The ACL stabilises the knee for cutting, twisting and jumping and pivoting action. The anterior cruciate ligament is in the middle on the knee joint. If you tear an ACL, you'll typically feel or listen to a pop, really feel the knee shift out of position and develop significant swelling https://www.theorthopaedicandpainpractice.com/what-should-i-do-if-i-have-a-collateral-ligament-injury-of-the-knee/?_gl=1*xbbxlb*_up*MQ..&gclid=Cj0KCQjwkt6aBhDKARIsAAyeLJ2krYJSOuy5mZksrNqH-VDjQwW1ScD49yD8BUWysDG6u6bJPCSbXVUaAuCPEALw_wcB