In-vivo Elongation Patterns of the Anteromedial and Posterolateral Bundles of the ACL at Low Flexion Angles
The kinematics of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) in hyperextension was not well understood. This study investigated elongations of the two bundles in hyperextended knee. Twenty living knees were CT-scanned and fluoroscopy-imaged during a weight-bearing flexion–extension cycle from hyperextension to maximal flexion. The knee positions and the relative elongations of the two bundles were reproduced along the motion path using a combined fluoroscopic imaging and CT modeling technique. Results showed the elongation patterns of the two bundles were distinctively different (p < 0.01). The elongation of the PL bundle was slightly higher than that of the AM bundle at hyperextension and then decreased sharply with flexion. The elongation of the AM bundle was highest between the full extension and 10° flexion, and then decreased gradually with flexion angles. In every 10° from hyperextension to 30° flexion, the increasing rates of the PL bundle elongation were significantly higher than those of the AM bundle (p < 0.01). These data may provide important implications for selection of knee flexion angles for fixation of the AM and PL graft bundles in an anatomic ACL reconstruction that can help prevent over-stretching of the graft and reduce the risk of graft failure.