A custom mandibular distraction device for the rat

In the last several years, the rat model has been used as a reliable means of studying distraction osteogenesis (DO). This model has several benefits, including lower cost, the availability of molecular reagents for the rat, and the ability to perform a large number of operations in a short time. We have recently developed an external device that is custom-made for the rat mandible and secured at the mandibular ramus. The device consists of a Leone (Florence, Italy) jackscrew distraction assembly (0.2 mm per one-quarter turn), 2 Luhr L-shaped 0.8-mm five-hole microplates, and four 0.8-mm x 3-mm microscrews (Stryker-Leibinger Corp., Kalamazoo, MI) for fixation. Additionally, there is a methylmethacrylate block that is placed on the lingual surface of the angle of the mandible to support the posterior screws. Sterile surgical technique was used, and the same two surgeons performed all operations. To date, we have operated on 153 Sprague-Dawley rats. The procedure has been well tolerated by the animals. We had 17 postoperative deaths (11% mortality), largely as a result of anesthetic complications. There were no wound infections or dehiscence. A mandible fracture was noted in 6 rats (4%), which occurred at the time of device placement. There were no device dislodgments. Postmortem examination showed the device to be well positioned in all rats, with good callous formation at the distraction site. The rats surpassed their preoperative weight after an average of 9.2 days. These results compare favorably with those of other models currently in use. We have developed a device that is currently being used in the study of DO in the rat mandible. Our device is small in size, does not require wide undermining for its placement, and has had a low incidence of device dislodgment or infection. This model has shown great reproducibility and thus should be effective in its application for the histologic and biochemical investigation of DO in the rat.

Proximal segment displacement in mandibular distraction osteogenesis

Distraction osteogenesis has been advocated for treatment of the mandibular deformity in patients with hemifacial microsomia (HFM). During the active phase, the force of distraction pushes the distal segment of the mandible down, creating a distraction gap. Because of the abnormal temporomandibular joint anatomy in HFM patients, the proximal segment may not seat in the glenoid fossa and thus may be displaced with distraction. The purpose of this study was to determine the vector(s) of proximal segment movement during mandibular distraction using a semiburied device. Two investigators traced the immediate pre-and postdistraction panoramic radiographs of 12 HFM patients (mean age at operation = 8.4 years, mean distraction = 28 mm) who had mandibular distraction with a semiburied device. Radiographic analysis, based on a vertical maxillary reference line, measured change in condylar position with angular and linear measurements. Inter-rater reliability for the tracing and analysis was shown with a correlation coefficient between 0.89 and 0.99 for all measures. Based on the angular and linear measurements, 10 of the 12 patients had superior movement of the proximal segment with distraction. Sagittal movement of the proximal segment could not be judged adequately. This study was based on measurements made on panoramic radiographs. Direct measurements could not be made; thus, it was not possible to estimate proximal segment movement in millimeters or as a percentage of total movement. Further studies to document proximal segment movement using computed tomography scans may provide more quantitative data.

LeFort III internal distraction in syndromic craniosynostosis

Distraction osteogenesis of the mid-face alleviates the requirements of substantial autogenous bone grafts and donor site morbidity and alleviates the restriction of the soft-tissue envelope in gaining advancement of the mid-face. A prospective study, over a 14-month period, was initiated to evaluate the results of seven consecutive patients undergoing mid-facial advancement who were treated with Le Fort III internal distraction using the MID device. All patients had syndromic craniosynostoses and six patients had previously undergone fronto-orbital advancement. Four patients had symptoms of airway obstruction and one patient was tracheostomy dependent. Six of the patients completed the distraction as planned. Lateral cephalograms were analyzed and the mean linear distraction was 18 mm with a range of 8 mm to 23 mm. Complications included infection (one patient), mechanical failure (one patient), intraoperative fragment dysjunction (three patients), velopharyngeal insufficiency (one patient), conjunctivitis (two patients), trismus (six patients), and bony irregularities. It was concluded that in our Unit's future protocol for managing infant syndromic synostoses, synostectomies and cranial vault remodeling will be undertaken in infants as before, but that in early childhood, patients with severe mid-facial hypoplasia and/or respiratory compromise will be offered distraction osteogenesis as a substitute for the traditional Le Fort III advancement and bone grafting.

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.

Condylar displacement related to mandibular symphyseal distraction

This study was undertaken to determine the true nature of condylar displacements associated with mandibular symphyseal distraction osteogenesis. Earlier investigators have assumed that each mandibular half rotated about a point near the center of each condyle as viewed on a submental radiograph. In a 12-patient sample, 10 with tooth-borne symphyseal distraction and 2 with bone-borne symphyseal distraction, it was found that each condyle was laterally displaced in direct relationship to the amount of symphyseal distraction. The rigidity of the distraction appliances and their attachments and the inability of the soft tissues and muscular attachments to cause the mandible to undergo compound bending require this to be the case. Temporomandibular joints appear to be able to accommodate the lateral displacements because symptoms were not introduced, or, if present before therapy, distraction did not exacerbate them.

Muscle fibre damage and regeneration resulting from surgical limb distraction

Using an animal model of limb distraction, the extent of muscle fibre damage and atrophy resulting from distraction at two different rates (1.3 or 3.0 mm day(-1)) was investigated. It was found that at the high rate of distraction there was a significantly greater loss of range of joint movement and more muscle fibre atrophy and fibre damage than at the low rate. Muscle fibre damage is usually followed by regeneration. This involves the expression of the neonatal form of myosin heavy chain, which can therefore be used as an indicator of regeneration. It was found that whilst many more fibres showed evidence of damage at the high compared to the low rate, the number of fibres expressing neonatal myosin was significantly reduced, indicating the presence of a population of fibres which was undergoing degeneration without subsequent regeneration. Thus it would appear that beyond a certain rate of distraction, regeneration may be insufficient to replace contractile material damaged by overstretching. It is suggested that these fibres are replaced with connective tissue. This process may contribute to the muscle weakness and loss of range of joint movement which sometimes accompanies limb distraction procedures.

