Immediate versus delayed midface distraction in a primate model using a new intraoral internal device

The theoretic advantage of distraction osteogenesis of the craniofacial skeleton, especially in cases of severe midface retrusion and in the presence of maxillary scarring, is prevention of relapse following significant advancements. The purpose of this study is to demonstrate the utility of a new low-profile, intraoral, internal device for midface distraction at the conventional or high Le Fort I level. In addition, the present study compares the efficacy of immediate versus delayed distraction on subsequent maxillary relapse. Four adult rhesus Macaca mulatta monkeys were divided into two groups. Group 1 underwent immediate midface distraction; group 2 underwent delayed distraction. All four monkeys underwent a modified Le Fort I osteotomy through an upper buccal sulcus incision and bilateral application of the intraoral midface distraction devices. No other osteotomies or incisions were necessary. Immediate distraction, performed in group 1, entailed intraoperative activation of the devices and distraction of 10 mm followed by a 5-day lag period before postoperative activation and distraction of an additional 10 mm at the rate of 1 mm/day. Delayed distraction, performed in group 2, entailed a 5-day postoperative lag period before device activation and distraction of 20 mm at the rate of 1 mm/day. Both groups thus underwent 20 mm of midface distraction. All devices were removed 6 weeks after completion of distraction. All monkeys tolerated the devices and daily distraction uneventfully. On the basis of serial cephalograms and dental models obtained throughout the experimental period, there was no evidence of relapse in either the immediate or delayed groups 6 months after distraction. In addition, on the basis of histologic, ultrastructural, and dry skull analysis, no significant differences were observed in the quality of regenerate bone obtained when comparing the immediate and delayed distraction groups. Significant midface advancement is thus feasible using this new internal, intraoral distraction device, which presents several advantages over other internal devices that require coronal incisions and additional osteotomies to achieve midface advancement. In addition, immediate distraction may abbreviate the distraction period without adverse sequelae.     

Dual midfacial distraction osteogenesis: Le Fort III minus I and Le Fort I for syndromic craniosynostosis

Midfacial hypoplasia has been corrected by Le Fort III or monobloc forward advancement in one stage in syndromic craniosynostosis, but recently developed distraction osteogenesis has been in use. Whereas the amount of forward mobilization in Le Fort III conventional osteotomy is determined by the preplanned fabricated interdental splint, that in Le Fort III distraction is determined by the positions of the inferior orbital rim, malar complex, and nose. Therefore, the forward mobilization of the upper part of the midface may sometimes be insufficient when one focuses on the final occlusion, and the occlusion might not be satisfied when the forward mobilization is sufficient. Correction of the midfacial hypoplasia should be considered differently in the upper and lower portions of the midface. The upper portion contains the inferior orbit and nose, and the lower portion contains the occlusal structure of the maxillary dentoalveolar portion with the mandible. Separating the midface into two portions and conducting the distraction osteogenesis in both portions separately in different amounts and vectors of distraction is described in this article. Although distraction of the upper portion of the midface can be conducted in one direction with an internal device, distraction of the lower portion of the midface is preferred for conduction by a controllable device because of the need to obtain the preferred occlusion. To obtain better functional and aesthetic results in midfacial distraction in adults and adolescents with syndromic craniosynostosis, dual Le Fort III minus I and Le Fort I midfacial distraction osteogenesis was performed in four cases (in two patients with Crouzon syndrome and in two patients with Apert syndrome). Two females and two males are described (age range, 13 to 26 years). An internal device was used for the upper portion of the midface and an external device was used for the lower portion. The amount of distraction ranged from 14 to 21 mm in the upper portion of the midface and from 11 to 18 mm in the lower portion. No particular complications were noticed over a follow-up period of 10 to 38 months (average follow-up, 19.8 months).     

The Le Fort III osteotomy: to distract or not to distract?

