Inability to abduct and externally rotate the arm is mainly considered to be related to shoulder joint lesion, nerve injury, muscle soft tissue injury and so on. 1. Shoulder joint lesions: when there are shoulder joint lesions, such as shoulder joint dislocation, fracture or frozen shoulder, etc., it is easy to affect the range of motion of the shoulder joint, thus producing the symptom that the arm can not be abducted and externally rotated. 2. Nerve injury: when there is brachial plexus nerve injury, brain injury or cervical spinal cord injury, it is easy to directly affect the motor function of the upper limb, thus the phenomenon of the arm not being able to abduct and externally rotate. 3. Muscle soft tissue injury: if the position of the arm has muscle soft tissue injury, such as rotator cuff injury, it is easy to have the symptom of local muscle contraction weakness, which affects the activity of the arm, and therefore leads to the arm can’t be abducted and externally rotated. If the arm can not be adduction external rotation, need to consult a doctor, a systematic assessment, clear specific causes, and then in the guidance of professional physicians targeted treatment, as soon as possible to restore the arm’s motor function, to prevent the later sequelae.