title: Biomechanical considerations for distraction of the monobloc, Le Fort III, and Le Fort I segments.
abstract: BACKGROUND
  Distraction osteogenesis is effective for correction of severe maxillary and midface hypoplasia. The vectors controlling the segment to be moved must be planned. This requires knowledge of the physical characteristics of the osteotomized bone segment, including the location of the center of mass (free body) and the center of resistance (restrained body). The purpose of this study was to determine the center of mass of the osteotomized monobloc, Le Fort III, and Le Fort I bone segments.
  
  
  METHODS
  A dry human skull was used to sequentially isolate three bone segments: monobloc, Le Fort III, and Le Fort I. Each segment was suspended from three different points, and digital photographs were obtained from each suspension. The photographs were digitally superimposed. The center of mass was determined by calculating the intersection of the suspension lines.
  
  
  RESULTS
  The center of mass for the monobloc segment was located at a point 43.5 percent of the total height from the occlusal plane to the superior edge of the frontal bone supraorbital osteotomy. For the Le Fort III, it was located 38 percent of the total height from the occlusal plane to the superior edge of the osteotomized base of the nasal bones. For the Le Fort I, it was 53 percent of the total height from the occlusal plane to the superior edge of the osteotomized maxillary bone.
  
  
  CONCLUSIONS
  Knowledge of the location of the center of mass in the monobloc, Le Fort III, and Le Fort I segments provides a starting point for the clinician when planning vectors for advancement with distraction.
authors.affiliation: Chicago, Ill. From the Rush Craniofacial Center and the Department of Plastic and Reconstructive Surgery, Rush University Medical Center.
authors.forename: Alvaro A
authors.initials: AA
authors.lastname: Figueroa
authors.forename: John W
authors.initials: JW
authors.lastname: Polley
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Figueroa
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D005147:Facial Bones / Q000033:anatomy & histology / Q000502:physiology*; D006801:Humans; D019857:Osteogenesis, Distraction
references.citation: McCarthy JG, Schreiber J, Karp N, Thorne CH, Grayson BH. Lengthening the human mandible by gradual distraction. Plast Reconstr Surg. 1992;89:1–8.
references.citation: Polley JW, Figueroa AA, Charbel FT, Berkowitz R, Reisberg D, Cohen M. Monobloc craniomaxillofacial distraction osteogenesis in a newborn with severe craniofacial synostosis: A preliminary report. J Craniofac Surg. 1995;6:421–423.
references.citation: Polley JW, Figueroa AA. Rigid external distraction: Its application in cleft maxillary deformities. Plast Reconstr Surg. 1998;102:1360–1372.
references.citation: Polley JW, Figueroa AA. Management of severe maxillary deficiency in childhood and adolescence through distraction osteogenesis with an external, adjustable, rigid distraction device. J Craniofac Surg. 1997;8:181–185.
references.citation: Figueroa AA, Polley JW, Ko E. Distraction osteogenesis for treatment of severe cleft maxillary deficiency with the RED technique. In: Samchukov ML, Cope JB, Cherkaskin AM, eds. Craniofacial Distraction Osteogenesis. St. Louis: Mosby; 2001:485–493.
references.citation: Figueroa AA, Polley JW. Management of the severe cleft and syndromic midface hypoplasia. Orthod Craniofac Res. 2007;10:167–179.
references.citation: Figueroa AA, Polley JW. Management of severe cleft and syndromic midface hypoplasia. Semin Orthod. 2009;15:244–256.
references.citation: Fearon J. Halo distraction of the Le Fort III in syndromic craniosynostosis: A long-term assessment. Plast Reconstr Surg. 2005;115:1524–1536.
references.citation: Shetye PR, Boutros S, Grayson BH, McCarthy JG. Midterm follow-up of midface distraction for syndromic craniosynostosis: A clinical and cephalometric study. Plast Reconstr Surg. 2007;120:1621–1632.
