Powers Ratio

The ration of the length of the line from the basion (anterior, midline rim of Foramen Magnum) to the posterior arch of C1 divided by the distance of the line from the anterior arch of C1 to the opisthion (posterior, midline rim of the Foramen Magnum).  An equal length in the two lines (quotient of one) is normal, whereas a ratio or quotient of first line divided by the second suggests a possible atlanta-occipital dislocation, ann odontoid fracture or a fracture of the ring of the atlas (C1).