The knee allows for flexion, extension and rotation.
The cruciate ligaments are structures related to knee stability located at the centre of the joint. The anterior cruciate ligament (ACL), as well as the posterior (PCL) are intra-articular.
The ACL originates on the femur, on the postero-lateral portion of the inter-condyle and is inserted anteriorly into the tibia. The tibia insertion is more resistant than the femoral.
This ligament has two bands: the antero-medial and the postero-lateral, and its purpose is to resist the anterior dislocation of the tibia as well as medial knee rotation. When this ligament is ruptured, the tibia projects itself onto the femur.
The main functions of knee ligaments are stabilization, kinematics control and prevention of dislocations as well as abnormal rotations that may cause lesions to the joint surface.
The ligaments, such as tendons, are dense collagen bands with little cellular material, which respond to linear tensions. Unlike tendons, ligaments have not so many parallel fibres and an enhanced amount of elastin, being able to support more stretching without causing damage to its structure. ACL and PCL have viscoelastic properties, allowing them to disperse energy, regulate their length and distribute load.