Angiogenesis is enhanced by continuous traction in rabbit mandibular distraction osteogenesis

Reverse Dynamization Accelerates Regenerate Bone Formation and Remodeling in a Goat Distraction Osteogenesis Model

UPDATE

This article was updated on December 20, 2023, because of previous errors, which were discovered after the preliminary version of the article was posted online. Figure 4 has been replaced with a figure that presents different p values. Also, on page 1943, the text that had read: "Quantitative microCT confirmed that the total volume of the regenerate in the RD group was much smaller compared with the SF (p = 0.06) and DF (p = 0.007) groups, although it was significantly smaller only compared with the DF group (Fig. 4-A). The total volume of the intact bone (contralateral tibia) was significantly smaller in the RD group compared with the other groups, but the RD group had values closest to those for the intact tibia. Similarly, the RD group had less bone volume compared with the SF and DF groups, and this value was significantly different from the DF group (p = 0.034; Fig. 4-B). Of the 3 groups, the RD group had vBMD that was the closest to that of intact bone. It also had significantly higher vBMD compared with the SF and DF groups (p < 0.0001 for both; Fig. 4-C).The results of torsional testing (Fig. 4-D) confirmed that the regenerate bone formed under conditions of RD was significantly stronger than that formed under SF or DF (p < 0.001 versus SF group, and p = 0.0493 versus DF group)."now reads: "Quantitative microCT confirmed that the total volume of the regenerate in the RD group was significantly smaller compared with the SF and DF groups (p < 0.01 for both groups; Fig. 4-A). The total volume of the intact bone (contralateral tibia) was significantly smaller compared with the SF and DF groups (p < 0.0001 for both). The RD group had values closest to those for the intact tibia, and this difference was not significant (Fig. 4-A). Similarly, the RD group had less bone volume compared with the SF and DF groups, and this value was significantly different from the DF group (p < 0.01; Fig. 4-B). Of the 3 groups, the RD group had vBMD that was the closest to that of intact bone, but the intact bone was significantly different compared with all of the other groups (p < 0.0001 for all groups). The RD group had significantly higher vBMD compared with the SF and DF groups (p = 0.042 and p = 0.046, respectively; Fig. 4-C).The results of torsional testing (Fig. 4-D) confirmed that the regenerate bone formed under conditions of RD was significantly stronger than that formed under SF or DF (p < 0.0001 versus SF group, and p = 0.0493 versus DF group). The intact group was significantly different compared with the SF group (p < 0.0001)."

Learning curve of tibial cortex transverse transport: a cumulative sum analysis

OBJECTIVE

This study aimed to describe the learning curve of surgeons performing tibial cortex transverse transport (TTT) and explore its safety and effectiveness during the initial stages of surgeon's learning.

METHODS

The clinical data of patients with diabetic foot ulcers classified as Wagner grade ≥ 2, who underwent TTT at our hospital from January 2020 to July 2021, were included in this retrospective analysis. The same physician performed all procedures. Patients were numbered according to the chronological order of their surgery dates. The cumulative sum and piecewise linear regression were used to evaluate the surgeon's learning curve, identify the cut-off point, and divide the patients into learning and mastery groups. A minimum follow-up period of 3 months was ensured for all patients. Baseline data, perioperative parameters, complications, and efficacy evaluation indicators were recorded and compared between the two groups.

RESULTS

Sixty patients were included in this study based on the inclusion and exclusion criteria. After completing 20 TTT surgeries, the surgeon reached the cut-off point of the learning curve. Compared to the learning group, the mastery group demonstrated a significant reduction in the average duration of the surgical procedure (34.88 min vs. 54.20 min, P < 0.05) along with a notable decrease in intraoperative fluoroscopy (9.75 times vs. 16.9 times, P < 0.05) frequency, while no significant difference was found regarding intraoperative blood loss (P = 0.318). Of the patients, seven (11.7%) experienced complications, with three (15%) and four cases (10%) occurring during the learning phase and the mastery phase, respectively. The postoperative ulcer area was significantly reduced, and the overall healing rate was 94.8%. Significant improvements were observed in postoperative VAS, ABI, and WIFI classification (P < 0.05). There were no significant differences in the occurrence of complications or efficacy indicators between the learning and mastery groups (P > 0.05).

CONCLUSION

Surgeons can master TTT after completing approximately 20 procedures. TTT is easy, secure, and highly efficient for treating foot ulcers. Furthermore, TTT's application by surgeons can achieve almost consistent clinical outcomes in the initial implementation stages, comparable to the mastery phase.

Forces Exerted in Craniofacial Distraction Osteogenesis

BACKGROUND

The purpose of this study was to develop a methodology for quantifying linear forces of distraction osteogenesis, and thereafter apply this methodology to measure and compare distraction force magnitudes between cranial vault distraction osteogenesis (CVDO) and mandibular distraction osteogenesis (MDO).

METHODS

Patients undergoing CVDO or MDO as inpatients had distraction forces acquired with a digital torque-measuring screwdriver. Torque measurements were then converted into linear distraction force values, which were then compared across distraction types and protocols with appropriate statistics.

RESULTS

CVDO was performed on 7 patients (41.2%), and MDO was performed on 10 patients (58.8%). Across the entire cohort, the average maximum force per activation was 27.0 N, and the average elastic force was 10.7 N. Maximum force (CVDO: 52.9 N versus MDO: 12.9 N; P < 0.001) and elastic force (CVDO: 22.0 N versus MDO: 4.5 N; P < 0.001) were significantly higher in patients undergoing CVDO than MDO. Multivariate regression demonstrated that maximum activation force was significantly associated with sequential days of distraction (B= + 1.1 N/day; P < 0.001), distraction rate (B= + 8.9 N/mm/day; P = 0.016), distractor hardware failure (B= + 10.3 N if failure; P = 0.004), and distraction type (B= + 41.4 N if CVDO; P < 0.001).

CONCLUSIONS

Cranial vault distraction requires significantly more linear distraction force than mandibular distraction. Maximum forces increase with each day of distraction, as well as with increased distraction rates. Linear distraction force methodology from this study may provide the foundation for future development of optimized procedure-specific or patient-specific distraction protocols.

Biodegradable magnesium combined with distraction osteogenesis synergistically stimulates bone tissue regeneration via CGRP-FAK-VEGF signaling axis

Critical size bone defects are frequently caused by accidental trauma, oncologic surgery, and infection. Distraction osteogenesis (DO) is a useful technique to promote the repair of critical size bone defects. However, DO is usually a lengthy treatment, therefore accompanied with increased risks of complications such as infections and delayed union. Here, we demonstrated that magnesium (Mg) nail implantation into the marrow cavity degraded gradually accompanied with about 4-fold increase of new bone formation and over 5-fold of new vessel formation as compared with DO alone group in the 5 mm femoral segmental defect rat model at 2 weeks after distraction. Mg nail upregulated the expression of calcitonin gene-related peptide (CGRP) in the new bone as compared with the DO alone group. We further revealed that blockade of the sensory nerve by overdose capsaicin blunted Mg nail enhanced critical size bone defect repair during the DO process. CGRP concentration-dependently promoted endothelial cell migration and tube formation. Meanwhile, CGRP promoted the phosphorylation of focal adhesion kinase (FAK) at Y397 site and elevated the expression of vascular endothelial growth factor A (VEGFA). Moreover, inhibitor/antagonist of CGRP receptor, FAK, and VEGF receptor blocked the Mg nail stimulated vessel and bone formation. We revealed, for the first time, a CGRP-FAK-VEGF signaling axis linking sensory nerve and endothelial cells, which may be the main mechanism underlying Mg-enhanced critical size bone defect repair when combined with DO, suggesting a great potential of Mg implants in reducing DO treatment time for clinical applications.

Review of automatic continuous distraction osteogenesis devices for mandibular reconstruction applications

Distraction osteogenesis (DO) is an emerging method for bone tissue reconstruction. In oral and maxillofacial reconstruction applications, DO is playing an important role as a technique without the need of bone graft. In addition, in a DO treatment procedure, a superior outcome could be achieved compared to conventional reconstruction techniques. Recently, a few automatic continuous distraction osteogenesis (ACDO) devices have been designed and developed to be used in human reconstruction applications. Experiments and animal studies have validated the functionality of the developed ACDO devices. It has shown that by using such ACDO devices in a DO procedure, compared to conventional manual DO methods, superior outcomes could be obtained. However, the application of such ACDO devices is still limited. More research and investigation need to be undertaken to study all requirements of ACDO devices to be used in successful human mandibular DO treatment. It is important to determine all requirements and standards that need to be considered and applied in the design and development of ACDO devices. The purpose of this review paper is to highlight the designed and developed ACDO procedures thus far in terms of their working principles, working parameters, and technical aspects for providing a better perspective of the development progress of ACDO devices for oral and maxillofacial reconstruction applications. In this paper, design principles, device specifications, and working parameters of ACDO devices are compared and discussed. Subsequently, current limitations and gaps have been addressed, and future works for enabling an ultimate automatic DO procedure have been suggested.

Continuous distraction osteogenesis device with MAAC controller for mandibular reconstruction applications

Background

Distraction osteogenesis (DO) is a novel technique widely used in human body reconstruction. DO has got a significant role in maxillofacial reconstruction applications (MRA); through this method, bone defects and skeletal deformities in various cranio-maxillofacial areas could be reconstructed with superior results in comparison to conventional methods. Recent studies revealed in a DO solution, using an automatic continuous distractor could significantly improve the results while decreasing the existing issues. This study is aimed at designing and developing a novel automatic continuous distraction osteogenesis (ACDO) device to be used in the MRA.

Methods

The design is comprised of a lead screw translation mechanism and a stepper motor, placed outside of the mouth to generate the desired continuous linear force. This externally generated and controlled distraction force (DF) is transferred into the moving bone segment via a flexible miniature transition system. The system is also equipped with an extra-oral ACDO controller, to generate an accurate, reliable, and stable continuous DF.

Results

Simulation and experimental results have justified the controller outputs and the desired accuracy of the device. Experiments have been conducted on a sheep jaw bone and results have showed that the developed device could offer a continuous DF of 38 N with distraction accuracy of 7.6 nm on the bone segment, while reducing the distraction time span.

Conclusion

Continuous DF with high resolution positioning control, along with the smaller size of the distractor placed in the oral cavity will help in improving the result of the reconstruction operation and leading to a successful DO procedure in a shorter time period. The developed ACDO device has less than 1% positioning error while generating sufficient DF. These features make this device a suitable distractor for an enhanced DO treatment in MRA.

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.

Systemic administration of an antagomir designed to inhibit miR-92, a regulator of angiogenesis, failed to modulate skeletal anabolic response to mechanical loading

The goal of this study is to evaluate if promotion of angiogenesis by systemic treatment with an antagomir against miR-92a, a well established inhibitor of angiogenesis, will maximize the benefits of exercise on bone. Ten week old female C57BL6/J mice were subjected to two weeks of external load by four point bending. During the first week of mechanical loading (ML), mice were injected (2.7 mg/kg of bodyweight) with antagomir against miR-92 or control antagomir (3 alternate days via retro-orbital). No difference in tissues weights (heart, kidney, liver) were found in mice treated with miR-92 vs. control antagomir suggesting no side effects. Two weeks of ML increased tibia TV, BV/TV and density by 6-15 %, as expected, in the control antagomir treated mice. Similar increases in the above parameters (7-16 %) were also seen in mice treated miR-92 antagomir. Administration of miR-92 antagomir was effective in reducing levels of mir-92 in heart, liver and skeletal muscle and in contrast, expression levels of two other microRNA's miR-93 and miR-20a remain constant, thus suggesting specificity of the antagomir used. Surprisingly, we failed to detect significant changes in the expression levels of vascular genes (VEGF, CD31 and Tie2) in heart, liver or skeletal muscle. Based on these findings, we conclude that systemic administration of antagomir against miR-92 while reduced expression levels of miR-92 in the tissues; it did not significantly alter either angiogenic or osteogenic response, thus suggesting possible redundancy in miR-92 regulation of angiogenesis.

