Test for posterolateral rotatory instability of elbow. A, With arm at side and forearm in supination, supination and valgus moments and axial forces are applied to elbow, which is flexed 20–30 degrees. Posterolateral subluxation is visibly and palpably reduced when elbow is flexed farther. B, Same procedure is done much more easily with patient’s arm over his or her head. Full external rotation of shoulder provides counterforce for supination of forearm and leaves one of examiner’s hands free to control valgus moments.