Development of a Failure Locus for a 3-Dimensional Anterior Crutiate Ligament: A Finite Element Analysis

This study investigated movement combinations which may cause injury to the anterior cruciate ligament (ACL). A 3-Dimensional finite element knee joint model, including bones and ligament bundles, was developed. Bone was modeled as rigid, and a transversely isotropic material was applied to the ligament structures. This study incorporates a novel approach for developing bundle specific prestrain within the ligament structures. The bundles were stretched from their zero load lengths to their reference lengths, producing a strain field mimicking in vivo conditions at full knee extension. A failure locus was created by performing multiple knee joint motion combination simulations until ligament failure. The locus shows which movement combinations of internal/external femoral rotation and varus/valgus angle cause failure within the ACL bundles at 25° of knee flexion. The 3D model provided improved accuracy for locating bundle ruptures. By monitoring stresses and strains within the ligament bundles during knee joint orientation simulations, ruptures were virtually diagnosed. The relationship between knee joint orientation and ligament rupture provides a spectrum for the propensity of ACL injury. The results highlight femoral external rotation relative to the tibia as an important factor related to ACL injury. The results also show the posterolateral bundle to be more susceptible to rupture than the anteromedial bundle. These results have various clinical applications. In sports where ACL injuries are prevalent, training programs can be adapted to address the avoidance of harmful knee orientations. Monitoring bundle rupture locations also increases insight for practitioners in identifying more precise injury mechanisms.