Strain of the anterior cruciate ligament increases linearly with quadriceps contraction

This work was designed to answer two important questions concerning injury mechanics of the anterior cruciate ligament (ACL). One question was whether strain of the ACL increased linearly with increasing quadriceps contraction, and the other was whether strains in the anteromedial (AMB) and posterolateral (PLB) bundles were different at any point in the flexion arch. To answer these questions experiments were performed to determine the relationship between increasing quadriceps force and strains in both the AMB and PLB. Five unembalmed knee specimens were instrumented on both bundles of the ACL using liquid mercury strain gages. Quadriceps loads of 0, 250, 500, 750, and 1000 N were applied at flexion angles of 0, 15, 30, 60, 90, and 120 degrees. Data were analyzed using repeated measures analysis of variance, as well as linear and quadratic regressions. The results indicated that there were no significant differences in strains between the two bundles and that the relationship between quadriceps load and ACL strain was highly linear for flexion angles of 60 degrees and less, where the quadriceps caused markedly increased strains above those developed during passive motion.