Treatment of the craniofacial dysostoses (e.g., Crouzon, Apert, Pfeiffer, Saethre-Chotzen syndromes) is critically dependent on the successful advancement of the midface with a Le Fort III procedure. The purpose of this retrospective clinical outcome study was to evaluate a new technique for distracting the Le Fort III procedure and to compare its results in growing children with those of the standard Le Fort III osteotomy. The records of 22 children were reviewed; 10 patients (mean age, 6.5 years) underwent a standard Le Fort III procedure, and 12 patients (mean age, 7.5 years) underwent a Le Fort III distraction procedure. The distraction group included two separate techniques, bilateral buried distraction (n = 2) and halo distraction (n = 10). Preoperative and 2- to 3-month postoperative cephalograms were analyzed. The average horizontal advancement achieved in the standard Le Fort III group was 6 mm, compared with 19 mm of advancement in the distraction group (p 相似文献   

Blindness as a complication of Le Fort I osteotomy for maxillary distraction

High Le Fort I osteotomy and maxillary distraction has become an accepted method for the treatment of maxillary retrusion in children and teenagers with cleft lip and palate or craniofacial anomalies. This procedure effectively corrects the dentofacial deformity in these patients. No major surgical morbidity has been reported. During the past 4 years, 94 cleft patients with maxillary hypoplasia received Le Fort I osteotomy and distraction osteogenesis at the authors' center. Two of them developed blindness after this operation. The first case was a girl with bilateral cleft lip and palate with median facial dysplasia. She received high Le Fort I osteotomy at age 12 years 4 months to correct maxillary retrusion. Right eye swelling and ecchymosis was found after surgery. The patient complained of vision loss in that eye 2 days later. Computed tomography showed subarachnoid hemorrhage and skull base hematoma. There were no atypical fractures in the orbit, pterygoid plates, sphenoid bone, and skull base. Angiogram revealed left ophthalmic and basilar artery aneurysm. The second case was a 12-year-old boy with left cleft lip and palate. He received Le Fort I osteotomy to correct maxillary retrusion. During surgery, abnormal pupil dilatation was found after the osteotomy and down-fracture of maxilla. Emergent computed tomography found no hemorrhage or atypical fractures. Examination revealed complete left optic neuropathy and partial right abducens nerve palsy with mydriasis. Magnetic resonance imaging, magnetic resonance angiography, and repeated computed tomography revealed no sign of orbital injury, vascular problem, or abnormal fractures. The cause of blindness was unknown. In both cases, a steroid was used. Maxillary distraction was continued. Recovery of meaningful visual sense did not occur after 3 and 2 years' follow-up, respectively. A review of the literature revealed five other patients who suffered from visual loss after Le Fort I osteotomy. Inadvertent skull base fractures were identified in two cases, but a cause for the blindness was not known in the others. Induced hypotension and indirect trauma may be responsible for the optic nerve injury. In none of the cases was meaningful visual sense recovered, although high-dose steroids were given. In conclusion, a total of seven cases developed blindness after Le Fort I osteotomy. Once blindness develops, the prognosis is poor. High Le Fort I osteotomy should be performed with extreme care, and perhaps the informed consent should include visual loss as a complication of the procedure.     

Long-term skeletal stability after maxillary advancement with distraction osteogenesis using a rigid external distraction device in cleft maxillary deformities

Rigid external distraction is a highly effective technique for correction of maxillary hypoplasia in patients with orofacial clefts. The clinical results after correction of sagittal maxillary deformities in both the adult and pediatric age groups have been stable. The purpose of this retrospective longitudinal cephalometric study was to review the long-term stability of the repositioned maxilla in cleft patients who underwent maxillary advancement with rigid external distraction. Between April 1, 1995, and April 1, 1999, 17 consecutive patients with cleft maxillary hypoplasia underwent maxillary advancement using rigid external distraction. There were 13 male patients and four female patients, with ages ranging from 5.2 to 23.6 years (mean, 12.6 years). After a modified complete high Le Fort I osteotomy and a latency period of 3 to 5 days, patients underwent maxillary advancement with rigid external distraction until proper facial convexity and dental overjet and overbite were obtained. After active distraction, a 3- to 4-week period of rigid retention was undertaken; this was followed by removable elastic retention for 6 to 8 weeks using, during sleep time, an orthodontic protraction face mask. Cephalometric radiographs were obtained preoperatively, after distraction, at 1 year after distraction, and 2 or more years after distraction. The mean follow-up was 3.3 years (minimum, 2.1 years; maximum, 5.3 years). The following measurements were obtained in each cephalogram: three linear horizontal and two linear vertical maxillary measurements, two angular craniomaxillary measurements, and one craniomandibular measurement. Differences between the preoperative and postoperative cephalometric values were analyzed by paired t tests (p < 0.05). The cephalometric analysis demonstrated postoperatively significant advancement of the maxilla. In addition, the mandibular plane angle opened 1.2 degrees after surgery. After the 1- to 3-year follow-up period, the maxilla was stable in the sagittal plane. Minimal anteroposterior growth was observed in the maxilla compared with that exhibited in the anterior cranial base. However, there was significant vertical maxillary growth over the 3-year observation period. The mandibular plane angle tended to decrease during the follow-up period. The cephalometric data from this study support the clinical impression of maxillary stability after maxillary advancement with rigid external distraction in cleft patients. This effective and stable technique is now considered for all pediatric patients with severe cleft maxillary hypoplasia and for adolescent and adult patients with moderate to severe deformities.     

