The anterior and posterior cruciate ligaments in the knee joint are also known as the “cruciate ligaments” because of their position in relation to each other, just like the Chinese character for “ten”. The cruciate ligament connects the femur to the tibia, or in simple terms, the thigh bone to the calf bone. The anterior cruciate ligament begins in front of the intercondylar tibial bulge and ends posteriorly, superiorly, and externally at the medial surface of the femoral epicondyle; the posterior cruciate ligament begins posteriorly at the intercondylar tibial bulge and ends anteriorly, superiorly, and internally at the medial surface of the femoral epicondyle. The anterior cruciate ligament prevents the tibia from moving forward and the posterior cruciate ligament prevents the tibia from moving backward, regardless of whether the knee is straightened or flexed. ACL injuries often occur in a variety of sports, the moment of injury, some people can even hear a “pop”, and then can not continue to exercise, if you can barely exercise, there will be knee instability, “playing soft leg” feeling. If the ACL rupture is difficult to heal, surgery should be performed to reconstruct the ACL arthroscopically, and post-operative knee flexion and extension exercises should be performed to strengthen the quadriceps. If the cruciate ligament injury is not treated properly, knee instability will persist and, over time, lead to increased wear and tear on the joint, which will then cause traumatic arthritis.