Distraction osteogenesis of costochondral bone grafts in the mandible

Costochondral grafting for reconstruction of the Pruzansky type III mandible has given variable results. Lengthening of the rib graft by means of distraction had been advocated when subsequent growth of the grafted mandible is inadequate. This retrospective study reviews a series of patients with mandibular costochondral grafts who underwent subsequent distraction osteogenesis of the graft. A retrospective review identified two patient groups: group 1 consisted of individuals (n = 9) who underwent costochondral rib grafting of the mandible followed by distraction osteogenesis several months later at a rate of 1 mm/day. Group 2 consisted of patients with Pruzansky type II mandibles who had distraction osteogenesis without prior rib grafting (n = 9). The biomechanical parameters, orthodontic treatment regimens, and complications were examined versus patient age and quality of the rib graft. Distraction osteogenesis was successfully performed in six of the rib graft patients (group 1) and in all of the group 2 individuals. On the basis of the Haminishi scale, the computed tomographic scan appearance of the regenerate was classified as "standard or external" in six of the group 1 patients and as either "agenetic" or "pillar" (fibrous union) in the remaining three patients. In group 1, the average device was expanded 23 mm (range, 20 to 30 mm). Group 2 mandibular distraction results were all classified as either standard or external, and there was an average device expansion of 22.4 mm (range, 16 to 30 mm). The length of consolidation averaged 12.6 weeks in group 1, compared with 8.5 weeks in the traditional mandibular distraction patients (group 2). The mean shift of the dental midline to the contralateral side was 2.5 mm in group 1 versus 4.0 mm in group 2. Complex multiplanar and transport distractions were successfully performed on grafts of adequate bony volume. All four patients in group 1 with tracheostomies were successfully decannulated after consolidation. Rib graft distraction complications included pin tract infections in two patients, hardware failure with premature pin pullout in one patient, and evidence of fibrous nonunions in three young patients with single, diminutive rib grafts. In group 2, there were no distraction failures. Distraction osteogenesis can be successfully performed on costochondral rib grafts of the mandible; however, the complication rate is higher than in non-rib-graft patients. Performing the technique on older, more cooperative individuals seems to reduce this risk. In addition, placement of a double rib graft or an iliac bone graft of sufficient volume to create a neomandible with greater bone stock is an absolute requirement to decrease the risk of fibrous nonunion and provide a bone base of sufficient size for retention of the distraction device and manipulation of the regenerate.     

Manipulation of callus after linear distraction: a "lifeboat" or an alternative to multivectorial distraction osteogenesis of the mandible?

Despite impressive results, distraction osteogenesis of the mandible is still compromised by difficulties with vector control. Because of the action of the masticatory muscles, the gonion angle has the tendency to open, resulting in an open bite. We report two patients, aged 10 and 12 years, who developed a severe open bite during mandibular distraction. As a salvage procedure, manual shaping of the soft regenerate was done immediately after distraction. Uneventful bony consolidation was observed, which resulted in anatomically shaped gonion angles. The fact that a regenerate created by distraction osteogenesis can be molded to virtually any shape offers interesting perspectives for the correction of complex mandibular deformities.     

Removal of mandibular tooth follicles before distraction osteogenesis

Distraction osteogenesis is an innovative technique that has transformed the treatment of craniofacial malformations in young children. Bone generation obviates the need for graft material, which is in short supply in young patients, thus making possible surgical procedures on the craniofacial skeleton in young children. Sufficient mandibular volume is required for the osteotomy and placement of the device screws and/or pins. To have adequate bone stock and to facilitate distraction, the authors preoperatively examined all patients radiographically and selected those with tooth follicles that precluded successful osteotomy and pin placement for planned mandibular distraction. This report is of the first 13 children, aged 9 months to 6 years, who underwent predistraction enucleation. The osteotomy and device placement were performed successfully at least 4 months after enucleation. The described procedure has minimal morbidity and has resulted in successful subsequent distraction. The advantages, disadvantages, and cost-benefit issues are discussed.     

