- Email: [email protected]
Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats
G Model JINJ 7753 No. of Pages 4
Injury, Int. J. Care Injured xxx (2018) xxx–xxx
Contents lists available at ScienceDirect
Injury journal homepage: www.elsevier.com/locate/injury
Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats Mohammad Zandia,b , Abbas Shokric,* , Maryam Mousavid, Sanaz Rajaeid , Naser Mohammad Gholi Mezerjie a
Department of Oral and Maxillofacial Surgery, Hamadan University of Medical Sciences, Hamadan, Iran Dental Research Center, Hamadan University of Medical Sciences, Hamadan, Iran Department of Oral and Maxillofacial Radiology, Hamadan University of Medical Sciences, Hamadan, Iran d Faculty of Dentistry, Hamadan University of Medical sciences, Hamadan, Iran e Department of Biostatistics and Epidemiology, Hamadan University of medical sciences, Hamadan, Iran b c
A R T I C L E I N F O
Keywords: Zoledronate Bisphosphonate Mandible Bone Fracture
A B S T R A C T
Introduction: The aim of this study was to evaluate the effect of zoledronate therapy on susceptibility of mandibular bone to fracture in rats. Methods: Fifty rats were randomly allocated to two groups of 25 animals. The rats in group Z received monthly intravenous infusion of 0.06 mg/kg zoledronate for 6 months. The rats in the group C were injected with an equal volume of saline in the same manner. A month after the last zoledronate/saline administration, all 50 rats were euthanized. Using a cone beam computed tomography, the cortical thickness of inferior border of mandible and the mandibular bone mineral density were calculated, and using a three-point bending test, the peak load failure and the ultimate stress of mandibular bone were determined. Results: The mean mandibular inferior cortical bone thickness and the mean bone mineral density were significantly larger in zoledronate-treated rats (0.30 0.02 mm and 1045.00 185.79, respectively) compared to control rats (0.21 0.01 mm and 878.66 166.53, respectively). The peak load and the ultimate stress were lower in the zoledronate-treated hemimandibles (84.61 33.62 N and 1.76 0.72 MPa, respectively) compared to the control hemimandibles (98.36 16.5 9 N and 2.03 0.44 MPa, respectively). Conclusion: Zoledronate therapy reduced the mechanical strength of the mandibles, implying an increased risk of mandibular fracture in rats. © 2018 Elsevier Ltd. All rights reserved.
Introduction Bisphosphonates (BPs) are considered one of the main pharmacological agents in the treatment of a large number of diseases in which bone resorption needs to be reduced or controlled [1]. Their primary action is on osteoclasts, where they inhibit osteoclast activity and proliferation and induce apoptosis, leading to suppression of bone turnover and increase in bone mineralization [2,3]. Since the first report of spontaneous peripheral fractures after long-term alendronate therapy, followed by several studies
* Corresponding author at: Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, University of Medical Sciences, Shahid Fahmideh Street, Hamadan, Iran. E-mail address: [email protected] (A. Shokri).
reporting subtrochanteric or diaphyseal femoral insufficiency fractures in patients under BP therapy, concerns have raised about possible association between prolonged BP therapy and spontaneous bone fractures [4–6]. It was hypothesized that long-term BP exposure and oversuppression of bone turnover have a worsening effect on bone quality, making bone brittle and prone to fracture [5,7,8]. There is now abundant evidence demonstrating that patients receiving prolonged oral BPs are at increased risk of several types of fractures including femur, pelvis, fibula, ankle, metatarsals, and long bones such as the humerus and tibia [4,9–15]. Patients with cancer-associated skeletal-related-events may receive doses of intravenous BPs that are up to ten times greater than that administered for management of osteoporosis and represent a highly exposed population [6]. Despite growing body of orthopedic studies evaluating the association between BP therapy and several type of fractures, there is scant information in the literature about susceptibility of
https://doi.org/10.1016/j.injury.2018.07.006 0020-1383/© 2018 Elsevier Ltd. All rights reserved.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006
G Model JINJ 7753 No. of Pages 4
2
M. Zandi et al. / Injury, Int. J. Care Injured xxx (2018) xxx–xxx
mandibular bone to fracture after exposure to long-term or highdose antiresorptive agents. Because the mandible and the appendicular skeleton are derived from distinct embryonic cell lineage and have different rates of bone turnover, they may show different responses to BP therapy [16,17] as is evidenced by the unique localization of medication-related osteonecrosis to the jaw bone. Therefore, site specific evaluation of susceptibility to fracture after BP therapy is required. The purpose of present study was to evaluate susceptibility of mandibular bone to fracture after exposure to high-dose zoledronic acid in a rat animal model. Materials and methods The protocol of this research was reviewed and approved by the Ethics Committee of the University. Fifty male Wistar rats aged 6 months and weighing about 330 g were obtained from the Animal House of the University and housed in a temperature- and humidity-controlled environment with food and water supplies ad libitum. After a 2-week acclimationperiod, rats were randomly allocated to two groups of 25 animals. The rats in group Z (Zoledronate-treated) received monthly intravenous infusion of 0.06 mg/kg zoledronate (Zometa, Novartis Pharma, Basel, Switzerland) for 6 months (a total of 7 doses). The 25 rats in the group C (Control) were injected with an equal volume of saline in the same manner. A month after the last zoledronate/saline administration, all 50 rats were euthanized by an overdose of anesthesia. The mandibles were dissected, defleshed, and scanned using a cone beam computed tomography (CBCT) scanner (CRANEX 3D, SOREDEX, Tuusula, Finland) with the following parameters: 0.136 mm voxel size and 60 60 mm field of view. For radiographic evaluation of each side of the mandible, a coronal slice perpendicular to the inferior border of the mandible, passing through the distobuccal cusp tip of the first molar was produced and the cortical thickness of the inferior mandibular border and the bone mineral density were measured (Fig. 1). To calculate the mandibular bone density, three areas of bone on each coronal section were randomly selected