references.citation: Nishimoto S, Oyama T, Shimizu F, et al. Fronto-facial monobloc advancement with rigid external distraction (RED-II) system. J Craniofac Surg. 2004;15:54–59.
references.citation: Ponniah AJ, Witherow H, Richards R, Evans R, Hayward R, Dunaway D. Three-dimensional image analysis of facial skeletal changes after monobloc and bipartition distraction. Plast Reconstr Surg. 2008;122:225–231.
references.citation: Kubler AC, Speder B, Zoller JE. Fronto-orbital advancement with simultaneous LeFort III-distraction. J Craniomaxillofac Surg. 2004;32:291–295.
references.citation: Satoh K, Mitsukawa N, Hosaka Y. Dual midfacial distraction osteogenesis: Le Fort III minus I and Le Fort I for syndromic craniosynostosis. Plast Reconstr Surg. 2003;111:1019–1028.
references.citation: Takashima M, Kitai N, Murakami S, et al. Dual segmental distraction osteogenesis of the midface in a patient with Apert syndrome. Cleft Palate Craniofac J. 2006;43:499–506.
references.citation: Hata S, Itoh T, Nakagawa M, et al. Biomechanical effects of maxillary protraction on the craniofacial complex. Am J Orthod Dentofacial Orthop. 1987;91:305–311.
references.citation: Lee KG, Ryu YK, Park YC, Rudolph DJ. A study of holographic interferometry on the initial reaction of maxillofacial complex during protraction. Am J Orthod Dentofacial Orthop. 1997;111:623–632.
references.citation: Nanda R. Protraction of maxilla in rhesus monkeys by controlled extraoral forces. Am J Orthod. 1978;74:121–141.
references.citation: Nanda R. Biomechanical and clinical considerations of a modified protraction headgear. Am J Orthod. 1980;78:125–139.
references.citation: Nanda R, Kuhlberg A. Principles of biomechanics. In: Nanda R, ed. Biomechanics in Clinical Orthodontics. Philadelphia: Saunders; 1996:1–22.
references.citation: Nanda R, Goldin B. Biomechanical approaches to the study of alterations of facial morphology. Am J Orthod. 1980;78:213–226.
references.citation: Ahn JG, Figueroa AA, Braun S, Polley JW. Biomechanical considerations in distraction of the osteotomized dentomaxillary complex. Am J Orthod Dentofacial Orthop. 1999;116:264–270.
references.citation: Figueroa AA, Polley JW. Management of severe cleft maxillary deficiency with distraction osteogenesis: Procedure and results. Am J Orthod Dentofacial Orthop. 1999;115:1–12.
references.citation: Figueroa AA, Polley JW, Ko EW. Maxillary distraction for the management of cleft maxillary hypoplasia with a rigid external distraction system. Semin Orthod. 1999;5:46–51.
references.citation: Sears FW, Zamansky MW. College Physics. 3rd ed. London: Addison-Wesley; 1960.
references.citation: Shetye PR, Giannoutsos E, Grayson BH, McCarthy JG. Le Fort III distraction: Part I. Controlling position and vectors of the midface segment. Plast Reconstr Surg. 2009;124:871–878.
references.citation: Gateno J, Teichgraeber JF, Xia JJ. Three-dimensional surgical planning for maxillary and midface distraction osteogenesis. J Craniofac Surg. 2003;14:833–839.
references.citation: Ortiz-Monasterio F, del Campo AF, Carrillo A. Advancement of the orbits and the midface in one piece, combined with frontal repositioning, for the correction of Crouzon's deformities. Plast Reconstr Surg. 1978;61:507–516.
references.citation: Havlik RJ, Seelinger MJ, Fashemo DV, Hathaway R. “Cat's cradle” midfacial fixation in distraction osteogenesis after Le Fort III osteotomy. J Craniofac Surg. 2004;15:946–952.
references.citation: Jensen JN, McCarthy JG, Grayson BH, Nusbaum AO, Eski M. Bone deposition/generation with LeFort III (midface) distraction. Plast Reconstr Surg. 2007;119:298–307.
references.citation: Santiago PE, Grayson BH. Role of the craniofacial orthodontist on the craniofacial and cleft lip and palate team. Semin Orthod. 2009;15:225–243.
references.citation: Delaire J. La croissance maxillaire: Deductions therapeutiques. Trans Eur Orthod Soc. 1971;81–102.
references.citation: Delaire J. Considerations on facial growth (particularly of the maxilla): Therapeutic deductions (in French). Rev Stomatol Chir Maxillofac. 1971;72:57–76.