THE ANTERIOR ???KICK-OUT??? DURING ACTIVE LEG EXTENSION IN THE ACL DEFICIENT KNEE 1468

Abstract

Anterior cruciate ligament (ACL) deficient knees have decreased stiffness and subsequently increased anterior tibial translation (ATT) during Lachman testing with mild knee flexion. The purpose of this study was to determine if a graphical interpretation of the tibial translation curve from an active leg extension test can provide distinctive information for diagnosing an ACL deficient knee. Twelve ACL deficient subjects performed three trials of a passive and active leg extension exam on both the injured and non-injured leg using the OSI CA-4000. Total translation during passive and active motion was measured at angles 10°, 20°, 30°, and 40° of knee flexion, and the side-to-side differences compared. There were significant differences in tibial translation between the injured and non-injured knees at all 4 angles of flexion (p<0.05). In particular, at 20° of knee flexion, the injured and non-injured knees averaged 12.9 mm and 6.6 mm of ATT, respectively, resulting in a maximal side-to-side difference of 6.3 mm (p<0.05). A reproducible and sudden increase in tibial translation (“kick-out”) occurred between 40° and 10° of active leg extension in the ACL deficient knee. Maximal total ATT occurred at approximately 20° of knee flexion. This“kick-out” was not seen in any of the non-injured knees. This study confirms that the distinctive “shape of the curve,” in addition to the absolute amount of tibial translation, can be used to aid in the diagnosis of an ACL deficient knee.