Microscopic changes in the condyle and disc in response to distraction osteogenesis of the minipig mandible

Modified internal curvilinear distraction device with a pre-embedding guide rail, drive screw, and universal joint for curvilinear lengthening of the mandible: A finite element analysis and animal experiment

OBJECTIVES

The semiburied design of the traditional internal distractor has a relatively high risk of infection and aesthetic problems. To reduce these potential risks, a modified internal distractor with design of pre-embedding curvilinear rail, drive screw, and universal joint was invented. Its stress distribution characteristics and the effect on curvilinear distraction osteogenesis (DO) in vivo were further tested.

MATERIALS AND METHODS

Finite element analysis (FEA) was performed on a model of the human mandible and distraction device to measure the stress distribution during curvilinear DO. Six beagles underwent curvilinear DO and consolidation using the new device. Radiological and histological examinations were performed on the new bone.

RESULTS

On FEA, the stress was concentrated in the condyle (128.6 MPa) and curved guide rails (324.8 MPa). Four of the six animals completed the DO period and were consolidated for 12 weeks. Secondary infections were not observed. Radiography showed that a new fan-shaped bone-15.5 ± 5.5 mm in length and 4.6 ± 1.6 mm in height-was formed in the bone gap. Micro-computed tomography and histological examinations of specimens indicated that the structure of the new bone was similar to that of the normal bone.

CONCLUSIONS

The modified internal curvilinear distraction device meets the mechanical strength requirement and achieve curvilinear DO in animal experiments.

Bilateral Continuous Automated Distraction Osteogenesis: Proof of Principle

The purpose of this study was to demonstrate that automated, continuous, curvilinear distraction osteogenesis (DO) in a minipig model is effective when performed bilaterally, at rates up to 3 mm/day, to achieve clinically relevant lengthening. A Yucatan minipig in the mixed dentition phase underwent bilaterally, at a continuous DO at a rate of 2 mm/day at the center of rotation; 1.0 and 3.0 mm/day at the superior and inferior regions, respectively. The distraction period was 13 days with no latency period. Vector and rate of distraction were remotely monitored without radiographs, using the device sensor. After fixation and euthanasia, the mandible and digastric muscles were harvested. The ex vivo appearance, stability, and radiodensity of the regenerate were evaluated using a semiquantitative scale. Percent surface area (PSA) occupied by bone, fibrous tissue, cartilage, and hematoma were calculated using histomorphometrics. The effects of DO on the digastric muscles and mandibular condyles were assessed via microscopy, and degenerative changes were quantified. The animal was distracted to 21 mm and 24 mm on the right and left sides, respectively. Clinical appearance, stability, and radiodensity were scored as "3" bilaterally indicating osseous union. The total PSA occupied by bone (right = 75.53 ± 2.19%; left PSA = 73.11 ± 2.18%) approached that of an unoperated mandible (84.67 ± 0.86%). Digastric muscles and condyles showed negligible degenerative or abnormal histologic changes. This proof of principle study is the first report of osseous healing with no ill-effect on associated soft tissue and the mandibular condyle using bilateral, automated, continuous, and curvilinear DO at rates up to 3 mm/day. The model approximates potential human application of continuous automated distraction with a semiburied device.

A histologic study of deformation of the mandibular condyle caused by distraction in a rat model

OBJECTIVE

This study investigated the bone resorption process of the rat mandibular condyle after mandibular distraction.

STUDY DESIGN

Male Wistar rats at 10 weeks of age underwent unilateral mandibular distraction at 0.175 mm per 12 hours for 10 days. Histologic and histochemical analyses were performed at postoperative day 1 and weeks 1 and 3.

RESULTS

High-resolution computed tomography (micro-CT) observations showed that deformation of the condyle occurred in the anterior region, where a discontinuity of the condylar cartilage layer was found in histologic sections. This destroyed area gathered many osteoclasts. In the central region, disorganization with a thin hypertrophic cell layer was recognizable by day 1 but later thickened. Morphologic recovery of the mandibular condyle could be attained by week 3 in this animal model.

