If you cannot lift your arm, the first thing you need to do is to clarify whether you have suffered any trauma. Trauma can lead to soft tissue damage or even fractures, which can cause severe pain and significant dysfunction, so the arm cannot be lifted. If there is no trauma, we need to actively improve the examination to clarify whether there is any neurological damage, such as severe cerebral infarction and intracranial hemorrhage, which can cause damage to the brain nerves, resulting in different degrees of hemiplegia and inability to lift the arm. Severe cervical spondylosis, including spinal cord cervical spondylosis and neurogenic cervical spondylosis, can cause compression of the nerves that govern the arm, which can lead to nerve damage over time, and can also lead to the inability to lift the arm. Frozen shoulder, which is a sterile inflammatory disease around the shoulder joint, can cause limited movement of the shoulder joint, especially the abduction and extension of the shoulder joint. Chronic strain on the soft tissues of the arm caused by prolonged posture can also lead to weakness of the arm and inability to lift it.