Injury to the medial collateral ligament of the knee occurs after artificial knee replacement and can be treated with conservative external fixation, surgical tendon suture, fixation at the stopping point of the tear, and tendon strengthening. 1. Postoperative injury to the medial collateral ligament refers to the possibility of injury to the medial collateral ligament when knee replacement is performed to release the medial contracture ligament, or to remove the medial meniscus, or when osteotomies are performed on the femur or tibia. 2. The medial collateral ligament injury manifests as pain in the medial side of the knee joint, which is aggravated during activities. Clinical examination of the medial knee is positive for pressure pain and percussion pain, and lateral stress test is positive. X-ray examination shows widening of the medial knee gap. If untreated, the prognosis can cause knee instability and accelerate the damage of knee prosthesis. 3. For artificial knee arthroplasty damage to the medial collateral ligament, without rupture and without avulsion at the femur and tibia, it can be treated conservatively by using external knee fixation support for 4 weeks, during which weightless knee flexion and extension exercises are performed, and then get out of bed after 4 weeks and gradually start weight bearing. 4. For ligament rupture, if the ligament is ruptured in the middle of the ligament, if it can be sutured directly, non-absorbable suture can be used for suturing. If the ligament is torn off at the end of femur or tibia, it can be fixed locally by anchors or screws with wires. If the ligament is missing much after rupture and cannot be sutured directly, artificial tendon or autologous tendon can be used for tendon reinforcement. The medial collateral knee ligament injury after artificial knee replacement suggests active consultation and physician-guided treatment.