Alteration in volumetric bone mineralization density gradation patterns in mandibular distraction osteogenesis following radiation therapy

Effects of ionizing radiation on woven bone: influence on the osteocyte lacunar network, collagen maturation, and microarchitecture

OBJECTIVES

Evaluate the effects of ionizing radiation on microarchitecture, the osteocyte lacunar network, and collagen maturity in a bone repair site.

MATERIALS AND METHODS

Bone defects were created on tibias of 20 New Zealand rabbits. After 2 weeks, the animals were randomly divided into (n = 10) NoIr (nonirradiated group) and Ir (irradiated group). In the Ir, the animals received single-dose irradiation of 30 Gy on the tibia and were euthanized after 2 weeks. Bone microarchitecture parameters were analyzed by using micro-CT, and the osteocyte lacunar network, bone matrix, and collagen maturation by histomorphometric analysis. The data were analyzed using unpaired Student's t test (α = 0.05).

RESULTS

Trabecular thickness in Ir was lower than that in NoIr (P = 0.028). No difference was found for bone volume fraction and bone area. Lacunae filled with osteocytes were more numerous (P < 0.0001) in NoIr (2.6 ± 0.6) than in Ir (1.97 ± 0.53). Empty lacunae were more prevalent (P < 0.003) in Ir (0.14 ± 0.10) than in NoIr (0.1 ± 0.1). The mean osteocyte lacunae size was higher (P < 0.01) in Ir (15.4 ± 4.41) than in NoIr (12.7 ± 3.7). Picrosirius red analysis showed more (P < 0.05) mature collagen in NoIr (29.0 ± 5.3) than in Ir (23.4 ± 4.5). Immature collagen quantification revealed no difference between groups.

CONCLUSIONS

Ionizing radiation compromised bone formation and an impairment in bone repair in irradiated woven bone was observed.

CLINICAL RELEVANCE

Before radiotherapy, patients usually need surgical intervention, which may be better performed, if clinicians understand the repair process in irradiated bone, using novel approaches for treating these individuals.

Radioprotection With Amifostine Enhances Bone Strength and Regeneration and Bony Union in a Rat Model of Mandibular Distraction Osteogenesis

BACKGROUND

Using distraction osteogenesis (DO) to regenerate robust endogenous bone could greatly enhance postoncologic reconstruction of head and neck cancer. However, radiation (XRT) corrosive effects still preclude DO's immense potential. We posit that adjunctive pretreatment with the radioprotectant amifostine (AMF) can optimize wound healing and allow for successful DO with quantifiable enhancements in bony union and strength despite previous surgical bed irradiation.

METHODS

Two groups of murine left hemimandibles were exposed to a human equivalent radiation dosage fractionated over 5 daily doses of 7 Gy. AMF-XRT-DO (n = 30) received AMF before radiation, whereas XRT-DO (n = 22) was untreated. All animals underwent left hemimandibular osteotomy and external fixator placement, followed by distraction to a 5.1-mm gap. Left hemimandibles were harvested and mechanically tested for parameters of strength, yield, and breaking load.

RESULTS

Radiation-related complications such as severe alopecia were significantly increased in XRT-DO compared with the AMF-treated group (P = 0.001), whereas infection and death were comparable (P = 0.318). Upon dissection, bony defects were grossly visible in XRT-DO distraction gap compared with AMF-XRT-DO, which exhibited significantly more complete unions (P = 0.004). Those results were significantly increased in the specimens prophylactically treated with AMF (yield: 39.41 N vs 21.78 N, P = 0.023; breaking load: 61.74 N vs 34.77 N, P = 0.044; respectively).

CONCLUSIONS

Our study revealed that AMF enhances biomechanical strength, regeneration, and bony union after radiation in a murine model of DO. The use of prophylactic AMF in combination with DO offers the promise of an alternative reconstructive option for patients afflicted with head and neck cancer.