and their grey values were determined using a rectangular ROI of approximately 10 10 pixels and the mean grey scale value representing the mean bone density profile of the hemimandible was calculated. All radiographic measurements were performed by two examiners separately and were recorded in a data sheet. The inter-examiner reliability was assessed using the intraclass correlation coefficient (ICC). After obtaining CBCT, the rat mandibles were split at the midline suture and the biomechanical properties of hemimandibles were measured by three-point bending test using a Universal Testing Machine (STM-20, Santam, Tehran, Iran). Mechanical properties were determined from each force (p) versus displacement (d) curve. Each hemimandible was placed on the two lower support points (10 mm span) of the machine with the lingual aspect facing down and a constant deformation rate of 5.0 mm/min was generated until fracture. From the load-displacement curve, the maximal load failure (N) and ultimate stress (MPa) were determined and recorded. The data were statistically analyzed using SPSS version 16.0 (SPSS inc., Chicago, IL, USA). Results were presented as the mean standard deviation. Comparisons between parameters were performed by unpaired Student's t-test and one way analysis of variance (ANOVA). A p-value less than 0.05 was selected as the criterion for statistical significance. Results All rats tolerated the experiment well and no complication was observed.
Fig. 1. Red hatched area indicates the area of mandibular bone on each coronal section of CBCT where the grey value measurements are performed. The doubleheaded green arrow shows the mandibular inferior cortical bone thickness (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
In present study, the mandibular inferior cortical bone thickness, the bone mineral density, the peak load, and the ultimate stress of 50 zoledronate-treated hemimandibles were compared with 50 control hemimandibles. The inter-rater ICC for both mandibular inferior cortical bone thickness and bone density measurements was found to be good (0.86 and 0.81, respectively). Evaluation of CBCT coronal sections showed that the mean mandibular inferior cortical bone thickness was significantly (P < 0.001) larger in rats receiving zoledronate (0.30 0.02 mm) compared to the control rats (0.21 0.01 mm). The mean bone mineral density was also significantly (P < 0.001) higher in zoledronate-treated rats (1045.00 185.79) than in the control group (878.66 166.53) (Table 1).
Table 1 Comparison of grey value and cortical thickness of mandible between groups. Group
Gray value
Inferior border thickness (mm)
Study Control
Mean SD Mean dif. 1045.00 185.79 166.33* 878.66 166.53
Mean SD Mean dif. 0.30 0.02 0.09* 0.21 0.01
*
P < 0.001, statistically significant difference between groups.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006
G Model JINJ 7753 No. of Pages 4
M. Zandi et al. / Injury, Int. J. Care Injured xxx (2018) xxx–xxx Table 2 Comparison of maximal load and ultimate stress of mandible between groups. Group
Maximal load (N)
Ultimate stress (MPa)
Study Control
Mean SD Mean dif. 84.61 33.62 -13.75* 98.36 16.59
Mean SD Mean dif. 1.76 0.72 -0.27* 2.03 0.44
*
P < 0.05, statistically significant difference between groups.
The results of biomechanical tests showed a significant (P < 0.05) lower peak load in the zoledronate-treated hemimandibles (84.61 33.62 N) compared to the control hemimandibles (98.36 16.5 9 N). The ultimate stress on three-point bending test was also significantly (P < 0.05) lower in zoledronatetreated hemimandibles (1.76 0.72 MPa) than in the control hemimandibles (2.03 0.44 MPa) (Table 2). Discussion In present preclinical study, the effect of administrating a high dose of zoledronate on mandibular bone susceptibility to fracture was biomechanically and radiographically evaluated. Zoledronate is one of the most frequently used and the most potent intravenous BP in cancer management. The dose of zoledronate used in this experiment corresponded to the recommended dose (4-mg dose every 3–4 weeks) for prevention of skeletal events in cancer patients. The results of the three-point bending tests revealed that a lower amount of force was required to fracture mandibular bone in zoledronate-treated rats compared to the control group. The drug-induced fragility of mandibular bone might be due to increased bone mineralization and suppressed bone turnover following zoledronate therapy. Although reduced bone turnover following BP administration improves the bone quantity and strength, long-term suppression of bone remodeling may have an adverse effect on microdamage repair, biomechanical properties, and the quality of bone [4]. High-dose BP therapy has been shown to elevate microdamage accumulation and is associated with increased production of advanced glycation end products, with a reduction in the toughness of bone [18–20]. In current experiment, radiological evaluation of mandibles demonstrated an increased cortical thickness of mandibular inferior border in zoledronate-treated rats compared to control rats. Mandibular inferior border cortical bone measurement has been shown to be a potentially useful tool for detection of bone changes associated with BP use. Increases in cortical bone thickness following BP therapy has been suggested to be due to suppressed endocortical and intracortical remodeling. A correlations between mandibular cortical bone thickness and the dose and duration of BP therapy has also been verified [1,21,22]. Similarly, orthopedic studies suggested that a radiographic characteristic of atypical femur fractures was thickening of the femoral cortex. This cortical thickening, which increases the chance of unusual bone fracture, has been postulated to be due to reduced bone remodeling and increased secondary mineralization of bone following long-term BP therapy [23–25]. In present study, CBCT assessments demonstrated that zoledronate-treated rats had an increased mandibular bone mineral density compared to the control group. Increase in bone mineral density for a long period of time has been shown to have a deleterious effect on bone quality, elasticity and resistance, leading to the brittleness of mandibular bone [26]. CBCT has been considered as a useful, non-destructive tool for indirect measurement of bone mineral density. Many studies have demonstrated a strong positive correlations between grey values of CBCT image with known density of reference materials and grey values obtained from the conventional clinical CT [27].