Midface distraction following Le Fort III and monobloc osteotomies: problems and solutions

Distraction osteogenesis has been used increasingly for midfacial advancement in patients with syndromic craniosynostosis and in severe developmental hypoplasia of the midface. In these patients, the degree of advancement required is often so great that restriction of the adjacent soft tissues may preclude stable advancement in one stage. Whereas distraction is an ideal solution by which to gradually lengthen both the bones and the soft tissues, potential problems remain in translating the distraction forces to the midface. In these patients, severe developmental hypoplasia may be associated with weak union between the zygoma and the maxilla, increasing the chance of zygomaticomaxillary dysjunction when using internal devices that translate distraction force to the maxilla through the zygoma. Eight cases are reported in which either internal or external distraction systems were used for midface advancement following Le Fort III (n = 7) or monobloc (n = 1) osteotomies. Cases of patients in whom hypoplasia at the zygomaticomaxillary junction altered or impaired plans for midface distraction were reported from three host institutions. Seven patients had midface hypoplasia associated with syndromic craniosynostosis, and one patient had severe developmental midface hypoplasia. The distraction protocol was modified to successfully complete midface advancement in light of weakness at the zygomaticomaxillary junction in seven patients. Modifications included change from an internal to an external distraction system in two patients, rigid fixation and bone graft stabilization of the midface in one patient, and plate stabilization of a fractured or unstable zygomaticomaxillary junction followed by resumption of internal distraction in four patients. Previous infection and bone loss involving both malar complexes precluded one patient from being a candidate for an internal distraction system. Using a problem-based approach, successful advancement of the midface ranging from 9 to 26 mm at the occlusal level as measured by preoperative and postoperative cephalograms was undergone by all patients. Advantages and disadvantages of the respective distraction systems are reviewed to better understand unique patient characteristics leading to the successful use of these devices for correction of severe midface hypoplasia.     

Rotation advancement of the midface by distraction osteogenesis

A wide variety of disease processes produce alteration of midfacial skeletal growth, resulting in moderate-to-severe midface deficiency presenting as retrusion associated with Angle's class III malocclusion. Le Fort III osteotomies with advancement can provide an excellent tool for correction of this deformity. Recently, the corrective procedure of choice for advancement of midfacial segments has been distraction osteogenesis after osteotomy. Straight linear advancement is the most common choice for corrective movement of the midfacial segment, whether accomplished through acute surgical advancement or through the progressive distraction technique. Unfortunately, linear advancement can produce abnormal configurations, both at the nasal root and lateral orbits, regardless of the technique used. Enophthalmos, caused by orbital enlargement, may limit the advancement necessary to achieve class I occlusion.The authors have extended the utility of the Le Fort III procedure and have improved the final outcome by creating a controlled rotation advancement of the midfacial segment using distraction. The application of an existing internal distraction device is modified to control the movement of the midfacial segment in a rotation advancement path. Included in the series were 10 patients with severe midface retrusion secondary to multiple congenital syndromes, along with cleft lip and palate. The ages of the patients ranged from 6 to 14 years. An internal distraction system was used in all cases. Application of the distractor was substantially modified to simplify both fixation and removal and to produce controlled rotation advancement. The team orthodontist determined the final occlusal relationship. Percutaneous distractor drive rods were removed 4 to 6 weeks after active distraction to increase patient comfort. The distractors and all associated hardware were removed after 12 to 16 weeks of consolidation; follow-up periods ranged from 1 to 3 years.By using the modified distractor application to produce rotation advancement, the contour abnormalities at the nasal root and lateral orbit and the enophthalmos produced by linear advancement were eliminated. Significant improvement in facial contour and class I occlusion was obtained in all cases. Complications consisted of near exposure of the device in one patient. Stability has been excellent, with no relapse reported by the orthodontist.Rotational advancement of facial segments by distraction allows successful early intervention in patients with significant midface retrusion. The abnormal nasal root and lateral orbital configurations produced by direct linear advancement are avoided, and a stable and normalized facial configuration is produced.     

