Overview
A torn ACL is an injury or teat to the anterior cruciate ligament (ACL). The ACL is one of the four main stabilizing ligaments of the knee which attaches the knee end of the femur (thigh bone) at the back of the joint and passes down through the knee joint to the front of the flat upper surface of the tibia (shin bone). It passes across the knee joint in a diagonal direction and with the PCL passing in the opposite direction, hence, the name cruciate ligaments. The role of the Anterior Cruciate Ligament is to prevent forward movement of the Tibia from underneath the femur. The Posterior Cruciate Ligament prevents movement of the Tibia in a backwards direction. Together these two ligaments are vitally important to the stability of the knee joint, especially in contact sports and those that involve fast changes in direction and twisting and pivoting movements. Therefore a torn ACL has serious implications for the stability and function of the knee joint.
Causes
Twisting force being applied to the knee whilst the foot is firmly planted on the ground or upon landing
Direct blow to the (usually outside) of the knee
Diagnosis
Physical examination
MRI
X-ray
Treatment
RICE (Rest, Ice, Compression, Elevation
Physical therapy
Surgery
Source: http://www.sportsinjuryclinic.net/sport-injuries/knee-pain/acl-injury