3
In present study, the results of biomechanical tests and radiographic assessments indicated that mandibular bone similar to femur might be at an increased risk of unusual fractures after high-dose BP exposure. The susceptibility of mandible to fracture may be explained by the fact that BPs preferentially accumulate in regions of high osteogenic and turnover activity such as mandible, thus focal adverse effects of these antiresorptive agents may be amplified by exposure to supranormal concentrations [28]. This may also explain why the medication-related osteonecrosis is uniquely localized to the jaw bone [29]. The overexposure of mandible to BPs has also an adverse effect on fracture healing of this bone [30]. Most of previous investigations evaluating the association between atypical femur fractures and BPs use were on patients under treatment with long-term oral BPs. Information about susceptibility to bone fracture in cancer patients receiving intravenous BPs is limited. In studies by Puhaindran et al. and Chang et al., a high prevalence of atypical femoral fractures among cancer patients treated with intravenous BPs was observed [6,31]. Cancer patients are exposed to doses of BPs that are up to ten times greater than the dose administrated for osteoporosis management [6,32]. It should be noted that BPs have a long duration of action and remain in bone for greater than ten years. So, patients with a past history of BP exposure may be still at increased risk of bone fracture. However, after BP discontinuation, the risk of residual BP effect decreases over time. The recovery of bone remodeling appears to be dose, time, and drug dependent [33,34]. The strengths of present study included the randomized controlled experimental design, the use of clinical dose and dosing interval of zoledronate, and evaluation of both radiological and biomechanical effects of drug exposure. Current study had several limitations. First, study was performed on an animal which has different physiology, drug metabolism, and bone turnover compared to human, leading to difficulty when trying to extrapolate the results to a clinical situation`. Second, the effects of only one type of BP agents and at a single time-point was assessed. Third, histological examination of the samples was not performed. Conclusion In present study, zoledronate therapy resulted in inferior border cortical thickening, increased bone mineral density, and brittleness of mandible. These findings indicated that zoledronate therapy reduced the mechanical strength of the mandibles, implying an increased risk of mandibular fracture in rats. Funding The study was funded by Vice-chancellor for Research and Technology, Hamadan University of Medical Sciences (No. 9607254682). Ethical approval Hamadan University of Medical Sciences Ethics Committee Conflict of interest There is no conflict of interest to declare. Acknowledgement This study has been adapted from a doctoral thesis at Hamadan University of Medical Sciences.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006
G Model JINJ 7753 No. of Pages 4
4
M. Zandi et al. / Injury, Int. J. Care Injured xxx (2018) xxx–xxx
References [1] Torres S.R., Chen CS, Leroux BG, et al. Mandibular inferior cortical bone thickness on panoramic radiographs in patients using bisphosphonates. Oral Surg Oral Med Oral Pathol Oral Radiol 2015;119:584. [2] Chou AC, Ng AC, Png MA, et al. Bone cross-sectional geometry is not associated with atypical femoral fractures in Asian female chronic bisphosphonate users. Bone 2015;79:170. [3] Bellido T, Plotkin LI. Novel actions of bisphosphonates in bone: preservation of osteoblast and osteocyte viability. Bone 2011;49:50. [4] Bissonnette L, April PM, Dumais R, et al. Atypical fracture of the tibial diaphysis associated with bisphosphonate therapy: a case report. Bone 2013;56:406. [5] Odvina CV, Zerwekh JE, Rao DS, et al. Severely suppressed bone turnover: a potential complication of alendronate therapy. J Clin Endocrinol Metab 2005;90:1294. [6] Chang ST, Tenforde AS, Grimsrud CD. Atypical femur fractures among breast cancer and multiple myeloma patients receiving intravenous bisphosphonate therapy. Bone 2012;51:524. [7] Park-Wyllie LY, Mamdani MM, Juurlink DN, et al. Bisphosphonate use and the risk of subtrochanteric or femoral shaft fractures in older women. JAMA 2011;305:783. [8] Chen F, Wang Z, Bhattacharyya T. Absence of femoral cortical thickening in long-term bisphosphonate users: implications for atypical femur fractures. Bone 2014;62:64. [9] Goh SK, Yang KY, Koh JS, et al. Subtrochanteric insufficiency fractures in patients on alendronate therapy: a caution. J Bone Joint Surg Br 2007;89:349. [10] Neviaser AS, Lane JM, Lenart BA, et al. Low-energy femoral shaft fractures associated with alendronate use. J Orthop Trauma 2008;22:346. [11] Odvina CV, Levy S, Rao S, et al. Unusual mid-shaft fractures during long-term bisphosphonate therapy. Clin Endocrinol (Oxf) 2010;72:161. [12] Shane E, Burr D, Ebeling PR, et al. Atypical subtrochanteric and diaphyseal femoral fractures: report of a task force of the American society for bone and mineral research. J Bone Miner Res 2010;25:2267. [13] Gedmintas L, Solomon DH, Kim SC. Bisphosphonates and risk of subtrochanteric, femoral shaft, and atypical femur fracture: a systematic review and meta-analysis. J Bone Miner Res 2013;28:1729. [14] Breglia MD, Carter JD. Atypical insufficiency fracture of the tibia associated with long-term bisphosphonate therapy. J Clin Rheumatol 2010;16:76. [15] Imbuldeniya AM, Jiwa N, Murphy JP. Bilateral atypical insufficiency fractures of the proximal tibia and a unilateral distal femoral fracture associated with long-term intravenous bisphosphonate therapy: a case report. J Med Case Rep 2012;6:50. [16] Eames BF, Helms JA. Conserved molecular program regulating cranial and appendicular skeletogenesis. Dev Dyn 2004;231:4. [17] Noden DM, Trainor PA. Relations and interactions between cranial mesoderm and neural crest populations. J Anat 2005;207:575.