Rat mandibular distraction osteogenesis: part III. Gradual distraction versus acute lengthening

Distraction osteogenesis is a well-established method of endogenous tissue engineering. This technique has significantly augmented our armamentarium of reconstructive craniofacial procedures. Although the histologic and ultrastructural changes associated with distraction osteogenesis have been extensively described, the molecular mechanisms governing successful membranous distraction remain unknown. Using an established rat model, the molecular differences between successful (i.e., osseous union with gradual distraction) and ineffective (i.e., fibrous union with acute lengthening) membranous bone lengthening was analyzed. Herein, the first insight into the molecular mechanisms of successful membranous bone distraction is provided. In addition, these data provide the foundation for future targeted therapeutic manipulations designed to improve osseous regeneration. Vertical mandibular osteotomies were created in 52 adult male Sprague-Dawley rats, and the animals were fitted with customized distraction devices. Twenty-six animals underwent immediate acute lengthening (3 mm; a length previously shown to result in fibrous union) and 26 animals were gradually distracted (after a 3-day latency period, animals were distracted 0.25 mm twice daily for 6 days; total = 3 mm). Four mandibular regenerates were harvested from each group for RNA analysis on 5, 7, 9, 23, and 37 days postoperatively (n = 40). Two mandibular regenerates were also harvested from each group and prepared for immunohistochemistry on postoperative days 5, 7, and 37 (n = 12). In addition to the 52 experimental animals, 4 control rats underwent sham operations (skin incision only) and mandibular RNA was immediately collected. Control and experimental specimens were analyzed for collagen I, osteocalcin, tissue inhibitor of metalloproteinase-1, and vascular endothelial growth factor mRNA and protein expression. In this study, marked elevation of critical extracellular matrix molecules (osteocalcin and collagen I) during the consolidation phase of gradual distraction compared with acute lengthening is demonstrated. In addition, the expression of an inhibitor of extracellular matrix turnover, tissue inhibitor of metalloproteinase-1, remained strikingly elevated in gradually distracted animals. Finally, this study demonstrated that neither gradual distraction nor acute lengthening appreciably alters vascular endothelial growth factor expression. These results suggest that gradual distraction osteogenesis promotes successful osseous bone repair by regulating the expression of bone-specific extracellular matrix molecules. In contrast, decreased production or increased turnover of bone scaffolding proteins (i.e., collagen) or regulators of mineralization (i.e., osteocalcin) may lead to fibrous union during acute lengthening.     

Complex maxillary fractures: role of buttress reconstruction and immediate bone grafts

Between 1978 and 1984, 558 patients with complex facial fractures have been treated. One hundred and seventy-one of these patients have had complex Le Fort fractures of the maxilla. In this group of patients, the importance of direct anatomic reconstruction of the anterior maxillary buttresses has been assessed. Complete exposure of the injured buttresses will facilitate assessment of the exact fracture pattern. Direct fixation of the medial and lateral maxillary buttresses on each side, in combination with immediate bone-graft reinforcement or replacement of comminuted or missing buttresses, will facilitate the reconstruction of even the most severely injured maxilla in one stage. This approach is combined with similar reconstructive techniques in other areas of the craniofacial skeleton. Associated mandibular fractures are managed with rigid internal fixation utilizing A-O techniques. The use of these techniques dramatically facilitates airway management and simplifies the treatment of the edentulous patient, the patient with bilateral condylar neck fractures, and those patients with sagittal splitting of the maxilla and palate. The use of both internal craniofacial suspension wires and external craniofacial suspension devices has become largely unnecessary, and reconstruction of even the most complex injuries in one stage with minimal complications and secondary deformities is made possible.     

