The only time ribs present any problem is on a sharp quartering away shot.
If the angle is to great and the shot is forward on the ribs instead of behind them the arrow will travel along the ribs without entering the chest cavity and exit out the front of the neck after traveling under the front shoulder blade.
I think this happens more than people realize, they think they made a great shot as the arrow will be covered in dark red blood and the deer will produce a decant blood trail for several hundred yards but no real harm has been inflicted. These deer do not bed down.And are never found.[:-]