A test for knee posterolateral rotatory instability.

A test for knee posterolateral instability, which is a modification of the standard posterolateral rotatory instability test, is described. In this test, the patient lies supine on the examination table with hips and knees flexed to 90 degrees. The examiner grasps both feet and attempts to maximally externally rotate them. A positive test is indicated by (1) excessive external rotation of the affected tibia, which is easily recognized since the feet act as pointers and amplify the external rotation, and (2) a slight posterior sag of the affected tibial tubercle, which is more subtle but still a very recognizable sign.