Complications of distraction osteogenesis: a changing pattern

We reviewed Mr. Simpson's first 80 consecutive limb-lengthening procedures, using either a circular or a unilateral frame, and analyzed the complication rates. The initially high complication rate (100%) decreased significantly (P < .01) with experience. Incidence of axial deviation was reduced by changing the configuration of the fixators; delayed consolidations and fractures were reduced by prophylactic bone-grafting and by minimizing the associated complication of muscle contractures; severe pin-track infection was reduced by introducing a simple protocol; and muscle contractures and joint subluxation were reduced by adjusting the bone screw insertion sites and ensuring adequate early analgesia to allow early movement.

Influence of distraction rates on the temporomandibular joint position and cartilage morphology in a rabbit model of mandibular lengthening

PURPOSE

Although various aspects of bone formation during distraction osteogenesis have been studied extensively, there are only limited experimental data concerning the influence of mandibular distraction rates on structural alterations in the temporomandibular joint (TMJ). In this study, a rabbit model of unilateral mandibular distraction was used to test the effects of various strain schedules on the position and morphology of the TMJ.

MATERIAL AND METHODS

Fifty-two immature white female rabbits were used. The distraction procedure was performed using physiologic (2,000 microstrains, 1 per day) and elevated strain magnitudes (20,000 microstrains, 1 per day), as well as high strain magnitudes (200,000 and 300,000 microstrains, 1 per day). The investigation of the TMJ included clinical, radiologic, and histologic aspects.

RESULTS

Clinical and radiologic examinations at the end of the distraction period showed no evidence of joint luxation even at maximal distraction rates. Histologic and ultrastructural analyses revealed a positive correlation between the degree of mechanical loading and the development of degenerative alterations in the cartilage. In samples distracted at hyperphysiologic strain magnitudes, all cartilaginous layers were reduced in the regions of the TMJ that had been exposed to the higher pressure forces. The fibrous layer became nearly completely destroyed.

CONCLUSIONS

These experimental data show that distraction schedules with single but hyperphysiologic loads may lead to degenerative or even early arthrotic changes in the condyle. These data support the principle that distraction protocols should be performed without extensive mechanical loading on the TMJ.

Effect of pamidronate on distraction osteogenesis and fixator-related osteoporosis

We examined the effect on bone mineral density (BMD), bone mineral content (BMC) and mechanical properties of a single 1.0 mg/kg dose of the bisphosphonate pamidronate (Novartis), in a distraction osteogenesis model in immature rabbits. Twenty rabbits underwent a tibial osteotomy. Ten rabbits received pamidronate 1.0 mg/kg via ear vein intra-operatively while 10 received saline infusions only. After a 24 h latency, all underwent distraction of 0.375 mm twice daily for 15 days. The animals were culled at 42 days. After culling, the distracted and non-distracted tibiae were examined by quantitative computer tomography (QCT). The volumetric bone mineral density (vBMD, mg/cm(3)) in the bone proximal and distal to the regenerate in the operated limb was increased by a mean of 11 and 14%, respectively, compared to controls (P<0.05). The vBMD of the regenerate bone was increased by a mean of 8% over controls (NS, P=0.17). The bone mineral content (BMC, mg) was increased by 23% (proximal and distal) (P<0.05) in the bone surrounding the lengthening and there was a 17% trend towards an increase in the regenerate (NS, P=0.3). Four-point bending analysis documented that the load to failure was increased by 32% from 436 to 574 N (P<0.01) in the pamidronate group. The modulus of elasticity was not different between the control and pamidronate groups (P=0.3), and in both groups was only approximately one-third of the intact tibiae (P<0.001). The administration of a single dose of pamidronate can improve the bone mineral density, content and mechanical properties of a bone undergoing distraction osteogenesis.

Response of the physis to leg lengthening

The physeal response to limb lengthening by callotasis was investigated in an animal model by measuring 1) the growth rate using an oxytetracycline labelling technique, 2) histomorphological changes, and 3) proliferative cellular activity using bromodeoxyuridine. An osteotomy without lengthening stimulated growth at the physis. At 20% lengthening, regardless of the rate of distraction, no significant changes were detected. However, the growth rate was drastically reduced after 30% or more of lengthening and in 50% of cases there was evidence of premature closure of the distal growth plate.

CLINICAL RELEVANCE

Caution should be exercised in carrying out high percentages of lengthening of children's bones.

Orthodontic spring guidance of bilateral mandibular distraction in rabbits

Although distraction osteogenesis can lengthen congenitally small mandibles, the distraction procedure can be difficult to control. To study the efficacy and safety of orthodontic spring guidance on bilateral mandibular distraction, an 8-mm anterior open bite was experimentally produced and corrected during bilateral mandibular distraction in rabbits. Orthodontic springs were attached to the anterior maxilla and mandible to redirect an ongoing distraction procedure. Sixteen rabbits underwent mandibular distraction: 6 rabbits received heavy springs (8 oz), 6 rabbits received light force springs (2 oz), and 4 rabbits served as control animals with anterior open bites without spring guidance. Nickel-titanium springs were applied during the last week of osseous distraction and the first week of consolidation. Distractors were left in place throughout a 2-month consolidation period. None of the animals developed fibrous union as a result of spring guidance. The 8-mm open bite did not close in the control group or in the light spring group after 2 weeks of spring wear or during the consolidation period. Heavy springs completely closed the experimental open bites within 2 weeks (P <.01, analysis of variance). Bite corrections did not change during the consolidation period. This study indicated that the addition of an orthodontic spring to a mandibular distraction procedure did not impair bone healing. With the distraction device in place, heavy spring forces redirected an ongoing mandibular distraction procedure and corrected an open bite, distraction side effect. Direct measurements, radiographic measurements, and tissue histologic factors described changes in segment position and shape of the distraction site.

Vector control in lower jaw distraction osteogenesis using an extra-oral multidirectional device

PURPOSE

This cephalometric study describes structural changes in facial features and occlusion during distraction of the mandible.

