Anatomy of Normal Human Anterior Cruciate Ligament Attachments Evaluated by Divided Small Bundles

Abstract

Background Double-bundle anterior cruciate ligament (ACL) reconstruction has several potential advantages over single-bundle reconstruction with hamstring tendons. However, there are still controversies regarding tunnel placement in tibial and femoral attachments. Hypothesis The macroscopically normal ACL consists of small bundles about 1 mm in diameter. Detailed observation of the divided smaller bundles will achieve better understanding of the tunnel placement in anatomic ACL reconstruction. Study Design Descriptive laboratory study. Methods This study used 20 cadaveric knees. The ACL was divided into anteromedial and posterolateral bundles, then separated into 10 small bundles of 2-mm diameters, with preservation of their attachment sites marked with color markers. The positional relationship between the femoral and tibial attachments of each small bundle was investigated. Results A layered positional correlation of small bundles was found between the tibial and femoral attachments. Small bundles aligned in the anterior-posterior direction in the tibia corresponded to the bundles aligned in a high-low direction in the femur in flexion. The femoral attachment pattern was relatively similar in each specimen; however, the tibial attachment showed 2 patterns: an oblique type (12 of 20) and a transverse type (8 of 20). The posterior portion of the posterolateral bundle was separately attached to the medial and lateral portions of the tibial attachment. There was no fibrous insertion in the center of the posterior portion of the ACL tibial attachment in any specimen. In this bare area, there was fat tissue and vascular bundles. Conclusion Small bundles constituting the ACL showed a relatively layered arrangement between 2 attachments. The tibial attachment showed 2 patterns of oblique and transverse types, and the vascular bundles were located in the center of the posterolateral bundle. Clinical Relevance The results of this study of the normal ACL will provide insights for surgeons when placing grafts during anatomic ACL reconstruction.