Swelling and pain in the arm may be the result of fractures, epicondylitis of the humerus, venous thrombosis of the upper extremity, and other diseases such as fibroma. 1. Fracture: Fracture may be caused by direct violence, indirect violence, long-term strain, osteomyelitis, osteoporosis and other factors. Patients will have localized pain, swelling, dysfunction, and deformity, so patients with fractures in the arm will have swelling and pain. 2. Epicondylitis of the humerus: Epicondylitis of the humerus is considered to be caused by long-term or repeated activities of the forearm or wrist, and the patient will experience pain, swelling, burning, and loss of grip strength on the outer side of the elbow. Therefore, patients with epicondylitis of the humerus will show swelling and pain in the arm. 3. Upper extremity venous thrombosis: Upper extremity venous thrombosis may be caused by excessive activity of the upper extremity, venous cannulation, coagulation dysfunction and other factors. Patients will show swelling, pain and bruising of the upper limbs, which will lead to arm swelling and pain. 4. Other: arm swelling and pain may be caused by fibroma, radiculopathy, shoulder arthritis and tumor. It is recommended that patients with arm pain need to consult a doctor in time, and the doctor will choose the appropriate measures according to the cause of the treatment.