The knee is made up of two crescent-shaped cartilage buildings named menisci, which act as shock absorbers and aid easy motion with the joint. Tears during the meniscus or cartilage can acquire from sudden twists, deep squats, or degenerative improvements eventually.  The orthopaedic surgeon will ask how the injury happened, https://www.theorthopaedicandpainpractice.com/what-happens-if-i-injure-my-posterior-cruciate-ligament/