Double-layered lateral meniscus. A rare anatomical aberration.

We report a case of double-layered lateral meniscus, where an accessory proximal hemimeniscus was overlying the body and posterior horn of the lateral meniscus. It lay 1-2 mm proximal and parallel to the normal lateral meniscus with its periphery attached to the capsule and was significantly thinner and more mobile than its underlying counterpart. The accessory hemimeniscus was resected arthroscopically. This case demonstrates an interesting and extremely rare anatomical abnormality of the lateral meniscus and is the first one described outside a Japanese population.