Lower knee pain may be caused by trauma, patellar ligamentitis, osteochondritis of the anterior tibial tuberosity, and so on. 1. Trauma: the symptoms of pain below the knee can occur when there are contusions or bruises on the lower part of the knee joint. 2. Patellar ligament inflammation: the patellar ligament is located between the patella and the tibial tuberosity, when there is more jumping, it will cause inflammation of the patellar ligament, and there will be pain in the lower side of the knee. 3. Anterior tibial tuberosity osteochondritis: It is common for teenagers to suffer from repeated knee sprains or a large trauma that damages the tibial tuberosity, resulting in anterior tibial tuberosity osteochondritis, which manifests itself as pain under the knee. The pain below the knee may also be related to bursitis, meniscus injury, etc., and should be timely to the hospital, identify the cause of the disease, and under the guidance of the doctor for treatment.