Abstract

Lateral instability of the knee is less frequent but more disabling than medial instability of a comparable amount. At the same time the diagnostic tests for lateral instability are more subtle and mpre frequently misinterpreted. Posterolateral rotatory subluxation is demonstrated by an apparently positive posterior drawer test with the tibia in neutral rotation or by the external rotation - recurvatum test with the knee in extension. Anterolateral rotatory subluxation is present when the anterior drawer testwiththetibia in neutral rotation demonstrates that the lateral tibial condyle appears to become more prominent or that both condyles appear to become equally prominent. This instability is confirmed by the jerk test: a jerk elicited at about 30 degrees of knee flexion as the moderately internally rotated tibia is brought from a position of 90 degrees of flexion to full extension while a mild abduction stress is applied. Combined anterolateral and posterolateral rotatory instability is characterized by a positive anterior drawer test and apparently positive posterior drawer test; an adduction stress test that is 1+ or 2+ at 30 degrees of flexion, and positive external rotation - recurvatum and jerk tests. Straight lateral instability is confirmed by a positive adduction stress test at full extension without associated external rotation and recurvatum of the tibia, and is present when the lateral - compartment ligaments are completely torn with an associated tear of the posterior cruciate ligament. Verf.-Referat