ACL is the abbreviation for “anterior cruciate ligament”.   It is one of four primary ligaments that provide stability to the knee by connecting the upper leg bone (the femur) to the lower larger leg bone (the tibia).

It is found in the middle front of the knee and forms a diagonal X with the PCL (or posterior cruciate ligament) behind it.  In fact, the word “cruciate” means “cross” and both ligaments are so named because of this X or cross formation.

The main role of the ACL is to prevent the tibia from sliding out in front of the femur.  It also provides stability against rotation for the knee joint.  The PCL prevents movement of the tibia behind the femur.

The ACL provides about 90% percent of the knee’s stability. 

The ACL and the MCL (the medial collateral ligament, which limits lateral movement on the inside of the knee) are the two most commonly injured of the four major knee ligaments.

Hamstring tendons (muscles on the back of the upper thigh) are frequently used in ACL reconstructions.

It is estimated that 90-95% of those who undergo an ACL reconstruction will return to full function within 6 months.