Fracture Repair Process Research Articles

Atypical femoral fractures and bisphosphonate use: current evidence and clinical implications.

Osteoporosis is a disease characterized by a low bone volume and deterioration of the bone quality, which increases the risk of low-energy fractures. Bisphosphonate (BP) treatment increases the bone mass and reduces the risk of fractures in patients with osteoporosis by suppressing bone resorption. In spite of its clinical benefits, the long-term use of BPs has been linked to the occurrence of atypical femoral fractures (AFFs). Although the evidence had been controversial regarding the association between the occurrence of AFFs and BP use, more recent studies with radiographic adjudication have indicated the significant associations between them. However, the pathogenesis of AFFs is not completely understood. The most popular hypothesis has suggested that the suppression of bone turnover by BPs is responsible; however, some recent reports have implied the involvement of pathophysiological alterations of the bone quality and fracture repair process. In this review, we summarize and discuss the epidemiology, risk factors and pathology of AFFs.

Local administration of AAV-DJ pseudoserotype expressing COX2 provided early onset of transgene expression and promoted bone fracture healing in mice.

We have previously obtained compelling proof-of-principle evidence for COX2 gene therapy for fracture repair using integrating retroviral vectors. For this therapy to be suitable for patient uses, a suitable vector with high safety profile must be used. Accordingly, this study sought to evaluate the feasibility of AAV as the vector for this COX2 gene therapy, because AAV raises less safety issues than the retroviral vectors used previously. However, an appropriate AAV serotype is required to provide early increase in and adequate level of COX2 expression that is needed for fracture repair. Herein, we reported that AAV-DJ, an artificial AAV pseudoserotype, is highly effective in delivering COX2 gene to fracture sites in a mouse femoral fracture model. Compared with AAV-2, the use of AAV-DJ led to ~5-fold increase in infectivity in mesenchymal stem cells (MSCs) and provided an earlier and significantly higher level of transgene expression at the fracture site. Injection of this vector at a dose of 7.5 × 10(11) genomic copies led to high COX2 level at the fracture site on day 3 after injections and significantly promoted fracture union at 21 days, as analyzed by radiography and μ-CT. The therapeutic effect appears to involve enhanced osteoblastic differentiation of MSCs and remodeling of callus tissues to laminar bone. This interpretation is supported by the enhanced expression of several key genes participating in the fracture repair process. In conclusion, AAV-DJ is a promising serotype for the AAV-based COX2 gene therapy of fracture repair in humans.

Interactions between MSCs and immune cells: implications for bone healing.

It is estimated that, of the 7.9 million fractures sustained in the United States each year, 5% to 20% result in delayed or impaired healing requiring therapeutic intervention. Following fracture injury, there is an initial inflammatory response that plays a crucial role in bone healing; however, prolonged inflammation is inhibitory for fracture repair. The precise spatial and temporal impact of immune cells and their cytokines on fracture healing remains obscure. Some cytokines are reported to be proosteogenic while others inhibit bone healing. Cell-based therapy utilizing mesenchymal stromal cells (MSCs) is an attractive option for augmenting the fracture repair process. Osteoprogenitor MSCs not only differentiate into bone, but they also exert modulatory effects on immune cells via a variety of mechanisms. In this paper, we review the current literature on both in vitro and in vivo studies on the role of the immune system in fracture repair, the use of MSCs in the enhancement of fracture healing, and interactions between MSCs and immune cells. Insight into this paradigm can provide valuable clues in identifying cellular and noncellular targets that can potentially be modulated to enhance both natural bone healing and bone repair augmented by the exogenous addition of MSCs.

Is sonic Hedgehog involved in human fracture healing? --a prospective study on local and systemic concentrations of SHH.

