Concepts of the pivot shift.

The pivot shift is a symptom and sign of anterior cruciate ligament (ACL) and lateral and posterolateral capsular deficiency of the knee. Either a subluxation or reduction, or both in rapid succession, plus a simultaneous impingement of the lateral compartment of the knee causes a pivot shift. The knee must twist to sublux the lateral tibial plateau anteriorly and the lateral femoral condyle posteriorly, to cause a misfit of the joint; the knee must be partially flexed to sublux symptomatically; the lateral compartment of the misfitted joint must be compressed simultaneously during a twist into or out of subluxation to cause impingement. When the knee is subluxed while compressing the lateral compartment and then flexed to more than 40 degrees, an intact iliotibial tract will cause reduction. However, an insufficient iliotibial tract will permit continued subluxation through further flexion.