PATIENTS

Seven patients aged 7-16 years with severely retrognathic lower jaws were treated by bilateral extra-oral distraction. The direction of the distraction was changed during the distraction period (mean 30 days) using the adjustable hinge in the distractor. Cephalometric follow-up documents were analysed for changes in facial and occlusal structures. The distraction therapy proceeded in two phases. First, horizontal distraction was undertaken to achieve a good incisor relationship. After this, the direction was changed to a more vertical plane with the use of a hinge axis, and the tips of the lower incisors were used as the axis of rotation.

RESULTS

The most remarkable changes were in the more anterior position of the lower jaw, the increase in ramus height and good dental overjet. The mandibular occlusal plane became more horizontal, creating a posterior open bite. By guiding the vector of distraction, no anterior open bite or lateral crossbite appeared.

CONCLUSION

This study points out the advantages of using extra-oral multidimensional distractors. Severe lower jaw deficiency requires not only a long working length of the device but also precise control of the vector during the active phase of distraction.

Changes in the inferior alveolar nerve after mandibular lengthening with different rates of distraction

PURPOSE

This study investigated the changes in the inferior alveolar nerve after mandibular lengthening with different rates of distraction.

MATERIALS AND METHODS

Bilateral mandibular corticotomies were performed in 8 goats. The mandibles in 6 goats were lengthened 10 mm using a custom-made distractor with 2 different rates of distraction (1 mm/d [n = 3] and 2 mm/d [n = 3]); the other 2 nondistracted mandibles served as a control. The goats with distracted mandibles were killed at 2 weeks after completion of distraction. The inferior alveolar nerve specimens from all animals were harvested and processed for histologic and ultrastructural evaluation.

RESULTS

The mandibles were lengthened successfully in the distracted animals. Morphologic changes in the inferior alveolar nerves were observed when compared with the nondistracted controls. Moreover, signs of nerve degeneration, such as demyelination, axonal swelling, axoplasmic darking, and decrease in the number of axons, were more extensive and prominent in those nerves distracted at a rate of 2 mm/d.

CONCLUSIONS

Degenerative changes in the inferior alveolar nerve occur after mandibular lengthening by distraction osteogenesis. The distraction rate of 1 mm/d appears to be tolerable and safe for the inferior alveolar nerve, but rapid distraction may cause serious degeneration.

Intravenous pamidronate reduces osteoporosis and improves formation of the regenerate during distraction osteogenesis. A study in immature rabbits

We examined the effect on bone mineral density (BMD) of a single dose of 3 mg/kg of the bisphosphonate, pamidronate (Novartis) in distraction osteogenesis in immature rabbits. Seventeen rabbits (9 control, 8 given pamidronate) were examined by dual-energy x-ray absorptiometry. There was a significant increase in the BMD in the pamidronate group compared with the control animals. The mean areal BMD (g/cm2) in the bone proximal and distal to the regenerate was increased by 40% and 39%, respectively, compared with the control group (p < 0.05). The BMD of the regenerate bone was increased by a mean of 43% (p < 0.05). There was an increase of 22% in the mean area of regenerate formed in the pamidronate group (p < 0.05). Histological examination of bone in nine rabbits (5 control, 4 pamidronate) showed an increase in osteoblastic rimming and mineralisation of the regenerate, increased formation of bone around the pin sites and an increase in the cortical width of the bone adjacent to the regenerate in the rabbits given pamidronate. Pamidronate had a markedly positive effect. It reduced the disuse osteoporosis normally associated with lengthening using an external fixator and increased the amount and density of the regenerate bone. Further study is required to examine the mechanical properties of the regenerate after the administration of pamidronate.

Fibrous ankylosis after distraction osteogenesis of a costochondral neomandible in a patient with grade III hemifacial microsomia

Distraction osteogenesis has recently become a mainstay for treatment of craniofacial syndromes with mandibular hypoplasia. This article presents the difficult case of a patient with a previous costochondral rib graft who underwent mandibular distraction and developed a fibrous pseudoarthrosis at the distraction site. This was attributed in part to an associated temporomandibular joint ankylosis. Resorption of the pseudoarthrosis occurred once the distractor was removed. It appears that distraction osteogenesis of a mandible with an ankylosed temporomandibular joint can result in healing with a fibrous union, presumably because of movement at the distraction site when masticating. This can result in a pseudo "temporomandibular joint" at the distraction site. A temporomandibular joint arthroplasty was performed, followed by repeat distraction. We conclude that if there is an ankylosed temporomandibular joint or a stiff temporomandibular joint that may ankylose during the course of the distraction process, then a temporomandibular joint arthroplasty should be performed before or at the time the distractor is placed.

Complications following orthognathic surgery that required early surgical intervention: fifteen years' experience

The aim of this study was to assess complications following various orthognathic surgical procedures that required early surgical intervention. This study was carried out on 821 patients who had undergone surgical treatment for correction of dentofacial deformities between 1985 and 2000. Only patients who required a second procedure to deal with immediate or early postoperative complications (i.e., those occurring within 4 weeks of surgery) were investigated in this study. Twelve patients underwent a second surgical procedure; 9 had undergone conventional osteotomy surgery, and 3 had undergone distraction osteogenesis. Three Le Fort I cases had to be further impacted and repositioned, and 4 vertical subsigmoid osteotomies had to be reexplored. The details of the complications are presented, and possible methods by which these problems could be reduced and/or prevented are discussed.

Bending of the distraction site during mandibular distraction osteogenesis in the rabbit: a model for studying segment control and side effects

PURPOSE

The purpose of this investigation was to develop an animal model for studying and correcting mandibular distraction side effects.

MATERIALS AND METHODS

Twenty-nine rabbits underwent bilateral mandibular distraction. Bending of the mandible was accomplished by offsetting a linear distraction by 35 degrees from the occlusal plane (4 screws per distractor), rotating the anterior segment inferiorly (2 screws per distractor), and removing a 3- or 6-mm wedge of the distraction site. The amount of bite opening varied according to the surgical design. Direct measurements, radiographs, and histology samples were compared.

RESULTS

Linear distraction produced a 4-mm anterior open bite and a Class III malocclusion after 2 weeks of distraction. Segmental rotation produced an 8-mm anterior open bite without complications. Removal of a wedge initiated rotation of the anterior segment. A large wedge (6 mm) produced fibrous union in the distraction site. The amount of bite opening or closure depended on the number of surgical screws and position of the distractor. Serial histologic sections showed bone formation at the rotated, triangular distraction site.

