The pathologic medical shelf.

It is now recognized that a previously normal fold of synovium on the medial side of the knee (a medial patellar plica) may, as a result of trauma, become pathologically inflamed and/or fibrosed, producing symptoms that may be mistakenly diagnosed as a torn meniscus or chondromalacia patellae. Clinical awareness, aided by arthroscopy, can establish the diagnosis. The correct treatment is simple and, if instituted early before irreversible changes have occurred in the femoral condyle articular cartilage, is extremely effective.