The following are common causes of sudden inability to lift the arm: 1. Due to acute injury, which can lead to dislocation or fracture of the shoulder joint, thus limiting the function of the arm. 2. Pathological fractures that can be seen, such as persistent pain in the upper limb or around the shoulder joint, may be due to infection or tumor, leading to destruction of the bone, which can occur under the action of a slight external force. The corresponding fracture, resulting in dysfunction and the inability to lift the arm. 3.See muscle damage, such as a rupture of the long head tendon of the biceps tendon, etc., which can lead to pain and decreased muscle strength, resulting in symptoms of inability to lift the arm. 4.Some patients have cervical spondylosis, which is prone to corresponding cervical marrow damage under the action of external forces, resulting in dysfunction of the upper limb and symptoms of inability to lift the arm. 5.Some Acute episodes of strain injury or short term hypoxia and ischemia, that is, poor blood circulation, may also produce transient upper limb dysfunction.