The anterior cruciate ligament (ACL) is one of the two cruciate ligaments inside the knee. It prevents the tibia (shinbone) from excessive forward motion relative to the femur (thighbone), and also prevents too much inwards twisting.
The word 'cruciate' means 'crossed', referring to the fact that the two cruciate ligaments cross over one another inside the knee - the one crossing over from front to back (the anterior cruciate ligament or ACL) and the other one crossing over from the back to the front (the posterior cruciate ligament or PCL).
The ACL is the more significant of the two but both are very important knee stabilisers. Rupture of either ACL or PCL is a major incident, often accompanied by a loud 'bang', and an inability to continue with the activity - with later swelling and collapsing of the joint.
Although a stretched ligament may heal satisfactorily on its own, a torn ACL usually requires reconstructive surgery.
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