1.What can cause joint pain? (1) Structural damage: trauma leading to fracture, cartilage and ligament damage; (2) Non-specific inflammatory stimulation: mechanical and physical stimulation such as uric acid crystals; (3) Direct stimulation by infection factors: such as pathogenic bacterial infection; (4) Immune reaction: autoimmune disorder producing autoantibodies, leading to inflammation of synovial membrane, cartilage, ligaments and attachment points causing arthropathy. 2.What diseases can arthralgia be seen in? (1) Diffuse connective tissue diseases: such as rheumatoid arthritis, systemic lupus erythematosus, dry syndrome, dermatomyositis, scleroderma, vasculitis, etc. (2) Spinal arthropathies: such as ankylosing spondylitis, psoriatic arthritis, reactive arthritis, enteropathic spinal arthritis; (3) Degenerative arthropathies: such as osteoarthritis, usually seen above 40 years of age, the older the age, the higher the incidence, due to wear and tear of the joints (4) infectious arthritis: such as septic arthritis, tuberculosis arthritis; (5) metabolic diseases: such as gouty arthritis, commonly found in the first metatarsophalangeal joint of the foot, due to the consumption of seafood, alcohol and other induced purine metabolism disorders; (6) tumors: such as bone tumors, other parts of the tumor metastasis to the bone and joint; (7) neurological lesions: such as radicular pain caused by disc herniation; ( (8)Bone diseases with joint manifestations: such as osteoporosis; (9)Non-joint rheumatism: such as pain caused by strain, due to relatively high activity in the joint area, resulting in strain on the muscles and other soft tissues around the joint, which in turn causes pain, commonly seen in frozen shoulder, tennis elbow, etc.; (10)Pseudoarthralgia: such as skin nodular erythema, which manifests as painful skin erythema and sometimes feels similar to joint pain. (11) Others: trauma, hemophilia, drug reactions, growing pains in children, etc.