How does one tear the ACL?

The ACL can be torn when the tibia is stressed suddenly in relation to the femur.

Usually the ligament is injured without contact with another player, eg running and cutting to the same side, landing on one foot while the body is still twisting (non-contact injury), or in situations where -

• the body is forward flexed
• the hip is abducted ('legs apart')
• the knee is internally or externally rotated with valgus ('stressed from the outer side')
• the foot is pronated('rolled over')

In this YouTube video, Michael Owen of the UK suffers a rupture of his cruciate ligament (2006) as his right knee contacts the ball. The angle of impact has caused a twisting movement of his lower leg.

Less frequently, the ACL is injured in a contact injury. Here you can see two types of contact injury - both of which can injure the ACL. On the left the knee is forcibly hyper-extended, and on the right the knee is forcibly hyper-flexed.

Watch this tackle on YouTube, and the man who rolls head-over-heels (red shirt).