Contraindications to unilateral knee replacement are divided into absolute contraindications and relative contraindications, such as peri-articular infections, cardiopulmonary diseases, functional disorders and so on. 1. Absolute contraindications: absolute contraindications mainly include periarticular infections, mostly caused by repeated puncture in the joint, hormone drug injection and other conservative treatments. Active infection; flexor dysfunction, inability to actively flex the knee; asymptomatic knee ankylosis; neuroarthritis. These conditions need to be controlled before knee replacement surgery. 2. Relative contraindications: Relative contraindications mainly refer to severe thrombotic diseases, poor cardiopulmonary function can not tolerate surgery, or diabetes mellitus with high glucose level; previous history of osteomyelitis of femur and tibia; obvious insufficient blood supply to the knee joint; poor general condition, severe osteoporosis, and excessive obesity. All of these require the necessary medical treatment to improve before surgery is considered. Whether or not to perform surgery should be based on the doctor’s examination, diagnosis and judgment, and the timing of surgery should follow the doctor’s instructions for selection.