Chapter 28: Distraction Osteogenesis

Distraction osteogenesis is a staged procedure that takes many months to complete. It relies on the principle that tissue generation is stimulated when tissues are placed under consistent, moderate tensile forces. The application of these principles allows bone to be lengthened after an osteotomy or corticotomy by progressive distraction of the divided bone ends using a surgically placed device. Soft tissues respond well to the process and typically hypertrophy, not atrophy. The characteristics of bone formed during distraction osteogenesis are identical to those of normal mature bone. Not only are these principles applicable to patients with micrognathia such as hemifacial microsomia and Treacher Collins syndrome, they are useful for bone transport in long bones after segmental loss of the tibia or femur.1–3

Distraction osteogenesis (DO) generates vascularized bone with normal cortical and medullary features. An osteotomy is first made in the bone, thereby creating a bone gap, which is then progressively distracted. The tissue within the bone gap in DO is similar to callus, but it has collagen fibers that run parallel to the vector of distraction. This area is called the generate. It has the following five key components, all of which are duplicated except the central cellular proliferation zone (Fig. 28.1). 1. A central zone in which proliferation of mesenchymal cells occurs 2. Two transitional zones of vasculogenesis that sandwich the central zone 3. Two paracentral zones in which osteoid production occurs 4. Two mineralization fronts in which primary mineralization occurs 5. Two mature bone zones in which bone is progressively calcified to form cortical and cancellous elements During the final phase of DO, the less mature central portions of the generate mature and merge with the mineralization fronts for union to create bone that is ultimately indistinguishable from natural mature bone.1,2 Fig. 28.1 Five zones and four transition areas are present in the generate during the activation phase of distraction osteogenesis (DO): a central zone of proliferating mesenchymal cells (C), two paracentral zones, and two zones where mature bone meets the generate. The four transitional areas comprise two areas of vasculogenesis (v) and two mineralization fronts. (Adapted from Yu JC, Fearon J, Havlik RJ, et al. Distraction osteogenesis of the craniofacial skeleton. Plast Reconstr Surg 114:1e–20e, 2004.)

3. Iacobellis C, Berizzi A, Aldegheri R. Bone transport using the Ilizarov method: a review of complications in 100 consec- utive cases. Strateg Trauma Limb Reconstr 2010;5(1):17–22

4. Maheshwari S, Verma SK, Tariq M, Prabhat KC, Kumar S. Biomechanics and orthodontic treatment protocol in maxillo- facial distraction osteogenesis. Natl J Maxillofac Surg 2011;2(2):120–128 The benefits of external craniofacial distractors are that they provide flexibility for alteration of distraction vectors and they can prevent formal reoperation to remove the device. However, a second general anesthetic is still often required to facilitate removal of the percutaneous pins. Furthermore, these pins will leave visible external scarring at the pin sites. In contrast, internal devices involve an intraoral approach, thus avoiding cutaneous scarring. However, they provide distraction only in a single vector that cannot be altered after insertion, and a second procedure will always be required for their removal. Careful planning should prevent disruption of the tooth buds in all distraction approaches. Complication rates are similar with either device.1,2

Mandibular distraction can help patients achieve proper occlusion, but it does not correct a class III deformity which is essentially where the mandibular dentition is prominent with respect to the maxillary dentition (i.e., the patient is prognathic). Correction requires orthodontic intervention, resetting of the mandible posteriorly, or advancement of the maxilla, depending on the underlying pathology. Mandibular distraction is often performed to improve the airway in patients with disorders such as Pierre Robin sequence. It provides more space for the tongue and moves the tongue base more anteriorly.1–3

A review of 3278 cases of craniofacial distraction published in 2001 showed that an inappropriate vector was the most common complication, occurring in almost 9% of cases in which a single vector device was used.1 This complication occurred in 7.2% of cases in which multivector devices were used. Other complications included pin tract infection (5.2%), compliance problems (4.7%), and hardware failure (4.5%) (see Table 28.1). Table 28.1 Incidence of Complications in Craniofacial Distraction Osteogenesis Frequency (%) Compliance problems 4.7 Hardware failure 4.5 Device dislodgement 3.0 Premature consolidation 1.9 Pain that prevents distraction 1.0 Fibrous nonunion 0.5 Inappropriate vector (single-vector device) 8.8 Inappropriate vector (multivector device) 7.2 Pin tract infection 5.2 (Adapted from Mofid MM, Manson PN, Robertson BC, et al. Craniofacial distraction osteogenesis: a review of 3278 cases. Plast Reconstr Surg 108:1103–1114; discussion 1115–1117, 2001.)