CONCLUSIONS

These morphologic findings indicate that rapid deformation of the condyle, with destruction of the cartilage layer and bone resorption, was caused by artificial distraction.

Automated continuous distraction osteogenesis may allow faster distraction rates: a preliminary study

PURPOSE

To determine if automated continuous distraction osteogenesis (DO) at rates faster than 1 mm/day results in bone formation by clinical and radiographic criteria, in a minipig model.

MATERIALS AND METHODS

An automated, continuous, curvilinear distraction device was placed across a mandibular osteotomy in 10 minipigs. After 12 mm of distraction and 24 days of fixation, the animals were sacrificed and bone healing was evaluated. The continuous distraction rates were 1.5 mm/day (n = 5) and 3 mm/day (n = 5). A semiquantitative scale was used to assess the ex vivo clinical appearance of the distraction gap (3 = osteotomy not visible; 2 = <50% visible; 1 = >50% visible; 0 = 100% visible), stability (3 = no mobility; 2 and 1 = mobility in 1 plane or 2 planes, respectively; 0 = mobility in 3 planes), and radiographic density (4 = 100% of gap opaque; 3 = >75%; 2 = 50% to 75%; 1 = <50%; 0 = radiolucent). Groups of 4 minipigs distracted discontinuously at 1, 2, and 4 mm/day served as controls.

RESULTS

Automated, continuous DO at 1.5-mm/day and 3-mm/day had similar bone formation compared to discontinuous DO at 1-mm/day. The continuous DO 1.5-mm/day group had significantly higher scores for appearance and radiographic density compared with the discontinuous 4-mm/day group. The continuous DO 3-mm/day group had significantly higher scores for appearance and radiographic density compared with the discontinuous 4-mm/day group and greater stability compared with the discontinuous 2- and 4-mm/day groups.

CONCLUSIONS

Results of this preliminary study indicate that continuous DO at rates of 1.5 and 3.0 mm/day produces better bone formation compared with discontinuous DO at rates faster than 1 mm/day.

Expression of chondromodulin-1 in the temporomandibular joint condylar cartilage and disc

BACKGROUND

The temporomandibular joint (TMJ) cartilage consists of condylar cartilage and disc and undergoes continuous remodeling throughout post-natal life. To maintain the integrity of the TMJ cartilage, anti-angiogenic factors play an important role during the remodeling process. In this study, we investigated the expression of the anti-angiogenic factor, chondromodulin-1 (ChM-1), in TMJ cartilage and evaluate its potential role in TMJ remodeling.

METHODS

Eight TMJ specimens were collected from six 4-month-old Japanese white rabbits. Safranin-O staining was performed to determine proteoglycan content. ChM-1 expression in TMJ condylar cartilage and disc was determined by immunohistochemistry. Three human perforated disc tissue samples were collected for investigation of ChM-1 and vascular endothelial growth factor (VEGF) distribution in perforated TMJ disc.

RESULTS

Safranin-O stained weakly in TMJ compared with tibial articular and epiphyseal cartilage. In TMJ, ChM-1 was expressed in the proliferative and hypertrophic zone of condylar cartilage and chondrocyte-like cells in the disc. No expression of ChM-1 was observed in osteoblasts and subchondral bone. ChM-1 and VEGF were both similarly expressed in perforated disc tissues.

CONCLUSIONS

ChM-1 may play a role in the regulation of TMJ remodeling by preventing blood vessel invasion of the cartilage, thereby maintaining condylar cartilage and disc integrity.

Distraction osteogenesis: advancements in the last 10 years

Distraction is still evolving in the management of patients with orthopedic and craniomaxillofacial deformities. The relationship among latency, gap size, rate, rhythm, and duration of fixation is not totally understood for all of the individual patients and variations in their needs seen in a clinical practice. Numerous factors can influence the quality and quantity of bone seen with distraction, including the age and nutritional status of the patient and the type of distractor that is used.