[18] Iwata K, Mashiba T, Hitora T. A large amount of microdamages in the cortical bone around fracture site in a patient of atypical femoral fracture after longterm bisphosphonate therapy. Bone 2014;64:183. [19] Tang SY, Vashishth D. Non-enzymatic glycation alters microdamage formation in human cancellous bone. Bone 2010;46:148. [20] Vashishth D, Gibson GJ, Khoury JI, et al. Influence of nonenzymatic glycation on biomechanical properties of cortical bone. Bone 2001;28:195. [21] Torres SR, Chen CSK, Leroux BG, et al. Mandibular cortical bone evaluation on cone beam computed tomography images of patients with bisphosphonate associated osteonecrosis of the jaws. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2012;113(695). [22] Recker RR, Delmas PD, Halse J, et al. Effects of intravenous zoledronic acid once yearly on bone remodeling and bone structure. J Bone Miner Res 2008;23:6. [23] Odvina CV, Levy S, Rao S. Unusual mid-shaft fractures during long-term bisphosphonate therapy. Clin Endocrinol Oxf 2010;72:161. [24] Ott SM. Long-term safety of bisphosphonates. J Clin Endocrinol Metab 2005;90:1897. [25] Giusti A, Hamdy NA, Dekkers OM, et al. Atypical fractures and bisphosphonate therapy: a cohort study of patients with femoral fracture with radiographic adjudication of fracture site and features. Bone 2011;48:966. [26] Allen MR, Burr DB. Mineralization, microdamage, and matrix: how bisphosphonates influence material properties of bone. BoneKEyOsteovision 2007;4:49. [27] Kim DG. Can dental cone beam computed tomography assess bone mineral density? J Bone Metab 2014;21:117. [28] Abrahamsen B, Einhorn TA. Beyond a reasonable doubt? Bisphosphonates and atypical femur fractures. Bone 2012;50(1196). [29] Zandi M, Dehghan A, Janbaz P, et al. The starting point for bisphosphonaterelated osteonecrosis of the jaw: alveolar bone or oral mucosa? A randomized, controlled experimental study. J Craniomaxillofac Surg 2017;45:157. [30] Zandi M, Dehghan A, Amini P, et al. Evaluation of mandibular fracture healing in rats under zoledronate therapy: a histologic study. Injury 2017;48:2683. [31] Puhaindran ME, Farooki A, Steensma MR. Atypical subtrochanteric femoral fractures in patients with skeletal malignant involvement treated with intravenous bisphosphonates. J Bone Joint Surg Am 2011;93:1235. [32] Coleman RE, McCloskey EV. Bisphosphonates in oncology. Bone 2011;49:71. [33] Allen MR, Burr DB. Bisphosphonate effects on bone turnover, microdamage, and mechanical properties: what we think we know and what we know that we don’t know. Bone 2011;49:56. [34] Zandi M, Dehghan A, Ghadermazi K, et al. Perioperative discontinuation of intravenous bisphosphonate therapy reduces the incidence and severity of bisphosphonate-related osteonecrosis of the jaw: a randomized, controlled, prospective experimental study in rats. J Craniomaxillofac Surg 2015;43:1823.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006
Injury, Int. J. Care Injured xxx (2018) xxx–xxx
Contents lists available at ScienceDirect
Injury journal homepage: www.elsevier.com/locate/injury
Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats Mohammad Zandia,b , Abbas Shokric,* , Maryam Mousavid, Sanaz Rajaeid , Naser Mohammad Gholi Mezerjie a
Department of Oral and Maxillofacial Surgery, Hamadan University of Medical Sciences, Hamadan, Iran Dental Research Center, Hamadan University of Medical Sciences, Hamadan, Iran Department of Oral and Maxillofacial Radiology, Hamadan University of Medical Sciences, Hamadan, Iran d Faculty of Dentistry, Hamadan University of Medical sciences, Hamadan, Iran e Department of Biostatistics and Epidemiology, Hamadan University of medical sciences, Hamadan, Iran b c
A R T I C L E I N F O
Keywords: Zoledronate Bisphosphonate Mandible Bone Fracture
A B S T R A C T
Introduction: The aim of this study was to evaluate the effect of zoledronate therapy on susceptibility of mandibular bone to fracture in rats. Methods: Fifty rats were randomly allocated to two groups of 25 animals. The rats in group Z received monthly intravenous infusion of 0.06 mg/kg zoledronate for 6 months. The rats in the group C were injected with an equal volume of saline in the same manner. A month after the last zoledronate/saline administration, all 50 rats were euthanized. Using a cone beam computed tomography, the cortical thickness of inferior border of mandible and the mandibular bone mineral density were calculated, and using a three-point bending test, the peak load failure and the ultimate stress of mandibular bone were determined. Results: The mean mandibular inferior cortical bone thickness and the mean bone mineral density were significantly larger in zoledronate-treated rats (0.30 0.02 mm and 1045.00 185.79, respectively) compared to control rats (0.21 0.01 mm and 878.66 166.53, respectively). The peak load and the ultimate stress were lower in the zoledronate-treated hemimandibles (84.61 33.62 N and 1.76 0.72 MPa, respectively) compared to the control hemimandibles (98.36 16.5 9 N and 2.03 0.44 MPa, respectively). Conclusion: Zoledronate therapy reduced the mechanical strength of the mandibles, implying an increased risk of mandibular fracture in rats. © 2018 Elsevier Ltd. All rights reserved.