CONCLUSION

Bite opening or closure can occur from loss of segment control or by altering surgical design. This information is needed to counter unwanted side effects or to plan segment rotations.

Intracranial migration of halo fixation pins: a complication of using an extraoral distraction device

OBJECTIVE

Distraction osteogenesis is a well-accepted technique in the treatment of patients with hypoplastic craniofacial components. Complications of distraction osteogenesis are well described in the literature. We describe a complication of using an external distraction device in a 9-year-old girl with Pfeiffer.

INTERVENTION AND RESULTS

A modified Lefort III osteotomy was performed for maxillary hypoplasia with application of an external distraction halo device by a pediatric neurosurgeon. A postoperative computed tomography (CT) scan showed 0.5-cm skull penetration of the cranial pins. The pins were repositioned and the patient was followed up on a regular basis until discharge from the hospital. At 3-week follow-up, a CT scan of the head showed migration of the pins 1.5 cm intracranially. The halo was removed and repositioned at a different site. No detectable neurological sequelae from the pin penetration were noted. The patient developed cellulitis at the site of the penetration and was admitted to the hospital for a course of intravenous antibiotics. There were no other complications, and the rest of her treatment course proceeded as planned. A review of the literature on complications of halo usage as well as suggestions for their management in association with distraction osteogenesis is described.

Mandibular advancement using an intra-oral osteogenic distraction technique: a report of three clinical cases

Osteogenic distraction has been used for decades to lengthen limbs and now attention is focused upon its use within the craniofacial skeleton. This paper addresses distraction of the mandible. It is proposed that mandibular osteogenic distraction could be a possible adjunct to the orthodontic treatment of those adult patients with skeletal anomalies, who would benefit from combined orthodontic/orthognathic treatment. Three consecutive cases from one unit are presented, where adult patients with severe Class II division 1 malocclusions have undergone orthodontic treatment combined with mandibular osteogenic distraction, instead of conventional bilateral sagittal split osteotomies.

Traumatic Cranial Injury Sustained From a Fall on the Rigid External Distraction Device

Distraction osteogenesis has become a popular treatment of congenital maxillocraniofacial anomalies. Many ingenious internal and external devices have been developed and used. The rigid external distraction system based on systems previously used in correction of maxillary retrusion offers postoperative adjustment in two dimensions. Figueroa and Polley reported the use of this device with minimal morbidity in children as young as 5 years of age. They reported no problems with infection, bleeding, pain, loosening of the intraoral splint, dental injury, or wear problems in a series of 14 consecutive cleft patients. Recent modification of the system, rigid external distraction II, has allowed it to be applied to more complex craniofacial deformities that require a LeFort III osteotomy. A review of the neurosurgery and orthopedic literature revealed that halo complications relate primarily to the skull pins. In most cases, these complications can be prevented if the device is carefully applied and monitored. Early recognition and prompt treatment of complications are important. After experience with this system for advancement at the LeFort III level, six patients with various syndromes involving the craniofacial skeleton have undergone LeFort III level distraction osteogenesis with the rigid external distraction device in combination with a planned and stabilized frontosupraorbital advancement. In one of these cases, a 7-year-old child fell on the device after discharge from the hospital and sustained a compound depressed skull fracture that required debridement and repair.

Changes in speech following maxillary distraction osteogenesis

OBJECTIVE

The purpose of this study was to describe changes in articulation and velopharyngeal function following maxillary distraction osteogenesis.

DESIGN

This is a descriptive, post hoc clinical report comparing the performance of patients before and after maxillary distraction. The independent variable was maxillary distraction while the dependent variables were resonance, articulation errors, and velopharyngeal function.

SETTING

The data were collected at a tertiary health care center in Chicago.

PATIENTS

The data from pre- and postoperative evaluations of 18 maxillary distraction patients were used.

OUTCOME MEASURES

The outcome measures were severity of hypernasality and hyponasality, velopharyngeal orifice size as estimated using the pressure-flow technique, and number and type of articulation errors.

RESULTS

At the long-term follow-up, 16.7% exhibited a significant increase in hypernasality. Seventy-five percent of patients with preoperative hyponasality experienced improved nasal resonance. Articulation improved in 67% of patients by the 1-year follow-up.

CONCLUSIONS

In a predominately cleft palate population, the risk for velopharyngeal insufficiency following maxillary distraction is similar to the risk observed in Le Fort I maxillary advancement. Patients being considered for maxillary distraction surgery should receive pre- and postoperative speech evaluations and be counseled about risks for changes in their speech.

Craniofacial distraction osteogenesis: a review of the literature: Part 1: clinical studies

A review of the literature dealing with distraction osteogenesis (DO) of the craniofacial skeleton, provided by a PUBMED search (National Library of Medicine, NCBI; revised 3 April 2000) from 1966 to December 1999 was conducted. Key words used in the search were distraction, lengthening, mandible, mandibular, maxilla, maxillary, midface, midfacial, monobloc, cranial, craniofacial and maxillofacial. This search revealed 285 articles. One hundred and nine articles were clinically orientated and were analysed in detail in this study. The type of distraction, indications, age, type of surgery, distraction rates and rhythms, latency and contention periods, amount of lengthening, follow-up period, relapse, complications and the nature of the distraction device were analysed. This review revealed that 828 patients underwent DO of the craniofacial skeleton; 579 underwent mandibular DO, 129 maxillary DO, 24 simultaneous mandibular and maxillary DO and 96 midfacial and/or cranial DO. Craniofacial DO has proven to be a major advance for the treatment of numerous congenital and acquired craniofacial deformities. Treatment protocols and success criteria for craniofacial DO are suggested on the basis of these results. There is still, however, a lack of sufficient data, especially on follow-up and relapse, so that treatment strategies have to be validated by long-term studies in the future.