Remodeling of the temporomandibular joint following mandibular distraction osteogenesis in the transverse dimension

Transverse mandibular distraction osteogenesis involves moving the osteotomized segments of the mandible in either a varus or valgus direction. This maneuver allows for widening of the bigonial distance or for a lateral shift of an asymmetric mandibular midline. During this process, a significant amount of torque is placed on the mandibular condyles, because they act as the pivot point for the mandibular translation. Although standard linear distraction osteogenesis induces transient, reversible changes in the temporomandibular joint, it is not known what effect the varus and valgus stresses of transverse distraction have on the temporomandibular joint. We therefore designed a study to document the temporomandibular joint changes following various degrees of transverse distraction.Bilateral transverse mandibular distraction was performed on 10 adult, female mongrel dogs using an external, multiplanar mandibular distraction device. The distraction protocol was as follows: (1) complete osteotomy at the angle of the mandible, (2) 5-day latency period, (3) distraction rate of 1 mm/day, (4) rhythm of one turn per day, (5) linear activation 16 to 30 mm bilaterally, and (6) 8-week consolidation period. A variety of varus and valgus distraction vectors were applied to the mandible only after 10 mm of initial linear distraction had been achieved. Posteroanterior and lateral cephalograms were performed throughout the entire process. Pre-distraction and post-consolidation computed tomographic scans were also performed. Changes in mandibular conformation, axis of rotation, temporomandibular joint structure, and glenoid fossa changes were directly assessed by evaluating the postmortem craniofacial skeleton. The findings were compared with those of normal, age-matched mongrel dog skulls.Significant remodeling changes were observed in the temporomandibular joints of all animals involved in the study. The mandibular condyles demonstrated varying degrees of flattening and erosion at all contact points with the craniofacial skeleton. In some cases, the condyle became part of the distraction regenerate process and was hypertrophied in all dimensions. The condyles were frequently displaced out of the glenoid fossa, particularly on the side in the direction of varus distraction. When the latter occurred, a new fossa was created on the undersurface of the zygomatic arch. Varying degrees of mandibular rotation in the sagittal plane were also observed, which led to abnormal torquing of the condyles in the coronal plane, depending on whether the axis of rotation occurred primarily around the condyle or around the distraction regenerate zone.In conclusion, transverse mandibular distraction is an effective means of producing a varus or valgus shift in the gonion relative to the midsagittal plane. However, unlike linear or angular mandibular distraction, transverse distraction has a multitude of nontransient effects on the temporomandibular joint. Therefore it must be emphasized that in clinical practice, transverse distraction should be used cautiously. One must also be aware that such a maneuver in distraction can have negative effects on the temporomandibular joint.     

Mandibular distraction in neonates: a strategy to avoid tracheostomy

Over the past 5 years, the authors developed an application of mandibular distraction osteogenesis to eliminate existing tracheostomy. That experience led the authors to attempt mandibular distraction osteogenesis in neonates as an alternative before tracheostomy. Success with this approach using supporting objective airway measurements has been reported previously. This report includes six neonates diagnosed with Pierre Robin sequence. Of the six, five neonates ranging in age from 6 to 26 days (mean, 14.5 days) were treated by the authors with mandibular distraction over a 22-month period. The sixth neonate was treated with tracheostomy, because of other airway abnormalities. Findings included retrognathia, glossoptosis, incomplete cleft palate, and airway obstruction in each patient. Birth weights ranged from 2.8 to 3.2 kg. All patients were unable to control their airway during feeding, as evidenced by repeated episodes of choking and obstruction. Resting oxygen saturations were in the 70 to 80 percent range in all patients, with further deterioration during attempted feeding. Bronchoscopy was performed in all patients under anesthesia before distraction. Recurrent near-complete and intermittent complete airway obstruction were present in all patients at the level of the tongue base. There was a consensus by a pediatric intensivist, a pediatric anesthesiologist, and a pediatric otolaryngologist in all cases. Each patient met all criteria requiring ventilation for life support. Tracheostomy would be required if mandibular distraction osteogenesis was not performed, or if it failed. Patients with other airway abnormalities were not considered for treatment. Maxillomandibular disharmony measured at the midline ranged from 8 to 15 mm (mean, 11.2 mm). Active distraction was performed at the rate of 1 to 2 mm a day, with a consolidation period of 4 weeks. Total time of treatment was less than 6 weeks in all cases. All patients were extubated by the completion of active distraction. Distraction distance ranged from 8 to 15 mm (mean, 12.4 mm). All patients were discharged to home on apnea monitors, the use of which was discontinued after 90 days with no further apneic events. Weight gains met or exceeded the average 500 g a month after distraction. Bronchoscopy at the time of distractor removal showed correction of airway obstruction at the tongue base. Radiographs showed bilateral ossification of the distraction sites. Tracheostomy was avoided in all cases selected for treatment by distraction. Patient follow-up range was 9 to 22 months. In selected Pierre Robin sequence patients with tongue base airway obstruction, mandibular distraction osteogenesis can successfully avoid the need for and the associated mortality and morbidity of indwelling tracheostomy.     

