Cruciate Ligaments. These are found inside your knee joint. They cross each other to form an “X” with the anterior cruciate ligament in front and the posterior cruciate ligament in back. The cruciate ligaments control the back and forth motion of your knee. The anterior cruciate ligament runs diagonally in the middle of the knee.

https://orthoinfo.aaos.org/en/diseases–conditions/anterior-cruciate-ligament-acl-injuries/