IntroductionSonic Hedgehog (SHH) is a new signalling pathway in bone repair. Evidence exist that SHH pathway plays a significant role in vasculogenesis and limb development during embryogenesis. Some in vitro and animal studies has already proven its potential for bone regeneration. However, no data on the role of SHH in the human fracture healing have been published so far.MethodsSeventy-five patients with long bone fractures were included into the study and divided in 2 groups. First group contained 69 patients with normal fracture healing. Four patients with impaired fracture healing formed the second group. 34 volunteers donated blood samples as control. Serum samples were collected over a period of 1 year following a standardized time schedule. In addition, SHH levels were measured in fracture haematoma and serum of 16 patients with bone fractures.ResultsFracture haematoma and patients serum both contained lower SHH concentrations compared to control serum. The comparison between the patients' serum SHH level and the control serum revealed lower levels for the patients at all measurement time points. Significantly lower concentrations were observed at weeks 1 and 2 after fracture. SHH levels were slightly decreased in patients with impaired fracture healing without statistical significance.ConclusionThis is the first study to report local and systemic concentration of SHH in human fracture healing and SHH serum levels in healthy adults. A significant reduction of the SHH levels during the inflammatory phase of fracture healing was found. SHH concentrations in fracture haematoma and serum were lower than the concentration in control serum for the rest of the healing period. Our findings indicate that there is no relevant involvement of SHH in human fracture healing. Fracture repair process seem to reduce the SHH level in human. Further studies are definitely needed to clarify the underlying mechanisms.

Ovariectomy-Induced Osteopenia Influences the Middle and Late Periods of Bone Healing in a Mouse Femoral Osteotomy Model.

It is known that bone healing is delayed in the presence of osteoporosis in humans. However, due to the complexities of the healing of osteoporotic fractures, animal models may be more appropriate for studying the effects of osteoporosis in more detail and for testing drugs on the fracture repair process. The purpose of this study was to investigate the influence of ovariectomy-induced osteopenia in bone healing in an open femoral osteotomy model, and to test the feasibility of this model for evaluating the healing process under osteopenic conditions. Ovariectomized (OVX) mouse models were employed to assess the effects of osteopenia on fracture healing, A mid-shaft femur osteotomy model was also established 3 weeks after ovariectomy as an osteopenic fracture group (OVX group). Femurs were then harvested at 2 weeks and 6 weeks after fracture for X-ray radiography, micro-computed tomography (micro-CT), histology, and biomechanical analysis. A sham-operated group (sham group) was used for comparison. The OVX mice had significantly lower bone volume density (BVF), volumetric bone mineral density (vBMD), and tissue mineral density (TMD) in the fracture calluses at 6 weeks (p<0.05), and similar trend was observed in 2 weeks. Additionally, larger calluses in OVX animals were observed via micro-CT and X-ray, but these did not result in better healing outcomes, as determined by biomechanical test at 6 weeks. Histological images of the healing fractures in the OVX mice found hastening of broken end resorption and delay of hard callus remodeling. The impaired biomechanical measurements in the OVX group (p<0.05) were consistent with micro-CT measurements and radiographic scoring, which also indicated delay in fracture healing of the OVX group. This study provided evidence that ovariectomy-induced osteopenia impair the middle and late bone healing process. These data also supported the validity of the mouse femoral osteotomy model in evaluating the process of bone healing under osteopenic conditions.

Haploinsufficiency of endogenous parathyroid hormone‐related peptide impairs bone fracture healing

Previous studies have demonstrated that endogenous parathyroid hormone-related peptide (PTHrP) plays a central role in the physiological regulation of bone formation. However, it is unclear whether endogenous PTHrP plays an important function in enhancing bone fracture healing. To determine whether endogenous PTHrP haploinsufficiency impaired bone fracture healing, closed mid-diaphyseal femur fractures were created in 8-week-old wild-type and Pthrp(+/-) mice. Callus tissue properties were analysed 1, 2 and 4 weeks after fracture by radiography, histology, histochemistry, immunohistochemistry and molecular biology. The size of the calluses was reduced 2 weeks after fracture, and the fracture repairs were poor 4 weeks after fractures, in Pthrp(+/-) compared with wild-type mice. Cartilaginous callus areas were reduced 1 week after fracture, but were increased 2 weeks after fracture in Pthrp(+/-) mice. There was a reduction in the number of ostoblasts, alkaline phosphatase (ALP)-positive areas, Type I collagen immunopositive areas, mRNA levels of ALP, Runt-related transcription factor 2 (Runx2) and Type I collagen, Runx2 and insulin-like growth factor-1 protein levels, the number of osteoclasts and the surface in callus tissues in Pthrp(+/-) compared with wild-type mice. These results demonstrate that endogenous PTHrP haploinsufficiency impairs the fracture repair process by reducing cartilaginous and bony callus formation, with downregulation of osteoblastic gene and protein expression and a reduction in endochondral bone formation, osteoblastic bone formation and osteoclastic bone resorption. Together, the results indicate that endogenous PTHrP plays an important role in fracture healing.

A new antiresorptive approach to the treatment of fragility fractures: long-term efficacy and safety of denosumab

An imbalance of the remodeling process for bone resorption leads to a loss of tissue with consequent microarchitectural damage, evident in conditions such as osteoporosis and related fragility fractures. Currently, pharmacological therapies are able to prevent or slow down bone resorption by inhibiting osteoclast activity. An innovative and targeted anti-resorptive approach is represented by the inhibition of RANK ligand (RANK-L), essential for the proliferation and activity of osteoclastic cells. The human monoclonal antibody against RANK-L (denosumab) has been approved for the treatment of osteoporosis. In clinical trials of patients with osteoporosis, inhibition of RANK-L has reduced bone loss and damage to the microarchitecture and was associated with an increase in mass and resistance at different skeletal sites, with most significant effects than those demonstrated by any other antiresorptive drugs. In addition, after 3 years of treatment, it showed a reduction in vertebral and non-vertebral fracture risk. Denosumab treatment also has not revealed any alteration in the physiological processes of fracture repair, showing no increase in the onset of complications 3 years after the fracture. The data show that denosumab offers an effective alternative therapeutic approach for the treatment of severe osteoporosis, with positive effects on BMD and reduction of fragility fractures risk. So, promising results in terms of therapeutic efficacy and reliability make desirable the wide clinical use of denosumab for the treatment of osteoporotic fractures in the near future.

Effects of radiation and surgery on healing of femoral fractures in a rat model

Management of soft tissue sarcoma involves multimodality treatment, including surgery and radiotherapy. Pathologic fracture of the femur after such treatment in the thigh is one serious, late complication and nonunion rates of 80-90% are reported. We hypothesize that the combination of radiotherapy and periosteal stripping (during tumor resection) leads to greater impairment of the fracture repair process than either intervention alone. Female Wistar retired breeder rats were randomized into four treatment groups (control, radiotherapy, surgery, and combination of radiotherapy and surgery) and three end-points (21, 28, and 35 days post-fracture). Designated animals first underwent radiotherapy, followed by surgical stripping of the periosteum 3 weeks later and femoral fracture with fixation after another 3 weeks. Animals were sacrificed and fractures examined using microCT and histomorphometry. Simple transverse or short oblique femoral fractures were produced. By 35 days, control animals formed unions, periosteum-stripped animals formed hypertrophic non-unions and irradiated animals formed atrophic non-unions. Histomorphometry revealed an absence of chondroid and osteoid production in animals undergoing radiotherapy. The relative contribution of periosteal stripping to occurrence of non-union was statistically insignificant. Radiation prior to fracture reliably resulted in atrophic non-union in our model. The contribution of periosteal stripping was negligible.