The Le Fort III advancement osteotomy in the child under 7 years of age

This is a longitudinal study of 12 patients with craniofacial synostosis syndromes (Crouzon's, Apert's, Pfeiffer's) who underwent Le Fort III advancement under the age of 7 years (average age 5.1 years, range 4.0 to 6.7 years). The average follow-up was 5.0 years and included clinical, dental, and cephalometric examinations according to a prescribed protocol. The study demonstrated that the procedure could be safely performed in the younger child with an acceptable level of morbidity. There was a remarkable degree of postoperative stability of the maxillary segment. However, although vertical (inferior) growth or movement of the midfacial segment was demonstrated, there was minimal, if any, anterior or horizontal growth. Any occlusal disharmony developing during the period of follow-up could be attributed to anticipated mandibular development and could be corrected by orthognathic surgery. The roles of surgical overcorrection and anterior-pull headgear therapy after release of intermaxillary fixation are also discussed. The Le Fort III osteotomy is justifiably indicated during early childhood for psychological and physiologic reasons.     

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.     

Craniofacial distraction osteogenesis: a review of 3278 cases

The nascent field of craniofacial distraction osteogenesis has not yet been subjected to a rigorous evaluation of techniques and outcomes. Consequently, many of the standard approaches to distraction have been borrowed from the experience with long bones in orthopedic surgery. The ideal "latency period" of neutral fixation, rate and rhythm of distraction, and consolidation period have not yet been determined for the human facial skeleton. In addition, because the individual craniofacial surgeon's experience with distraction has generally been small, outcomes and meaningful complication rates have not yet been published.In this study, a four-page questionnaire was sent to 2476 craniofacial and oral/maxillofacial surgeons throughout the world, asking about their experiences with distraction osteogenesis. Information about the types of cases, indications for surgery, surgical techniques, postoperative management, outcomes, and complications were tabulated. Of 274 respondents (response rate, 11.4 percent), 148 indicated that they used distraction in their surgical practice. One hundred forty-five completed surveys were entered into a database that provided information about 3278 craniofacial distraction cases. Statistical analyses were performed comparing the rates of premature consolidation, fibrous nonunion, and nerve injury, on the basis of the use of a latency period and different rates and rhythms of distraction. In addition, the rates of all complications were determined and compared on the basis of the number of distraction cases performed per surgeon.The results of the study clearly show a wide variation in the surgical practice of craniofacial distraction osteogenesis. Although the cumulative complication rate was found to be 35.6 percent, there is a pronounced learning curve, with far fewer complications occurring among more experienced surgeons (p < 0.001). The presence of inferior alveolar nerve injury as a result of mandibular distraction was much lower for respondents whose distraction regimens consisted of no more than 1 mm of distraction per day (19.5 percent versus 2.4 percent; p < 0.001). No evidence was found to support the use of a latency period or to divide the daily distraction regimen into more than one session per day. Conclusions could not be drawn from this study regarding the length of the consolidation period. Overall, the surgeon-reported outcomes are comparable with those published for other craniofacial procedures, despite the higher incidence of complications.Although conclusions made on the basis of a subjective questionnaire need to be interpreted cautiously, this study has strength in the large numbers of cases reviewed. Because of the anonymity of responses, it has been assumed that surgeons who responded to the survey reported accurate numbers of complications and successful outcomes. Finally, additional clinical and animal studies that will be of benefit in advancing the field of craniofacial distraction osteogenesis are outlined.     

Lengthening the human mandible by gradual distraction.

Lengthening of the mandible by gradual distraction was performed on four young patients (average age 78 months). The amount of mandibular bone lengthening ranged from 18 to 24 mm; one patient with Nager's syndrome underwent bilateral mandibular expansion. Following the period of expansion, the patients were maintained in external fixation for an average of 9 weeks to allow ossification. The patients were followed for a minimum of 11 months to a maximum of 20 months with clinical and dental examinations as well as photographic and radiographic documentation. The technique holds promise for early reconstruction of craniofacial skeletal defects without the need for bone grafts, blood transfusion, or intermaxillary fixation.     

Le Fort fractures without mobility

The Le Fort fracture without maxillary mobility constitutes 9 percent of maxillary fractures observed over a 3-year period. A high Le Fort (level II or III) injury exists as a one- or two-piece incomplete fracture. The degree of fracture is insufficient to permit mobility of the maxillary alveolus. Frequently, an obvious unilateral zygomatic fracture is present. Physical findings consist of bilateral eyelid ecchymosis and malocclusion. The occlusal disturbance may consist of either crossbite, open bite, maxillary rotation, or lack of proper dental intercuspation. On CT scan, fractures are best demonstrated in the posterior and medial maxillary walls at the Le Fort I level; they are most obvious unilaterally with contralateral fractures that may be subtle. Bilateral maxillary sinus fluid is consistently present on CT. Treatment usually consists of observation and traction elastics but may require mobilization of the fragments followed by open reduction and rigid fixation.     

