A systematic review of current osteoporotic metaphyseal fracture animal models

Impact of osteoporosis and osteoporosis medications on fracture healing: a narrative review

Antiresorptive medications do not negatively affect fracture healing in humans. Teriparatide may decrease time to fracture healing. Romosozumab has not shown a beneficial effect on human fracture healing.

BACKGROUND

Fracture healing is a complex process. Uncertainty exists over the influence of osteoporosis and the medications used to treat it on fracture healing.

METHODS

Narrative review authored by the members of the Fracture Working Group of the Committee of Scientific Advisors of the International Osteoporosis Foundation (IOF), on behalf of the IOF and the Société Internationale de Chirurgie Orthopédique et de Traumatologie (SICOT).

RESULTS

Fracture healing is a multistep process. Most fractures heal through a combination of intramembranous and endochondral ossification. Radiographic imaging is important for evaluating fracture healing and for detecting delayed or non-union. The presence of callus formation, bridging trabeculae, and a decrease in the size of the fracture line over time are indicative of healing. Imaging must be combined with clinical parameters and patient-reported outcomes. Animal data support a negative effect of osteoporosis on fracture healing; however, clinical data do not appear to corroborate with this. Evidence does not support a delay in the initiation of antiresorptive therapy following acute fragility fractures. There is no reason for suspension of osteoporosis medication at the time of fracture if the person is already on treatment. Teriparatide treatment may shorten fracture healing time at certain sites such as distal radius; however, it does not prevent non-union or influence union rate. The positive effect on fracture healing that romosozumab has demonstrated in animals has not been observed in humans.

CONCLUSION

Overall, there appears to be no deleterious effect of osteoporosis medications on fracture healing. The benefit of treating osteoporosis and the urgent necessity to mitigate imminent refracture risk after a fracture should be given prime consideration. It is imperative that new radiological and biological markers of fracture healing be identified. It is also important to synthesize clinical and basic science methodologies to assess fracture healing, so that a convergence of the two frameworks can be achieved.

An adaptive biodegradable zinc alloy with bidirectional regulation of bone homeostasis for treating fractures and aged bone defects

Healing of fractures or bone defects is significantly hindered by overactivated osteoclasts and inhibited osteogenesis in patients with abnormal bone metabolism. Current clinical approaches using titanium alloys or stainless steel provide mechanical support but have no biological effects on bone regeneration. Therefore, designing and fabricating degradable metal materials with sufficient mechanical strength and bidirectional regulation of both osteoblasts and osteoclasts is a substantial challenge. Here, this study first reported an adaptive biodegradable Zn-0.8 Mg alloy with bidirectional regulation of bone homeostasis, which promotes osteogenic differentiation by activating the Pi3k/Akt pathway and inhibits osteoclast differentiation by inhibiting the GRB2/ERK pathway. The anti-osteolytic ability of the Zn-0.8 Mg alloy was verified in a mouse calvarial osteolysis model and its suitability for internal fracture fixation with high-strength screws was confirmed in the rabbit femoral condyle fracture model. Furthermore, in an aged postmenopausal rat femoral condyle defect model, 3D printed Zn-0.8 Mg scaffolds promoted excellent bone regeneration through adaptive structures with good mechanical properties and bidirectionally regulated bone metabolism, enabling personalized bone defect repair. These findings demonstrate the substantial potential of the Zn-0.8 Mg alloy for treating fractures or bone defects in patients with aberrant bone metabolism.

Synergistic effect of umbilical cord extracellular vesicles and rhBMP-2 to enhance the regeneration of a metaphyseal femoral defect in osteoporotic rats

BACKGROUND

The aim of this study was to evaluate potential synergistic effects of a single, local application of human umbilical cord MSC-derived sEVs in combination with a low dose of recombinant human rhBMP-2 to promote the regeneration of a metaphyseal femoral defect in an osteoporotic rat model.

