Anatomic guidelines for the placement of external references for maxillary repositioning

External reference points, particularly Kirschner pins (K-wire), placed in the region of the nasion have been shown to improve the accuracy of maxillary vertical repositioning. Although no complications associated with this technique have been reported, there is a potential for injury to the anterior cranial fossa or frontal sinus. The purpose of this study was to measure the shortest distance from the nasion to the anterior cranial fossa and from the nasion to the frontal sinus. These measurements were used to establish anatomic guidelines governing safe placement of external reference point pins.

Twenty-seven cadaver heads were sectioned in the midsagittal plane for gross study. Using a Boley gauge, two specific measures were obtained: (1) distance from deepest depression of nasion to the most anterior and inferior projection of the anterior cranial fossa, and (2) distance from nasion to the most inferior aspect of the frontal sinus. All measurements were made in the midsagittal plane.

The average distance from nasion to anterior cranial fossa was 16.9 mm (range 13.0 to 20.0 mm) and the smallest distance, 13.0 mm, was seen in two specimens. The average distance from nasion to the frontal sinus was 6.2 mm (range 2.0 to 10.0 mm) and the smallest distance, 2.0 mm, was seen in three specimens.

Based on our findings, we recommend the following: (1) place pin to a depth of no more than 8 mm into bone, (2) place pin 5 to 10 mm inferior to soft tissue nasion, and (3) place pin in an anterosuperior to posteroinferior direction (i.e., roughly perpendicular to the nasal dorsum). When these anatomic guidelines are followed, one would expect minimal morbidity associated with the placement of ERP pins.