Restoring the ACL Back to Normal

Studies show that the anterior cruciate ligament (ACL) is not a single-bundle ligament. Instead, it has two bundles: the anteromedial bundle and the posterolateral bundle. Each of these bundles has its own unique function. Together, they keep the knee stable during weight-bearing and pivoting activities. In this study, special computer-assisted navigation technology was used to measure how each bundle works to stabilize the knee joint during motion. Each patient included in the study had a two-bundle, four-tunnel technique for ACL repair. The surgeon used computer-aided navigation to perform the procedure. Details of the operative technique are described. Location of the tunnels for each of the bundles was also described. Computer software used in the study allowed for measurement of rotation and translation of the tibia (lower leg bone). An optical sensor recorded motion during three special tests. Tests included the anterior drawer test, the pivot-shift test, and the Lachman test. These tests are performed by the surgeon or examiner. They are used to look for knee instability. The authors report the following findings:

The anteromedial (AM) bundle restrains forward motion of the tibia during the anterior drawer test.

The posterolateral (PL) bundle restrains forward motion of the tibia during the Lachman test.

Both tests worked together to restrain forward motion during the pivot shift test.

The posterolateral bundle was more important in controlling tibial rotation. The results of this study support the idea that both ACL bundles must be repaired in order to restore normal knee motion. This is especially true when it comes to the control of tibial rotation. Each bundle is responsible for separate stabilizing measures. The PL bundle works more during knee extension. The AM bundle stabilizes as the knee bends.

Return to previous page