High tibial osteotomy using a dynamic axial external fixator

High tibial osteotomy is an accepted treatment for unicompartmental osteoarthritis of the knee. Conventional osteotomy can be a demanding procedure with potential for complications. Opening wedge high tibial osteotomy using an external fixator is an alternative that may have advantages in comparison with classic methods. The aims of the current study were to determine if opening wedge osteotomy using hemicallotasis techniques is safer than, and the outcome comparable with that of, conventional techniques. Seventy-six high tibial osteotomies were performed in 65 patients for primary osteoarthritis. The mean age of the patients was 54.8 years (range, 36-70 years). The mean followup was 6 years. The only serious complication occurred in one patient, who had chronic osteomyelitis develop 2 years after surgery. There were no neurologic or vascular complications. The authors think this technique is safer than conventional techniques. Survivorship at 5 and 10 years was 89% and 63%, respectively. The mean knee score in osteotomies was 26.6 (maximum possible score, 48). The outcome is comparable with, or better than, that of other techniques for osteotomy. Subsequent knee replacement, in cases requiring conversion, was straightforward. The mean score in knees that had osteotomies that were converted to total knee replacements was 33.7.

Functional impact of distraction osteogenesis of the midface on expressive language development

This is a discussion of the impact of distraction osteogenesis on the major function of communication as noted in oral motor control for expressive language. Our experience has been primarily with preadolescent and adolescent patients of school age whose expressive language skills are undergoing continuing development.

Fracture after distraction osteogenesis

We reviewed 173 patients undergoing distraction osteogenesis to determine the incidence, location and timing of fractures occurring as a complication of the procedure. There were 17 fractures in 180 lengthened segments giving an overall rate of fracture of 9.4%. Unexpectedly, the pattern and location of the fractures were very variable; six were within the regenerate itself, six at the junction between the regenerate and the original bone and five at distant sites in the limb. Of those occurring in the regenerate, five were noted to be associated with compression and partial collapse of the regenerate. In three patients collapse and deformity developed gradually in the distracted segment over the six months after removal of the frame. The method of treatment of these fractures should be chosen to take into account multiple factors, which are additional and often different from those to be considered during management of acute traumatic injuries. Internal fixation appears to be most appropriate for displaced fractures, although in small children, or in those in whom there has been, or is, infection of the screw tracks, a new period of treatment using external fixation may be needed. Fixation by intramedullary nailing was associated with a risk of infection, even if screw tracks were assessed as healthy at the time of insertion of the nail. Internal fixation with the use of plates is safe for displaced, unstable fractures in children.

Craniofacial distraction osteogenesis en bloc

Bone distraction of the superior and medial thirds of the craniofacial skeleton en bloc, avoiding a frontal craniectomy is presented. We applied this procedure in eight patients who were more than 5 years old with different types of craniofacial synostosis and who had not received previous treatment, and with a normal frontal shape. During monobloc advancement, major complications were encountered in older patients, especially the impossibility of the brain to expand rapidly to fill the retrofrontal dead space. Distraction osteogenesis of the craniofacial skeleton en bloc (without craniectomy) is feasible. Miniplates and screws are avoided as well as the possibility of frontal relapse or fractures of the frontozygomatic region. The patients did not need skull vault remodeling, except for a small cranioplasty at the bregma zone. The results obtained were satisfactory and stable at the time. This procedure avoids any kind of osteosynthesis, there is no extradural dead space, the operative time is brief, and blood loss is minimal. The inconvenience is the necessity of a second operation to remove the distractor.

[Distraction osteogenesis in maxillofacial surgery]

With distraction osteogenesis (DOG) formation of new bone is initiated by gradual separation of osteotomized bone fragments. Both external and internal distraction devices are available. Since its first application in craniomaxillofacial surgery in the early nineties, developments in distraction osteogenesis have been tremendous. Important advantages of this technique are: lack of a donorsite and its associated morbidity; increase of the volume of the soft tissue envelop; less surgical trauma compared to conventional craniomaxillofacial procedures; and the usability of the technique in growing individuals. Disadvantages of DOG are: the sofar limited experience and follow-up in craniomaxillofacial surgery; and the unknown influences on growth. The technique will gradually find its niche and the general dentist will therefore be increasingly confronted with its specific indications. In this paper the general principles of DOG and a number of indications in craniomaxillofacial surgery are discussed.

Controlled multiplanar distraction of the mandible. Part III: Laboratory studies of sagittal (anteroposterior) and horizontal (mediolateral) movements

Distraction osteogenesis has proven to be an effective technique for the correction of mandibular deficiencies. However, problems have been encountered in achieving a final, idealized form of the mandible when using distraction devices capable of moving the bone segments in only one dimension (uniplanar). Specifically, occlusal irregularities and deficiencies in lower facial contour have been seen following uniplanar distraction. To address these problems, a distraction device capable of independent movements in three planes (multiplanar) was developed. Previously reported studies in a canine model have demonstrated that this device can successfully distract the mandible along both the sagittal axis (anteroposterior or z-axis) and the vertical axis (superoinferior or y-axis). This study examines the ability of the multiplanar device to distract along the sagittal and horizontal axes (mediolateral or x-axis). A total of 12 dogs were included in the study. All animals underwent unilateral or bilateral mandibular distraction using an external multiplanar device. After a latency period of 5 days, primary distraction along the anteroposterior axis at a rate of 1 mm/day for 10 days (10 mm total) was performed. During the following 10 days, along with an additional 11 mm to 20 mm of anteroposterior axis distraction, concomitant secondary distraction was performed along the horizontal (mediolateral) axis at a rate of 5 degrees/day (50 degrees total). Cephalometric radiographs were obtained preoperatively and at the conclusion of both anteroposterior and combined anteroposterior-mediolateral distraction. Computed tomography (CT) scans were obtained preoperatively and at the end of consolidation (28 days), after which all animals were sacrificed and the dry skulls examined. In all animals, distraction along the mediolateral or x-axis was found to change the anteroposterior projection of the mandible. Varus angulation of the device with respect to the midline of the mandible caused compression of the distracted segments and reduced the anteroposterior thrust of the mandible. In contrast, valgus positioning of the device, with respect to the midline of the mandible, created the opposite effect, increasing the distracted length in the anteroposterior direction. The bone (mandibular) segments being distracted assumed the orientation of the device only for valgus positioning of the device (producing a decrease in the bigonial distance). Conversely, there was no effect from the mediolateral angulation on the distracted segments during varus positioning of the device. A possible explanation for this finding may be a greater resistance to an increase in the bigonial distance (varus positioning of the device) posed by obstruction of lateral movement of the condyle. This stands in contrast to a decrease in the bigonial distance observed following valgus positioning of the device. These findings confirm the clinical impression that distraction along the anteroposterior or sagittal axis remains the critical or keystone therapeutic maneuver in distraction of the mandible. Mediolateral or horizontal axis distraction is best used only as a supplementary movement; in essence, it only affects the anteroposterior dimension with little impact on clinically relevant changes to the bigonial distance.

