Kinematics of active knee extension after tear of the anterior cruciate ligament

Three-dimensional movements of the knees in 13 pa tients with unilateral old tears of ACLs were studied during extension. Roentgen stereophotogrammetric methods were used to measure tibial movements in the injured and the intact knees. Reduced internal rotation and adduction were recorded at the end of extension on both sides. The injured knees displayed increased anterior and distal displacements of the tibial intercon dylar eminence. Abnormal tibial displacements in our patients indicate that the absence of the ACL is not completely compensated for during active extension past 30°; close to the extended position, the tibial movements tend to normalize.