METHODS

6 weeks after induction of osteoporosis by bilateral ventral ovariectomy and administration of a special diet, a total of 64 rats underwent a distal femoral metaphyseal osteotomy using a manual Gigli wire saw. Defects were stabilized with an adapted Y-shaped mini-locking plate and were subsequently treated with alginate only, or alginate loaded with hUC-MSC-sEVs (2 × 109), rhBMP-2 (1.5 µg), or a combination of sEVs and rhBMP-2 (n = 16 for each group). 6 weeks post-surgery, femora were evaluated by µCT, descriptive histology, and biomechanical testing.

RESULTS

Native radiographs and µCT analysis confirmed superior bony union with callus formation after treatment with hUC-MSC-sEVs in combination with a low dose of rhBMP-2. This finding was further substantiated by histology, showing robust defect consolidation 6 weeks after treatment. Torsion testing of the explanted femora revealed increased stiffness after application of both, rhBMP-2 alone, or in combination with sEVs, whereas torque was only significantly increased after treatment with rhBMP-2 together with sEVs.

CONCLUSION

The present study demonstrates that the co-application of hUC-MSC-sEVs can improve the efficacy of rhBMP-2 to promote the regeneration of osteoporotic bone defects.

Hydrogel Delivery of DNase I and Liposomal Vancomycin to Eradicate Fracture-related Methicillin-resistant Staphylococcus aureus Infection and Support Osteoporotic Fracture Healing

Fracture-related infection (FRI) is a devastating complication in orthopedic surgery. A recent study showed that FRI causes more severe infection and further delays healing in osteoporotic bone. Moreover, bacterial biofilm formed on implants cannot be eradicated by systemic antibiotics, warranting novel treatments. Here, we developed a DNase I and Vancomycin hydrogel delivery vehicle to eradicate Methicillin-resistant Staphylococcus aureus (MRSA) infection in vivo. Vancomycin was encapsulated in liposomes, and DNase I and Vancomycin/liposomal-Vancomycin was loaded on thermosensitive hydrogel. In vitro drug release test showed a burst release of DNase I (77.2%) within 72 hours and sustained release of Vancomycin (82.6%) up to day 14. The in vivo efficacy was evaluated in a clinically relevant ovariectomy (OVX) induced osteoporotic metaphyseal fracture model with MRSA infection, and a total of 120 Sprague Dawley rats were used. In the OVX with infection group, biofilm development caused a drastic inflammatory response, trabecular bone destruction, and non-union. In the DNase I and Vancomycin co-delivery hydrogel group (OVX-Inf-DVG), bacteria on bone and implant were eradicated. X-ray and micro-CT showed preservation of trabecular bone and bone union. HE staining showed the absence of inflammatory necrosis, and fracture healing was restored. The local elevation of TNF-α and IL-6 and increased number of osteoclasts were prevented in the OVX-Inf-DVG group. Our findings suggest that dual release of DNase I and Vancomycin initially followed by Vancomycin only later up to 14 days effectively eliminates MRSA infection, prevents biofilm development and provides a sterile environment to promote fracture healing in osteoporotic bone with FRI. STATEMENT OF SIGNIFICANCE: The biofilm formation on the implant is difficult to eradicate, causing recurrent infection and non-union in fracture-related infection (FRI). Here we developed a hydrogel therapy with high in vivo efficacy to eliminate MRSA biofilm infection in a clinically-relevant FRI model in osteoporotic bone. By loading DNase I and vancomycin/liposomal-vancomycin on thermosensitive poly-(DL-lactic acidco-glycolic acid) (PLGA)-polyethylene glycol (PEG)-PLGA hydrogel, a dual release of DNase I and Vancomycin was achieved whilst preserving enzyme activity. In this model, the progressive development of infection caused a drastic inflammatory response, osteoclastogenesis, trabecular bone destruction, and non-union of fracture. These pathological changes were successfully prevented by the dual delivery of DNase I and vancomycin. Our findings provide a promising strategy for FRI in osteoporotic bone.

