Pain on stairs after anterior cruciate ligament reconstruction consider joint stiffness, joint instability, infrapatellar fat pad inflammation, and so on. 1. Joint stiffness: After ACL reconstruction, pain on stairs may occur due to joint stiffness caused by the lack of formal rehabilitation exercises or the failure of exercises to achieve the effect. It can be gradually recovered through hot compresses and rehabilitation exercises. 2. Joint instability: there may be joint loosening and joint instability after reconstruction, which can be strengthened by strengthening the muscle exercise around the knee joint, such as quadriceps exercise or the exercise of hooking the leg, and wearing knee pads for protection. 3. Infrapatellar fat pad inflammation: the infrapatellar fat pad is extruded to cause aseptic inflammation, you can apply non-steroidal anti-inflammatory drugs, such as diclofenac sodium enteric coated tablets, and ultrashort wave physiotherapy. After the reconstruction of the anterior cruciate ligament, if the pain of going up the stairs persists, it is necessary to go to the hospital to check the specific cause of the disease, and strengthen the exercise or treatment for the cause of the disease.