ACL augmentation is a relatively new technique which preserves and augments the ACL remnant using extra graft. Under arthroscopic examination, if any of the ACL bundles, anteromedial (AM) and posterolateral (PL), shows a partial tear remnant of reasonable size, thickness and tension, augmentation may be performed instead of reconstruct the whole ligament. Instead of removing the remaining stump, it would be preserved as much as possible, and a formal ACL reconstruction would be performed. A commonly used graft is single-bundle autogenous semitendinosus gracilis tendon. As the retaining ACL fiber contains mechanoreceptor responsible for proprioception, it is believed that better knee proprioception and postural sense could be achieved by preserving the ACL remnant. Also, better vascularization and stronger mechanical protection is expected as native ACL fiber is retained.