Stem cells are the most potent healing and regenerative factors present in our body. Healing subsequent to an injury or surgery involves a complex but specific sequence of events that requires various cells, such as proteins and growth factors to promote faster healing. When used in ACL reconstructive surgery, stem cells have the ability to promote graft ligamentization (maturation) and incorporation (healing) into bone. During ACL reconstructive surgery stem cells are commonly harvested from the upper tibia and then are injected into the graft subsequent to its placement.