Anatomic Double-Bundle ACL Reconstruction Patient Information Handout / Frequently Asked Questions Freddie H. Fu, MD, DSc (Hon), DPs (Hon) Sam G. Tejwani, MD Rebecca Singleton, PA-C University of Pittsburgh, Department of Orthopaedic Surgery What is the ACL and what does it do? The ACL, or Anterior Cruciate Ligament, connects the femur to the tibia in the center of the knee joint. It is made up of two functional bundles of tissue, the anteromedial (AM) and posterolateral (PL) bundles.  The AM bundle of the ACL primarily controls anterior (forward) movement of the tibia underneath the femur. The PL bundle of the ACL plays a significant role in rotational stability in the knee, such as in pivoting, twisting and jumping. [9,10] The ACL is critical to the stability of the knee during daily activities and sports that require twisting, pivoting, balancing, running and jumping. Fetal research has demonstrated that humans are born with a double-bundle ACL. Cadaver research has shown the two bundles are still present at the end of our lives. Anatomy of ACLACL AnatomyFetus 22 weeksFetus 22 weeksPLPLAMAMAMPLPLFetus 16 weeksChhabraet al, JBJS 2006et al, JBJS 200640 total specimens examined40 total specimens examinedNOTES:
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Cadaver studies have also demonstrated that the AM bundle is approximately twice as long as the PL bundle, and that the two bundles have a similar cross-sectional diameter. The AM and PL bundles have a complex relationship with each other. When the knee is straight they are parallel with each other. As the knee is flexed, they cross each other. In normal knees both bundles of the ACL can be seen during arthroscopic surgery: 2