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.     

Callus stimulation in distraction osteogenesis

Distraction osteogenesis has been described as in vivo tissue engineering. The ability to stimulate this process for the repair of bony defects or lengthening of congenitally shortened facial structures is likely to significantly impact the field of craniofacial surgery. The purpose of this study was to determine whether mechanical stimulation of the distracted rabbit mandible would accelerate the maturation of the bony callus when applied during the early consolidation period. Twenty adult New Zealand White rabbits underwent unilateral mandibular osteotomy. A uni-directional internal distractor device (Synthes, Paoli, Pa.) was positioned along a plane perpendicular to the line of osteotomy. After a 7-day latency period, distraction was commenced at a rate of 1.0 mm/day for 12 days in all animals. In a control group of 10 rabbits, a consolidation period of 8 weeks was observed before they were killed. In the experimental group of 10 rabbits, daily alternate compression and distraction of 1 mm (sequential compression and distraction) was performed for 3 weeks followed by a 5-week period of rigid fixation. Each animal received a dose of a fluorescent label at three different time points during the study: at the end of the distraction period, 3 weeks after the completion of the distraction phase, and 3 days before it was killed. All animals were killed 8 weeks after the completion of the distraction phase. Undecalcified histologic analysis and 3-point bending tests to failure were performed on the extracted mandibles. The results of the experimental and control groups were compared.Four animals in the control group and three animals in the experimental group were excluded from the study because of screw loosening resulting in distractor dislodgment or because of infection. On histologic analysis, cortical thickness at the center of the callus was found to be significantly greater in the experimental group compared with the control group when normalized to the contralateral hemimandible (83 percent versus 49 percent, respectively; p < 0.007). The ratio of cortical to cancellous bone in the distracted callus was uniformly found to be greater in the experimental specimens. The mineral apposition rate was calculated by using fluorescence microscopy and found to be significantly greater in the experimental group both during the period of sequential compression and distraction (3.2 microm/day versus 2.1 microm/day, p = 0.02) and after the period of sequential compression and distraction (1.4 microm/day versus 1.1 microm/day, p = 0.006). Mechanical testing revealed no significant differences in bending strength or stiffness between experimental or control groups (p = 0.54 and 0.47, respectively). This study has demonstrated that daily alternating compression and distraction of 1 mm amplitude during the early consolidation period has a stimulatory impact on callus formation with respect to osteoblastic activity, remodeling, and maturation of bone. Optimal timing and amplitude of sequential movement, long-term biomechanical differences, and molecular pathways have yet to be elucidated.     

Focal adhesion kinase expression during mandibular distraction osteogenesis: evidence for mechanotransduction

Distraction osteogenesis is an established treatment strategy in the reconstruction of the craniofacial skeleton. The underlying mechanisms that drive bone formation during this process are largely unknown, but a regulatory role for mechanical force is believed to be critical. The integrin-mediated signal transduction cascade is a primary pathway by which signal transduction of mechanical stimuli (i.e., mechanotransduction) occurs. Focal adhesion kinase (FAK) is a significant regulator in this pathway. The authors hypothesize that mechanical forces created during distraction osteogenesis are responsible for the osteogenic response that takes place, and that these changes arise through integrin-dependent mechanotransduction. Using a rat model of distraction osteogenesis, the authors examined the expression of FAK in critical size defects (n = 15), subcritical size defects (n = 15), and mandibles undergoing distraction osteogenesis (n = 15). Their findings demonstrated FAK immunolocalization in mandibles undergoing distraction osteogenesis, but not in the critical size defects or in subcritical size defects, despite varying degrees of bone formation in the latter two groups. Furthermore, bone sialoprotein mRNA in situ hybridization patterns were found to mirror FAK immunolocalization patterns in mandibles undergoing distraction osteogenesis, demonstrating an association of FAK expression with the osteogenic process specific to distraction osteogenesis. These findings suggest that the bone formation in distraction osteogenesis is regulated by mechanical force by means of integrin-dependent mechanotransduction pathways.     

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.     

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.