Transport distraction osteogenesis: a new method to heal adult calvarial defects

Popularized by Gavril Ilizarov in the 1960s, monofocal distraction osteogenesis has become a well-established method of endogenous bone engineering. This revolutionary surgical technique has significantly augmented the available reconstructive orthopedic and craniomaxillofacial procedures. Bifocal distraction osteogenesis, or bone transportation, is a modification of monofocal distraction that involves moving a free segment of living bone to fill an intercalary bone defect. Bifocal distraction has been applied successfully to reconstruct complex mandibular and long bone defects. Because traumatic or postsurgical calvarial defects do not spontaneously heal in humans older than 18 to 24 months of age, we hypothesized that bifocal distraction osteogenesis could be applied to the skull to close critical size calvarial defects. Critical size (15 x 15 mm) calvarial defects were created in eight New Zealand White rabbits. Next, a 15-mm x 10-mm calvarial box osteotomy was created just anterior to the skull defect. This osteotomy created a free bone segment that could be transported. A custom-made transport distraction device was fixed into place and the skin incision was closed. After a 4-day latency period, the distraction device was activated (0.5 mm once daily for 30 days) in seven animals; the distraction device in one animal was not activated and served as a control. All animals underwent 30 days of consolidation and were then killed. Radiographs and computed tomographic scans were performed at the following time points: end of latency period (postoperative day 4), mid-distraction (postoperative day 19), and end of consolidation period (postoperative day 64). Gross and histologic analysis was performed to evaluate the quality of the bony regenerate. The control animal healed with a fibrous union. Complete closure of the skull defects was observed in five of seven rabbits at the end of the consolidation period. One animal was removed from the study because of an early loosening of the distraction device, and one was removed because of device failure. Of the remaining five animals that completed the distraction protocol, radiographs and computerized tomographic scans showed successful ossification in all five rabbits at the end of the consolidation period. This study suggests that transport distraction osteogenesis is a promising technique that may be applied to a variety of commonly encountered craniofacial problems such as nonhealing calvarial defects.     

Effect of distraction osteogenesis of the mandible on upper airway volume and resistance in children with micrognathia

Children with craniofacial anomalies often have compromise of the upper airway, a condition with potential for morbidity and mortality. In children with microretrognathia, the diminutive size and retruded position of the mandible reduces the size of the oropharynx, thereby predisposing to glossoptosis and airway obstruction. Although several authors have reported successful use of mandibular distraction osteogenesis to alleviate this type of upper airway obstruction, the physiologic relationship between changes in mandibular shape, size, and position and upper airway dynamics remains undefined. The purpose of this study was to develop methodologies to quantitatively evaluate upper airway dynamics in children with micrognathia both before and after mandibular distraction osteogenesis. The patient population consisted of four children with micrognathia who had successfully undergone upper airway stabilization by bilateral mandibular distraction osteogenesis. The data used were digitally archived computed tomographic scan data from high-resolution, thin-slice head computed tomographic scans obtained before and after mandibular distraction. Upper airway evaluation was performed in two ways: static and dynamic. Static analysis consisted of computer quantification of predistraction and postdistraction mandibular and upper airway volumes using Analyze imaging software. Dynamic analysis consisted of fabrication of rigid stereolithographic hollow cast models of the upper airway produced from computed tomographic scan data. Models were used for characterization of upper airway resistance and flow patterns as related to respiration. After distraction osteogenesis, mandibular total volume increased 32, 32, 18, and 25 percent (mean, 27 percent) and upper airway volume increased by 20, 31, 23, and 71 percent (mean, 37 percent). A significant decrease in flow resistance, both inspiratory and expiratory, was observed in the patient with the greatest upper airway volume increase (71 percent) after distraction. After distraction, the inspiratory resistance was diminished by 51 percent and the expiratory resistance diminished by 85 percent. However, the three patients with more modest upper airway volume increases of 20 to 31 percent demonstrated no statistically significant change in flow resistance after distraction. Results of this study support the conclusion that distraction osteogenesis of the micrognathic mandible increases the volume of the upper airway, roughly paralleling the increase in mandibular volume. In the biomechanical airway model studied, upper airway volume expansion has been shown to be able to decrease the flow resistance over the length of the airway, presumably secondary to an increase in the average cross-sectional area. The artificial rigidity of the stereolithographic "airway" compared with the elasticity of the human upper airway may account for the insensitivity of this model to smaller but clinically significant airway changes.     

