There are several possibilities for a patient to have pain in the arm. If a patient has sudden pain in the arm and cannot lift it, it is most likely due to an acute sprain or external force on the patient’s shoulder joint, which leads to damage to the rotator cuff, which can occur when the injured muscle is pulled when the arm is lifted; if there is prolonged heavy work, an acute muscle strain is suspected; if there is a history of trauma, a fracture or ligament strain is considered.