Long-term effect of mandibular midline distraction osteogenesis on the status of the temporomandibular joint, teeth, periodontal structures, and neurosensory function

PURPOSE

This study retrospectively evaluated the long-term effects of transverse symphyseal distraction osteogenesis (DO) on the temporomandibular joint (TMJ) symptoms, periodontal health, tooth vitality, and nerve injury after surgery.

PATIENTS AND METHODS

Twenty-three patients were treated with symphyseal DO during a 4-year period. Fifteen patients were available for follow-up from 7 to 45 months postoperatively (ave, 24.5 months). The patients were clinically evaluated for TMJ symptoms, periodontal pocket formation, tooth vitality and mobility, crestal bone loss, and attached gingival tissue changes. Radiographs of the mandibular anterior teeth were used to evaluate for periodontal bone loss, periapical lesions, or widening of the periodontal ligament (PDL).

RESULTS

Preoperatively, 47% of the patients had TMJ symptoms. No patient had symptom worsening or developed new symptoms postoperatively. Five patients' TMJ symptoms improved, and 3 experienced complete resolution of symptoms. No periodontal bone loss or soft tissue recession were evident. Tooth vitality was maintained in 13 patients. Two patients developed Class II mobility of 1 mandibular central incisor, 1 patient had tooth pain and a widened PDL adjacent to the osteotomy/corticotomy site, and 1 patient experienced mental nerve paresthesia.

CONCLUSIONS

DO can be used to treat transverse discrepancies of the mandible with limited morbidity.

Tooth-borne distraction of the mandible. An experimental study

Two mini-pigs and 6 micropigs were fitted with a dentally fixed device for osteodistraction of the mandible. Following bilateral osteotomy and after a latency period of 7 days, the apparatus was activated 1 mm per day. A 9 mm lengthening of the mandible was achieved. After a retention period of 6 weeks, the device was removed followed by a consolidation period of 6 weeks. During the experiment, the callus and bone formation and potential dental and periodontal reactions were radiologically examined. Polychrome sequential labelling was performed by injecting calcein green and xylenol orange for histological assessment of bone. The animals were killed at the 14th postoperative week and the area of distraction and the roots of the adjacent teeth were histologically studied. After 12 weeks, the osteogenesis in the distraction gap was complete, showing lamellar bone. No detrimental effects at the roots or in the periodontium of the adjacent teeth were seen. Thus, lengthening or widening of the mandible using a tooth-borne distraction device seems feasible in selected cases.

Changes in osseous correction after proximal tibial osteotomy: radiostereometry of closed- and open-wedge osteotomy in 33 patients

33 patients (22 men), median age 54 (40-68) years, with medial gonarthrosis grades 1-3, were treated by closed-wedge osteotomy (high tibial osteotomy = HTO, n 16) or open-wedge osteotomy by hemicallotasis (hemicallotasis osteotomy = HCO, n 19). 2 patients were operated on bilaterally. The patients were studied by RSA (radiostereometric analysis) for measuring 3-D changes in the correction achieved. In the HTO group the RSA measurements were obtained at the time of plaster removal, 1 month later and 1 year after surgery. In the HCO group, the RSA measurements were performed at the time of removal of the external fixator, 1 month later and 1 year after surgery. After removal of the fixation, HTO was associated with increased medial/lateral and distal translation of the proximal segment, compared to HCO. In addition, the tibial plateau rotated more around the longitudinal axis of the tibia after HTO.

Velopharyngeal changes after maxillary advancement in cleft patients with distraction osteogenesis using a rigid external distraction device: a 1-year cephalometric follow-up

The effect of maxillary advancement on speech may have benefits on articulation improvement but compromises velopharyngeal (VP) closure by increasing the nasopharyngeal distance. The purpose of this study was to evaluate the static VP anatomic changes on lateral cephalograms in patients who underwent maxillary advancement through distraction osteogenesis (DO) with a rigid external distraction device and to correlate these changes with clinical speech data. Twenty-two patients (5 female and 17 male) underwent maxillary advancement through DO utilizing a rigid external distraction device (age, 5.2 to 25.7 years) with various diagnoses, including 13 unilateral cleft lip and palate (CLP) patients, 5 bilateral CLP patients, 1 isolated cleft palate patient, 2 facial cleft patients, and 1 patient with craniosynostosis. Lateral cephalograms of preoperative, immediate postdistraction, and 1-year postdistraction were obtained for analysis. Speech evaluation was performed preoperatively, immediate postdistraction, and then at 6-month intervals, and included assessment of air pressure flow, hypernasality, and articulation. With an average amount of 8.9 mm maxillary forward advancement, 14% of patients (3 of 21) presented deterioration in hypernasality. However, 57% of patients (12 of 21) demonstrated improvement in articulation. The cephalometric analysis demonstrated an increase in nasopharyngeal depth by 8.5 mm (1:1 ratio with bony movement) and velar angle by 14.1 deg. The length of the soft palate remained unchanged. The need ratio (intersection of palatal plane and posterior pharyngeal wall-posterior nasal spine/posterior nasal spine--tip of uvula) worsens after distraction. The deterioration of hypernasality was related to the amount of forward distraction, especially in patients without a preexisting pharyngeal flap (PF). Speech evaluation is an important aspect concerning treatment planning for maxillary distraction. The increase in nasopharyngeal depth may compromise VP closure. The increase in velar angle was considered to be part of the compensation in the VP mechanism. An adverse effect of a preexisting PF on maxillary distraction was not observed; however, it prevented postoperative hypernasality.

