Dynamic posterior shift test

Abstract

The dynamic posterior shift test, a clinical method for evaluating both straight posterior instability and pos terolateral rotatory instability, (PLRI), is a simple, dy namic, and reliable (reproducible) test that serves as an adjuvant to other clinical tests designed to evaluate an injury or insufficiency of posterior structures in the knee. The examiner maintains the hip at near 90° of flexion to control rotation of the femur while slowly extending the knee passively. The hamstrings should be stretched to maintain their tightness. The tightened hamstrings assist gravity in subluxating the tibia posteriorly; they also provide dynamic axial loading to the joint as the knee is extended. In knees with posterior instability, the posteriorly subluxated tibia suddenly reduces as the knee joint nears full extension, and a jerk or "clunk" is felt by both the patient and the examiner. Thus, the patient's feeling of instability is reproduced by the test. We have used the dynamic posterior shift test for 5 years (as an adjuvant in our physical examination) to evaluate signs of posterior instability of the knee. Not only is the test reliable, but it is more definitive than other tests in evaluating straight posterior instability and PLRI. It is easy to perform and the results are reproducible. Because this test is dynamic rather than passive, it enhances the accuracy of evaluating poste rior instability of the knee.