Force level and strain patterns during bilateral mandibular osteodistraction

External versus Internal Distraction Devices in Treatment of Obstructive Sleep Apnea in Craniofacial Anomalies

Background:

Obstructive sleep apnea is often associated with congenital craniofacial malformations due to hypoplastic mandible and decreased pharyngeal airway. In this study, we will compare external and internal distraction devices for mandibular lengthening in terms of effectiveness, results, patient comfort, and complications.

Methods:

Thirty-seven patients were treated by bilateral mandibular distraction osteogenesis for obstructive sleep apnea: 20 with external and 17 with internal distraction devices.

Results:

Lengthening of the mandible and increase of the pharyngeal airway were obtained in all patients. Using the external devices, the average mandibular elongation was 30 mm versus 22 mm with the internal devices; however, after 1 year, the results were more stable with internal devices. External devices carried greater risk for pin tract infection than the internal devices (27.5% vs 5.88%). In addition, pin loosening in 22.5% required pin replacement or led to reduced retention period. Internal devices had a precise and predictable vector of lengthening and left less visible scars at the submandibular area but carried the disadvantage of requiring a second operation for device removal. In very young children with severe micrognathia, it was impossible to place internal devices, and external devices were used.

Conclusions:

Internal devices should be the first choice because they are more comfortable to the patients, more predictable vector of lengthening, are less vulnerable to dislodgement, and leave reduced scarring, with the great disadvantage of second operation for removal. However, external devices still should be considered mainly in severely hypoplastic cases, and the surgeon should be prepared for both options.

In Vitro Mechanical Evaluation of Mandibular Bone Transport Devices

Bone transport distraction osteogenesis (BTDO) is a surgical procedure that has been used over the last 30 years for the correction of segmental defects produced mainly by trauma and oncological resections. Application of BTDO has several clinical advantages over traditional surgical techniques. Over the past few years, several BTDO devices have been introduced to reconstruct mandibular bone defects. Based on the location and outline of the defect, each device requires a uniquely shaped reconstruction plate. To date, no biomechanical evaluations of mandibular BTDO devices have been reported in the literature. The present study evaluated the mechanical behavior of three different shaped prototypes of a novel mandibular bone transport reconstruction plate and its transport unit for the reconstruction of segmental bone defects of the mandible by using numerical models complemented with mechanical laboratory tests to characterize strength, fatigue, and stability. The strength test evaluated device failures under extreme loads and was complemented with optimization procedures to improve the biomechanical behavior of the devices. The responses of the prototypes were characterized to improve their design and identify weak and strong regions in order to avoid posterior device failure in clinical applications. Combinations of the numerical and mechanical laboratory results were used to compare and validate the models. In addition, the results remark the importance of reducing the number of animals used in experimental tests by increasing computational and in vitro trials.

[Evaluation of potential damage to the regenerate during callus molding after mandibular distraction osteogenesis. Experimental study using an animal model]

BACKGROUND

Molding the regenerate created by distraction osteogenesis has clinically been shown to be an efficient lifeboat, good enough that for complex three-dimensional deformities final adjustments by molding the regenerate may be part of the treatment plan. The study assessed the limits of molding a regenerate, taking into consideration compressive and tensile forces acting simultaneously on the fresh callus.

MATERIAL AND METHODS

Distraction osteogenesis was performed in 15 beagle mandibles using custom-made devices which allowed for lengthening as well as for angulation. After linear distraction of 10 mm, a defined 20 degrees angulation was performed in one acute step. The position of the fulcrum of the device allowed the regenerate to be compressed and stretched simultaneously. The effects on bone healing were assessed after 6 or 13 weeks of consolidation and compared to a control group where only linear distraction was performed.

RESULTS

Radiological and histological investigations demonstrated that no significant difference between the biological behavior of the compressed and the stretched zone of the regenerate could be found. However, there were signs, showing the more critical character of the stretched area. After 6 weeks of consolidation, some specimens revealed delayed ossification of the stretched zone. Under stable conditions, this delay was compensated after 13 weeks of consolidation and complete osseous healing occurred.

CONCLUSIONS

Under stable conditions, a fresh regenerate can be molded to a considerable extent without endangering osseous healing permanently. Nevertheless, tensile forces acting on the regenerate should be minimized to prevent damage to the new bone. This can be achieved by overdistraction prior to callus molding or by gradually changing the vector of distraction during the lengthening process.

Distraction osteogenesis of the canine mandible: the impact of acute callus manipulation on vascularization and early bone formation

PURPOSE

Manipulations of the newly created regenerate, using adjustable multiplanar devices during distraction osteogenesis or as a 1-step molding procedure at the end of the distraction process, may be necessary to correct the position of the mandible. Treatment of complex deformities may require preplanned major angulation provided by adjustable devices. We sought to assess the effects of molding the fresh regenerate on vascularization and early bone formation within clinically relevant dimensions.

