In general, patellar tenderness, fracture, ligament injury, osteoarthritis, local soft tissue contusion, etc. may cause pain in the patella of the knee. 1, chondromalacia patella, manifested as knee joint pain, fear of cold, may repeatedly appear swollen fluid, improve after rest, pain is more than relieved, will aggravate when going downstairs, in serious cases need to cross downstairs, and often suddenly weak fall when going downstairs or walking. 2, patellar ligament injury, is one of the most powerful ligaments in the body, patellar ligament for the continuation of the quadriceps tendon, located directly in front of the knee capsule. After the injury, local pain and swelling, knee movement is limited. Local hematoma, if present, requires aspiration therapy if necessary. 3. Patellar fractures can result in local swelling, bruising, swelling and pain, impaired knee movement, and inability to walk on the ground. If the displacement is obvious, external fixation in a cast can be performed conservatively. If the displacement is obvious, surgery must be performed to avoid pain after activity. 4, osteoarthritis, patellofemoral bone degeneration, resulting in walking knee pain and discomfort, restricted movement, local swelling, and even a “click” sound. 5, local soft tissue contusions, such as bumps, falls and other accidental injuries, can lead to local bruising, swelling, pain and limited movement of the knee. Generally bed rest, 2-4 weeks can gradually relieve. The above conditions are common causes of patellofemoral pain in the knee joint. If these conditions occur, the patient needs to rest, local braking, and prohibit activities on the ground. If the condition is not relieved, the patient needs to go to the hospital for examination and treatment.