Introduction Bisphosphonates (BPs) are considered one of the main pharmacological agents in the treatment of a large number of diseases in which bone resorption needs to be reduced or controlled [1]. Their primary action is on osteoclasts, where they inhibit osteoclast activity and proliferation and induce apoptosis, leading to suppression of bone turnover and increase in bone mineralization [2,3]. Since the first report of spontaneous peripheral fractures after long-term alendronate therapy, followed by several studies
* Corresponding author at: Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, University of Medical Sciences, Shahid Fahmideh Street, Hamadan, Iran. E-mail address: [email protected] (A. Shokri).
reporting subtrochanteric or diaphyseal femoral insufficiency fractures in patients under BP therapy, concerns have raised about possible association between prolonged BP therapy and spontaneous bone fractures [4–6]. It was hypothesized that long-term BP exposure and oversuppression of bone turnover have a worsening effect on bone quality, making bone brittle and prone to fracture [5,7,8]. There is now abundant evidence demonstrating that patients receiving prolonged oral BPs are at increased risk of several types of fractures including femur, pelvis, fibula, ankle, metatarsals, and long bones such as the humerus and tibia [4,9–15]. Patients with cancer-associated skeletal-related-events may receive doses of intravenous BPs that are up to ten times greater than that administered for management of osteoporosis and represent a highly exposed population [6]. Despite growing body of orthopedic studies evaluating the association between BP therapy and several type of fractures, there is scant information in the literature about susceptibility of
https://doi.org/10.1016/j.injury.2018.07.006 0020-1383/© 2018 Elsevier Ltd. All rights reserved.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006
G Model JINJ 7753 No. of Pages 4
2
M. Zandi et al. / Injury, Int. J. Care Injured xxx (2018) xxx–xxx
mandibular bone to fracture after exposure to long-term or highdose antiresorptive agents. Because the mandible and the appendicular skeleton are derived from distinct embryonic cell lineage and have different rates of bone turnover, they may show different responses to BP therapy [16,17] as is evidenced by the unique localization of medication-related osteonecrosis to the jaw bone. Therefore, site specific evaluation of susceptibility to fracture after BP therapy is required. The purpose of present study was to evaluate susceptibility of mandibular bone to fracture after exposure to high-dose zoledronic acid in a rat animal model. Materials and methods The protocol of this research was reviewed and approved by the Ethics Committee of the University. Fifty male Wistar rats aged 6 months and weighing about 330 g were obtained from the Animal House of the University and housed in a temperature- and humidity-controlled environment with food and water supplies ad libitum. After a 2-week acclimationperiod, rats were randomly allocated to two groups of 25 animals. The rats in group Z (Zoledronate-treated) received monthly intravenous infusion of 0.06 mg/kg zoledronate (Zometa, Novartis Pharma, Basel, Switzerland) for 6 months (a total of 7 doses). The 25 rats in the group C (Control) were injected with an equal volume of saline in the same manner. A month after the last zoledronate/saline administration, all 50 rats were euthanized by an overdose of anesthesia. The mandibles were dissected, defleshed, and scanned using a cone beam computed tomography (CBCT) scanner (CRANEX 3D, SOREDEX, Tuusula, Finland) with the following parameters: 0.136 mm voxel size and 60 60 mm field of view. For radiographic evaluation of each side of the mandible, a coronal slice perpendicular to the inferior border of the mandible, passing through the distobuccal cusp tip of the first molar was produced and the cortical thickness of the inferior mandibular border and the bone mineral density were measured (Fig. 1). To calculate the mandibular bone density, three areas of bone on each coronal section were randomly selected and their grey values were determined using a rectangular ROI of approximately 10 10 pixels and the mean grey scale value representing the mean bone density profile of the hemimandible was calculated. All radiographic measurements were performed by two examiners separately and were recorded in a data sheet. The inter-examiner reliability was assessed using the intraclass correlation coefficient (ICC). After obtaining CBCT, the rat mandibles were split at the midline suture and the biomechanical properties of hemimandibles were measured by three-point bending test using a Universal Testing Machine (STM-20, Santam, Tehran, Iran). Mechanical properties were determined from each force (p) versus displacement (d) curve. Each hemimandible was placed on the two lower support points (10 mm span) of the machine with the lingual aspect facing down and a constant deformation rate of 5.0 mm/min was generated until fracture. From the load-displacement curve, the maximal load failure (N) and ultimate stress (MPa) were determined and recorded. The data were statistically analyzed using SPSS version 16.0 (SPSS inc., Chicago, IL, USA). Results were presented as the mean standard deviation. Comparisons between parameters were performed by unpaired Student's t-test and one way analysis of variance (ANOVA). A p-value less than 0.05 was selected as the criterion for statistical significance. Results All rats tolerated the experiment well and no complication was observed.
Fig. 1. Red hatched area indicates the area of mandibular bone on each coronal section of CBCT where the grey value measurements are performed. The doubleheaded green arrow shows the mandibular inferior cortical bone thickness (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
In present study, the mandibular inferior cortical bone thickness, the bone mineral density, the peak load, and the ultimate stress of 50 zoledronate-treated hemimandibles were compared with 50 control hemimandibles. The inter-rater ICC for both mandibular inferior cortical bone thickness and bone density measurements was found to be good (0.86 and 0.81, respectively). Evaluation of CBCT coronal sections showed that the mean mandibular inferior cortical bone thickness was significantly (P < 0.001) larger in rats receiving zoledronate (0.30 0.02 mm) compared to the control rats (0.21 0.01 mm). The mean bone mineral density was also significantly (P < 0.001) higher in zoledronate-treated rats (1045.00 185.79) than in the control group (878.66 166.53) (Table 1).
Table 1 Comparison of grey value and cortical thickness of mandible between groups. Group
Gray value
Inferior border thickness (mm)
Study Control
Mean SD Mean dif. 1045.00 185.79 166.33* 878.66 166.53
Mean SD Mean dif. 0.30 0.02 0.09* 0.21 0.01
*
P < 0.001, statistically significant difference between groups.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006
G Model JINJ 7753 No. of Pages 4
M. Zandi et al. / Injury, Int. J. Care Injured xxx (2018) xxx–xxx Table 2 Comparison of maximal load and ultimate stress of mandible between groups. Group
Maximal load (N)
Ultimate stress (MPa)
Study Control
Mean SD Mean dif. 84.61 33.62 -13.75* 98.36 16.59
Mean SD Mean dif. 1.76 0.72 -0.27* 2.03 0.44
*
P < 0.05, statistically significant difference between groups.
The results of biomechanical tests showed a significant (P < 0.05) lower peak load in the zoledronate-treated hemimandibles (84.61 33.62 N) compared to the control hemimandibles (98.36 16.5 9 N). The ultimate stress on three-point bending test was also significantly (P < 0.05) lower in zoledronatetreated hemimandibles (1.76 0.72 MPa) than in the control hemimandibles (2.03 0.44 MPa) (Table 2). Discussion In present preclinical study, the effect of administrating a high dose of zoledronate on mandibular bone susceptibility to fracture was biomechanically and radiographically evaluated. Zoledronate is one of the most frequently used and the most potent intravenous BP in cancer management. The dose of zoledronate used in this experiment corresponded to the recommended dose (4-mg dose every 3–4 weeks) for prevention of skeletal events in cancer patients. The results of the three-point bending tests revealed that a lower amount of force was required to fracture mandibular bone in zoledronate-treated rats compared to the control group. The drug-induced fragility of mandibular bone might be due to increased bone mineralization and suppressed bone turnover following zoledronate therapy. Although reduced bone turnover following BP administration improves the bone quantity and strength, long-term suppression of bone remodeling may have an adverse effect on microdamage repair, biomechanical properties, and the quality of bone [4]. High-dose BP therapy has been shown to elevate microdamage accumulation and is associated with increased production of advanced glycation end products, with a reduction in the toughness of bone [18–20]. In current experiment, radiological evaluation of mandibles demonstrated an increased cortical thickness of mandibular inferior border in zoledronate-treated rats compared to control rats. Mandibular inferior border cortical bone measurement has been shown to be a potentially useful tool for detection of bone changes associated with BP use. Increases in cortical bone thickness following BP therapy has been suggested to be due to suppressed endocortical and intracortical remodeling. A correlations between mandibular cortical bone thickness and the dose and duration of BP therapy has also been verified [1,21,22]. Similarly, orthopedic studies suggested that a radiographic characteristic of atypical femur fractures was thickening of the femoral cortex. This cortical thickening, which increases the chance of unusual bone fracture, has been postulated to be due to reduced bone remodeling and increased secondary mineralization of bone following long-term BP therapy [23–25]. In present study, CBCT assessments demonstrated that zoledronate-treated rats had an increased mandibular bone mineral density compared to the control group. Increase in bone mineral density for a long period of time has been shown to have a deleterious effect on bone quality, elasticity and resistance, leading to the brittleness of mandibular bone [26]. CBCT has been considered as a useful, non-destructive tool for indirect measurement of bone mineral density. Many studies have demonstrated a strong positive correlations between grey values of CBCT image with known density of reference materials and grey values obtained from the conventional clinical CT [27].