Mandibular distraction osteogenesis in Pierre Robin sequence: application of a new internal single-stage resorbable device

Pierre Robin sequence may result in physiologically significant obstructive apnea in the neonatal and infant period. This may be life threatening and is most often treated by tracheostomy. To avoid tracheostomy or allow for early decannulation in severely affected infants and children, the authors have developed a new class of neonatal and infant mandibular bone distraction devices. These devices require a single operative procedure for placement and no operative removal is necessary. Fifteen infants (aged 7 days to 11 months; mean age, 3 months) and five children (aged 2 to 8 years; mean age, 5.5 years), 10 boys and 10 girls, with severe obstructive apnea and Pierre Robin sequence were treated with the mandibular infant devices over a 24-month period. Tracheostomy was avoided in 14 patients, whereas five of six patients who had previous tracheostomy were decannulated after mandibular distraction. The final tracheostomy status in one patient will be determined after surgery for gastroesophageal reflux. There were no major complications and no structural device failures.     

Computer planning for distraction osteogenesis

Distraction osteogenesis of the mandible has found an application in the treatment of patients with a variety of different mandibular deformities. Compared with the relatively simple unidirectional distraction of long bones as described by Ilizarov, the three-dimensional distraction of the mandible is extremely complex. Whereas experience with orthognathic surgery clearly demonstrates that careful presurgical planning is necessary to achieve predictable outcomes, there are few reported methods for the planning of mandibular distraction. The authors have developed a method for planning distraction osteogenesis of the mandible that involves the use of three-dimensional modeling and animation to simulate distraction osteogenesis in virtual reality. The first step in the authors' treatment planning process is to obtain a three-dimensional computerized scan of the facial skeleton. From this scan, a three-dimensional wire-mesh model is built using animation software. With the same software, a virtual distractor is built and installed on the wire-mesh model. The osteotomies and the distraction process are then simulated. Finally, a recipe for sequencing the linear and angular changes of the distractor is calculated. The authors have used this planning process in seven patients (age range, 4 to 10 years): four with unilateral mandibular deformities and three with bilateral. The planning process has yielded predictable and reproducible results.     

Evaluation of Inferior Alveolar Nerve Regeneration by Bifocal Distraction Osteogenesis with Retrograde Transportation of Horseradish Peroxidase in Dogs

Background

Bifocal distraction osteogenesis has been shown to be a reliable method for reconstructing segmental mandibular defects. However, there are few reports regarding the occurrence of inferior alveolar nerve regeneration during the process of distraction. Previously, we reported inferior alveolar nerve regeneration after distraction, and evaluated the regenerated nerve using histological and electrophysiological methods. In the present study, we investigated axons regenerated by bifocal distraction osteogenesis using retrograde transportation of horseradish peroxidase in the mandibles of dogs to determine their type and function.

Methods and Findings

Using a bifocal distraction osteogenesis method, we produced a 10-mm mandibular defect, including a nerve defect, in 11 dogs and distracted using a transport disk at a rate of 1 mm/day. The regenerated inferior alveolar nerve was evaluated by retrograde transportation of HRP in all dogs at 3 and 6 months after the first operation. At 3 and 6 months, HRP-labeled neurons were observed in the trigeminal ganglion. The number of HRP-labeled neurons in each section increased, while the cell body diameter of HRP-labeled neurons was reduced over time.

Conclusions

We found that the inferior alveolar nerve after bifocal distraction osteogenesis successfully recovered until peripheral tissue began to function. Although our research is still at the stage of animal experiments, it is considered that it will be possible to apply this method in the future to humans who have the mandibular defects.     

