Histomorphometric comparison between continuous and discontinuous distraction osteogenesis

Bone Volume Analysis and Associated Influencing Factors in Mandibular Distraction Osteogenesis: A Retrospective Analysis

BACKGROUND

Distraction osteogenesis is a progressively popular technique for maxillofacial bone reconstruction, but there is a notable gap in the analysis of bone volume within the distraction segment and the exploration of associated influencing factors.

PURPOSE

The purpose of this study was to quantitatively analyze the new bone volume and the distraction gap volume in the three-dimensional (3D) model and explore the influencing factors associated with the percentage of the new bone volume to the distraction gap volume.

STUDY DESIGN, SETTING, SAMPLE

This retrospective study included patients who underwent maxillofacial distraction osteogenesis treatment at the West China Hospital of Stomatology between 2014 and 2022, utilizing the mandibular distractor (Cebei, Ningbo, China). Exclusion criteria encompassed individuals with incomplete clinical or radiographical records as well as those who loss to follow-up.

PREDICTOR VARIABLE

The predictor variables were age, sex, diagnosis, consolidation period duration, distraction modality, osteotomy area, distraction gap volume, and proximal bone segment volume.

MAIN OUTCOME VARIABLE(S)

The outcome variable was osteogenic effect which defined as the percentage of the new bone volume to the distraction gap volume in the 3D model.

COVARIATES

Not applicable.

ANALYSES

T-tests were used to describe categorical variables, and Pearson correlation analysis was used to describe continuous variables. Linear regression was employed to assess the predictiveness of variables for osteogenic effect. Data are described as mean ± standard deviation; statistical significance was established at a P value < .05.

RESULTS

The study sample contained 35 patients(11 males and 24 females) with a mean age of 21.17 ± 11.82 years (range: 5 to 47 years) were included. The mean osteogenic effect of all samples was 78.89 ± 24.70%. Multiple linear regression models confirmed that the osteogenic effect was significantly influenced by the distraction gap volume (P = .003), proximal bone segment volume (P = .009), osteotomy area (P = .034), diagnosis (P = .004), and distraction modality (P = .021).

CONCLUSION AND RELEVANCE

The percentage of new bone mass to simulated volume based on 3D model measurement can serve as an effective quantitative indicator for evaluating the osteogenic effect; our study demonstrates that distraction gap volume, proximal bone segment volume, osteotomy area, diagnosis, and distraction modality can statistically significantly influence the osteogenic effect.

Mechanical Characterization at the Microscale of Mineralized Bone Callus after Bone Lengthening

Distraction osteogenesis (DO) involves several processes to form an organized distracted callus. While bone regeneration during DO has been widely described, no study has yet focused on the evolution profile of mechanical properties of mineralized tissues in the distracted callus. The aim of this study was therefore to measure the elastic modulus and hardness of calcified cartilage and trabecular and cortical bone within the distracted callus during the consolidation phase. We used a microindentation assay to measure the mechanical properties of periosteal and endosteal calluses; each was subdivided into two regions. Histological sections were used to localize the tissues. The results revealed that the mechanical properties of calcified cartilage did not evolve over time. However, trabecular bone showed temporal variation. For elastic modulus, in three out of four regions, a similar evolution profile was observed with an increase and decrease over time. Concerning hardness, this evolves differently depending on the location in the distracted callus. We also observed spatial changes in between regions. A first duality was apparent between regions close to the native cortices and the central area, while latter differences were seen between periosteal and endosteal calluses. Data showed a heterogeneity of mechanical properties in the distracted callus with a specific mineralization profile.

Effect of bone morphogenic protein-2 and desferoxamine on distraction osteogenesis

BACKGROUND

Angiogenesis is crucial for formation of a stable regenerate during distraction osteogenesis (DO). This experimental study evaluates if bone morphogenic protein-2 (BMP-2) and desferrioxamine (DFO), two agents which are known to induce neoangiogenesis in vivo, would increase angiogenesis and osteogenesis, and improve mechanical properties of bone regenerate in DO model.

