Change in Mandibular Position in Patients with Syndromic Craniosynostosis after Midfacial Advancement with Distraction Osteogenesis

Thursday, October 10, 2013
Naeem Ali , Harvard School of Dental Medicine, Boston, MA
Katherine A. Brustowicz , Department of Plastic & Oral Surgery, Boston Children's Hospital, Boston, MA
Naoshi Hosomura DDS, Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA
Richard A Bruun DDS, Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Boston, MA
Bonnie L. Padwa DMD, MD, Depart of Plastic & Oral Surgery, Boston Children's Hospital, Boston, MA
LeFort III advancement improves the position of the midface in patients with syndromic craniosynostosis.1 The purpose of this study is to characterize the mandibular morphology in syndromic patients and to understand the changes that occur in the position of the mandible after midfacial advancement using distraction osteogenesis (DO). Information about how the mandible moves with midfacial advancement will help clinicians counsel patients regarding changes in facial profile and the need for future operations.

Data were collected from patients with syndromic craniosynostosis who had midfacial DO performed at a tertiary care center. Pre- and post-operative cephalograms of patients were digitized and traced to obtain linear and angular measurements. Mandibular morphology was characterized by measuring ramus height (Ar-Go), body length (Go-Me), mandibular length (Co-Pg), and gonial angle (Ar-Go-Me) prior to DO.  Preoperative and postoperative measurements were compared to each other and to standard age and sex-matched data from the Michigan Growth Study.2  Horizontal and vertical changes were compared using maxillary and mandibular protrusion/retrusion angles (SNA, SNB), and mandibular plane angle (SN-GoMe). The change in the facial profile was assessed using anterior facial height (N-Me) and the angle of convexity (N-A-Pg). A paired t-test analyzed significant differences between preoperative and growth study variables as well as between pre- and post-operative variables. Each cephalogram was traced twice to establish intra-examiner reliability.

Twenty-six patients (15 males and 11 females) with syndromic craniosynostosis underwent LeFort III midfacial advancement with DO at a mean age of 11 years.  Comparison of preoperative mandibular measurements to standard growth study data showed that syndromic patients have a longer ramus height (mean difference for Ar-Go, 3.67 mm ± 5.33) shorter mandibular body (Go-Me, 22.47 mm ± 7.01), shorter mandibular length (Co-Pg, 20.57 mm ± 8.16), a larger angle formed by the ramus and mandibular body (Ar-Go-Me, 6.68 degrees ± 7.44), and a protruded mandible (SNB, 3.67 degrees ± 8.23). Only 17 of the 26 patients (10 males and 7 females) had a pre- and post-operative cephalograms taken within a 2-year period. In these 17 patients, the maxilla moved forward (SNA, 70.61° ± 7.81 to 84.25° ± 7.57), the mandible moved backward (SNB, 82.90° ± 9.01 to 78.84° ± 7.40), the mandible moved downward (SN-GoMe, 34.64° ± 10.85 to 39.84° ± 10.57). The skeletal profile increased in vertical dimension (N-Me, 100.82° ± 13.42 to 109.14° ± 12.57) and changed from concave to convex (N-A-Pg, -19.19° ± 8.94 to 11.24° ± 12.76) following surgery. There were no significant differences for intra-examiner reliability.

As compared to the standard norms, patients with syndromic craniosynostosis possess a distinct mandibular morphology. Syndromic patients have a protruded mandible with a longer ramus height, shorter mandibular body, smaller mandibular length, and greater gonial angle. Correction of midfacial hypoplasia using LeFort III advancement with DO results in an inferior and posterior movement of the mandible, which contributes to the convexity and increased vertical dimension of the facial profile. Clinicians can use this information to counsel their patients regarding changes in facial profile and the need for adjunct procedures.

1. Kaban, L.B., West, B., Conover, M., Will, L., Mulliken, J.B., Murray, J.E. Midface position after LeFort III advancement. Plast Reconstr Surg. 73:758, 1984

2. Riolo, M.L., Moyers, R.E., McNamara, J.A., Hunter, W.S. Monograph 2, Craniofacial Growth Series. An atlas of craniofacial growth: Cephalometric standards from The University School Growth Study, The University of Michigan. Michigan: Center for Human Growth and Development, The University of Michigan; 1974.