Histogenesis of skeletogenic tissue in bone regeneration during distraction

Light and electron microscopy were employed to study the histogenesis of the skeletogenous tissue during stable distraction osteosynthesis according to G. A. Ilizarov. Osteosynthesis proceeded on the basis of the invariably existing fibrillar connective tissue growth plate situated in the medium part of the distraction regenerate. Osteogenesis was continuously accompanied by angiogenesis. Preservation of the connective tissue plate is accounted for by the stimulating influence of distraction on fibrillogenesis. The authors suggest the common character of the histogenesis of the vascular and bone tissues in the connective tissue blastema of the interfragmental distraction regenerate.     

To distract or not to distract: an algorithm for airway management in isolated Pierre Robin sequence

Approaches advocated for treatment of airway obstruction among neonates with Pierre Robin sequence include positioning, tongue-lip adhesion, mandibular distraction, and tracheostomy, with no established guidelines regarding which modality is appropriate for a specific patient. This report proposes an algorithm for the management of neonatal upper airway obstruction among patients with isolated Pierre Robin sequence. Data for 21 patients with isolated Pierre Robin sequence who were treated by one surgeon during a 9-year period were reviewed. Eighteen patients presented during the first 1 week of life and three patients presented late, between 12 and 33 months of age. Follow-up periods ranged from 9 to 70 months (median, 33 months). Successful airway management was achieved with positioning alone for 10 patients, with tongue-lip adhesion for seven of nine patients, with tracheostomy for two patients, and with mandibular distraction for three patients. Changes in the maxillary-mandibular discrepancy were significant with natural mandibular growth during the first 1 year of life (p < 0.0001). Oromotor studies performed 3 months or more after tongue-lip adhesion reversal (n = 9) demonstrated no appreciable deficits in tongue function, relative to other children with cleft lips/palates. A multidisciplinary team should evaluate all patients with isolated Pierre Robin sequence, to fully assess the maxillary-mandibular relationship, anatomically define the site of airway obstruction, and identify feeding difficulties. Patients should be evaluated for episodes of desaturation occurring spontaneously, during feeding, or during sleeping. Patients with desaturation should be further evaluated with double endoscopy (nasoendoscopy and bronchoscopy). If the airway obstruction is localized to the tongue base alone and cannot be controlled with positioning, then tongue-lip adhesion is the initial treatment of choice, because such patients demonstrate significant mandibular growth during the first 1 year of life. Mandibular distraction among neonates is reserved for failures of tongue-lip adhesion in which isolated tongue-base airway obstruction is documented. Neither of the patients who experienced failure of tongue-lip adhesion in this series would have been a candidate for distraction with the algorithm presented. Avoiding routine neonatal distraction serves to avoid facial scarring, nerve and tooth bud injury, and potential disturbances of intrinsic mandibular growth. Patients with persistent respiratory difficulties beyond age 9 months require reevaluation for multiple sites of airway obstruction. Mandibular distraction may be one of several modalities required to avoid tracheostomy for such patients.     

Distraction osteogenesis in correction of micrognathia accompanying obstructive sleep apnea syndrome

To evaluate the effect of distraction osteogenesis in correction of micrognathia accompanying obstructive sleep apnea syndrome, a total of 28 patients with different severities of obstructive sleep apnea syndrome underwent mandibular distraction osteogenesis. A total of 51 distraction devices were placed for bilateral distraction in 23 patients and for unilateral distraction in five patients. The mean age of patients was 21.2 years (range, 3 to 60 years). Eleven patients had micrognathia accompanying obstructive sleep apnea syndrome secondary to bilateral temporomandibular joint ankylosis, and 10 patients had micrognathia accompanying obstructive sleep apnea syndrome secondary to unilateral temporomandibular joint ankylosis. Three patients had developmental micrognathia accompanying obstructive sleep apnea syndrome. The other four patients had micrognathia and concomitant obstructive sleep apnea syndrome induced by trauma, infection, or tumor resection. Each patient had been evaluated preoperatively and postoperatively with cephalometry and polysomnography. Mandible advancement ranged from 9 to 30 mm (average, 20.4 mm) and was successfully achieved after distraction. Fine new bone formed in the distraction gap when the distraction devices were removed 3 to 4 months after distraction was completed. No infection or other complications occurred in any patients. Complete curative effects were achieved in nine severe, six moderate, and eight mild obstructive sleep apnea syndrome patients after distraction, and the other five patients had been improved to the mild level. After distraction was completed, the posterior airway space was increased on average from 4.6 mm to 12.5 mm and the sella-nasion-point B angle was increased on average from 66 degrees to 75 degrees on cephalometric studies. The polysomnographic examination showed that the apnea hypopnea index was lowered on average from 58.0 to 3.15, and the lowest oxygen saturation was increased on average from 77 percent to 90.3 percent after distraction was completed. The follow-up period was 3 to 61 months (average, 18.1 months). The curative effect was stable and no relapse occurred. Therefore, the authors conclude that mandibular distraction osteogenesis is an effective method for correcting micrognathia accompanying obstructive sleep apnea syndrome. Compared with other current routine surgical procedures, it has many advantages, such as low risk, simple manipulation, high curative rate, low relapse rate, and stable result. It is presently the most effective method for the treatment of this difficult and complicated disorder.     