MATERIALS AND METHODS

Evaluation of the nature of the problem in mechanical terms was based on a geometrical model, its dimensions chosen with clinical relevance. Custom-made devices, allowing the simultaneous compression and stretching of a regenerate 10 mm long, were fixed bilaterally in the angular region of beagle mandibles (n = 14). Angulation of 20 degrees (n = 7) or 30 degrees (n = 7) was performed immediately after ending the lengthening period, and the animals were killed after a 7-day consolidation period. The vascular system was stained via intravital Procion red infusion and post mortem carbon ink (Deperussol P130; Degussa AG, Frankfurt, Germany) perfusion to assess possible damages. Qualitative and quantitative evaluations of the mineralized tissue were performed with contact radiography, quantified computed tomography, and histologic assessment.

RESULTS

The only finding indicating mechanical forces acting on the regenerate was related to orientation of the collagenous fibers. Vascular damage was not observed. Mineralization patterns were identical in both the compressed and the stretched zone. The degree of angulation had no visible impact on early bone formation, even if compression and stretching of the regenerate at a range of 33% to 54% exceeds most clinical requirements. However, the amount of callus formation differed independent of the shaping angle, revealing parameters other than the degree of angulation to be important.

CONCLUSIONS

Although the newly forming bone is highly sensitive to nonphysiologic strain during the lengthening process, a completed fresh regenerate, created by distraction osteogenesis, can be manipulated to a considerable extent without endangering early callus formation. Manipulation of the regenerates would provide a precise final result, minimizing the need for secondary corrections and diminishing treatment duration and costs.

Theoretical considerations for the surgical correction of mandibular deformity in hemifacial microsomia patients using multifocal distraction osteogenesis

PURPOSE

This theoretical pilot study investigated the geometric changes necessary to normalize the mandibular shape in hemifacial microsomia. Using the mandibular deformity of a 13-year-old patient affected by hemifacial microsomia as an example, we addressed 2 main issues. First, the number of segments needed for adequate reshaping of the deformed mandible is evaluated. Second, the geometry of the intersegmental gaps resulting from reposition of the segments is correlated with established parameters of distraction osteogenesis to theoretically predict the practicability of correction using multifocal distraction osteogenesis.

MATERIALS AND METHODS

Virtual surgery was performed on a solid mandible model created from computed tomography (CT) data from a patient with hemifacial microsomia type IIB. In the first step, ideal mandibular reshaping was achieved according to anthropometric standard measurements using 7 osteotomies. By scanning and superimposition of the virtual models and variation of distraction sites and numbers, we assessed the minimal number of osteotomies necessary for optimal correction of the deformity. Geometrical evaluation of the regeneration and assessment of the possibilities of continuous curved distraction were also performed.

RESULTS

Three osteotomies were shown to be sufficient for complete mandibular reshaping. Using accepted parameters for distraction osteogenesis, the geometry of the regenerate allows for continuous curved distraction. However, simultaneous movements at several distraction sites result in interfering vector forces, making coordination of multifocal distraction difficult.

CONCLUSION

Theoretical assessment of a severe mandibular hypoplasia in hemifacial microsomia revealed the 3-dimensional (3D) complexity of the deformity for corrective procedures, especially distraction osteogenesis. Despite precise planning and transfer of the plan to the patient, multifocal 3D distraction may result in deviations from the planned result. Manipulation of the fresh regeneration may be necessary to correct inaccuracies.

Cranio-facial distraction osteogenesis: a review of the literature. Part II: Experimental studies

In this study the literature dealing with experimental cranio-facial distraction osteogenesis (DO) was reviewed. A PUBMED search (National Library of Medicine [NCBI] revised 1 April 2001) from 1966 through December 2000 was conducted. Key words used in the search were: distraction, lengthening, mandible, mandibular, maxilla, maxillary, midface, midfacial, monobloc, cranial, cranio-facial, maxillofacial. This search revealed a total of 120 experiment-orientated articles that were all analyzed in detail in this study. The purpose of the experimental study, animal model, animal growth status, type of distraction, type of surgery, distraction rate and rhythm, latency and contention period, amount of lengthening, relapse, complications and nature of the distraction device were analyzed. This review revealed that a total of 1207 animals were used in seven different animal models for research on cranio-facial DO: 54 using dogs (45.0%), 25 using rabbits (20.8%), 18 using sheep (15.0%), 11 using minipig (9.2%), seven using monkeys (5.8%), four using rats (3.3%) and one using a cat model (0.8%). Based on the results of this study, an attempt was made to provide biological DO parameters and guidelines for future research on experimental cranio-facial DO related to the appropriate animal model.

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.

