Description of the ACL Injury
The cruciate ligaments controls the front - back motion between the femur and the tibia in the knee joint. The anterior cruciate ligament keeps the tibia from sliding too far forward in relation with the femur while the posterior cruciate ligament keeps the tibia from sliding too far backward in relation with the femur.


Mechanism of Injury
The anterior cruciate ligament injury occurs when the knee is forcefully twisted during a pivot mechanism or hyperextended. By far the most common cause is sports related.



Symptoms
During the acute injury usually the patient:

hears a pop when the ligament tears,
has pain and has to give up the match,
develops swelling within a few hours due to bleeding inside the knee and
feels that the knee gives way.


Chronic Phase
The symptoms of a chronic ACL tear are: pain, swelling and giving way. The pain and swelling usually resolve after two to four weeks, but the instability remains. In the beginning, the symptoms can occur while practicing pivoting sports but later they can also happen during daily activities. Long standing instability can lead to the development of early osteoarthritic changes in the articular cartilage due to the abnormal motion between the femur and tibia.