Reambulation following hindlimb unloading attenuates disuse-induced changes in murine fracture healing

Patients with bone and muscle loss from prolonged disuse have higher risk of falls and subsequent fragility fractures. In addition, fracture patients with continued disuse and/or delayed physical rehabilitation have worse clinical outcomes compared to individuals with immediate weight-bearing activity following diaphyseal fracture. However, the effects of prior disuse followed by physical reambulation on fracture healing cellular processes and adjacent bone and skeletal muscle recovery post-injury remains poorly defined. To bridge this knowledge gap and inform future treatment and rehabilitation strategies for fractures, a preclinical model of fracture healing with a history of prior unloading with and without reambulation was employed. First, skeletally mature male and female C57BL/6J mice (18 weeks) underwent hindlimb unloading by tail suspension (HLU) for 3 weeks to induce significant bone and muscle loss modeling enhanced bone fragility. Next, mice had their right femur fractured by open surgical dissection (stabilized with 24-gauge pin). The, mice were randomly assigned to continued HLU or allowed normal weight-bearing reambulation (HLU + R). Mice given normal cage activity throughout the experiment served as healthy age-matched controls. All mice were sacrificed 4-days (DPF4) or 14-days (DPF14) following fracture to assess healing and uninjured hindlimb musculoskeletal properties (6-10 mice per treatment/biological sex). We found that continued disuse following fracture lead to severely diminished uninjured hindlimb skeletal muscle mass (gastrocnemius and soleus) and femoral bone volume adjacent to the fracture site compared to healthy age-matched controls across mouse sexes. Furthermore, HLU led to significantly decreased periosteal expansion (DPF4) and osteochondral tissue formation by DPF14, and trends in increased osteoclastogenesis (DPF14) and decreased woven bone vascular area (DPF14). In contrast, immediate reambulation for 2 weeks after fracture, even following a period of prolonged disuse, was able to increase hindlimb skeletal tissue mass and increase osteochondral tissue formation, albeit not to healthy control levels, in both mouse sexes. Furthermore, reambulation attenuated osteoclast formation seen in woven bone tissue undergoing disuse. Our results suggest that weight-bearing skeletal loading in both sexes immediately following fracture may improve callus healing and prevent further fall risk by stimulating skeletal muscle anabolism and decreasing callus resorption compared to minimal or delayed rehabilitation regimens.

Development of a Metaphyseal Non-Union Model in the Osteoporotic Rat Femur

The aim of this current study was to establish a metaphyseal femoral non-union model in osteoporotic rats by comparing a power tool versus a manual tool for fracture creation. Twelve adult female Sprague Dawley rats were ovariectomized (OVX) and received a special diet for 6 weeks. Biweekly pQCT measurements confirmed a significant reduction in the cancellous and total bone mineral density in OVX rats compared to control (CTRL) animals. After 6 weeks, OVX rats underwent surgery creating a distal metaphyseal osteotomy, either using a piezoelectric- (n = 6) or a manual Gigli wire (n = 6) saw. Fractures were stabilized with a Y-shaped mini-locking plate. Within each group, three rats received Alginate directly into the fracture gap. OVX animals gained more weight over 8 weeks compared to CTRL animals. pQCT analysis showed a significant difference in the volumetric cancellous bone mineral density between OVX and CTRL rats. A histological examination of the osteoporotic phenotype was completed. Radiographic evaluation and Masson–Goldner trichrome staining with the piezoelectric saw failed to demonstrate bony bridging or a callus formation. New bone formation and complete healing were seen after 6 weeks in the Gigli group. For the creation of a metaphyseal atrophic non-union in the osteoporotic bone, a piezoelectric saw should be used.

A modified method for constructing experimental rat periodontitis model

Background: Periodontitis is a prevalent disease caused teeth lost. The present rat models inducing periodontitis with thread ligature and metal steel ligature have some disadvantages. Methods: We modified the existing rat ligature periodontitis model by fixing the thread ligature on the metal steel ligature passed through the gap between the first and second molars of rats with detailed modeling steps and illustrations. We research the pathological process of the periodontitis induced by the modified model, and briefly compared the modified model with the thread ligature model and the metal steel ligature model. Result: Our experimental results showed that there was an aggravation in inflammatory infiltration and alveolar bone resorption in modeling area within 14 days of initial induction. After that, the inflammatory infiltration was reduced. And no significant increase in alveolar bone destruction appeared. The modified model was more reliable compared to the thread ligature model, and had greater ability of bacterial aggregation compared to the metal steel ligature model. Conclusion: The modified method covered pathological process of the periodontitis, and showed sufficient efficiency and reliability in inducing rat periodontitis.

