Kinematics of the anterior cruciate ligament during gait.

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.