia