Comparison of gene expression of osteogenic factors between continuous and intermittent distraction osteogenesis in rabbit mandibular lengthening

Nonvascular transport distraction osteogenesis in bone formation and regeneration. Is it an accidental phenomenon?

PURPOSE

To explore the osteogenic mechanism of nonvascular transport distraction osteogenesis (NTDO) by constructing mandibular defects in dogs.

METHODS

Sixty adult dogs were randomly divided into three groups with 20 dogs in each group. Canine mandibular defect models of NTDO were constructed. Animals were euthanized 1, 4 and 12 weeks after distraction, and the transport disc and surrounding tissue were collected and fixed. Histochemical staining using hematoxylin and eosin (H&E) and electron microscopic observations were used to examine bone regeneration.

RESULTS

Distraction bone regeneration was observed in the distraction gap and around the transport disc, and osseous connections had formed between new bone and the transport disc after one week. Osteoclasts gathered around the transport disc, and bone absorption pit formation could be seen. After 4 weeks of distraction, the new bone around the transport disc was close to maturity with thick sclerostin on the middle of the transport disc. After 12 weeks the new bone and the transport disc were fully integrated, and were difficult to distinguish by H&E staining and electron microscopy.

CONCLUSIONS

Canine mandibular defects were successfully repaired by NTDO resulting in ideal new bone formation and fully recovered mandibular physiological function. The surrounding tissues, including musculoskeletal tissues, the periosteum and other soft tissues and the nonvascular transport disc, together contribute to bone regeneration and neovascularization in NTDO.

The effect of altering the mechanical loading environment on the expression of bone regenerating molecules in cases of distraction osteogenesis

Distraction osteogenesis (DO) is a surgical technique where gradual and controlled separation of two bony fragments following an osteotomy leads to the induction of new bone formation in the distracted gap. DO is used for limb lengthening, correction of bony deformities, and the replacement of bone loss secondary to infection, trauma, and tumors. Although DO gives satisfactory results in most cases, one major drawback of this technique is the prolonged period of time the external fixator has to be kept on until the newly formed bone consolidates thus leading to numerous complications. Numerous attempts at accelerating bone formation during DO have been reported. One specific approach is manipulation of the mechanical environment during DO by applying changes in the standard protocol of distraction. Attempts at changing this mechanical environment led to mixed results. Increasing the rate or applying acute distraction, led to poor bone formation in the distracted zone. On the other hand, the addition of compressive forces (such as weight bearing, alternating distraction with compression or by over-lengthening, and then shortening) has been reported to increase bone formation. It still remains unclear why these alterations may lead to changes in bone formation. While the cellular and molecular changes occurring during the standard DO protocol, specifically increased expression of transforming growth factor-β1, platelet-derived growth factor, insulin-like growth factor, basic fibroblast growth factor, vascular endothelial growth factor, and bone morphogenic proteins have been extensively investigated, the literature is sparse on the changes occurring when this protocol is altered. It is the purpose of this article to review the pertinent literature on the changes in the expression of various proteins and molecules as a result of changes in the mechanical loading technique in DO and try to define potential future research directions.

Responses of distraction regenerate to high-frequency traction at a rapid rate

BACKGROUND

Continuous traction is capable of creating an optimal biological environment for bone healing which may finally compensate for the rapid distraction rate in distraction osteogenesis. This study was designed to investigate the response of distraction callus to continuous distraction at a rapid rate using a rabbit model of mandibular lengthening.

METHODS

Thirty adult New Zealand white rabbits were randomly assigned to the intermittent (1 step/d) or continuous distraction (8 steps/s) group, with 15 in each. After osteotomy, manual-driven or autodriven distractor was adapted accordingly. The distraction was activated at a rate of 3.0 mm/d for 4 days. Five rabbits in each group were killed at week 2, week 4, and week 12 of consolidation, respectively. Plain radiography, microcomputed tomography, and histology examinations were used to evaluate the bone regeneration status.

RESULTS

Plain radiographs and histologic studies demonstrated more advanced bone healing in continuous distraction group than that in intermittent distraction group at all the examined time points. Quantitative microcomputed tomography analysis showed significantly higher bone volume in continuous distraction group at week 2 (p < 0.01) and week 4 (p < 0.05) of consolidation.

CONCLUSIONS

Continuous traction by autodriven distractor could be a promising clinical alternative to shorten the treatment course of distraction osteogenesis. Further studies to test its clinical potential using large animals that have similar metabolic rate and muscular resistance with human being are necessary.

Comparison of gene expression of tissue inhibitor of matrix metalloproteinase-1 between continuous and intermittent distraction osteogenesis: a quantitative study on rabbits

BACKGROUND

Distraction osteogenesis is a controlled surgical procedure that initiates a regenerative process and uses mechanical strain to enhance the biological responses of the injured tissues to create new bone. To explore the effect of high-frequency mechanical traction on the expression of tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), we compared the gene expression of TIMP-1 between continuous and intermittent distraction osteogenesis using a rabbit model of mandibular lengthening.

MATERIALS AND METHODS

Forty adult New Zealand white rabbits were randomly assigned to the intermittent and continuous distraction groups. A unilateral mandibular osteotomy was performed and a custom-designed manual-driven or auto-driven distractor was bridged over the osteotomy segments. Animals were sacrificed at day-6, day-10, day-14 and day-21 after osteotomy. Samples were examined with real-time polymerase chain reaction (PCR).

RESULTS

Real-time PCR examination showed significantly higher mRNA levels of TIMP-1 under continuous distraction than that under intermittent distraction at day-6 and day-10. No significant differences were found at day-14 and day-21.

CONCLUSION

High-frequency traction provides a good mechanical environment for accelerating bone formation by up-regulating TIMP-1.

Quasi-Continuous Autodriven System With Multiple Rates for Distraction Osteogenesis

Introduction. For a given rate of distraction a greater frequency of distraction improves bone formation. However, the current distractors used in clinic are activated manually and produces intermittent advancement. Method. The authors developed an automatic driver that is capable of producing quasi-continuous distraction at a set of rates of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm/d. Using a customized in vitro experimental system, the function and stability of the autodriven system were tested during loading. Results. The angular displacement of the automatic driver was quite regular while driving a constant torque of 4.268 × 10−3 kg m. The driving achieved the target speed with the constant torque. Conclusions. The automatic driven system provides a useful tool to assess the tissue healing at variable distraction rates with quasi-continuous traction. It demonstrates a potential for clinical application to shorten the treatment course of distraction osteogenesis.

Why high frequency of distraction improved the bone formation in distraction osteogenesis?

Distraction osteogenesis, currently a standard method of bone lengthening, is based upon the "tension-stress principle", as proposed by G.A. Ilizarov. Mechanical stimulation by distraction induces biological responses of skeletal regeneration that is accomplished by a cascade of biologic processes including differentiation of pluripotential tissue, angiogenesis, mineralization, and remodeling. The exact mechanism by which strain stimulates bone formation remains unclear. Distraction rate and rhythm must have great influence on the quality of the newly formed bone generated by mechanical traction. The preliminary results demonstrated that for a given rate higher frequency of distraction improved the bone formation, but the mechanism remains unclear. In this article we present a hypothesis that the reason why higher frequency of distraction improved the bone formation for a given rate is that higher frequency of distraction provides smaller microtrauma to tissues within the gap and longer existence time of the microenvironment stimulating tissues within the gap than low frequency distraction. This hypothesis, if proven to be valid, will not only represent a breakthrough in research of mechanism of distraction osteogenesis, but also will open a new door to the bone regeneration.