The ACL, anterior cruciate ligament, is one of the structures that supports your knee joint by connecting from the backside of your femur (thigh bone) to the frontside of your tibia (shin bone). It stabilizes the knee joint by limiting the forward motion of the tibia (shin bone) on the femur (thigh bone) and becomes most taught when the knee is straight.
It can be injured, partially torn or completely torn, during a sudden cut or deceleration (often non-contact), hyperextension (when your knee is past straight), or pivoting in place combined with a force on the outside or inside of your knee. Most people describe hearing a "pop" when they tear their ACL. Symptoms of a torn ACL could include the following: persistent pain (or painless if its a complete tear), swelling, hemathrosis (bleeding within the joint noticed as swelling within 2 hours of injury), loss of range of motion at the knee, and possibly a feeling of instability or "giving way."
Depending on the severity of the injury, ACL injuries can be treated with physical therapy alone or surgically repaired with physical therapy afterwards. More information about ACL injuries can be found on Star Physical Therapy's Website at http://www.star-physicaltherapy.com/Injuries-Conditions/Knee/Knee-Issues/Anterior-Cruciate-Ligament-Injuries/a~338/article.html.
Heather Chatt PT, DPT, OCS, Cert. MDT