Four months after the patella fracture surgery, knee joint fever is not a normal phenomenon, at this time the knee joint may still not be healed, the blood circulation in the knee joint is not good, at this time the knee joint is susceptible to infection, or complication of knee joint synovitis. 1. Infection: mainly due to bacterial infection caused by fever in the knee joint, in addition to the knee joint flexion pain, swelling, impaired mobility and other symptoms. Infection can be determined by knee joint puncture, and if purulent joint fluid is present, further bacterial examination can clarify the diagnosis. 2. Knee synovitis: symptoms such as knee joint fever may appear. For treatment, non-steroidal anti-inflammatory drugs such as ibuprofen are generally used for anti-inflammatory and analgesic purposes; pay attention to rest, avoid excessive movement of the joints after the operation, avoid the use of spicy and stimulating foods, and maintain balanced nutrition. Patella fracture surgery four months after the knee joint fever may have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.