Your ACL crosses from the back of your femur to the front of your tibia. Although it acts like a strong brace for your knee, the ACL is injured more often than the PCL because it’s smaller and more susceptible to twisting.
Torn from a twist
Your ACL may be injured when you twist your knee beyond its normal range of motion. When you’re on skis, for example, you may “catch an edge”, twisting your lower leg outward or inward. You might hear or feel a pop and have pain, swelling or too much “play” in your knee. A complete tear of your ACL is like unraveling of rope fibers. A partial tear can also occur. You may injure other parts of your knee at the same time as you injure your ACL.
After an ACL injury, your knee more easily buckles, allowing the tibia to shift forward.