Amifostine Treatment Mitigates the Damaging Effects of Radiation on Distraction Osteogenesis in the Murine Mandible

According to the American Society of Clinical Oncology, in 2012, more than 53,000 new cases of head and neck cancers (HNCs) were reported in the United States alone and nearly 12,000 deaths occurred relating to HNC. Although radiotherapy (XRT) has increased survival, the adverse effects can be unrelenting and their management is rarely remedial. Current treatment dictates surgical mandibular reconstruction using free tissue transfer. These complex operations entail extended hospitalizations and attendant complications often lead to delays in initiation of adjuvant therapy, jeopardizing prognosis as well as quality of life. The creation of new bone by distraction osteogenesis (DO) generates a replacement of deficient tissue from local substrate and could have immense potential therapeutic ramifications. Radiotherapy drastically impairs bone healing, precluding its use as a reconstructive method for HNC. We posit that the deleterious effects of XRT on bone formation could be pharmacologically mitigated. To test this hypothesis, we used a rodent model of DO and treated with amifostine, a radioprotectant, to assuage the XRT-induced injury on new bone formation. Amifostine had a profound salutary effect on bone regeneration, allowing the successful implementation of DO as a reconstructive technique. The optimization of bone regeneration in the irradiated mandible has immense potential for translation from the bench to the bedside, providing improved therapeutic options for patients subjected to XRT.

Role of parathyroid hormone in regeneration of irradiated bone in a murine model of mandibular distraction osteogenesis

BACKGROUND

The purpose of this study was to measure the histologic and histomorphometric effects of parathyroid hormone (PTH) treatment on irradiated bone undergoing distraction osteogenesis (DO).

METHODS

Thirty-four rats were divided into 3 groups. The control group underwent DO and the radiation control group underwent radiotherapy (RT) before DO. The PTH group underwent RT and received PTH during DO. Quantitative histology and histomorphometry were performed.

RESULTS

RT resulted in a depletion of osteocytes and increase in empty lacunae. Treatment with PTH resulted in an increase in osteocyte counts and decrease in empty lacunae (p < .05), restoring osteocytes to levels seen in nonradiated bone (p = .121). RT decreased bone volume to tissue volume (BV-TV) ratio and increased osteoid volume to tissue volume (OV-TV) ratio, signifying increased immature bone formation. PTH treatment restored OV-TV ratio to that observed in nonradiated bone.

CONCLUSION

PTH treatment of irradiated bone enhanced bone regeneration and restored osteocyte counts and OV-TV ratio to levels comparable to nonradiated bone. © 2016 Wiley Periodicals, Inc. Head Neck 39: 464-470, 2017.

Dose-response effect of human equivalent radiation in the mandible

BACKGROUND

Despite widespread use of adjuvant irradiation for head and neck cancer, the extent of damage to the underlying bone is not fully understood but is associated with pathologic fractures, nonunion, and osteoradionecrosis. The authors' laboratory previously demonstrated that radiation significantly impedes new bone formation in the murine mandible. We hypothesize that the detrimental effects of human equivalent radiation on the murine mandible results in a dose-dependent degradation in traditional micro-computed tomography (micro-CT) metrics.

METHODS

Fifteen male Sprague-Dawley rats were randomized into 3 radiation dosage groups: low (5.91 Gy), middle (7 Gy), and high (8.89 Gy), delivered in 5 daily fractions. These dosages approximated 75%, 100%, and 150%, respectively, of the biologically equivalent dose that the human mandible receives during radiation treatment. Hemimandibles were harvested 56 days after radiation and scanned using micro-CT. Bone mineral density, tissue mineral density, and bone volume fraction were measured along with microdensitometry measurements.

RESULTS

Animals demonstrated dose-dependent adverse effects of mucositis, alopecia, weight loss, and mandibular atrophy with increasing radiation. Traditional micro-CT parameters were not sensitive enough to demonstrate statistically significant differences between the radiated groups; however, microdensitometry analysis showed clear differences between radiated groups and statistically significant changes between radiated and nonradiated groups.

CONCLUSIONS

The authors report dose-dependent and clinically significant adverse effects of fractionated human equivalent radiation to the murine mandible. The authors further report the limited capacity of traditional micro-CT metrics to adequately capture key changes in bone composition and present microdensitometric histogram analysis to demonstrate significant radiation-induced changes in mineralization patterns.

Does a change in bone mineral density occur in the mandible of Göttingen minipigs after irradiation in correlation with radiation dose and implant surgery?

PURPOSE

To date, studies have not agreed on the effects of irradiation on bone mineral density. The aim of our study was to investigate the changes in mandibular bone mineral density after irradiation at various doses with and without surgery.

MATERIALS AND METHODS

We implemented a descriptive animal experiment. The sample included 16 female Göttingen Minipigs, randomly assigned to 4 groups and irradiated with equivalent doses of 0, 25, 50, and 70 Gy to the mandibular region. At 3 months after irradiation, the mandibular left premolars and molars were removed, and dental implants were placed. Computed tomography scans were taken before and 6 months after irradiation. The measured bone density was related to a bone phantom to calculate the bone mineral density quotient (BMDQ). The outcome variable was the BMDQ. Other study variables were the radiation dose and surgery. Descriptive and univariate analyses were computed, and significance was set at P ≤ .05.

RESULTS

In the left hemimandible, compared with the control group, a significant decrease in BMDQ was observed: 0.01 at 0 Gy, -0.01 at 25 Gy, -0.06 at 50 Gy, and -0.11 at 70 Gy (P = .023). The right hemimandible compared with the control group also showed a significant decrease in BMDQ: -0.02 at 0 Gy, -0.08 at 25 Gy, -0.09 at 50 Gy, and -0.11 at 70 Gy (P = .007).

CONCLUSIONS

The present study used a large animal model to simulate the tissue reactions induced by various radiation doses in the mandible. We found a significant decrease in the BMDQ after irradiation, but no significant correlation could be found between the irradiation dose and a decrease in the BMDQ.

New approach for the treatment of osteoradionecrosis with pentoxifylline and tocopherol

Osteoradionecrosis (ORN) of the jaw is a significant complication of radiotherapy for oral cavity cancer. In addition to antibiotic medication, treatment options such as hyperbaric oxygen therapy, surgical approaches, and combined therapy with pentoxifylline and tocopherol have been recently introduced. In this review article, we will discuss the definition and classifications of osteoradionecrosis, its etiology and pathophysiology, previous treatment options, oral and maxillofacial complications of radiotherapy, basic information on pentoxifylline and tocopherol, recent reports of pentoxifylline and tocopherol combined therapy, and, finally, ORN-induced animal models and future approaches.

Parathyroid hormone therapy mollifies radiation-induced biomechanical degradation in murine distraction osteogenesis

OBJECTIVE

Descriptions of mandibular distraction osteogenesis for tissue replacement after oncologic resection or for defects caused by osteoradionecrosis have been limited. Previous work demonstrated radiation decreases union formation, cellularity and mineral density in mandibular distraction osteogenesis. The authors posit that intermittent systemic administration of parathyroid hormone will serve as a stimulant to cellular function, reversing radiation-induced damage and enhancing bone regeneration.

METHODS

Twenty male Lewis rats were randomly assigned to three groups: group 1 (radiation and distraction osteogenesis, n = 7) and group 2 (radiation, distraction osteogenesis, and parathyroid hormone, n = 5) received a human-equivalent dose of 35 Gy of radiation (human bioequivalent, 70 Gy) fractionated over 5 days. All groups, including group 3 (distraction osteogenesis, n = 8), underwent a left unilateral mandibular osteotomy with bilateral external fixator placement. Distraction osteogenesis was performed at a rate of 0.3 mm every 12 hours to reach a gap of 5.1 mm. Group 2 was injected with parathyroid hormone (60 µg/kg) subcutaneously daily for 3 weeks after the start of distraction osteogenesis. On postoperative day 40, all left hemimandibles were harvested. Biomechanical response parameters were generated. Statistical significance was considered at p ≤ 0.05.

RESULTS

Parathyroid hormone-treated mandibles had significantly higher failure load and higher yield than did untreated mandibles. However, these values were still significantly lower than those of nonirradiated mandibles.

CONCLUSIONS

The authors have successfully demonstrated the therapeutic efficacy of parathyroid hormone to stimulate and enhance bone regeneration in their irradiated murine mandibular model of distraction osteogenesis. Anabolic regimens of parathyroid hormone, a U.S. Food and Drug Administration-approved drug on formulary, significantly improve outcomes in a model of postoncologic craniofacial reconstruction.

Quantitative histologic evidence of amifostine-induced cytoprotection in an irradiated murine model of mandibular distraction osteogenesis

BACKGROUND

Head and neck cancer management requires adjuvant radiotherapy. The authors have previously demonstrated the damaging effect of a human equivalent dose of radiation on a murine mandibular model of distraction osteogenesis. Using quantitative histomorphometry, the authors' specific aim was to objectively measure amifostine radioprotection of the cellular integrity and tissue quality of an irradiated and distracted regenerate.

METHODS

Sprague-Dawley rats were assigned randomly into two groups: radiotherapy/distraction osteogenesis and amifostine/radiotherapy/distraction osteogenesis, which received amifostine before radiotherapy. Both groups received a fractionated human equivalent dose of radiation prior to left mandibular osteotomy with fixator placement. Distraction to 5.1 mm was followed by a 28-day consolidation period. Quantitative histomorphometry was performed on left hemimandibles for osteocytes, empty lacunae, bone volume-to-tissue volume ratio, and osteoid volume-to-tissue volume ratio.

RESULTS

Amifostine/radiotherapy/distraction osteogenesis exhibited bony bridging as opposed to radiotherapy/distraction osteogenesis fibrous unions. Quantitative histomorphometry analysis revealed statistically significant higher osteocyte count and bone volume-to-tissue volume ratio in amifostine-treated mandibles compared with irradiated mandibles. There was a corresponding decrease in empty lacunae and the ratio of osteoid volume-to-tissue volume between both groups.

CONCLUSIONS

The authors have successfully established the significant osseous cytoprotective and histoprotective capacity of amifostine for distraction osteogenesis in the face of radiotherapy. The amifostine-sparing effect on bone cellularity correlated with increased bony unions and elimination of fibrous union. The authors posit that the demonstration of similar efficacy of amifostine in the clinic may allow the successful implementation of distraction osteogenesis as a viable reconstructive option for head and neck cancer in the future.

Role of parathyroid hormone therapy in reversing radiation-induced nonunion and normalization of radiomorphometrics in a murine mandibular model of distraction osteogenesis

BACKGROUND

The use of mandibular distraction osteogenesis (MDO) for tissue replacement after oncologic resection or for defects caused by osteoradionecrosis has been described but, in fact, has seen limited clinical utility. Previous laboratory work has shown that radiation (XRT) causes decreased union formation, decreased cellularity, and decreased mineral density in an animal model of MDO. Our global hypothesis is that radiation-induced bone damage is partly driven by the pathologic depletion of both the number and function of osteogenic cells. Parathyroid hormone (PTH) is a U.S. Food and Drug Administration-approved anabolic hormonal therapy that has demonstrated efficacy for increasing bone mineral density for the treatment of osteoporosis. We postulate that intermittent systemic administration of PTH will serve as an anabolic stimulant to cellular function that will act to reverse radiation-induced damage and enhance bone regeneration in a murine mandibular model of DO.

