Arthrography of the discoid lateral meniscus.

Twenty-seven cases of discoid lateral meniscus (DLM) were diagnosed during the course of 985 knee arthrograms; 19 had the classic discoid shape while eight were less large and believed to represent a forme fruste. Based on anatomic and arthrographic appearances, DLM was classified into six types. Criteria for the arthrographic diagnosis of intact and torn DLM are discussed. The wide variety of size and shape is believed to result from a combination of congenital and environmental factors. It is speculated that some may arise entirely secondary to trauma without congenital predisposition. Many undoubtedly remain asymptomatic: more than one-third of cases in this series were diagnosed incidentally during evaluation for symptoms and signs referrable to a torn medial meniscus.