Strain inhomogeneity in the anterior cruciate ligament under application of external and muscular loads.

To determine whether mathematical relations between strains in different bundles and loads would be needed to predict injury of the anterior cruciate ligament (ACL), this work tested the hypothesis that strains developed in two bundles of the ACL were significantly different under the application of a number of loads important to injury etiology of the ACL. To provide the data for testing this hypothesis, liquid mercury strain gages were installed on both the anteromedial (AMB) and posterolateral (PLB) bundles of the ACL of ten specimens, which were then subjected to passive flexion/extension, hyperextension moment, anterior force, internal and external axial moments, quadriceps, and hamstrings forces. Various combinations of these loads were also applied. Flexion angles ranged from 8 deg of hyperextension through 120 deg of flexion. The data were analyzed using a repeated measures analysis of variance. The analyses indicated that significant strain differences existed between the two bundles only for passive flexion/extension. However, the analyses did not support the hypothesis that AMB and PLB strains are significantly different from each other under the application of external and muscular loads. Because noticeable differences (> 3 percent) between bundle strains did exist in some load cases for limited ranges of flexion and the PLB strain was consistently higher than the AMB strain, it may be sufficient to consider strain in only the PLB when predicting ligament damage based on strain-load relations.