Evaluation of inferior alveolar nerve function during distraction osteogenesis in the dog

PURPOSE

A series of electrophysiologic studies were performed in a canine model to evaluate inferior alveolar nerve (IAN) function during distraction osteogenesis of the mandible.

MATERIALS AND METHODS

Fourteen dogs, including two controls, were used in the study. Twelve dogs underwent a 10-mm bilateral mandibular lengthening with an intraoral bone-borne appliance and midbody osteotomy. By using sensory nerve action potentials, IAN function was assessed before and immediately after surgery, before and at the completion of distraction, and before necropsy after 4, 6, or 8 weeks of fixation.

RESULTS

Twelve of the 24 nerves showed a complete loss of evoked potential after surgery without recovery at any point throughout the study. Acute nerve injury caused by either the osteotomy or screw encroachment was identified at necropsy. The other 12 nerves showed reproducible responses after surgery. Eight of these nerves had significant amplitude attenuation of the evoked potentials, which was identified at necropsy as a result of acute injury. The remaining four nerves did not show significant evoked potential abnormalities and appeared to be grossly normal at necropsy. During distraction, the amplitude of evoked potentials in all 12 nerves remained at the postoperative level, whereas latency showed a significant delay. In 7 of these 12 nerves, various degrees of evoked potential recovery were identified at the completion of the study.

CONCLUSIONS

The high incidence of acute IAN injury in the current study was primarily related to device construction and osteotomy technique. If acute nerve injury is avoided at surgery, distraction osteogenesis with 10 mm mandibular lengthening appears to produce minimal deleterious effect on IAN function.

Seven years clinical experience with mandibular distraction in children

Mandibular distraction was performed on 14 children, between September 1991 and December 1997. Their average age was 6.9 years, ranging from 1.5 to 13.5 years. All patients had severe hypoplastic mandibles with retromandibulism. Seven of the children (50%) had respiratory distress due to obstruction of the upper airway before distraction. This resolved in every case. Five patients underwent unilateral and nine bilateral distraction. A total of 23 distractors were used, 15 were applied extraorally and 8 endorally. The average latency time after operation was 2.8 days, but for the past 2 years, distraction was started beginning with the operation. The distraction was increased twice daily for an average of 5.5 weeks, by 0.4 or 0.5 mm each time, depending on the distractor. Computed tomography and ultrasound were used to follow the ossification process in the distraction gap and to measure the lengthening achieved. Subsequent retention time averaged 2.4 weeks. The mandibles were elongated by up to 18 mm (average 9.3 mm) and the respiratory distress symptoms resolved in all patients. Several minor complications which are reported occurred. Six patients were followed up for periods between 3 and 7 years. During this time further growth of the distracted mandibles was recorded.

[A postoperative osteosarcoma recurrence after bone distraction by Ilizarov method in a dog]

Distraction osteogenesis by Ilizarov's method is becoming popular for limb saving surgery today. In this article we report a case of osteosarcoma recurrence after using bone distraction in a dog with osteogenic sarcoma. This case suggests that stimulation of osteogenesis by bone distraction promotes tumor recurrence and metastases in osteosarcoma. We recommend to use this method only when allograft or endoprostheses can not save the limb after wide bone resection.

The morphological basis of increased stiffness of rabbit tibialis anterior muscles during surgical limb-lengthening

When the tibialis anterior muscle of the rabbit is progressively stretched during surgical limb distraction, the muscle fibres lengthen by addition of new serial sarcomeres, provided that stretch is carried out at an appropriate rate. However, in spite of the apparent adaptation to the new functional length, range of joint movement is greatly decreased. In this study we have first, made measurements of the passive tension developed by distracted muscles over the range of joint movement and secondly made quantitative measurements of endomysial and perimysial connective tissue content. It was found that at all ankle joint angles greater than 90 degrees, the passive tension developed by the distracted muscles was greater than both contralateral and sham-operated controls. Image analysis showed that the ratio of collagen to contractile material was increased in distracted muscles compared with muscles from sham-operated controls, due to increased deposition of collagen type III. Scanning electron microscopy showed the presence of a dense perimysial weave surrounding the distracted muscle fibres. These quantitative and qualitative changes in the connective tissue component could account for the increased stiffness demonstrated by the physiological measurements. It would seem that in distracted muscle the connective tissue element adapts less readily than the contractile component, with prolonged stretch leading to damage to the perimysial and endomysial network, with subsequent fibrosis and loss of muscle compliance. Such changes could help explain the loss of range of movement noted in the distracted limbs of patients undergoing surgical limb-lengthening and in other conditions that result in muscle contractures.

Distraction osteogenesis of the lower extremity with use of monolateral external fixation. A study of two hundred and sixty-one femora and tibiae

