The classification and early diagnosis of knee joint instability.

A working classification of knee joint instability includes anatomic and pathologic classifications. The anatomic classification defines the direction of the instability causing the abnormal function to the patient. A structural classification delineates the pathologic lesion. An ability to correlate one with the other ensures proper understanding of the subject. An accurate diagnosis following the acute injury is the basis of effective treatment. Residual chronic disability in many instances will be avoided. Injuries involving the cruciate ligaments constitute difficult diagnostic problems. Anterior cruciate ligament lesions lead to predictable patterns of chronic instability. Posterior cruciate ligament lesions may be associated with trauma sufficiently severe to impair the neurovascular status of the limb.