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The clinical presentation, diagnosis, radiographic features, mechanism, pathologic changes, and treatment of elbow instability are understood better now. Elbow instability can be classified according to five criteria: (1) the timing (acute, chronic or recurrent); (2) the articulation(s) involved (elbow versus radial head); (3) the direction of displacement (valgus, varus, anterior, posterolateral rotatory); (4) the degree of displacement (subluxation or dislocation); and (5) the presence or absence of associated fractures. Posterolateral rotatory instability is the most common pattern of elbow instability, particularly that which is recurrent. Posterolateral rotatory instability can be considered a spectrum consisting of three stages according to the degree of soft tissue disruption. Patients typically present with a history of recurrent painful clicking, snapping, clunking, or locking of the elbow and careful examination reveals that this occurs in the extension portion of the arc of motion with the forearm in supination. There are four principle physical examination tests. The most sensitive is the lateral pivot-shift apprehension test, or posterolateral rotatory apprehension test, just as the anterior apprehension test of the shoulder is the most sensitive test for a patient with shoulder instability. Next is the lateral pivot-shift test, or posterolateral rotatory instability test. Reproducing the actual subluxation and the clunk that occurs with reduction usually can be accomplished only with the patient under general anesthesia or occasionally after injecting local anesthetic into the elbow. The third test is the posterolateral rotatory drawer test, which is a rotatory version of the drawer or Lachman test of the knee. The final test is the stand up test as reported by Regan. The patient's symptoms are reproduced as he or she attempts to stand up from the sitting position by pushing on the seat with the hand at the side and the elbow fully supinated. A lateral stress radiograph can show the rotatory subluxation.