Classification of knee ligament instabilities.

1) The intactness of the posterior cruciate ligament is a key to the basic classification system of the knee. 2) With an intact posterior cruciate ligament, single or combined rotatory instability may occur. 3) With a tear of the posterior cruciate ligament, straight instability may be found. 4) An intact posterior cruciate ligament limits the instability of the knee in full extension (adduction or abduction stress test). 5) The anterior drawer test is somewhat equivocal. A strongly positive result of the anterior drawer test does suggest that the anterior cruciate ligament is not intact, although a moderately positive result may not implicate this ligament.