Stimulated angiogenesis for fracture healing augmented by low-magnitude, high-frequency vibration in a rat model-evaluation of pulsed-wave doppler, 3-D power Doppler ultrasonography and micro-CT microangiography

This study aimed to investigate the mechanism of low-magnitude high-frequency vibration (LMHFV) treatment on angiogenesis and blood flow for enhancement of fracture healing. Nine-month-old ovariectomized (OVX) and sham-operated (Sham) rats received closed fractures creation at the femora and were randomized into LMHFV treatment (Sham-V, OVX-V) or control (Sham-C, OVX-C) groups. Pulsed-wave Doppler indicated an increase in blood flow velocity of the femoral artery at weeks 2 (OVX pair: p = 0.030) and 4 (OVX pair: p = 0.012; Sham pair: p = 0.020) post-treatment. Significantly enhanced vascular volume (VV) at the fracture site in the vibration groups was demonstrated by 3-D high-frequency power Doppler at week 2 (Sham pair: p = 0.021) and micro-computed tomography (microCT) microangiography at weeks 2 (OVX pair: p = 0.009) and 4 (OVX pair: p = 0.034), which echoed the osteogenesis findings by radiographic and microCT analysis. VV in the OVX groups was inferior to the Sham groups. However, OVX-V showed higher percentages of angiogenic enhancement than Sham-V. Despite impaired neo-angiogenesis in osteoporotic fractures, LMHFV could increase blood flow and angiogenesis in both normal and osteoporotic fractures, thus enhancing fracture healing.

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.

The effect of continuous elastic outside distraction on the expressions of vascular endothelial cell growth factor and microvessel density in female porcine nipple

BACKGROUND

We have proposed a method to correct the inverted nipple with good clinical results. The aim of the study presented here is to show the effect of continuous elastic distraction on the expression of vascular endothelial growth factor and microvessel density in the female porcine nipple. This article also explores the probable mechanism correction of inverted nipples.

METHODS

Four female 3-month-old pigs each with 12 nipples were used. Four nipples of each minipig were used as control with the other eight nipples continuously distracted with prefabricated instruments. The nipples were excised at weeks 2, 4, 8, and 12 after distraction. Immunohistochemical staining was performed to observe the expression of vascular endothelial cell growth factor (VEGF) and CD34 in those tissues. The integral optical density of VEGF-positive cells and microvessel density (MVD) were also counted.

RESULTS

The volumes of the nipples all increased after traction compared with those of the control group. The diameters and heights of the nipples showed significant changes (P<0.01). In immunohistochemical staining, the expressions of VEGF and CD34 of all distracted groups were positive. The staining intensity of traction groups was moderate and that of the control groups was weakly positive. The integral optical density of VEGF-positive cells and MVD compared with the control group were significantly different (P<0.01), and there was a significant positive correlation in MVD and VEGF.

CONCLUSION

Continuous elastic distraction can promote the expression of some growth factors in nipples.

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.

Immunohistochemical study of NF-E2-related factor 2 (Nrf2) in an end-to-end anastomosis of the rat carotid artery

INTRODUCTION

The detailed process and underlying mechanism of stenosis following microvascular anastomoses remains unclear. NF-E2-related factor 2 (Nrf2), is a pleiotropic regulator of cell survival and plays a crucial role in modulating acute inflammatory response. An animal experiment was employed to obtain new information on the histomorphological changes and distribution of Nrf2 in anastomoses.

METHODS

An end-to-end anastomotic model in rat carotid arteries was carried out. The stoma was examined by H&E staining and immunostaining to evaluate histomorphological change as well as the intensity of anti-Nrf2 and а-SMA staining.

RESULTS

Compression, dehiscence and inflammatory cells infiltration were often seen following vessel anastomoses. Inflammatory cells infiltrate was reduced and the granulation tissue fibrosis and endothelium reforming become apparent with times. Marked tunica media hyperplasia consisting of a packed layer of neogenetic smooth muscle cell was present around the anastomosis. Nrf2 expression was upregulated after the operation and was mainly distributed in the neogenetic smooth muscle cells.

CONCLUSION

Stenosis following the micro-artery anastomoses may be mainly due to the progressive myointimal hyperplasia in the media of the arteries. Nrf2 was involved in the pro-inflammatory stress during the vascular morphogenesis/angiogenesis and can be a valuable tool for studying the process of wound healing.

