[The lateral capsule sign in the traumatized knee joint].

The lateral capsular sign is a simple radiographic finding visible on routine anteroposterior knee x-ray near the tibial articular surface at the lateral point of the lateral tibial plateau. The lateral capsular sign is a flake of bone superior and posterior to the insertion of the iliotibial tract, and represents an avulsion of the meniscotibial portion of the lateral capsular ligament. A positive lateral capsular sign implies disruption of the lateral capsule and a tear of the anterior cruciate ligament. These findings are illustrated by clinical examples.