The imminent risk of a fracture-existing worldwide data: a systematic review and meta-analysis

The overall incidence of imminent fracture after a prior fragility fracture was 7.58% in the first year and 11.58% in the first 2 years. Approximately half of re-fractures occurred in the first 2 years after a fragility fracture. Older patients that have suffered from a fragility fracture should be treated promptly, with immediate care and a secondary fracture prevention to prevent the high imminent risk of a fracture.

INTRODUCTION

Imminent fractures refer to the fractures that occur within 2 years of an initial fracture. It is well known that the risk of a subsequent fracture is not constant with time and occurs shortly after the initial one. This systematic review and meta-analysis aimed to present the existing data on imminent fracture worldwide.

METHODS

Literature search was conducted in Pubmed, Embase, and Web of Science databases until 26 October 2021 for studies reporting the incidence of imminent osteoporotic fractures among people aged 50 years or older. The overall incidence of imminent fracture was pooled and subgroup analyses of index fracture sites and regions on incidence of imminent fracture were performed, with the 95% confidence interval (CI) being calculated. Percentage of imminent fracture occurring in follow-up period was calculated and pooled by meta-analysis. Hazard ratio (HR) was used to estimate the gender differences on the imminent risk of fracture.

RESULTS

A total of 1446 articles were identified. Nineteen observational studies were eligible for our systematic review, in which 18 were used for quantitative analysis. Pooled overall incidence of imminent fracture in the first year after an osteoporotic fracture was 7.58% (95% CI 5.84 to 9.31%) and cumulative incidence in the first 2 years was 11.58% (95% CI 8.94 to 14.21%). Subgroup analysis showed that in the first 2 years, the pooled incidence in Asia was 7.30% (95% CI 3.42 to 11.18%), whilst incidence in Europe/North America was 13.17% (95% CI 10.14 to 16.20%). In included studies with follow-up period of more than 5 years, pooled imminent fracture percentage in the first 2 years was 47.24% (95% CI 26.18 to 68.30%). Hazard ratio (HR) on gender showed that women had an overall slight increase in risk of imminent fractures (HR 1.18, 95% CI 1.11 to 1.25).

CONCLUSION

The incidence of imminent fracture is high globally at 11.58%. Approximately half of all refractures occur in the first 2 years after an index fragility fracture. Older patients that have suffered from a fragility fracture should be treated promptly. Also, immediate care and secondary fracture prevention are necessary to prevent the high imminent risk of a fracture, especially within the first 2 years.

Osteogenic Potential of Sheep Mesenchymal Stem Cells Preconditioned with BMP-2 and FGF-2 and Seeded on an nHAP-Coated PCL/HAP/β-TCP Scaffold

Mesenchymal stem cells (MSCs) attract interest in regenerative medicine for their potential application in bone regeneration. However, direct transplantation of cells into damaged tissue is not efficient enough to regenerate large bone defects. This problem could be solved with a biocompatible scaffold. Consequently, bone tissue engineering constructs based on biomaterial scaffolds, MSCs, and osteogenic cytokines are promising tools for bone regeneration. The aim of this study was to evaluate the effect of FGF-2 and BMP-2 on the osteogenic potential of ovine bone marrow-derived MSCs seeded onto an nHAP-coated PCL/HAP/β-TCP scaffold in vitro and its in vivo biocompatibility in a sheep model. In vitro analysis revealed that cells preconditioned with FGF-2 and BMP-2 showed a better capacity to adhere and proliferate on the scaffold than untreated cells. BM-MSCs cultured in an osteogenic medium supplemented with FGF-2 and BMP-2 had the highest osteogenic differentiation potential, as assessed based on Alizarin Red S staining and ALP activity. qRT-PCR analysis showed increased expression of osteogenic marker genes in FGF-2- and BMP-2-treated BM-MSCs. Our pilot in vivo research showed that the implantation of an nHAP-coated PCL/HAP/β-TCP scaffold with BM-MSCs preconditioned with FGF-2 and BMP-2 did not have an adverse effect in the sheep mandibular region and induced bone regeneration. The biocompatibility of the implanted scaffold-BM-MSC construct with sheep tissues was confirmed by the expression of early (collagen type I) and late (osteocalcin) osteogenic proteins and a lack of an elevated level of proinflammatory cytokines. These findings suggest that FGF-2 and BMP-2 enhance the osteogenic differentiation potential of MSCs grown on a scaffold, and that such a tissue engineering construct may be used to regenerate large bone defects.