Do position and soft tissue affect distraction vector? An in vitro investigation

OBJECTIVES

The purpose of this investigation was to provide an in vitro evaluation of the effects of soft tissue and position on vector during distraction.

MATERIALS AND METHODS

A polyurethane skull and mandible replica (Synbone, Landquart, Switzerland) was used in this study along with an internal distraction device (Synthes Maxillofacial, Paoli, PA). The first portion of the investigation evaluated the effects of distractor position (inferior body, midbody, and superior body) on distraction vector. The second portion of the investigation used polyethylene straps to simulate the suprahyoid muscles and muscles of mastication, and polysulfide to simulate periosteum and mucosa. A laser light source attached to the synthetic mandible was projected on a grid 7.1 m from the construct to measure deflection from the starting point. The distractor was advanced 8.0 mm for each trial. Five trials each for inferior, middle, and superior, with and without simulated soft tissues (N = 30) were performed. Vertical and horizontal deflection along with absolute distance were measured and recorded. Means and standard deviations were derived for groups, and compared for statistical significance (P <.05) with a 1-way analysis of variance for the effects of position with and without simulated soft tissue, and with a paired t-test for the effects of simulated soft tissue within groups of similar distractor position.

RESULTS

Statistically significant differences (P <.05) for distractors without simulated soft tissues were only noted for vertical deflection between the inferior and superior distractor groups. Statistically significant differences were noted for all measures, for all distractor positions with simulated soft tissues. Statistically significant differences were noted for all measures between similar distractor positions with and without simulated soft tissues. Distractors without simulated soft tissues were deflected lateral to the y-axis and above the x-axis. Distractors with simulated soft tissues were deflected lateral to the y-axis, but below the x-axis. For distractors with simulated soft tissues, the closer to the inferior border, the less the deflection from the x-axis.

CONCLUSION

Position alone had minimal effects on distraction vector. Simulated soft tissues affected the vector of distraction. The combination of position and simulated soft tissues affected distraction vector.

Original sagittal split osteotomy revisited for mandibular distraction

INTRODUCTION

A malformed mandible and an abnormally positioned mandibular foramen make it difficult to plan an ideal osteotomy line for mandibular distraction. In addition, there have been reports of such complications as nonunion, damage and stretch injury of the inferior alveolar nerve and tooth germ damage when conventional osteotomy or corticotomy are used for mandibular distraction. The authors utilized the original sagittal split ramus osteotomy for mandibular distraction.

PATIENTS AND METHODS

Five patients (three unilateral hemifacial microsomia, one bilateral hemifacial microsomia, and one mandibular retrusion) were included in this study of distraction osteogenesis using the sagittal split ramus osteotomy. Extraoral distraction devices were applied to the first four patients. An intraoral device with mono-cortical screw fixation was used for the fifth patient.

RESULT

In all five cases, the results of the distraction were satisfactory. Complications (as listed) of conventional osteotomy when used for distraction were avoided. Satisfactory results were achieved and these were also well maintained postoperatively (mean follow up: 36 months).

CONCLUSION

The authors believe that sagittal osteotomy for mandibular distraction osteogenesis makes it possible, to avoid injury to the inferior alveolar nerve during operation and stretching injury during distraction and to prevent tooth germ injury. It is also possible to diversify the osteotomy line for various force vectors to enlarge the bony contact surface area. Therefore, we suggest that sagittal split ramus osteotomy should be used as a preferred modification of osteotomy for mandibular distraction.

Mandibular distraction force: laboratory data and clinical correlation

PURPOSE

In vitro data were collected to measure torque-force values of an internal distraction device. The measurements were correlated with in vivo torque readings in an attempt to better understand the force required to distract the osteogenic bone callus of the human mandible during distraction osteogenesis.

METHODS AND MATERIALS

Five internal craniofacial distraction devices were mounted on an apparatus to test load limits and torque measurements. The apparatus aligned the devices so that weight provided a force opposite and parallel to the vector of distraction. Weights were added in 5-lb increments, and the devices were activated 0.5 mm for each torque reading. Torque readings were obtained from a calibrated torque wrench. Measurements were plotted on a graph and correlated with clinical torque readings obtained from 8 patients undergoing mandibular lengthening.

RESULTS

The average torque for distracting the human mandible 0.5 mm twice a day was 4.2 +/- 1.6 Newton-centimeters (N-cm). The average slope of the in vitro data shows that 4.2 N-cm of torque is equivalent to a force of 35.6 N. The average force of device failure was 235.8 N.

CONCLUSION

Torque-force diagrams offer an effective means for calibrating safety margins and load capabilities for internal distraction devices. Quantification of axial forces encountered in mandibular lengthening will help contribute to the overall understanding and biomechanics of mandibular distraction osteogenesis.