3
In present study, the results of biomechanical tests and radiographic assessments indicated that mandibular bone similar to femur might be at an increased risk of unusual fractures after high-dose BP exposure. The susceptibility of mandible to fracture may be explained by the fact that BPs preferentially accumulate in regions of high osteogenic and turnover activity such as mandible, thus focal adverse effects of these antiresorptive agents may be amplified by exposure to supranormal concentrations [28]. This may also explain why the medication-related osteonecrosis is uniquely localized to the jaw bone [29]. The overexposure of mandible to BPs has also an adverse effect on fracture healing of this bone [30]. Most of previous investigations evaluating the association between atypical femur fractures and BPs use were on patients under treatment with long-term oral BPs. Information about susceptibility to bone fracture in cancer patients receiving intravenous BPs is limited. In studies by Puhaindran et al. and Chang et al., a high prevalence of atypical femoral fractures among cancer patients treated with intravenous BPs was observed [6,31]. Cancer patients are exposed to doses of BPs that are up to ten times greater than the dose administrated for osteoporosis management [6,32]. It should be noted that BPs have a long duration of action and remain in bone for greater than ten years. So, patients with a past history of BP exposure may be still at increased risk of bone fracture. However, after BP discontinuation, the risk of residual BP effect decreases over time. The recovery of bone remodeling appears to be dose, time, and drug dependent [33,34]. The strengths of present study included the randomized controlled experimental design, the use of clinical dose and dosing interval of zoledronate, and evaluation of both radiological and biomechanical effects of drug exposure. Current study had several limitations. First, study was performed on an animal which has different physiology, drug metabolism, and bone turnover compared to human, leading to difficulty when trying to extrapolate the results to a clinical situation`. Second, the effects of only one type of BP agents and at a single time-point was assessed. Third, histological examination of the samples was not performed. Conclusion In present study, zoledronate therapy resulted in inferior border cortical thickening, increased bone mineral density, and brittleness of mandible. These findings indicated that zoledronate therapy reduced the mechanical strength of the mandibles, implying an increased risk of mandibular fracture in rats. Funding The study was funded by Vice-chancellor for Research and Technology, Hamadan University of Medical Sciences (No. 9607254682). Ethical approval Hamadan University of Medical Sciences Ethics Committee Conflict of interest There is no conflict of interest to declare. Acknowledgement This study has been adapted from a doctoral thesis at Hamadan University of Medical Sciences.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006
G Model JINJ 7753 No. of Pages 4
4
M. Zandi et al. / Injury, Int. J. Care Injured xxx (2018) xxx–xxx
References [1] Torres S.R., Chen CS, Leroux BG, et al. Mandibular inferior cortical bone thickness on panoramic radiographs in patients using bisphosphonates. Oral Surg Oral Med Oral Pathol Oral Radiol 2015;119:584. [2] Chou AC, Ng AC, Png MA, et al. Bone cross-sectional geometry is not associated with atypical femoral fractures in Asian female chronic bisphosphonate users. Bone 2015;79:170. [3] Bellido T, Plotkin LI. Novel actions of bisphosphonates in bone: preservation of osteoblast and osteocyte viability. Bone 2011;49:50. [4] Bissonnette L, April PM, Dumais R, et al. Atypical fracture of the tibial diaphysis associated with bisphosphonate therapy: a case report. Bone 2013;56:406. [5] Odvina CV, Zerwekh JE, Rao DS, et al. Severely suppressed bone turnover: a potential complication of alendronate therapy. J Clin Endocrinol Metab 2005;90:1294. [6] Chang ST, Tenforde AS, Grimsrud CD. Atypical femur fractures among breast cancer and multiple myeloma patients receiving intravenous bisphosphonate therapy. Bone 2012;51:524. [7] Park-Wyllie LY, Mamdani MM, Juurlink DN, et al. Bisphosphonate use and the risk of subtrochanteric or femoral shaft fractures in older women. JAMA 2011;305:783. [8] Chen F, Wang Z, Bhattacharyya T. Absence of femoral cortical thickening in long-term bisphosphonate users: implications for atypical femur fractures. Bone 2014;62:64. [9] Goh SK, Yang KY, Koh JS, et