METHODS

A total of 20 isogenic male Lewis rats were randomly assigned into 3 groups. Group 1 (XRT-DO, n = 7) and group 2 (XRT-DO-PTH, n = 5) received a human bioequivalent dose of 70 Gy fractionated over 5 days. All groups including group 3 (DO, n = 8) underwent a left unilateral mandibular osteotomy with bilateral external fixator placement. Four days later, mandibular DO was performed at a rate of 0.3 mm every 12 hours to reach a maximum gap of 5.1 mm. Group 2 was injected PTH (60 μg/kg) subcutaneously daily for 3 weeks following the start of MDO. On postoperative day 41, all left hemimandibles were harvested. Micro-CT at 45-μm voxel size was performed and radiomorphometrics parameters of bone mineralization were generated. Union quality was evaluated on a 4-point qualitative grading scale. Radiomorphometric data were analyzed using 1-way ANOVA, and union quality assessment was analyzed via the Mann-Whitney test. Statistical significance was considered at p ≤ .05.

RESULTS

Groups 1 and 2 appropriately demonstrated clinical signs of radiation-induced stress ranging from alopecia to mucositis. Union quality was significantly higher in PTH-treated XRT-DO animals, compared with XRT-DO group animals (p = .02). Mineralization metrics, including bone volume fraction (BVF) and bone mineral density (BMD), also showed statistically significant improvement. The groups that were treated with PTH showed no statistical differences in union or radiomorphometrics when compared with DO in nonradiated animals.

CONCLUSION

We have successfully demonstrated the therapeutic efficacy of PTH to stimulate and enhance bone regeneration in our irradiated murine mandibular model of DO. Our investigation effectively resulted in statistically significant increases in BMD, BVF, and clinical unions in PTH-treated mandibles. PTH demonstrates immense potential to treat clinical pathologies where remediation of bone regeneration is essential.

Quantifying mineralization using bone mineral density distribution in the mandible

BACKGROUND

Micro-computed tomography is an efficient method for quantifying the density and mineralization of mandibular microarchitecture. Conventional radiomorphometrics such as bone and tissue mineral density are useful in determining the average overall mineral content of a scanned specimen; however, relying solely on these metrics has limitations. Using bone mineral density distribution (BMDD), the complex array of mineralization densities within a bone sample can be portrayed. This information is particularly useful as a computational feature reflective of the rate of bone turnover. We demonstrate the utility of BMDD analyses in the rat mandible and generate a platform for further exploration of mandibular pathology and treatment.

METHODS

Male Sprague-Dawley rats (n = 8) underwent micro-computed tomography, and histogram data were generated from a selected volume of interest. A standard curve was derived for each animal, and reference criteria were defined. An average histogram was produced for the group, and descriptive analyses including the means and SDs are reported for each of the normative metrics.

RESULTS

M(peak) (3444 Hounsfield units [SD, 138]) and M(width) (2221 Hounsfield units [SD, 628]) are 2 metrics demonstrating reproducible parameters of BMDD with minimal variance. A total of 8 valuable metrics quantifying biologically significant events concerning mineralization are reported.

CONCLUSIONS

We quantify the vast wealth of information depicted in the complete spectrum of mineralization established by the BMDD analysis. We demonstrate its potential in delivering mineralization data that encompass and enhance conventional reporting of radiomorphometrics. Moreover, we explore its role and translational potential in craniofacial experimentation.

Radiomorphometric quantitative analysis of vasculature utilizing micro-computed tomography and vessel perfusion in the murine mandible