Hypolipemiant Treatment: Making the Right Choice for Osteoporotic Patients

Abstract Introduction: It has been shown that dyslipidemia is related to bone mineral density and fragility. Hypolipemiant drugs as statins or fibrates seem to increase the bone mineral density and probably to protect against fractures. The question that arises in this context is whether statins or fibrates have a positive effect on bone fracture repair process and which is their behaviour in an osteoporotic context. Our objective was to study the incidence of osteoporosis, dyslipidemia and of the association of these diseases, and to compare the effect of statins and fibrates on fracture repair in experimental conditions. Material and method: We studied the incidence of dyslipidemia and osteoporosis in the activity of a private family medicine cabinet. In the experimental part we observed from a radiographic point of view the fracture repair process of rats’ femurs. We analyzed 6 subgroups of 12 rats each: (1) ovariectomized control, (2) ovariectomized treated with statins, (3) ovariectomized treated with fibrates, (4) nonovariectomized control, (5) ) nonovariectomized treated with statins, (6) ) nonovariectomized treated with fibrates. The radiographic aspect has been objectified with a score at 2, 4, 6 and 8 weeks. Results: From the total of 646 patients included in the study, 193 (29.87%) had dyslipidemia while osteoporosis was diagnosed at 152 (23.53%) patients. 301 (46.6%) patients presented the association of these diseases. Comparing the subgroups of the OVX group, we had the following results: subgroup 1 - 5.5 points, group 2 - 11 points and group 3 - 4.5 points. In the case of the NOVX subgroups, the scores were: subgroup 4 - 7.5 points, subgroup 5 - 10 points and subgroup 6 - 6.5 points. Conclusions: The fact that the incidence of dyslipidemia is higher than that of osteoporosis is an argument for the necessity of choosing a hypolipemiant treatment that has, at the same time, a protective effect on bone. Hypolipemiant treatment influences the fracture repair process. The positive effect of statins on this process is more important on the ovariectomized group, in contrast with fibrates which have an accentuated effect on the nonovariectomized group and this suggests an interference between hypolipemiant treatment and estrogens level. However, the treatment with fibrates delays the fracture repair, groups (3) and (6) scores being inferior to those of the control group. We sustain the helping effect of statins treatment on fracture repair process.

Laser Evoked Bio-stimulation for Bone Fracture Healing (Case Report Study)

Summary: BACKGROUND: The stimulating effect of low level laser phototherapy on bone healing has been shown in a number of in vitro and animal studies. However, the effect of LLLT on the bone healing in human has not been previously wide demonstrated. The article reports an accidentally injury pattern and reported as fractures of the mid third of the left tibia. OBJECTIVE: The purpose of this case study was to demonstrate the biological effects of low-level laser therapy (LLLT) on tibial fractures treated surgically using radiographic, examinations. CASE REPORT: The case hospitalized for conventional surgery and followed by applying Low Level Laser Therapy LLLT to enhance and accelerate the bone fracture healing of the left tibia using the effect of laser bio-stimulation. Radiological x-ray imaging evaluation follow up for our case showed a significant bone healing rate as result of exposure of Diode Laser 650 nm with energy density of 5 J/cm 2 three times/week for one month. Radiographic findings revealed no significant fracture callus thickness difference before using LLLT however, the fractures showed significant callus formation after using LLLT. CONCLUSION: The study suggests that LLLT accelerates the process of fracture repair or cause increases in callus volume

Systemic Treatment with Vanadium Absorbed by Coprinus comatus Promotes Femoral Fracture Healing in Streptozotocin-Diabetic Rats

The purpose of this study was to analyze the impact of vanadium absorbed by Coprinus comatus (VACC) on fracture healing in streptozotocin-diabetic rats. Forty-five male Wistar rats used were divided into three groups: normal rats (control), diabetic rats, and diabetic rats treated with VACC. A standardized fracture-healing model with a stable plate fixation was established for the rat femoral fracture. After a 4-week stable fixation, callus quality was assessed by microcomputerized tomography and histological and biomechanical examinations. In addition, bone samples were obtained to evaluate the content of mineral substances in bones. Compared with the diabetic group, vanadium treatment significantly increased bone mineral content and biomechanical strength and improved microstructural properties of the callus. The ultimate load was increased by 29.1 % (P<0.05), and the total bone volume of callus enhanced by 11.2 % (P<0.05) at 4 weeks post fracture. Vanadium also promoted callus bone formation, which caused a 35.5 % increase in the total area of callus. However, VACC did not accelerate the fracture repair process in histological analysis. In conclusion, the current study suggests that systemic treatment with vanadium could promote fracture healing in streptozotocin-diabetic rats.

Vitamin MK-7 enhances vitamin D3-induced osteogenesis in hMSCs: modulation of key effectors in mineralization and vascularization

The osteoblast is the bone-forming cell and is derived from mesenchymal stem cells (MSCs). Osteo-inductive substances could represent a useful therapeutic approach during the fracture repair process. The aim of this work was to evaluate the effects of vitamin MK-7, alone or in association with vitamin D3, in differentiating human MSCs (hMSCs) in vitro along the osteoblastic lineage. In particular, primary endpoints of the study include gene and protein markers of osteoblast differentiation. Considering genes involved in bone formation and mineralization, our data show that vitamin MK-7 enhances vitamin D3 gene induction of osteocalcin (OC). Among genes related to cell growth and differentiation, a specific effect of vitamin MK-7 was observed for growth differentiation factor-10 (GDF10) and insulin-like growth factor 1 (IGF1), the latter being also involved in the induction of vascular endothelial growth factors (VEGFA). Accordingly, vitamin co-supplementation greatly affected VEGFA and its receptor fms-related tyrosine kinase 1 (FLT1), a key factor in both angiogenic and osteogenic processes. These results stress the relevance of MK-7 and D3 co-supplementation in the bone-healing process as able to modulate the expression of genes involved in both mineralization and angiogenesis. Moreover, at the protein level co-association of vitamins might provide an optimal balance between induction and carboxylation of osteocalcin, essential for its functionality in the extracellular matrix (ECM). Our results may provide hints for therapeutic application of hMSCs in bone disease, clarifying mechanisms involved in stem cell-mediated bone development, and they also highlight the relevance of co-supplementation strategies, since single supplementations might result in a suboptimal effect.

Biologic adjuvants for fracture healing

Bone tissue has an exceptional quality to regenerate to native tissue in response to injury. However, the fracture repair process requires mechanical stability or a viable biological microenvironment or both to ensure successful healing to native tissue. An improved understanding of the molecular and cellular events that occur during bone repair and remodeling has led to the development of biologic agents that can augment the biological microenvironment and enhance bone repair. Orthobiologics, including stem cells, osteoinductive growth factors, osteoconductive matrices, and anabolic agents, are available clinically for accelerating fracture repair and treatment of compromised bone repair situations like delayed unions and nonunions. Preclinical and clinical studies using biologic agents like recombinant bone morphogenetic proteins have demonstrated an efficacy similar or better than that of autologous bone graft in acute fracture healing. A lack of standardized outcome measures for comparison of biologic agents in clinical fracture repair trials, frequent off-label use, and a limited understanding of the biological activity of these agents at the bone repair site have limited their efficacy in clinical applications.

Correlation between Computerized Tomography Densimetry and Histomorphometry in Assessment of Bone Healing

Background: Assessment of fracture healing is a common problem in orthopedic practice and research. Computerized Tomography (CT) is a reliable tool for quantification of the fracture repair process in experimental animals. Histomorphometric evaluation provides a clear quantitative evidence of the bone healing process. The evaluation by micro-architectures in healing bone showed variable correlation between CT and histomorphometry.Material and methods: open ulnar osteotomy induced in twenty young male rabbits under general anesthesia without internal fixation, and divided into five groups. A group of animals were sacrificed at end of 2nd week, 3rd week, 4th week, 5th week, and 6th week. The right ulna isolated and the bone specimens taken for radiological examination, CT scan densimetry and histomorphometric evaluation carried out for the callus at the site of osteotomy for all animals in both group.Results: The mean of histomorphometric evaluation of callus at the site of ulnar osteotomy at the end of second week were 2.9, and increased with duration to reach 9.3 at end of sixth week. The mean of CT densimetry of callus in site ulnar osteotomy at the end of second week were 96.2, and increased with duration to reach 723.3 at end of sixth week. The correlation coefficient between histomorphometric evaluations of callus in site ulnar osteotomy and value of CT densimetry measurements was 0.958, which considered very highly significant, (the P value &lt; 0.0001).Conclusion: The present study demonstrate that, there is strong correlation between CT scan bone densimetry of callus in site of osteotomy and the results of histomorphometric evaluation of callus. The CT scan bone densimetry of callus can be used to assess the bone healing in experimental and clinical studies, as it is noninvasive technique.

