ANATOMIC GUIDELINES FOR THE PLACEMENT OF EXTERNAL REFERENCES FOR MAXILLARY REPOSITIONING

Objective. External reference points, particularly Kirschner pins (K-w ire), placed in the region of the nasion have been shown to improve th e accuracy of maxillary vertical repositioning. Although no complicati ons associated with this technique have been reported, there is a pote ntial for injury to the anterior cranial fossa or frontal sinus. The p urpose of this study was to measure the shortest distance from the nas ion to the anterior cranial fossa and from the nasion to the frontal s inus. These measurements were used to establish anatomic guidelines go verning safe placement of external reference point pins. Study design. Twenty-seven cadaver heads were sectioned in the midsagittal plane fo r gross study. Using a Boley gauge, two specific measures were obtaine d: (1) distance from deepest depression of nasion to the most anterior and inferior projection of the anterior cranial fossa, and (2) distan ce from nasion to the most inferior aspect of the frontal sinus. All m easurements were made in the midsagittal plane. Results. The average d istance 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 specim ens. 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 t hree specimens. Conclusion. Based on our findings, we recommend the fo llowing: (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 perp endicular to the nasal dorsum). When these anatomic guidelines are fol lowed, one would expect minimal morbidity associated with the placemen t of ERP pins.