Theoretical considerations for the surgical correction of mandibular deformity in hemifacial microsomia patients using multifocal distraction osteogenesis.

Purpose: This theoretical pilot study investigated the geometric changes necessary to normalize the mandibular shape in hemifacial microsomia. Using the mandibular deformity of a 13-year-old patient affected by hemifacial microsomia as an example, we addressed 2 main issues. First, the number of segments needed for adequate reshaping of the deformed mandible is evaluated. Second, the geometry of the intersegmental gaps resulting from reposition of the segments is correlated with established parameters of distraction osteogenesis to theoretically predict the practicability of correction using multifocal distraction osteogenesis.

Materials And Methods: Virtual surgery was performed on a solid mandible model created from computed tomography (CT) data from a patient with hemifacial microsomia type IIB. In the first step, ideal mandibular reshaping was achieved according to anthropometric standard measurements using 7 osteotomies. By scanning and superimposition of the virtual models and variation of distraction sites and numbers, we assessed the minimal number of osteotomies necessary for optimal correction of the deformity. Geometrical evaluation of the regeneration and assessment of the possibilities of continuous curved distraction were also performed.

Results: Three osteotomies were shown to be sufficient for complete mandibular reshaping. Using accepted parameters for distraction osteogenesis, the geometry of the regenerate allows for continuous curved distraction. However, simultaneous movements at several distraction sites result in interfering vector forces, making coordination of multifocal distraction difficult.

Conclusion: Theoretical assessment of a severe mandibular hypoplasia in hemifacial microsomia revealed the 3-dimensional (3D) complexity of the deformity for corrective procedures, especially distraction osteogenesis. Despite precise planning and transfer of the plan to the patient, multifocal 3D distraction may result in deviations from the planned result. Manipulation of the fresh regeneration may be necessary to correct inaccuracies.