Effect of low-intensity pulsed ultrasound on fracture callus mineral density and flexural strength in rabbit tibial fresh fracture

BackgroundLow-intensity ultrasound is a biophysical intervention on a fracture repair process. However, the effect of low-intensity ultrasound therapy on fracture healing is controversial. The aim of the present study was to evaluate the effect of low-intensity pulsed ultrasound (LIPUS) therapy on the fracture healing process, including mineral density and strength of callus using a rabbit model. MethodsA total of 30 rabbits underwent unilateral, transverse, and mid-tibia open osteotomies that were stabilized with external fixators. Then, the animals were divided into two study groups composed of 15 rabbits each: the case group (US), which were exposed to low-intensity pulsed ultrasound with 30 mW/cm2 intensity and 1.5 MHz sine waves; and the control group (C), which underwent sham ultrasound treatment. Callus development and mineral density were evaluated using multidetector computed tomography at 2, 5, and 8 weeks, after which the animals were killed. Three-point bending tests of both healed and intact bones were assessed and compared. ResultsThe results demonstrated that the callus mineral density in the US group was higher than in the C group (1202.20 ± 81.30 vs. 940.66 ± 151.58 HU; P = 0.001) at the end of the 8th week. The mean recorded three-point bending test score of healed bones in the US group was not significantly different from that of the C group (359.35 ± 173.39 vs. 311.02 ± 80.58 N; P = 0.114). ConclusionsThe present study showed that low-intensity pulsed ultrasound enhanced callus mineral density with an insignificant increase in the strength of the fractured bone.

Effect of low-level laser therapy on the fracture healing process

Low-level laser therapy (LLLT) is a biophysical form of intervention in the fracture-repair process, which, through several mechanisms, accelerates the healing of fractures and enhances callus formation. The effect of laser on fracture healing is controversial. Some authors affirm that LLLT can accelerate bone formation by increasing osteoblastic activity. The objective of our study was to evaluate the effect of laser therapy on fracture healing. Thirty rabbits were subjected to tibial bone open osteotomies that were stabilized with external fixators. The animals were divided into two study groups: laser group and control group. Callus development and bone mineral density were quantitatively evaluated by CT; the animals were then killed and the fractures were assessed for biomechanical properties. The results demonstrated that the increasing rate of bone mineral density was higher in the laser (L) group than in the control (C) group. CT at 5 weeks revealed a mean callus density of 297 Hounsfield units (HU) for the control group and 691 HU for the L group, which was statistically significant (P = 0.001). In the L group, the mean recorded fracture tension was 190.5 N and 359.3 N for healed and intact bones, respectively, which was statistically significant (P < 0.001). The result of the study showed that the use of laser could enhance callus development in the early stage of the healing process, with doubtful improvement in biomechanical properties of the healing bone; therefore, laser therapy may be recommended as an additional treatment in non-union fractures in humans.

Regenerative Effects of Transplanted Mesenchymal Stem Cells in Fracture Healing

Mesenchymal stem cells (MSC) have a therapeutic potential in patients with fractures to reduce the time of healing and treat nonunions. The use of MSC to treat fractures is attractive for several reasons. First, MSCs would be implementing conventional reparative process that seems to be defective or protracted. Secondly, the effects of MSCs treatment would be needed only for relatively brief duration of reparation. However, an integrated approach to define the multiple regenerative contributions of MSC to the fracture repair process is necessary before clinical trials are initiated. In this study, using a stabilized tibia fracture mouse model, we determined the dynamic migration of transplanted MSC to the fracture site, their contributions to the repair process initiation, and their role in modulating the injury-related inflammatory responses. Using MSC expressing luciferase, we determined by bioluminescence imaging that the MSC migration at the fracture site is time- and dose-dependent and, it is exclusively CXCR4-dependent. MSC improved the fracture healing affecting the callus biomechanical properties and such improvement correlated with an increase in cartilage and bone content, and changes in callus morphology as determined by micro-computed tomography and histological studies. Transplanting CMV-Cre-R26R-Lac Z-MSC, we found that MSCs engrafted within the callus endosteal niche. Using MSCs from BMP-2-Lac Z mice genetically modified using a bacterial artificial chromosome system to be beta-gal reporters for bone morphogenic protein 2 (BMP-2) expression, we found that MSCs contributed to the callus initiation by expressing BMP-2. The knowledge of the multiple MSC regenerative abilities in fracture healing will allow design of novel MSC-based therapies to treat fractures.