Purpose Biomechanical, densitometric, and histological analyses have been the mainstay for reproducible outcome measures for investigation of new bone formation and osseous healing. Here we report the addition of radiomorphometric vascular analysis as a quantitative measure of vascularity in the murine mandible. To our knowledge this is the first description of using micro-computed tomography (micro-CT) to evaluate the temporal and spatial pattern of angiogenesis in the craniofacial skeleton. Methods The vessel perfusion technique was performed on 10 Sprague-Dawley rats using Microfil (MV-122, Flow Tech; Carver, MA). After decalcification, hemimandibles were imaged using high-resolution micro-CT. Six separate radiomorphometric vascular metrics were calculated. Results Radiomorphometric values were analyzed using three different thresholds on micro-CT. Experimentally, 1000 Hounsfield units was found to be the optimal threshold for analysis to capture the maximal vascular content of the bone. Data from seven hemimandibles were analyzed. Minimal statistical variance in each of the quantitative measures of vascularity resulted in reproducible metrics for each of the radiomorphometric parameters. Conclusions We have demonstrated that micro-CT vascular imaging provides a robust methodology for evaluation of vascular networks in the craniofacial skeleton. This technique provides 3D quantitative data analysis that differs significantly from laser Doppler and microsphere methods, which simply measure flow. This technique is advantageous over labor-intensive 2D conventional analyses using histology and X-ray microangiography. Our data establish the appropriate thresholding for optimal vascular analyses and provide baseline measurements that can be used to analyze the role of angiogenesis in bone regeneration and repair in the craniofacial skeleton.

Amifostine remediates the degenerative effects of radiation on the mineralization capacity of the murine mandible

BACKGROUND

Radiotherapy, a cornerstone of head and neck cancer treatment, causes substantial morbidity to normal adjoining bone. The authors assessed the radioprotective effect of amifostine therapy on the mineralization of the mandible using micro-computed tomography. They hypothesized that amifostine would safeguard the mandible from radiation-induced disruption of the mineralization process and the associated failure of new bone creation.

METHODS

Male Sprague-Dawley rats were randomized into three groups: control (n = 8), radiation therapy (n = 5), and amifostine (n = 8). Animals in the radiation therapy and amifostine groups underwent human bioequivalent radiation of 70 Gy in five fractions to the left hemimandible. Fifty-six days after irradiation, the hemimandibles were harvested for radiomorphometric analyses.

RESULTS

Amifostine-treated animals exhibited less alopecia, mucositis, and weight loss in addition to increased cortical density in comparison with those treated with radiation therapy. Bone and tissue mineral densities showed statistically significant improvement in amifostine versus radiation therapy, and no difference was observed between amifostine and control groups. Detailed micro-computed tomographic analysis further demonstrated significant differences in the mineralization profile when comparing radiation therapy and amifostine. Amifostine maintained regions of lower mineralization consistent with the preservation of normal remodeling.

CONCLUSIONS

The authors have successfully demonstrated the ability of amifostine pretreatment to protect the natural mineralization profile of bone. This reflects the capacity of amifostine prophylaxis to safeguard the normal surrounding mandible from the impediments of collateral damage imposed by irradiation. Further study can correlate these findings with the potential use of amifostine to prevent the devastating associated morbidities of radiotherapy such as pathologic fractures and osteoradionecrosis.

Dose-response effect of human equivalent radiation in the murine mandible: Part II. A biomechanical assessment

BACKGROUND

Despite the widespread use of adjuvant irradiation for head and neck cancer, the extent of damage to the underlying bone is not well understood. However, patients can suffer serious clinical consequences, including pathologic fractures, nonunion, and osteoradionecrosis. The authors' specific aim was to objectively quantify the human equivalent radiation dose-response effect of radiation on the biomechanical properties of the murine mandible.

METHODS

Twelve Sprague-Dawley rats were randomized into three radiation dosage groups--low (5.91 Gy), middle (7 Gy), and high (8.89 Gy)--delivered in five daily fractions. The fractionation regimen was used to approximate 75, 100, and 150 percent, respectively, of the bioequivalent dose humans receive in conventional head and neck cancer treatment. Fifty-six days after irradiation, hemimandibles were loaded to failure in a uniaxial tension at 0.5 mm/second. Load displacement curves were analyzed for yield and breaking load, and values were considered statistically significant at p<0.05.

RESULTS

The authors' data demonstrated a statistically significant decrease in the yield and breaking load metrics. The authors' reported averages for low, middle, and high radiation dosages were 162, 136, and 69 N, respectively, for yield; and 215, 211, and 141 N, respectively, for breaking load. Both of these quantitative biomechanical properties were diminished in a dose-response pattern.

