Measurement · ANPERP
A point to Nasion-perpendicular
Loading the reference ceph.
Definition
The horizontal distance from A point to the Nasion-perpendicular — a vertical line dropped through Nasion at right angles to the Frankfort horizontal. McNamara's maxillary position read.
How
Draw Frankfort (Po–Or); erect the perpendicular to it through Nasion; measure how far A point sits anterior (+) or posterior (−) to that vertical (norm ≈ 0–1 mm).
Purpose
Positions the maxilla against a near-true-vertical reference instead of an angle — so it reads intuitively ('the maxilla is 4 mm back') and converts directly into surgical/orthopedic movement planning.
High
Above the norm reads as the maxilla sits anterior to the facial vertical (maxillary protrusion).
Low
Below the norm reads as the maxilla sits behind the facial vertical (maxillary retrusion — the finding that supports protraction/expansion approaches).
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so A point to Nasion-perpendicular here is a real reading and not a diagram.