Approach Considerations
In addition to the history and physical examination, a radiograph is recommended to exclude other causes of knee pain. As stated previously, plica syndrome is difficult to differentiate from other pathology and remains a diagnosis of exclusion. Other adjunctive diagnostic studies include contrast pneumoarthrography and double-contrast arthrography, yet arthroscopy remains the diagnostic standard. [30, 31]
Imaging Studies
Plain radiographs of the knee are appropriate in the evaluation of a patient with plica syndrome. However, they are useful only in that they help eliminate other diagnoses. [32]
Magnetic resonance imaging (MRI) is of limited value in detecting normal or pathologic plicae about the knee. [33] It rarely demonstrates these structures conclusively (see the image below). Jee et al published one of the only papers that touts the usefulness of MRI in diagnosing medial parapatellar plicae. [34] They reported 95% sensitivity and 72% specificity with their MRI approach. It should also be noted that plica syndrome has been a major research interest at their center. To the best of the authors' knowledge, no other center has matched these numbers.
Arthroscopy
Arthroscopy is the standard for definitive diagnosis of plica syndrome. [30, 31] Most plicae are found incidentally during knee arthroscopy.
Munzinger classified the mediopatellar plica into four types on the basis of appearance, as follows [35] :
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A - Cordlike
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B - Shelflike, does not cover medial femoral condyle
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C - Does cover medial femoral condyle
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D - Double insertion
Other authors believe that to differentiate between symptomatic and asymptomatic plicae, the following criteria must be met upon arthroscopic examination:
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Plica must appear
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Impingement must be visualized
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Chondromalacia must be present in the areas of impingement
Histologic Findings
The histology of a symptomatic plica is typically that of synovial tissue (type A macrophagelike cells and type B fibroblastlike cells) immersed in an inflammatory reaction. [36] In other instances, the histology may show dense fibrotic tissue that only secondarily impinges upon articular surfaces to produce pain. Kasim and Fulkerson found fibrosis, vascular proliferation, and small nerves with deceased myelin (neuromata) on histologic analysis of specimens from their plica patients. [26]
Staging
Jee et al staged medial parapatellar plicae according to how far the plica extends into the region of the patellofemoral joint, as follows [34] :
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1+ (does not extend to the medial edge of the patella)
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2+ (extends to the medial third of medial facet of the patella)
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3+ (extends over one third to two thirds of the medial facet)
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4+ (extends over more than two thirds of the medial facet)
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Plica syndrome. Typical appearance of a large beefy medial parapatellar plica.
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Plica syndrome. Patient pointing to the painful area of her knee.
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Plica syndrome. The inferomedial quadrant is usually the most painful region by physical examination. This area is highlighted by several X's in this figure. A painful taut band of tissue that emanates from the central portion of the medial patella may often be palpated (3 o'clock position on the figure).
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Plica syndrome. Axial MRI demonstrating abundant medial plical tissue.
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Plica syndrome. Preoperative appearance of medial parapatellar plica (a 4+ plica by the Jee classification, extending across more than two thirds of the medial facet of the patella).
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Plica syndrome. Postoperative appearance of the same patient as in Image 5 after plical resection.