Modulating macrophage polarization for the enhancement of fracture healing, a systematic review

Background

All fracture repairs start with the innate immune system with the inflammatory response known as the inflammatory stage guided and driven by the secretion of chemokine by the ruptured tissue, followed by the sequential recruitment of neutrophils, monocytes and macrophages. These innate immune cells would infiltrate the fracture site and secrete inflammatory cytokines to stimulate recruitment of more immune cells to arrive at the fracture site coordinating subsequent stages of the repair process. In which, subsidence of pro-inflammatory M1 macrophage and transformation to anti-inflammatory M2 macrophages promotes osteogenesis that marks the start of the anabolic endochondral stage.

Methods

Literature search was performed on Pubmed, Embase, and Web of Science databases (last accessed 15th April 2021) using “macrophage AND fracture”. Review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline.

Results

Eleven pre-clinical animal studies out of 429 articles were included in this systematic review according to our inclusion and exclusion criteria. All of which investigated interventions targeting to modulate the acute inflammatory response and macrophage polarization as evident by various markers in association with fracture healing outcomes.

Conclusion

This systematic review summarizes attempts to modulate the innate immune response with focuses on promoting macrophage polarization from M1 to M2 phenotype targeting the enhancement of fracture injury repair. Methods used to achieve the goal may include applications of damage-associated molecular pattern (DAMP), pathogen-associated molecular pattern (PAMP) or mechanical stimulation that hold high translational potentials for clinical application in the near future.

Osteocyte-specific dentin matrix protein 1 : the role of mineralization regulation in low-magnitude high-frequency vibration enhanced osteoporotic fracture healing

Aims

There is an increasing concern of osteoporotic fractures in the ageing population. Low-magnitude high-frequency vibration (LMHFV) was shown to significantly enhance osteoporotic fracture healing through alteration of osteocyte lacuno-canalicular network (LCN). Dentin matrix protein 1 (DMP1) in osteocytes is known to be responsible for maintaining the LCN and mineralization. This study aimed to investigate the role of osteocyte-specific DMP1 during osteoporotic fracture healing augmented by LMHFV.

Methods

A metaphyseal fracture was created in the distal femur of ovariectomy-induced osteoporotic Sprague Dawley rats. Rats were randomized to five different groups: 1) DMP1 knockdown (KD), 2) DMP1 KD + vibration (VT), 3) Scramble + VT, 4) VT, and 5) control (CT), where KD was performed by injection of short hairpin RNA (shRNA) into marrow cavity; vibration treatment was conducted at 35 Hz, 0.3 g; 20 minutes/day, five days/week). Assessments included radiography, micro-CT, dynamic histomorphometry and immunohistochemistry on DMP1, sclerostin, E11, and fibroblast growth factor 23 (FGF23). In vitro, murine long bone osteocyte-Y4 (MLO-Y4) osteocyte-like cells were randomized as in vivo groupings. DMP1 KD was performed by transfecting cells with shRNA plasmid. Assessments included immunocytochemistry on osteocyte-specific markers as above, and mineralized nodule staining.

Results

Healing capacities in DMP1 KD groups were impaired. Results showed that DMP1 KD significantly abolished vibration-enhanced fracture healing at week 6. DMP1 KD significantly altered the expression of osteocyte-specific markers. The lower mineralization rate in DMP1 KD groups indicated that DMP1 knockdown was associated with poor fracture healing process.

Conclusion

The blockage of DMP1 would impair healing outcomes and negate LMHFV-induced enhancement on fracture healing. These findings reveal the importance of DMP1 in response to the mechanical signal during osteoporotic fracture healing.

Cite this article: Bone Joint Res 2022;11(7):465–476.

