ACL injuries are common sports injuries to the knee joint, with high-risk sports such as basketball, skiing, soccer, and rugby, mostly seen in adolescents who love sports. Acute ACL injuries are common when the knee joint is sprained during jumping and landing during sports, and sometimes the joint feels misaligned in the hand. Also, ACL injuries may be accompanied by meniscal and/or medial collateral ligament injuries, so early diagnosis and treatment is important. After ACL rupture, the typical symptoms are knee instability and a sense of misalignment, especially when doing sharp turns or sharp stops. For long ACL ruptures, there may also be symptoms of joint aliasing or interlocking due to meniscal tears. Even some movements in daily life such as turning can cause a knee joint misalignment sensation. For acute knee sprains, if the joint is significantly swollen and painful, it is necessary to apply ice immediately and go to the hospital for diagnosis and treatment as soon as possible. Current hospital testing technology is very convenient for diagnosing ACL injuries. Knee MRI can clearly visualize the ACL, as well as observe damage to the meniscus and articular cartilage. Patients with ACL injuries who continue to participate in jumping and twisting sports have repeated instability in the knee joint putting the meniscus and articular cartilage at high risk. Conservative treatment is only indicated for older patients with minimal sporting requirements, simple ACL injuries, or those who are physically unable to tolerate surgery, or who have adapted to the ACL deficit in the knee and do not wish to undergo surgery. The goal of conservative treatment is to restore most daily activities such as walking up and down stairs, walking, and light physical activity, while not being able to meet the demands of strenuous sports such as variable speed running, directional running, soccer, and basketball. While the previous conservative treatment included rest, ice, and brace braking, the new conservative treatment places more emphasis on functional rehabilitation. The rehabilitation process consists of two steps: the first step aims to eliminate the inflammatory response and restore joint mobility and muscle control. Ice is usually used to reduce pain and swelling, and joint mobility and patellar movement can be started immediately, along with muscle strength training to avoid muscle atrophy. The second step can be started once the patient returns to normal gait. The second step emphasizes N-cord and quadriceps strength training with open and closed chain exercises, ranging from high frequency and low intensity to low frequency and high intensity. Balance training and proprioceptive training are then performed. Conservative treatment should involve wearing a functional brace (ACL brace), which provides patients with ACL injuries with adjunctive stabilization to avoid abnormal misalignment or sprain of the knee and allows for a range of motion. The functional brace serves two purposes: first, to improve proprioception and second, to avoid reinjury. Surgical treatment The classic surgical treatment for ACL rupture is currently arthroscopic ACL reconstruction surgery. Graft is needed to replace the ruptured ACL during the surgery, and there are three major types of grafts available. The preferred graft is the use of an autologous N-cord tendon or a mid-1/3 bone-patellar tendon-bone graft, the second is an allograft tendon, and the third is an artificial ligament, all of which can be used as grafts to replace the ruptured ACL. In general, for young patients with high motor requirements, autologous tendons are our recommended first choice, while for patients with lower motor requirements and older age, allograft tendons may be considered. Surgery should be considered in younger patients with complete rupture of the ACL, combined with meniscal or other ligament injuries, participation in high sporting level sports, to reconstruct the ruptured ACL and repair the torn meniscus and articular cartilage to restore motor function and avoid premature joint degeneration and osteoarthritis. After surgery, a knee brace in the extended position is required, with double crutches and no weight-bearing on the affected limb. Functional exercises such as straight leg raising can be started on the second to third day after surgery, and passive knee flexion and extension activities can be practiced at the same time. We recommend the use of a knee passive motion machine (CPM), which can be used in the range of 0° to 90° for 4 weeks after surgery, and basically returns to normal in 6 to 8 weeks. A brace is required for protection and no weight bearing on the affected limb for 6 weeks after surgery, and a review is performed after 6 weeks to determine the time to start partial weight bearing. Generally, we ask patients to start partial weight bearing with the protection of a brace at 8 weeks after surgery. After recovery to normal ambulation (2-3 months after surgery) you can start to use a stationary bike for muscle strength and joint mobility recovery training, and start to gradually perform lower limb muscle strength recovery exercises. Running and jumping exercises can be started 3-4 months after surgery, simple sports can be resumed six months after surgery, and normal sports activities can be basically resumed one year after surgery.