METHODS

Twenty-four tibias of 24 New Zealand rabbits were osteotomized and fixed with semi-circular fixators. Three groups of 8 animals were formed. BMP-2 soaked scaffolds were used in the first group, whereas daily local DFO injections were made in the second group. Subjects in the control group did not receive any agents during the surgery or in the distraction period. The rabbits in all three groups underwent distraction at a rate of 0.6 mm/day for 15 days following the 7-day latent period. Animals were sacrificed on day 38, and the tibia were harvested for histological and mechanical examination of the regenerate.

RESULTS

All 24 rabbits survived the surgical procedure, and there were no side effects against the BMP-2 and local DFO. Three-point bending tests revealed a higher force (361 ± 267 N.) required for fracture in Group 1 (p: 0.018). Similarly, the bending moment in Group 1 (5.4 ± 4.0 Nmm) was significantly higher than the other groups (p: 0.021). There was no significant difference between the groups in terms of deflection and stiffness (p ˃ 0.05). Histologically, there was no statistical difference between the groups in terms of endochondral, periosteal, and intramembranous ossification and VEGF activity (p ˃ 0.05).

CONCLUSION

BMP-2 and DFO stimulate angiogenesis by increasing VEGF activity. Angiogenesis is one of the most important mechanisms for the initiation and maintenance of new bone formation. Stimulation of angiogenesis in unfavorable biomechanical conditions may not be sufficient for ideal bone formation.

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.

Skeletal and soft tissue response to automated, continuous, curvilinear distraction osteogenesis

PURPOSE

To document the bone formation and soft tissue changes in response to automated, continuous, curvilinear distraction osteogenesis (DO) at rates greater than 1 mm/day in a minipig model.

MATERIALS AND METHODS

Two groups of Yucatan minipigs underwent automated, continuous, curvilinear DO of the right mandible: group A, 1.5 mm/day (n = 5); and group B, 3.0 mm/day (n = 5). Each minipig underwent 12 mm of distraction followed by 24 days of fixation. The distracted and contralateral mandibles were harvested at the end of fixation. The percentage of surface area (PSA) of the regenerate occupied by bone, fibrous tissue, cartilage, and hematoma was determined using computerized histomorphometric analysis. The control groups consisted of DO wounds distracted discontinuously at 1 mm/day and the nonoperated contralateral mandible. The ipsilateral and contralateral digastric muscles were harvested and stained for proliferating cell nuclear antigen (PCNA), myogenic differentiation-1 (MyoD), and paired Box 7 protein (PAX7).

RESULTS

All 10 minipigs completed the distraction and fixation period. The PSA occupied by bone was similar for groups A (PSA 64.36% ± 5.87%) and B (PSA 63.83% ± 3.37%) and the control group (1 mm/day; PSA 64.89% ± 0.56%) but was less than that on the nonoperated side (PSA 84.67% ± 0.86%). The PSA occupied by cartilage and hematoma in all groups was minimal (<1.1%). The digastric muscles had no abnormal tissue or inflammation, and PAX7, MyoD, and PCNA expression had returned to the baseline levels.

CONCLUSIONS

The results of the present study indicate that bone formation in response to automated, continuous, and curvilinear DO at a rate of 1.5 and 3.0 mm/day is nearly identical to that with discontinuous DO at 1 mm/day. In addition, no deleterious effects were found on the digastric muscles.

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.

Histological and physical analysis of bone neoformation by osteogenesis distraction: A preliminary report

INTRODUCTION

Osteogenesis distraction (OD) is a mainstream technique in maxillofacial surgical reconstruction with varied applications. OD technique employs a distractor with the aim to get new bone in the site of interest. Osseous maturation time is necessary before the device can be removed and few patients' complaint of related discomfort, especially when these devices are external, and induces superficial infections, paresthesia, hypertrophic scars and social relationship difficulties. The use of Low Level Laser Therapy (LLLT) has been proved beneficial to soft tissue and osseous repairs.

