An in-vivo study of ACL strain in the normal knee during Lachman and Drawer tests

To diagnose an anterior cruciate ligament (ACL) injury, clinicians perform a Lachman test at 30° of flexion or a Drawer test at 90° of flexion to record how far the tibia displaces anteriorly with respect to the femur. A study was undertaken to characterize the normal strain pattern of the ACL in vivo during the Lachman and Drawer tests, and to determine if there is a significant difference between the strain patterns at clinically applied load levels. Five patients were studied. After routine arthroscopic surgery a Hall-effect displacement transducer was attached arthroscopically to the ACL to measure strain. Loads were applied by a hand-held load cell in a transverse plane directed through the midtibial tuberosity at flexion angles of 90° and 30°. The difference in percentage strain between the Lachman and Drawer tests was highly significant at p<0.01 level. These results clearly show that the Lachman test produces a greater elongation or strain in the ACL in comparison to the Drawer test at loads to 35 lb. From these data the authors characterize the normal ACL strain pattern