Patellar tendonitis, tibial tuberosity osteochondritis, patellar tendon bursitis, fracture. 1. Patellar tendonitis: aseptic inflammation caused by repeated pulling of the patellar tendon due to frequent running and jumping, pain when jumping, walking is not affected. 2. Tibial tuberosity osteochondritis dissecans: mostly occurs in growing children, localized swelling, tenderness, passive knee flexion, active knee extension pain is obvious. 3. Patellar tendon bursitis: aseptic inflammation of the bursa due to strain or trauma, enlargement of the bursa causes pain in the infrapatellar bulge. 4. Fracture: tibial fracture occurs due to trauma, pain, swelling, and activity limitation. It is best to go to the hospital to check the pain of patellar luxation to get a clear diagnosis for further treatment.