CONCLUSIONS

In this article, the authors report a dose-response effect in the degradation of the biomechanical properties of the mandible after fractionated human equivalent radiation. The authors' findings and model can now be used to formulate therapies aimed at remediating those effects and augmenting bone regeneration and healing after adjuvant radiotherapy in head and neck cancer patients.

Dose-response effect of human equivalent radiation in the murine mandible: part I. A histomorphometric assessment

BACKGROUND

The authors' laboratory previously demonstrated that radiation significantly alters new bone formation in the murine mandible, impeding the use of distraction osteogenesis as a viable reconstructive option after radiotherapy in head and neck cancer. The authors hypothesize that the deleterious effects of radiation on regenerate formation results from a dose-response depletion of essential osteogenic cells. The authors' specific aim was to use quantitative histomorphometry to objectively measure the human equivalent dose-response effects of radiation on the integrity of the mandible's cellular and tissue composition.

METHODS

Twenty Sprague-Dawley rats were randomized into three radiation dosage groups: low (5.91 Gy), middle (7 Gy), and high (8.89 Gy), delivered in five daily fractions. These dosages approximated 75, 100, and 150 percent, respectively, of the biological equivalent dose the mandible experiences in the clinical regimen of head and neck cancer patients. Hemimandibles were harvested 56 days after radiation and stained with Gomori trichrome. Quantitative histomorphometry was performed using Bioquant software and analysis with a one-way analysis of variance Kruskal-Wallis test.

RESULTS

The authors' data revealed a statistically significant diminution in the mean number of osteocytes. The authors also demonstrated a corresponding significant increase in the mean values of empty lacunae. Both of these quantitative histomorphometric changes demonstrated a dose-response relationship.

CONCLUSIONS

The authors' study supports their hypothesis that radiation induces a dose-response depletion in osteocytes and an increase in empty lacunae. These reliable and reproducible metrics can now be used to determine the efficacy of therapies aimed at safeguarding the cells essential for optimal bone regeneration and potentially enhance the use of distraction osteogenesis in head and neck cancer patients.

Quantitative histomorphometric assessment of regenerate cellularity and bone quality in mandibular distraction osteogenesis after radiation therapy

BACKGROUND

The use of mandibular distraction osteogenesis (MDO) for tissue replacement after oncologic resection in head and neck cancer could have immense therapeutic ramifications. We have previously demonstrated significantly decreased mechanical and microdensitomeric metrics of our MDO regenerate after 36-Gy radiation. Quantitative histomorphometry, a third metric, would permit objective investigation of the effects of radiation on tissue and cellular composition. Our hypothesis is that radiation-induced cellular depletion and diminution in function impair optimal bone regeneration.

METHODS

Five rats received radiation to the left mandible; 5 received none. All animals underwent surgical placement of external fixators, creation of mandibular osteotomies, distraction to a 5.1-mm gap width, and consolidation. Point counting and color thresholding were performed.

RESULTS

There was a significant increase in empty lacunae and a corresponding diminution in osteocytes after radiation. Whereas the volume fraction of mineralized, mature bone was not different, that of nonmineralized, immature osteoid was significantly increased in the radiated group compared with that in the nonradiated group.

CONCLUSIONS

Our findings confirm our prior 2 metrics. Actually, all 3 diverse metrics--microdensitometry, biomechanical analysis, and histomorphometry--corroborate our hypothesis of cellular depletion and diminution of function as the potential mechanism of radiation-induced attenuation in the distracted regenerate. Furthermore, our findings of tissue and cellular changes in the irradiated regenerate elucidate the pathophysiology of decreased bone quality when amalgamated with our previous results. Therapeutic agents may now be introduced, and their effects on the irradiated regenerate critically measured, so that MDO may be used as a viable reconstructive option in patients with head and neck cancer.