Measurement · POGNPERP
Pogonion to Nasion-perpendicular
Loading the reference ceph.
Definition
The horizontal distance from Pogonion (bony chin) to the Nasion-perpendicular. McNamara's mandibular position read.
How
Erect the perpendicular to Frankfort through Nasion; measure Pog's horizontal distance to it (adults ≈ −4 to 0 mm; more negative in children).
Purpose
Positions the chin against the same facial vertical as the maxilla, so the two reads together localize a Class II/III to the correct jaw in plain millimeters — the language surgeons and parents both understand.
High
Above the norm reads as the chin sits at/ahead of the facial vertical (prognathic mandible).
Low
Below the norm reads as the chin sits well behind the facial vertical (retrognathic mandible — the common Class II finding, and a small-airway risk marker).
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Pogonion to Nasion-perpendicular here is a real reading and not a diagram.