Cortical bone thickness of the distal radius predicts the local bone mineral density

AIMS

The distal radius is a major site of osteoporotic bone loss resulting in a high risk of fragility fracture. This study evaluated the capability of a cortical index (CI) at the distal radius to predict the local bone mineral density (BMD).

METHODS

A total of 54 human cadaver forearms (ten singles, 22 pairs) (19 to 90 years) were systematically assessed by clinical radiograph (XR), dual-energy X-ray absorptiometry (DXA), CT, as well as high-resolution peripheral quantitative CT (HR-pQCT). Cortical bone thickness (CBT) of the distal radius was measured on XR and CT scans, and two cortical indices mean average (CBTavg) and gauge (CBTg) were determined. These cortical indices were compared to the BMD of the distal radius determined by DXA (areal BMD (aBMD)) and HR-pQCT (volumetric BMD (vBMD)). Pearson correlation coefficient (r) and intraclass correlation coefficient (ICC) were used to compare the results and degree of reliability.

RESULTS

The CBT could accurately be determined on XRs and highly correlated to those determined on CT scans (r = 0.87 to 0.93). The CBTavg index of the XRs significantly correlated with the BMD measured by DXA (r = 0.78) and HR-pQCT (r = 0.63), as did the CBTg index with the DXA (r = 0.55) and HR-pQCT (r = 0.64) (all p < 0.001). A high correlation of the BMD and CBT was observed between paired specimens (r = 0.79 to 0.96). The intra- and inter-rater reliability was excellent (ICC 0.79 to 0.92).

CONCLUSION

The cortical index (CBTavg) at the distal radius shows a close correlation to the local BMD. It thus can serve as an initial screening tool to estimate the local bone quality if quantitative BMD measurements are unavailable, and enhance decision-making in acute settings on fracture management or further osteoporosis screening. Cite this article: Bone Joint Res 2021;10(12):820-829.

Vibration therapy as an intervention for enhancing trochanteric hip fracture healing in elderly patients: a randomized double-blinded, placebo-controlled clinical trial

BACKGROUND

There are more than 300,000 hip fractures yearly in the USA with mortality rates of 20% within 1 year. The treatment of osteoporotic fractures is a major challenge as bone quality is poor, and healing is expected to delay due to the impaired healing properties with respect to bone formation, angiogenesis, and mineralization. Enhancement of osteoporotic fracture healing and function is therefore critical as a major goal in modern fracture management. Previous pre-clinical studies have shown that low-magnitude high-frequency vibration (LMHFV) accelerates osteoporotic fracture healing. The objective of this study is to investigate the effect of LMHFV on accelerating trochanteric hip fracture healing and functional recovery.

METHODS

This is a randomized, double-blinded, placebo-controlled clinical trial to evaluate the effect of LMHFV in accelerating trochanteric hip fracture healing. All fractures undergo cephalomedullary nail fixation. The primary outcome of this study is time to fracture healing by X-ray. Computed tomography (CT) and dual-energy X-ray absorptiometry (DXA) will also be performed. Blood circulation at the fracture site will be assessed by dynamic perfusion magnetic resonance (MR). Clinical results include functional recovery by muscle strength, timed up and go test (TUG), quality of life questionnaire (SF-36), balancing, falls, and mortality.

DISCUSSION

Previous animal studies have demonstrated LMHFV to improve both normal and osteoporotic fracture healing by accelerating callus formation and mineralization. The mechanical stimulation stimulates angiogenesis by significantly enhancing vascular volume and blood flow velocity. This is the first study to translate LMHFV to enhancing hip fracture healing clinically. Positive results would provide a huge impact in the recovery of hip fracture patients and save healthcare costs.

TRIAL REGISTRATION

Clinicaltrials.gov NCT04063891. Registered on August 21, 2019.

