Knee joint pain can be caused by a variety of factors, such as trauma, infection, degenerative joint disease, metabolic bone disease, osteoarthritic tumors, metabolic reactions and autoimmune diseases, etc. It is recommended to consult a doctor in time. 1. Trauma: such as bone, muscle, ligament and other structural injuries caused by external collision, as well as chronic joint injuries caused by over-activity and long-term weight-bearing. 2. Infection: such as osteomyelitis adjacent to the joints, soft tissue inflammation spreading to the joints, or intra-articular infection caused by unstrict aseptic operation during joint puncture. 3. Degenerative arthropathy: also known as hypertrophic arthritis, which is a disease caused by the destruction of articular cartilage due to degenerative changes in the joints. In addition to joint pain, the patients may also have symptoms such as limitation of joint movement, joint deformity, bone friction sound and other discomforts. 4. Metabolic bone disease: such as osteoporotic arthropathy, hyperlipidemic arthropathy, gout, diabetic arthropathy, etc. 5. Bone and joint tumors: such as osteoid osteoma, osteochondroma, osteosarcoma, chondrosarcoma, osteofibrosarcoma, etc., which occur in the knee joint can have the manifestation of knee joint pain. 6. Metabolic reaction and autoimmune disease: such as rheumatoid arthritis, systemic lupus erythematosus caused by arthropathy, etc., patients may also have morning stiffness, joint deformity, joint swelling and other discomforts. Patients with symptoms of knee joint pain, persistent unrelieved or with other discomforts, should promptly consult a doctor to improve the relevant examinations, such as routine blood, autoantibody test, X-ray, ultrasound, MRI, etc., so as to clarify the diagnosis of the disease, and if necessary, need to comply with the doctor’s instructions for the appropriate treatment.