Discoid lateral meniscus in children.

The discoid meniscus is the most common abnormal meniscal variant in children. It is most likely a congenital deviation and usually occurs laterally. The discoid shape results in greater coverage of the tibia and usually is associated with increased thickness of the meniscus that may lead to abnormal shearing forces across the knee joint. The Watanabe classification divides this anomaly into three distinct types: complete, incomplete, and Wrisberg ligament. The complete and incomplete types are often asymptomatic; unless symptomatic, they generally should be left alone. Tears should be treated with resection back to a stable rim. The Wrisberg ligament type is a hypermobile meniscus secondary to a lack of posterior tibial attachment. This type may or may not be associated with an abnormal shape and may appear in childhood as a classic snapping knee syndrome. These children complain of intermittent popping and snapping within the knee that clinically manifests as a dramatic audible and visible adjustment of the knee with each flexion and extension. Treatment of a symptomatic Wrisberg ligament type requires surgical repair of the posterior disruption. Saucerization of the remaining meniscus may be required to protect the repair from abnormal shear forces.