We reviewed the results of distraction osteogenesis of 114 femora and 147 tibiae that had been lengthened to treat a variety of diagnoses. The femora had been lengthened an average of eleven centimeters (range, 3.5 to 17.0 centimeters), or 48 per cent (range, 8 to 86 per cent) of the original femoral length. The average total time for the treatment of the femora (use of the fixator and any subsequent immobilization) was 257 days (range, 105 to 420 days). There were 114 complications related to the femoral lengthenings, which led to eighty-seven additional operations. The tibiae were lengthened an average of nine centimeters (range, 3.0 to 15.6 centimeters), or 41 per cent (range, 9 to 100 per cent) of the original tibial length. The average total time for the treatment of the tibiae was 268 days (range, 110 to 497 days). There were 196 complications related to the tibial lengthenings, which led to 219 additional operations. The Achilles tendon was lengthened during or after seventy-three (50 per cent) of the tibial lengthenings. The femoral lengthenings that were performed to treat a limb-length discrepancy were associated with significantly higher rates of complications overall (p = 0.010) and additional operations (p = 0.023) for each percentage of length gained than those that were performed to treat achondroplasia or another skeletal dysplasia. The femoral lengthenings that were performed to treat short stature (of an endocrine or idiopathic etiology) were also associated with higher rates of complications overall and additional operations than those performed to treat skeletal dysplasias, but the rates were lower than those for lengthenings performed to treat limb-length discrepancy. The rate of complications overall associated with femoral lengthening in patients who were fourteen years old or more was significantly higher than that associated with lengthening in patients who were less than fourteen years old (p = 0.047). Femoral lengthening through the metaphysis was associated with significantly higher rates of complications overall (p = 0.031) and additional operations (p = 0.042) for each percentage of length gained than femoral lengthening through the diaphysis. The tibial lengthenings that were performed to treat Turner syndrome and idiopathic short stature were associated with significantly higher rates of complications overall (p = 0.026) and additional operations (p = 0.003) for each percentage of length gained than those performed to treat skeletal dysplasias. The rate of joint-related problems (p = 0.044) and that of additional operations (p = 0.053) after tibial lengthening in patients who were fourteen years old or more were significantly higher than those rates after tibial lengthening in patients who were less than fourteen years old. The site of the tibial osteotomy did not affect the rate of complications or additional operations. The femoral healing indices (in terms of both days per centimeter [p = 0.002] and days for each percentage of length gained [p = 0.019]) were significantly higher in the patients who were fourteen years old or more than in those who were less the fourteen years old. These values could not be used to predict an increase in the complications because of poor bone formation. The results of the present review suggest that the use of healing indices to gauge the final outcome of distraction osteogenesis is questionable; we were unable to discern significance or clinical importance from appropriately adjusted values.

Acute correction and distraction osteogenesis for the malaligned and shortened lower extremity

In limbs with combined shortening with angulation or malrotation, deformity may be quickly or slowly corrected before lengthening with external fixation. We examined a series of 35 patients with 40 limbs that underwent acute deformity correction and subsequent gradual lengthening. The average deformity corrected was 19 degrees, with subsequent average lengthening of 4.1 cm. Good radiographic callus formation was noted in 34 of the 40 segments studied. The magnitude of deformity correction had no effect on the quality of lengthened bone, incidence of complications, or the healing index. Skeletally mature segments had statistically significant decreased bone formation (p = 0.001), increased prevalence of callus complications (p = 0.001), and a higher healing index (p = 0.003). Based on this experience, it is our conclusion that immediate correction and lengthening is suitable in children and adolescents who have malaligned and shortened lower extremities. Because of poorer results in older patients, we believe that other techniques should be considered in adults.

Statistical analysis of axial deformity during distraction osteogenesis of the tibia

In this study, we documented the prevalence of coronal axis malalignment in a series of 93 tibias (from 54 patients) lengthened with monolateral fixation. The average length obtained by distraction osteogenesis was 8.9 cm (range, 3.5-15.6) or 38% of the original bone length (range, 11-78%). Fifty (54%) of 93 tibias had documented valgus angulation of > or = 10 degrees or had fixator manipulation during the lengthening process for undesirable or progressive angulation; no cases of varus angulation were noted. Thirteen (14%) segments had later corrective osteotomy for unsatisfactory valgus malalignment. Statistical analysis revealed two factors to have a significant effect on the rate of malalignment. Those cases that had tibial osteotomy below the proximal one third of the original tibial length and those cases in which the fixator was placed > 5 degrees out of parallel had higher rates of angulation or manipulation (p < 0.001 and p = 0.002). Although the percentage of original bone lengthened was not statistically significant (p = 0.083), it did have an important effect on rates of axial malalignment. From this study we conclude that relatively high rates of malalignment in the tibia during distraction osteogenesis with monolateral external fixation are predominately the result of more distal osteotomies and nonparallel fixator placement. Attention to these details in general, and particularly where long lengthenings are planned, may significantly reduce this common complication.

Lower-limb lengthening in short stature. An electrophysiological and clinical assessment of peripheral nerve function

We assessed peripheral nerve function during and after lower-limb lengthening by callotasis in 14 patients with short stature, using motor conduction studies. Four patients with short stature of varying aetiology showed unilateral and one showed bilateral weakness of foot dorsiflexion. Both clinical and electrophysiological abnormalities consistent with involvement of the peroneal nerve were observed early after starting tibial callotasis. There was some progressive electrophysiological improvement despite continued bone distraction, but two patients with Turner's syndrome had incomplete recovery. A greater percentage increase in tibial length did not correspond to a higher rate of peroneal nerve palsy. The function of the posterior leg muscles and the conduction velocity of the posterior tibial nerve were normal throughout the monitoring period. The F-wave response showed a longer latency at the end of the bone distraction than in basal conditions; this is probably related to the slowing of conduction throughout the entire length of the nerve.

Mandibular distraction osteogenesis. Preliminary results of an animal study with a dentally fixed distraction device

Lengthening of the human mandible by distraction osteogenesis has become an accepted treatment for correction of severe mandibular disto-basal discrepancies in recent years. This usually entails the deployment of extra-orally located distraction devices. This type of device often causes conspicuous scarring. To avoid this scarring, an intra-oral device is to be developed. In the present animal study, 2 "Troll" mini-pigs and 2 "Yucatan" micro-pigs were fitted with a new solely dentally fixed orthodontic device for mandibular distraction osteogenesis. Following bilateral osteotomy in the dentigerous area of the mandibular body and a latent period of 2 to 7 days, the apparatus was activated 1 mm per day. Within a period of 9 days, a mandibular lengthening of 9 mm was reached. This situation was retained using the distraction device for 6 weeks. After removal of the apparatus, there followed another 6-week period of consolidation. During the experiment, the callus and bone formation and potential dental and periodontal reactions were radiologically examined and underwent histological examination at the end of the experiment. Twelve weeks after the mandibular lengthening, the osteogenesis in the distraction areas was complete. No destructive processes were recognizable, either at the roots or at the periodontium of the teeth near the osteotomy gap. Lengthening of the mandibular body using distraction osteogenesis with the help of a solely dentally fixed distraction device is thus feasible and can, in the future, become the appropriate treatment in the correction of severe mandibular deficiency.