The anterior cruciate ligament (ACL) is one of 2 cruciate ligaments that aids in stabilizing the knee joint. It is a strong band made of connective tissue and collagenous fibers that originate from the anteromedial aspect of the intercondylar region of the tibial plateau and extends posterolaterally to attach to the medial aspect of the lateral femoral condyle, where there are two important landmarks; The lateral intercondylar ridge which defines the anterior boundary of the ACL, and the bifurcate ridge which separates the 2 ACL bundles. The ACL measures 32 mm long and is 7 to 12 mm wide. It has two bundles; an isometric anteromedial and a posterolateral bundle with more versatile length changes.
The anteromedial bundle is the tightest in flexion and is mainly responsible for anterior tibial translation (85% of the stability), whereas the posterolateral bundle is the tightest in extension, with the main role in providing medial-lateral and rotational stability (secondary restraint).
The ACL has 2200 N strength. The ACL and the posterior cruciate ligament (PCL) together form a cross (or an “x”) within the knee and prevent excessive forward or backward motion of the tibia relative to the femur during flexion and extension. Histologically, the ACL is composed of type I collagen (90%) and type III collagen (10%). It receives blood supply predominantly from the middle geniculate artery. Neurological innervation from the posterior articular nerve is a branch of the tibial nerve.
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