al. Subtrochanteric insufficiency fractures in patients on alendronate therapy: a caution. J Bone Joint Surg Br 2007;89:349. [10] Neviaser AS, Lane JM, Lenart BA, et al. Low-energy femoral shaft fractures associated with alendronate use. J Orthop Trauma 2008;22:346. [11] Odvina CV, Levy S, Rao S, et al. Unusual mid-shaft fractures during long-term bisphosphonate therapy. Clin Endocrinol (Oxf) 2010;72:161. [12] Shane E, Burr D, Ebeling PR, et al. Atypical subtrochanteric and diaphyseal femoral fractures: report of a task force of the American society for bone and mineral research. J Bone Miner Res 2010;25:2267. [13] Gedmintas L, Solomon DH, Kim SC. Bisphosphonates and risk of subtrochanteric, femoral shaft, and atypical femur fracture: a systematic review and meta-analysis. J Bone Miner Res 2013;28:1729. [14] Breglia MD, Carter JD. Atypical insufficiency fracture of the tibia associated with long-term bisphosphonate therapy. J Clin Rheumatol 2010;16:76. [15] Imbuldeniya AM, Jiwa N, Murphy JP. Bilateral atypical insufficiency fractures of the proximal tibia and a unilateral distal femoral fracture associated with long-term intravenous bisphosphonate therapy: a case report. J Med Case Rep 2012;6:50. [16] Eames BF, Helms JA. Conserved molecular program regulating cranial and appendicular skeletogenesis. Dev Dyn 2004;231:4. [17] Noden DM, Trainor PA. Relations and interactions between cranial mesoderm and neural crest populations. J Anat 2005;207:575.
[18] Iwata K, Mashiba T, Hitora T. A large amount of microdamages in the cortical bone around fracture site in a patient of atypical femoral fracture after longterm bisphosphonate therapy. Bone 2014;64:183. [19] Tang SY, Vashishth D. Non-enzymatic glycation alters microdamage formation in human cancellous bone. Bone 2010;46:148. [20] Vashishth D, Gibson GJ, Khoury JI, et al. Influence of nonenzymatic glycation on biomechanical properties of cortical bone. Bone 2001;28:195. [21] Torres SR, Chen CSK, Leroux BG, et al. Mandibular cortical bone evaluation on cone beam computed tomography images of patients with bisphosphonate associated osteonecrosis of the jaws. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2012;113(695). [22] Recker RR, Delmas PD, Halse J, et al. Effects of intravenous zoledronic acid once yearly on bone remodeling and bone structure. J Bone Miner Res 2008;23:6. [23] Odvina CV, Levy S, Rao S. Unusual mid-shaft fractures during long-term bisphosphonate therapy. Clin Endocrinol Oxf 2010;72:161. [24] Ott SM. Long-term safety of bisphosphonates. J Clin Endocrinol Metab 2005;90:1897. [25] Giusti A, Hamdy NA, Dekkers OM, et al. Atypical fractures and bisphosphonate therapy: a cohort study of patients with femoral fracture with radiographic adjudication of fracture site and features. Bone 2011;48:966. [26] Allen MR, Burr DB. Mineralization, microdamage, and matrix: how bisphosphonates influence material properties of bone. BoneKEyOsteovision 2007;4:49. [27] Kim DG. Can dental cone beam computed tomography assess bone mineral density? J Bone Metab 2014;21:117. [28] Abrahamsen B, Einhorn TA. Beyond a reasonable doubt? Bisphosphonates and atypical femur fractures. Bone 2012;50(1196). [29] Zandi M, Dehghan A, Janbaz P, et al. The starting point for bisphosphonaterelated osteonecrosis of the jaw: alveolar bone or oral mucosa? A randomized, controlled experimental study. J Craniomaxillofac Surg 2017;45:157. [30] Zandi M, Dehghan A, Amini P, et al. Evaluation of mandibular fracture healing in rats under zoledronate therapy: a histologic study. Injury 2017;48:2683. [31] Puhaindran ME, Farooki A, Steensma MR. Atypical subtrochanteric femoral fractures in patients with skeletal malignant involvement treated with intravenous bisphosphonates. J Bone Joint Surg Am 2011;93:1235. [32] Coleman RE, McCloskey EV. Bisphosphonates in oncology. Bone 2011;49:71. [33] Allen MR, Burr DB. Bisphosphonate effects on bone turnover, microdamage, and mechanical properties: what we think we know and what we know that we don’t know. Bone 2011;49:56. [34] Zandi M, Dehghan A, Ghadermazi K, et al. Perioperative discontinuation of intravenous bisphosphonate therapy reduces the incidence and severity of bisphosphonate-related osteonecrosis of the jaw: a randomized, controlled, prospective experimental study in rats. J Craniomaxillofac Surg 2015;43:1823.
Please cite this article in press as: M. Zandi, et al., Does zoledronate therapy make mandibular bone susceptible to fracture? A radiographical and biomechanical study in rats, Injury (2018), https://doi.org/10.1016/j.injury.2018.07.006