Mandibular distraction in temporomandibular joint ankylosis

Condylar damage during childhood can produce ankylosis and alteration of the mandibular growth. In case of unilateral ankylosis occurring in early childhood, a mandibular hypoplasia of the affected side may develop. The patients have limitation of mouth opening, facial asymmetry, and chin deviation toward the affected side. The aims of this study are to show the use of distraction osteogenesis in mandibular hypoplasia associated with ankylosis and to present our experience with a new therapeutic option for the treatment of mandibular hypoplasia with unilateral ankylosis in the childhood consisting of the association of arthroplasty to treat the ankylosis and mandibular distraction to correct the facial asymmetry, both accomplished in the same surgical procedure. From November of 1996 to November of 1997, three male patients aged 2, 7, and 13 years with mandibular hypoplasia and ankylosis were treated by distraction osteogenesis. An arthroplasty consisting of the resection of the ankylotic block and interposition of a temporalis muscle flap, plus coronoidectomy was done in two of them and mandibular distraction was done in all three patients. Articular functional rehabilitation began on the first postoperative day. Mandibular distraction began on the fifth postoperative day with a rate of 1 mm per day, ending when the facial symmetry was achieved. From the first postoperative day, an increase in the mouth opening was achieved; this increase continued until ending the distraction. The average duration of distraction was 22 days. Average duration of consolidation was 6 weeks. Oral opening increased from 10 mm to 35 mm in the 7-year-old patient, from 9 mm to 27 mm in the 2-year-old patient, and from 14 mm to 38 mm in the 13-year-old patient. To date, oral opening and facial symmetry persist. Osseous mandibular distraction together with arthroplasty offers an excellent new alternative for treatment of patients with mandibular hypoplasia and associated ankylosis, with minimal morbidity and complications.     

Long-term outcome study of bilateral mandibular distraction: a comparison of Treacher Collins and Nager syndromes to other types of micrognathia

A long-term follow-up study of patients who underwent bilateral mandibular distraction is presented, and the results of patients with Treacher Collins syndrome and Nager syndrome are compared with results for other forms of congenital micrognathia. It was hypothesized that the factors responsible for the predetermined, syndrome-specific shape of the mandible in patients with Treacher Collins and Nager syndromes would alter the long-term results of linear (uniplanar) distraction of the mandible. Thus, over time, the mandibles would remodel to preoperative form while maintaining the increase in volume. To investigate this hypothesis, all patients treated with bilateral mandibular distraction who had at least 1.5 years of follow-up, including satisfactory cephalometric examinations, were retrospectively reviewed. Two groups were identified. Group 1 (n = 6) were Treacher Collins and Nager syndrome patients (ages, 2 to 13 years; mean, 5.2 years) and group 2 (n = 6) included other forms of bilateral, congenital micrognathia (ages, 1.5 to 19 years; mean, 8.4 years). Serial cephalometric measurements were recorded before distraction, after distraction, and at least 18 months after distraction. Mandibular mean linear distraction distance (as recorded on the device) averaged 24.5 mm in group 1 and 26.2 mm in group 2. In group 1, the antegonial angle (angle from the mandibular plane to the top of the antegonial notch) decreased after distraction by 3.8 degrees, and the antegonial notch height was reduced by 1.6 mm. The posttreatment morphologic change was modified significantly over time, with a 3.7-degree increase of the antegonial angle and a 1.2-mm deepening of the antegonial notch. In group 2, the immediate reduction in height of the antegonial notching was subtler; however, long-term recurrence of the antegonial notching was also observed. At the end of distraction, the mean group 1 gonial angle became 8 degrees more obtuse. In contrast, patients in group 2 developed a more acute angle (mean, 8 degrees). The mandibles of the Treacher Collins syndrome patients (group 1) maintained their more obtuse postdistraction gonial angle during the period of follow-up, whereas over time this change was reversed in group 2 patients. In conclusion, experience with bilateral mandibular distraction has demonstrated that long-term determination of mandibular form is more complex than either the amount of distraction or the direction of the distraction vector. The underlying genotype and the musculoskeletal milieu must be taken into account when planning distraction, as these factors tend to remodel the mandible into its preoperative shape over time, despite the fact that the increased mandibular volume and projection are maintained.     