Eel calcitonin (elcatonin) suppressed callus remodeling but did not interfere with fracture healing in the femoral fracture model of cynomolgus monkeys

We investigated the effect of eel calcitonin (elcatonin) on the process of fracture repair in the osteotomized femur of cynomolgus monkeys, since they possess a Haversian remodeling system similar to that of humans. Alendronate was used for comparison. Twenty female cynomolgus monkeys (Macaca fascicularis), aged 18-22 years, were allocated into five groups: control (CNT, n = 4), low-dose elcatonin group (0.5 U/kg; ELL, n = 4), high-dose elcatonin group (5 U/kg; ELH, n = 4), low-dose alendronate group (10 microg/kg; ALL, n = 4) and high-dose alendronate group (100 microg/kg; ALH, n = 4). All animals were given subcutaneous injections twice a week for 3 weeks. Then fracture was produced surgically by transversely cutting the midshaft of the right femur and fixing with stainless steel plate. After fracture, treatments were continued until sacrifice at 26 weeks after surgery. The femora were assessed by micro CT, contact microradiograph, three-point bending mechanical test and histomorphometry. Micro CT showed that callus sizes in elcatonin-treated groups were similar to CNT, whereas alendronate-treated groups had larger calluses than those in the CNT and elcatonin-treated groups. Fracture lines almost disappeared in the CNT and elcatonin-treated groups but remained clear in the alendronate-treated groups. Total area did not differ significantly between the elcatonin-treated groups and the CNT but was significantly greater in the ALH compared to the CNT and elcatonin-treated groups, due to increased callus area in the ALH group. Callus remodeling was less suppressed in the elcatonin-treated groups than in the alendronate-treated groups when compared with callus remodeling in the CNT. Although no significant differences in structural mechanical properties such as ultimate load, stiffness and work to failure were found among all groups, ultimate stress was significantly reduced in the ALH group compared with CNT and ELL groups. In conclusion, mild suppression of callus remodeling by elcatonin did not impair overall fracture healing process. In contrast, alendronate delayed structural fracture healing process by strongly suppressing callus remodeling.

Secreted frizzled related protein 1 is a target to improve fracture healing

Genetic studies have identified a high bone mass of phenotype in both human and mouse when canonical Wnt signaling is increased. Secreted frizzled related protein 1 (sFRP1) is one of several Wnt antagonists and among the loss-of-function mouse models in which 32-week-old mice exhibit a high bone mass phenotype. Here we show that impact fracture healing is enhanced in this mouse model of increased Wnt signaling at a physiologic level in young (8 weeks) sFRP1(-/-) mice which do not yet exhibit significant increases in BMD. In vivo deletion of sFRP1 function improves fracture repair by promoting early bone union without adverse effects on the quality of bone tissue reflected by increased mechanical strength. We observe a dramatic reduction of the cartilage callous, increased intramembranous bone formation with bone bridging by 14 days, and early bone remodeling during the 28-day fracture repair process in the sFRP1(-/-) mice. Our molecular analyses of gene markers indicate that the effect of sFRP1 loss-of-function during fracture repair is to accelerate bone healing after formation of the initial hematoma by directing mesenchymal stem cells into the osteoblast lineage via the canonical pathway. Further evidence to support this conclusion is the observation of maximal sFRP1 levels in the cartilaginous callus of a WT mouse. Hence sFRP1(-/-) mouse progenitor cells are shifted directly into the osteoblast lineage. Thus, developing an antagonist to specifically inhibit sFRP1 represents a safe target for stimulating fracture repair and bone formation in metabolic bone disorders, osteoporosis and aging.

Fibroblast growth factor expression during skeletal fracture healing in mice

Fibroblast growth factors (FGFs) are important signaling molecules that regulate many stages of endochondral bone development. During the healing of a skeletal fracture, several features of endochondral bone development are reactivated. To better understand the role of FGFs in skeletal fracture healing, we quantitatively evaluated the temporal expression patterns of Fgfs, Fgf receptors (Fgfrs), and molecular markers of bone development over a 14-day period following long bone fracture in a mouse model. These studies identify distinct groups of FGFs that are differentially expressed and suggest active stage-specific roles for FGF signaling during the fracture repair process.