Thanks for writing to me. Most common cause of inability to raise the am after a fall is a fracture. If you have already had an xray done, and the doctor ruled out a fracture, then the next common cause is rotator cuff tear. An MRI of the shoulder can reveal this really. Only if these two conditions are doled out, will I think of a neurological cause for inability to lift the arm. If you have any further queries, please wrote to :  bdbaruah@orthodoc.in Thanks again.