Recommendations for optimal distraction protocols for various animal models on the basis of a systematic review of the literature

The principles of orthopaedic distraction osteogenesis (DO) have been successfully applied to the craniofacial skeleton, but the latency time, rate and rhythm of distraction, and length of the consolidation period that are optimal for long-bone distraction may be suboptimal for craniofacial DO. The aim of this study was to provide recommendations for optimal distraction parameters in animal experimental research on craniofacial DO. The data used were from studies, added to the PubMed database between 1 January 1973 and 1 January 2007, on the outcome of DO resulting from variations in a single distraction parameter while standardizing the other distraction parameters. Although experimental animal group sizes were rather small, especially in those studies that used large animals, and both skeletally mature and immature animals were used, the (in most cases quantitative) data provided useful information on the optimal parameters in craniofacial DO. A latency period may not be necessary at all. Distraction should be performed at a rate of 1mm/day (this may be halved when small animals such as rats are used) preferably with a continuous rhythm, followed by a consolidation period of 6-8 weeks. These recommendations can be used as basic guidelines for further animal experimental studies on craniofacial DO.

Changes in growth and morphology of the condyle following mandibular distraction in minipigs: overloading or underloading?

OBJECTIVE

Loading of temporomandibular tissues during mandibular distraction may cause changes in condylar growth and cartilage thickness. This study examines the effects of distraction on the condyle in a large animal model by explicitly measuring growth and in vivo loading.

DESIGN

Unilateral mandibular distraction was carried out on 20 growing minipigs divided into three groups. One group underwent distraction but not consolidation, whereas the other two groups were allowed a period of consolidation of either 1 or 2 weeks. Animals received fluorochrome and 5-bromo-2'-deoxyuridine (BrdU) labelling and masticatory strain was measured from the condylar neck. Condylar strain was also recorded in an age-matched sample of eight animals that received no distraction surgery. Immunohistochemical procedures were used to identify dividing prechondroblasts and histological analysis was used to measure mineral apposition rate, count dividing cells, and measure the thickness of condylar cartilage.

RESULTS

Strain magnitude, particularly compressive strain, was much larger on the non-distraction side compared to the distraction side condyle. Compared to normal loading levels, the distraction side condyle was underloaded whereas the condyle on the intact side was overloaded. Mineral apposition and cartilage thickness were greater on the distraction side condyle compared to the opposite side. Differences between the sides were most pronounced in the group with no consolidation and became progressively reduced with consolidation time.

CONCLUSIONS

Increased mineralisation and cartilage thickness on the distraction side condyle are associated with reduced, not increased loading, perhaps because of disruption of the distraction side masseter muscle.

Histological evaluation of the temporomandibular joint after bilateral vertical ramus mandibular distraction in a canine model

The aim of this pilot study was to histologically evaluate the effect of bilateral vertical mandibular distraction osteogenesis (DO) on the temporomandibular joint (TMJ) in a canine model. Eight male beagle dogs underwent DO, with the placement of single-vector internal distractors. One unoperated animal served as control. After a latency period of 7 days, distraction was performed at a rate of 1 mm a day for an average of 12 days. The animals were divided into two groups (n = 4) and sacrificed after one or two months of consolidation. Eighteen TMJs were prepared for histological evaluation. Control TMJs surfaces were smooth, with no irregularities and trabecular bone was thick and multiply connected. In the one-month group, thinning of the trabecular bone was evident. The trabeculae were long, not multiply connected, parallel to each other and perpendicular to the articular surface. Although overall fibrous-cartilaginous tissues covering the TMJs were maintained with no signs of degenerative changes, one condyle from the one-month group had depressions and erosions of the fibro-cartilage layer and subcortical bone. In the two-month group, overall bone and cartilage architecture was more similar to the control specimens. This study indicates that, in the short term, gross changes can occur in the TMJ after bilateral mandibular vertical ramus distraction. These changes seem to be a process of biological adaptation to the pressure and functional changes secondary to surgery and distraction. However, long-term studies are needed to confirm whether the changes are completely reversible.