The most common cause is osteoarthritis of the elbow joint. Patients with osteoarthritis of the elbow joint can have bony pain in the elbow joint, with narrowing of the joint space and stiffness of the joint, which can cause dysfunction when straightening the arm and cause pain when straightening. Second, medial epicondylitis or epicondylitis of the humerus is usually a clinical syndrome caused by chronic neuromuscular injury, which can also cause painful straightening of the arm. Thirdly, the symptoms can be relieved quickly due to bony tumors and cartilaginous tumors, which can cause arm pain and straightening. The symptoms should be diagnosed and treated at the hospital in time.