Grabb-Oakes Line

Also referred to as the pB-C2 line. A line drawn through the odontoid that is perpendicular to a line extending from the posterior basion to posterior-inferior body of C2. The distance of the segment of this line from the anterior edge of the odontoid to the ventral dura represents the degree of encroachment of the odontoid into the upper spinal canal and potential ventral brainstem compression.