Acute Inflammatory Response in Osteoporotic Fracture Healing Augmented with Mechanical Stimulation is Regulated In Vivo through the p38-MAPK Pathway

Low-magnitude high-frequency vibration (LMHFV) has previously been reported to modulate the acute inflammatory response of ovariectomy-induced osteoporotic fracture healing. However, the underlying mechanisms are not clear. In the present study, we investigated the effect of LMHFV on the inflammatory response and the role of the p38 MAPK mechanical signaling pathway in macrophages during the healing process. A closed femoral fracture SD rat model was used. In vivo results showed that LMHFV enhanced activation of the p38 MAPK pathway at the fracture site. The acute inflammatory response, expression of inflammatory cytokines, and callus formation were suppressed in vivo by p38 MAPK inhibition. However, LMHFV did not show direct in vitro enhancement effects on the polarization of RAW264.7 macrophage from the M1 to M2 phenotype, but instead promoted macrophage enlargement and transformation to dendritic monocytes. The present study demonstrated that p38 MAPK modulated the enhancement effects of mechanical stimulation in vivo only. LMHFV may not have exerted its enhancement effects directly on macrophage, but the exact mechanism may have taken a different pathway that requires further investigation in the various subsets of immune cells.

Systemically impaired fracture healing in small animal research: A review of fracture repair models

Fracture healing is a complex process requiring mechanical stability, an osteoconductive matrix, and osteoinductive and osteogenic biology. This intricate process is easily disrupted by various patient factors such as chronic disease and lifestyle. As the medical complexity and age of patients with fractures continue to increase, the importance of developing relevant experimental models is becoming paramount in preclinical research. The objective of this review is to describe the most common small animal models of systemically impaired fracture healing used in the orthopedic literature including osteoporosis, diabetes mellitus, smoking, alcohol use, obesity, and ageing. This review will provide orthopedic researchers with a summary of current models of systemically impaired fracture healing used in small animals and present an overview of the methods of induction for each condition.

Effect of ovariectomy induced osteoporosis on metaphysis and diaphysis repair process

The fracture repair process is known to be delayed in postmenopausal women, under estrogen-deficient status. Osteoporotic fracture mainly occurs in the metaphyseal region of the long bone; however, most studies on fracture healing have focused on the diaphyseal region. In this study, we compared the repair process between metaphysis and diaphysis of ovariectomized (OVX) and Sham mice, and analyzed the effects of short-term estrogen administration in OVX mice. Mice were divided into four experimental groups, including Sham, OVX, OVX + vehicle, and OVX + 17β-estradiol (E2). Bone apertures were formed in the tibial metaphysis and diaphysis. The samples were collected and examined by micro-computed tomography, and using histological, histochemical, and immunohistochemical analysis at different time points after the surgery. The cartilaginous callus was formed at the diaphysis site of both the groups, which was sequentially replaced by bone on the periosteum side. Medullary callus was formed in all the groups; however, the volume of the callus in OVX mice was significantly lesser (˜30%) than that in Sham mice. Furthermore, in the metaphysis, no differences were observed in the medullary callus and bone mineral density between the two groups from day 21 to 28. The diaphysis of OVX group was not completely repaired even by day 28. In both the sites of OVX mice, ALP activity and disappearance of Gr-1 positive cells were delayed compared to that of Sham. Estrogen administration improved medullary callus formation in the diaphysis, however not in the metaphysis. The effect of ovariectomy on the repair process in diaphysis was greater than that in metaphysis. Our findings clarify the differences between the metaphysis and diaphysis repair process using OVX mouse model and suggest that the estrogen sensitivities differ between the sites during the bone repair process.

Enhancement of osteoporotic fracture healing by vibration treatment: The role of osteocytes

