Pain in the medial side of the right arm may be caused by the following: 1. Trauma, such as soft tissue contusions caused by direct violent blows or muscle or tendon strains caused by pulling or other injuries. 2. Cold may be present here. If the patient is underclothed or exposed to cold objects for a long time, it may cause spasm of the muscles and tendons here, and then cause pain. 3. There may be peripheral nerve lesions, for example, during the onset of neurogenic cervical spondylosis, it may cause pain here to stimulate the nerve roots, and then cause pain. 4. The presence of golf elbow, that is, the patient’s prolonged gripping action involving the hand, may lead to strain inflammation of the medial epicondyle of the humerus.