Musculoskeletal Imaging

Synovial plica

a ridge or fold, as of a membrane. Numerous plicae exist within the body, but among the more important examples are synovial plicae, which are remnants found in the knee that may divide the joint into compartments. These plicae may cause symptoms if they become thickened (plica syndrome) or persist in embryonic form (as complete septa).

Three structures (suprapatellar, medial patellar and infrapatellar plicae) are commonly encountered and can be identified by various means, such as arthrography, computed arthrotomography, MR imaging or arthroscopy. Different combinations of these three plicae may also occur.

In the plica syndrome, the plicae of the knee become symptomatic owing to thickening, which in turn may be the result of traumatic synovitis (Fig.1). Injuries, strenuous exercise, inflammation, osteochondritis dissecans and intra-articular osteocartilaginous bodies may play a role in development of this syndrome. Fibrous repair may be accompanied by increasing collagenization and progressive loss of elasticity. Irritation, abrasion and erosion of the cartilage may ensue. A clicking sensation, locking of the joint, or an audible or palpable snap may also be noted.

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Fig.1

Sagittal proton-density (a) and T2-weighted (b) MR images of the knee demonstrate a loculated fluid collection containing debris in the suprapatellar pouch owing to a suprapatellar plica.
Synovial plica, Fig.1 (a)
Synovial plica, Fig.1 (b)