[Autologous tissue engineering by means of distraction osteogenesis: Biomechanical considerations]

Tissue engineering consists in producing functional replacement tissue. Distraction osteogenesis is a tissue engineering technique that uses the mechanical environment of cells to induce tissue regeneration, without need for exogenous biochemical factors. A better understanding of the optimal mechanical conditions of distraction callus stretching may reduce the duration, discomfort, and even social impact of distraction protocols, and complications and failures. We present the current state of knowledge in this field by addressing the fundamentals of elongating bone tissue biomechanics, the influence of rhythm and rate of distraction, and that of vectors and stability. Finally, we present the innovations currently studied, which may modify our clinical protocol in the short term.

Local application of VEGF compensates callus deficiency after acute soft tissue trauma--results using a limb-shortening distraction procedure in rabbit tibia

Acute soft tissue trauma influences callus formation and fracture healing. Several studies showed a relationship between angiogenesis and bone formation during distraction osteogenesis. The purpose of this study was to investigate the influence of controlled release of vascular endothelial growth factor (VEGF) on callus formation in a limb-shortening distraction procedure after acute compartment syndrome. Acute soft tissue trauma with critical increased compartment pressure was generated in 22 rabbits, and the limb was shortened simulating fracture site debridement. In the test group (n=11), a VEGF-coated collagen matrix was locally applied around the fracture, while no collagen was applied in the control group (n=11). Following 10 days in limb shortening, a gradual distraction of 0.5 mm/12 h was performed using an external fixation device and followed up for 40 days. Osseous consolidation occurred in all animals. Average callus diameter (1.54 ± 0.8 vs. 1.27 ± 0.14 mm) and torsional strength (72% vs. 46% of normal) were significantly higher in the test versus the control group. Blood vessel formation increased with a significantly higher number of vessels (6.3 vs. 3.81/mm2 ) and larger cross-sectional area (>40 µm, 90.5% vs. 86%) in the test versus control group. The results showed that locally applied VEGF stimulates fracture healing after acute soft tissue trauma and might be an option for fracture treatment in cases with severe soft tissue damage.

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.

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

OBJECTIVES

This study aimed to evaluate the effect of distraction frequency on the gene expression of osteogenic mediators in mandibular distraction osteogenesis.

STUDY DESIGN

Forty adult New Zealand white rabbits were randomly assigned to the continuous and intermittent distraction groups. Unilateral mandibular osteotomy was performed and custom-designed manual-driven or autodriven distractor was bridged over the osteotomy segments. Animals were humanely killed at day 6, day 10, day 14, and day 21 after osteotomy. mRNA expression of the osteogenic mediators in the distraction regenerate was examined by real-time polymerase chain reaction.

RESULTS

The expression of transforming growth factor-beta(1) was significantly higher at day 6, and the expression of the bone morphogenetic protein-2 was significantly higher from day 6 to day 14, in the continuous distraction group.

CONCLUSION

High-frequency traction up-regulates the expression of osteogenic mediators contributing to the enhanced bone formation.

In vivo self-expanding engineering of bone

In vivo bone formation and vascularization are interdependent process with complex regulatory mechanism. In vitro tissue engineering has meet great difficulty to copy all internal environment conditions, and the technology worked well only for relatively simple, thin tissues such as skin and cartilage that do not depend on a well-formed network of blood vessels to deliver food and oxygen. For more complex tissue of bone segments shot through with vessels, we hypothesize that an altered strategy might be effective: starting from in vitro tissue engineering for a thin sheet of primary product, then transferring to in vivo cultivation with a self-expanding procedure activated by interweaving metal springs of shape memory alloy (SMA). It is easy for thin sheet of engineering tissues to survive after implantation in vivo. Super-elasticity of SMA spring can gradually expand and re-shape the engineering product. More important, the continuous mechano-transduction effect can activate internal environment as a bioreactor for bone regeneration and vascularization. Our hypothesis integrates the existing knowledge and technologies, and could be a hopeful strategy for more convenient and safe use of bone engineering in clinics.