Knee pain is one of the common ailments of the elderly, and it seriously affects their daily lives. The main causes are: 1. Osteoarthrosis of the knee joint: also known as osteoarthritis of the knee joint. The pain can be seen on X-rays as a sharp tibial spine, narrowing of the joint space, and formation of bone spurs at the edge of the joint. 2, rheumatoid arthritis: due to rheumatoid invasion of the synovial membrane of the joint and tendon sheath, causing synovial swelling, hypertrophy and joint effusion. The manifestation is morning knee stiffness, pain, local pressure pain is obvious, swollen knee joint fluid, skin temperature is elevated, if puncture can be drawn slightly cloudy yellowish fluid, quadriceps muscle atrophy. In the later stages, the knee joint is flexed and contracted, and the patient has difficulty walking. Improper treatment can lead to disability and paralysis. 3. Subpatellar fat pad strain: Pain in the knee radiates to the N-fossa and even along the posterior calf muscles to the heel, and the symptoms increase after exertion. Knee extension and flexion are limited, and squatting is difficult. The patient has weakness and difficulty in walking, and the pain is obvious when the knee is suddenly extended. If the fat pad is embedded in the joint space, limping and severe pain will occur. 4. Chondromalacia patellae: The patient has a history of long-term overwork or trauma. Intermittent pain in the knee, aggravated in a semi-squatting position, especially when going up and down stairs and when the joint starts to move, suddenly feels unstable and tender in the affected knee. Pain is felt when the patella is pressed and rotated during knee extension, and friction sounds appear. 5.Old meniscal injury: feeling of knee instability or slipping when walking, especially when walking up and down stairs or on uneven surfaces. The quadriceps muscle atrophy, about half of the patients occur joint strangulation, when barely straightened, patients feel pain is obvious, a little massage activity, hear the sound, the symptoms immediately disappear. Sometimes there is also a popping sound. 6, idiopathic osteonecrosis of the knee joint: mostly elderly obese women, patients often come to the clinic because of sudden severe pain in the medial knee during walking. The clinical examination shows local swelling, significant pressure pain, and limited activity. x-ray lateral films show dense bone in the medial femoral condyle near the joint surface, and sometimes free bodies are visible. 7, femoral head necrosis: The innervation of hip joint has closed pore nerve, femoral nerve and sciatic nerve, which is mainly closed pore nerve, and closed pore nerve also innervates the knee joint. Therefore, the hip joint lesion is manifested as knee pain, and osteonecrosis of the femoral head can be seen on X-ray. 8, free body in the knee joint: also known as “knee joint rat”. Patients above middle age, with symptoms of interlocking, i.e., weak legs or stuck joints, and grinding sounds under the patella, can be diagnosed by X-ray.