Knee ligaments are bands of fibrous tissue that bind the thigh & leg bones and keep them together. Ligaments maintain the anteroposterior & rotatory stability of the  knee. There are four ligaments in the knee. Among them,  anterior (ACL) and posterior (PCL) cruciate ligaments are inside of the knee. Lateral (LCL) and medial (MCL) collateral ligaments are outside of the knee. Torn or damaged ligament is reconstructed by arthroscope.