The anterior cruciate ligament tethers the femur to the tibia, attaching to the femur within the notch.
The ligament is comprised of two bundles - the anteromedial and the posterolateral bundle, and they separately take the loads in flexion and extension.
Complex anatomy of the anterior cruciate ligament (ACL)
The ACL prevents the tibia from excessive forward motion relative to the femur, and also prevents too much inwards twisting. The wide footprint and the complexity of the two bundles have given surgeons a lot of headaches in their attempts over the years to reproduce the anatomy during a reconstruction procedure.
Anatomy of the anterior cruciate ligament. Duthon VB, Barea C, Abrassart S, Fasel JH, Fritschy D and Ménétrey J. Knee Surg Sports Traumatol Arthrosc. 2006 Mar;14(3):204-13. Epub 2005 Oct 19.
A Systematic Summary of Systematic Reviews on the Topic of the Anterior Cruciate Ligament. Anderson MJ, Browning WM III, Urband CE, Kluczynski MA and Bisson LJ. Orthop J Sports Med. 2016 Mar; 4(3): 2325967116634074.