Controlled multiplanar distraction of the mandible part III: Laboratory studies of sagittal (anteroposterior) and horizontal (mediolateral) movements

Distraction osteogenesis has proven to be an effective technique for the co rrection of mandibular deficiencies. However, problems have been encountere d in achieving a final, idealized form of the mandible when using distracti on devices capable of moving the bone segments in only one dimension (unipl anar). Specifically, occlusal irregularities and deficiencies in lower faci al contour have been seen following uniplanar distraction. To address these problems, a distraction device capable of independent movements in three p lanes (multiplanar) was developed. Previously reported studies in a canine model have demonstrated that this device can successfully distract the mand ible along both the sagittal axis (anteroposterior or z-axis) and the verti cal axis (superoinferior or y-axis). This study examines the ability of the multiplanar device to distract along the sagittal and horizontal axes (med iolateral or x-axis). A total of 12 dogs were included in the study. All an imals underwent unilateral or bilateral mandibular distraction using an ext ernal multiplanar device. After a latency period of 5 days, primary distrac tion along the anteroposterior axis at a rate of 1mm/day for 10 days (10mm total) was performed. During the following 10 days, along with an additiona l 11mm to 20mm of anteroposterior axis distraction, concomitant secondary d istraction was performed along the horizontal (mediolateral) axis at a rate of 5 degrees/day (50 degrees total), Cephalometric radiographs were obtain ed preoperatively and at the conclusion of both anteroposterior and combine d anteroposterior-mediolateral distraction. Computed tomography (CT) scans were obtained preoperatively and at the end of consolidation (28 days), aft er which all animals were sacrificed and the dry skulls examined. In all an imals, distraction along the mediolateral or x-axis was found to change the anteroposterior projection of the mandible. Varus angulation of the device with respect to the midline of the mandible caused compression of the dist racted segments and reduced the anteroposterior thrust of the mandible. In contrast, valgus positioning of the device, with respect to the midline of the mandible, created the opposite effect, increasing the distracted length in the anteroposterior direction. The bone (mandibular) segments being dis tracted assumed the orientation of the device only for valgus positioning o f the device (producing a decrease in the bigonial distance). Conversely, t here was no effect from the mediolateral angulation on the distracted segme nts during varus positioning of the device. A possible explanation for this finding may be a greater resistance to an increase in the bigonial distanc e (varus positioning of the device) posed by obstruction of lateral movemen t of the condyle. This stands in contrast to a decrease in the bigonial dis tance observed following valgus positioning of the device. These findings c onfirm the clinical impression that distraction along the anteroposterior o r sagittal axis remains the critical or keystone therapeutic maneuver in di straction of the mandible. Mediolateral or horizontal axis distraction is b est used only as a supplementary movement; in essence, it only affects the anteroposterior dimension with little impact on clinically relevant changes to the bigonial distance.