Pain below the knee may be caused by patellofemoral arthritis, synovitis and osteochondritis dissecans of the tibial tuberosity. 1. Patellofemoral arthritis: chronic wear and tear or chondritis of the cartilage surface in contact with the patella and the femur can lead to pain in the knee joint, if the cartilage wear is more serious and the bone is exposed, that is, it turns into osteoarthritis. 2. Synovitis: in the process of walking or squatting, the synovial membrane is stimulated by certain aseptic inflammatory reaction, the synovial membrane appears to be swollen, and localized pressure and pain may appear, and in the process of checking, we can see that the patellar ligament on both sides of the knee appears to have the phenomenon of below-the-knee pain. 3. Tibial tuberosity osteochondritis: Tibial tuberosity osteochondritis is common in adolescents, when the tibial tuberosity is not fully developed, tibial tuberosity injury can occur after a strenuous exercise, resulting in pain below the knee. Pain below the knee can also be caused by other reasons, patients should consult the doctor in time, after clarifying the cause of the disease and active treatment.