An ACL tear isn’t simply a broken ligament—it can fundamentally change how the knee moves, senses, and distributes force. In this episode, we unpack the biomechanics and biology of ACL injury, exploring rotational instability, proprioception, graft healing, tunnel placement, and how the surrounding structures adapt when the ACL can no longer do its job. We examine what happens when athletes keep playing through a tear, how stress fractures and other injuries alter knee loading, and why some structures become vulnerable to secondary damage. From graft choice and revision surgery to biologics, rehabilitation, and return-to-sport testing, we trace the long road from injury to recovery—and ask whether rebuilding the ligament truly restores the knee, or simply teaches the body a new way to move.