Le Fort III distraction: Part I. Controlling position and vectors of the midface segment.

Background: The purpose of this investigation was to determine the response of the osteotomized Le Fort III midface bony segment to variations in the location and direction, or vector, of force application on using the rigid external distraction device.

Methods: This retrospective study involved 18 consecutive syndromic craniosynostotic patients (average age, 5.7 years) who underwent Le Fort III midface advancement distraction. Various cephalometric and novel landmarks, located on the mobilized Le Fort III segment and on the components of the distraction device, were identified before activation and at mid-activation. The direction and magnitude of change for these points were recorded.

Results: Based on the observed change in the position of the midface during distraction, the sample was divided into the following groups. In group 1 (n = 5), the Le Fort III segment translated forward and no rotation was noted. In group 2 (n = 3), the Le Fort III segment rotated clockwise and showed downward displacement. In group 3 (n = 6), the Le Fort III segment showed forward displacement and rotated counterclockwise. In group 4 (n = 4), the Le Fort III segment translated forward and downward.

Conclusions: Direction of movement and resultant change in position of the Le Fort III segment during distraction are directly related to the location and direction of force application. Translation forward, with minimal rotation, was achieved when the force was applied at a location 55 percent above the occlusal plane (between the occlusal plane and the nasion) and in a direction parallel to the maxillary occlusal plane.