Distraction osteogenesis of the craniofacial skeleton

In summary, distraction osteogenesis is a safe and effective means of achieving bone lengthening. These techniques were originally applied to the long bones of the extremities; over the past 10 years they have been effectively applied to the bones of the craniofacial skeleton. The new bone regenerate that is observed after distraction osteogenesis is stable, and relapse rates after skeletal advancement are believed to be lower than with conventional osteotomy and bone graft techniques. There is considerable variability in distraction protocols employed in clinical practice, including differences in the types of devices used and in the rate, rhythm, latency, and period of consolidation for distraction osteogenesis. The greatest application for distraction osteogenesis in the craniofacial skeleton has been with mandible lengthening, for which there is presently a 10-year clinical experience. Midfacial advancement is a newer application of distraction osteogenesis, for which clinical experience has been accrued over the past 5 years. This latter experience indicates that distraction osteogenesis is a viable treatment option for lengthening of the hypoplastic mandible and midface. These techniques have advantages over conventional means of bone graft and rigid fixation because of the quality of the bone regenerate, the decrease in the long-term relapse rate of the advanced bone segments in both the mandible and the midface, and the simultaneous soft-tissue elongation that accompanies the distraction process. Distraction osteogenesis is particularly applicable to the correction of severe deformities of the mandible and midface in children with developmental hypoplasia and syndromic craniosynostosis. However, growth is an added variable in this patient population. The amount of overcorrection in lengthening of the hypoplastic bone required to compensate for continued growth discrepancy of the adjacent facial bones is difficult to predict. Therefore, the families of these patients should be informed that many children will require repeated operations at a later age as they reach skeletal maturity.     

Distraction osteogenesis of the porcine mandible: histomorphometric evaluation of bone

Distraction osteogenesis is a technique for skeletal lengthening that exploits the body's innate capacity for bone formation in response to tension forces on the repair callus. The authors developed a distraction osteogenesis model with a semiburied device in the Yucatan minipig mandible because of similarities between human and porcine mandibular anatomy, temporomandibular function, chewing patterns, and bone turnover rates. The purpose of this study was to measure histomorphometric bone fill after different latency periods, rates of distraction, and duration of neutral fixation in the minipig mandible. In addition, the relationship between histomorphometric bone fill and clinical stability was investigated. Mandibular osteotomies in 20 female Yucatan minipigs weighing 25 to 30 kg were distracted with modified semiburied distraction devices. Variables included 0-day or 4-day latency; 1-mm, 2-mm, or 4-mm daily distraction rates; gap size of 7 or 12 mm; and evaluation after neutral fixation for various lengths of time. Specimens were fixed in 2% paraformaldehyde, pH 7.4, before being embedded in methylmethacrylate. Sections were prepared from the region just below the inferior alveolar canal. The area of new bone formation within the gap was measured and expressed as a percentage of the total area of the distraction gap. Bone fill ranged from 0 to 100 percent. A pilot study with 7-mm advancements showed similar bone fill with 0-day or 4-day latency, but with poor reproducibility. Mandibles that were distracted to 12 mm at 1 mm per day exhibited nearly complete bone fill, either with 0-day latency (average, 93 percent) or 4-day latency (average, 100 percent). Mandibles that had been distracted for 3 days at 4 mm per day showed moderate osteogenesis and clinical stability with increasing time of neutral fixation. Bone fill was significantly correlated with clinical stability (Spearman r = 0.801, p = 0.001). Histological examination showed exuberant periosteal osteogenesis in distracted mandibles, even in those that showed poor bone fill and clinical stability. Thus, the periosteum appears to be a major source of new bone formation. These results show that osteogenesis was nearly complete with 1 mm per day and 0-day or 4-day latency. These results are consistent with the authors' previously reported clinical and radiographic observations that a latency period is not necessary for successful healing of the mandibular distraction osteogenesis wound.     

