Background: The function of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) during gait has not been reported.
Hypothesis: The AM and PL bundles have distinct functional behavior during the stance phase of treadmill gait.
Study Design: Descriptive laboratory study.
Methods: Three-dimensional models of the knee were created by magnetic resonance images from 8 healthy subjects. The contour of the 2 bundle attachments were constructed on each model. Each bundle was represented by a straight line connecting its tibial and femoral attachment centroids. Next, the knee kinematics during the stance phase of gait was determined with a dual fluoroscopic imaging system. The relative elongation, sagittal plane elevation, coronal plane elevation, and transverse plane deviation of the 2 bundles were measured directly from heel strike to toe-off.
Results: At heel strike, the AM and PL bundles had first peak elongation of 9% ± 7% and 9% ± 13%, respectively. At 50% progress of the stance phase, both bundles were maximally elongated, 12% ± 7% for the AM bundle and 13% ± 15% for the PL bundle. No significant difference was found for each bundle between 40% and 60% of the stance phase (P > .05). With increasing knee flexion, the sagittal plane and coronal plane elevations of the 2 bundles decreased, whereas the deviation angles increased.
Conclusion: Both bundles are anisometric and function in a similar manner during the stance phase of gait. They were maximally elongated throughout the midstance where they were stretched maximally to resist anterior tibial translation.
Clinical relevance: This information can be useful for further improving anatomical ACL reconstructions to better reproduce the 2 bundle functions. It may also be useful for designing postoperative rehabilitation regimens to prevent overstretch of the grafts.