MATERIALS AND METHOD

12 rabbits were randomly divided in to two groups. In all animals, distractor was placed and one group was exposed to LLLT while the other group served as control. After consolidation, animals were sacrificed, the new bone formed were subjected to investigations including histomorphometric, physical analysis and tomographical analysis. Statistical analyses were performed using SPSS software.

RESULT

Newly formed bone was significantly different between the groups. The physical properties of the neobone were comparatively better when the animals were exposed to LLLT with varying statistical significance.

CONCLUSION

The results obtained with smaller sample size in this study need to be interpreted with care. The results of this preliminary pilot study encourage the use of LLLT during healing period. However the histological, tomographical and physical findings need to be ascertained using a larger sample size to study the bio-stimulatory effects with laser therapy from basics to clinical relevance on wound and bone healing.

The effect of bone morphogenic protein-2-coated tri-calcium phosphate/hydroxyapatite on new bone formation in a rat model of femoral distraction osteogenesis

BACKGROUND AIMS

Distraction osteogenesis (DO) is an increasingly popular technique used to stimulate new bone formation to treat orthopedic disorders resulting from bone defects and deficits. Because of various possible complications that can occur during the long consolidation period, the development of procedures to accelerate regenerated ossification is clearly desirable. The purpose of this study was to evaluate the effect of single insertions of bone morphogenic protein-2 (BMP-2), delivered by tri-calcium phosphate (TCP)/hydroxyapatite (HA), administered at osteotomy sites, on the rate of new bone formation during DO in a rat model.

METHODS

Thirty-six male Sprague-Dawley rats, aged 12 weeks and weighing a mean (± standard deviation) of 401 ± 14 g, were used in this study. The animals were randomized into three groups of 12 rats each. Group I served as a control, group II was treated with only TCP/HA, and group III was treated with recombinant human (rh) BMP-2-coated TCP/HA. Materials were inserted into the medullary canal at the femoral osteotomy site at the end of the lengthening period. After a 7-day latent phase, distraction was commenced on day 0 at a rate of 0.50 mm every 6 h for 5 days (2 mm daily), resulting in a total of 10 mm of lengthening by day 5. At two different time-points [at 4 weeks (day 33) and 8 weeks (day 61) after cessation of distraction], the progress of bone formation was determined with microcomputed tomography (micro-CT), histology and real-time polymerase chain reaction (PCR). The mean and standard deviation of the values obtained from the experiment were computed and statistical analyses performed using anova. Statistical significance was established at P < 0.05. Results. Radiographically, all group III rat femurs exhibited bridging callus formation 8 weeks after cessation of distraction, whereas group II rat femurs demonstrated non-bridging callus formation. None of the group I rat femurs showed callus in the central zone of the distraction gap. For micro-CT, bone formation and remodeling of the distraction regeneration with beta-TCP/HA coated with rhBMP-2 had greater values than the control sides at all time-points. Two-dimensional quantitative analysis of the distraction regeneration showed that the bone volume of group III had higher values than groups I and II at 4 weeks (P < 0.05). This difference was also evident at 8 weeks. With hematoxylin and eosin (H&E) staining, the control group (group I) did not show any bone tissue at the distraction site. In group II at 4 weeks, abundant fibrous tissue surrounding the particles was visible with some areas of woven bone. At 8 weeks, the woven bone covered the particles but not the whole circumference. In group III at 4 weeks, much of the woven bone surrounded the particle with some fibrocartilagenous materials. At 8 weeks, woven bone covering the whole circumference of the particles was visible.

CONCLUSIONS

Application of rhBMP-2, at the end of the rather rapid distraction period, as a single bolus significantly increased the osteogenic process, while beta-TCP/HA behaved effectively as a sustained delivery system for this osteoinductive protein.

[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.

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.