A new device to quantify regenerate torsional stiffness in distraction osteogenesis.

We present a newly developed torsional stiffness measurement device with the potential to quantitatively assess the in vivo torsional stiffness of bone regenerate during distraction osteogenesis. We describe the form and function of this device and its application in a model of regenerate consolidation. The device was able to produce data to assess stiffness of the regenerate with an accuracy between +/- 3 and +/- 9% for material stiffness ranging between 0.1 and 2.4 Nm/o and with a precision of +/- 3.6%. This method provides advantages over similar methods of bone fracture healing assessment with guaranteed maintenance of bone axis, minimized risk of bone misalignment during the bone healing process and a close relation to the functional loading pattern in torsion of bones such as tibia and femora.     

Vascular leak syndrome of Sprague-Dawley rats in a mandibular distraction osteogenesis study

Vascular leak syndrome (VLS) is a common and often fatal sequela of multiple bone traumas, and of infectious, toxic, and allergic insults in human patients. Although an animal model for VLS has not been fully established, rats have shown sensitivity to the syndrome that approximates that of the human population. We describe cases of VLS in three-month-old adult and one-month-old Sprague-Dawley rats in an osteogenesis study aimed at optimizing correction of bone hypoplasias and other craniofacial deformities in children, using a mandibular distraction device. In the study reported here, VLS was diagnosed in 40% of the rats that were necropsied after dying or being euthanized early, subsequent to mandibular osteotomy, a procedure that involves minimal bone trauma. The gross and histologic findings, as well as the clinical course of VLS in the rats of the osteogenesis study, were similar to those of documented human cases. Hence, the rat may be a useful animal model to h elp characterize the physiologic and molecular events that accompany this syndrome.     

Comparison of canine mandibular bone regeneration by distraction osteogenesis versus acute resection and rigid external fixation

The present study was performed (1) to explore the mechanism of skeletal healing following distraction osteogenesis of the mandible and to evaluate whether the same process is involved following acute mandibular resection and rigid external fixation, and (2) to examine the role of the periosteum in skeletal healing in both models. The study was performed using 16 mongrel dogs divided into two equal groups. In the first group, distraction of 20 mm was performed at a rate of 1 mm/day. In the second group, bone resection of 20 mm was performed, followed by rigid external fixation. The buccal periosteum was stripped in four dogs from each group, and the periosteum was left intact in the remaining four dogs. Dogs were euthanized after a survival period of either 2 or 3 months, and the new bone regenerate was evaluated. Analysis consisted of three-dimensional computed tomography scanning, histometric analysis, and immunostaining. Analysis of bone mineral content in the residual gap was conducted. Bone mineral content was increased in 3- versus 2-month survival for all groups (p < 0.05). The distracted groups had greater bone mineral content than their acutely resected counterparts, with the difference achieving statistical significance by 3-month survival (p < 0.05). Although periosteal preservation resulted in increased bone mineral content over time for all groups (p = 0.044), periosteal preservation had no significant effect on bone mineral content in the distracted groups. After periosteal stripping, however, bone mineral content was significantly increased in dogs that underwent distraction rather than acute resection and rigid external fixation (p = 0.022). Regarding histometric analysis, analysis of fibrous tissue content in the bone regenerate demonstrated that by 3 months the distracted groups had significantly less fibrous tissue in the new bone regenerate than did the acutely resected groups (p < 0.001). Regarding immunostaining, diffuse localization of transforming growth factor-beta1 was observed in all groups at 2 months, returning to nearly baseline levels by 3 months. These data demonstrate that significant bone formation in a segmental gap can be achieved after acute mandibular resection and rigid external fixation if the periosteum is preserved. However, after periosteal injury or stripping, significant bone formation can only be achieved by distraction osteogenesis. In both processes, bone formation is preceded by up-regulation of transforming growth factor-beta1.