The prevalence of osteoporotic fracture is high due to global aging problem. Delayed and impaired healing in osteoporotic fractures increase the socioeconomic burden significantly. Through intensive animal and clinical research in recent years, the pathogenesis of osteoporotic fracture healing is unveiled, including decreased inflammatory response, reduced mesenchymal stem cells and deteriorated angiogenesis, etc. The enhancement of osteoporotic fracture healing is important in shortening hospitalization, thus reducing related complications. Mechanical stimulation is currently the most well-accepted approach for rehabilitation of osteoporotic fracture patients. Some new interventions providing mechanical signals were explored extensively in recent years, including vibration treatment, and osteoporotic fracture healing was found to respond very well to these signals. Vibration treatment could accelerate osteoporotic fracture healing with improved callus formation, mineralization and remodeling. However, the mechanism of how osteoporotic fracture bones sense mechanical signals and relay to bone formation remains unanswered. Osteocytes are the most abundant cells in bone tissues. Cumulative evidence confirm that osteocyte is a type of mechanosensory cell and shows altered morphology and reduced cell density during aging. Meanwhile, osteocytes serve as endocrine cells to regulate bone and mineral homeostasis. However, the contribution of osteocytes in osteoporotic fracture healing is largely unknown. A recent in vivo study was conducted to examine the morphological and functional changes of osteocytes after vibration treatment in an osteoporotic metaphyseal fracture rat model. The findings demonstrated that vibration treatment induced significant outgrowth of canaliculi and altered expression of various proteins (E11, DMP1, FGF23 and sclerostin), particularly osteocyte-specific dentin matrix protein 1 (DMP1) which was greatly increased. DMP1 may play a major role in relaying mechanical signals to bone formation, which may require further experiments to consolidate. Most importantly, vibration treatment significantly increased the mineralization and accelerated the osteoporotic fracture healing in metaphyseal fracture model. In summary, osteocyte is the major cell type to sense mechanical signals and facilitate downstream healing in osteoporotic fracture bone. Vibration treatment has good potential to be translated for clinical application to benefit osteoporotic fracture patients, while randomized controlled trials are required to validate its efficacy.

Large Animal Model of Osteoporotic Defect Healing: An Alternative to Metaphyseal Defect Model

Osteoporosis is a common metabolic disorder diagnosed by lower bone density and higher risk of fracture. Fragility fractures because of osteoporosis are associated with high mortality rate. Deep understanding of fracture healing in osteoporosis is important for successful treatment. Therefore, the FDA approved the use of small and large animal models for preclinical testing. This study investigated the clinical relevance of a fracture defect model in the iliac crest of the osteoporotic sheep model and its several advantages over other models. The osteoporosis was achieved using ovariectomy (OVX) in combination with diet deficiency (OVXD) and steroid administration (OVXDS). Fluorochrome was injected to examine the rate of bone remodelling and bone mineralization. The defect areas were collected and embedded in paraffin and polymethyl metha acrylate (PMMA) for histological staining. OVXDS showed significantly lower bone mineral density (BMD) and bone mineral content (BMC) at all time points. Furthermore, variations in healing patterns were noticed, while the control, OVX and OVXD showed complete healing after 8 months. Bone quality was affected mostly in the OVXDS group showing irregular trabecular network, lower cortical bone thickness and higher cartilaginous tissue at 8 months. The mineral deposition rate showed a declining pattern in the control, OVX, and OVXD from 5 months to 8 months. One the contrary, the OVXDS group showed an incremental pattern from 5 months to 8 months. The defect zone in osteoporotic animals showed impaired healing and the control showed complete healing after 8 months. This unique established model serves as a dual-purpose model and has several advantages: no intraoperative and postoperative complications, no need for fixation methods for biomaterial testing, and reduction in animal numbers, which comply with 3R principles by using the same animal at two different time points.

Fibrinolysis as a target to enhance osteoporotic fracture healing by vibration therapy in a metaphyseal fracture model

Aims

Fibrinolysis plays a key transition step from haematoma formation to angiogenesis and fracture healing. Low-magnitude high-frequency vibration (LMHFV) is a non-invasive biophysical modality proven to enhance fibrinolytic factors. This study investigates the effect of LMHFV on fibrinolysis in a clinically relevant animal model to accelerate osteoporotic fracture healing.

Methods

A total of 144 rats were randomized to four groups: sham control; sham and LMHFV; ovariectomized (OVX); and ovariectomized and LMHFV (OVX-VT). Fibrinolytic potential was evaluated by quantifying fibrin, tissue plasminogen activator (tPA), and plasminogen activator inhibitor-1 (PAI-1) along with healing outcomes at three days, one week, two weeks, and six weeks post-fracture.

Results

All rats achieved healing, and x-ray relative radiopacity for OVX-VT was significantly higher compared to OVX at week 2. Martius Scarlet Blue (MSB) staining revealed a significant decrease of fibrin content in the callus in OVX-VT compared with OVX on day 3 (p = 0.020). Mean tPA from muscle was significantly higher for OVX-VT compared to OVX (p = 0.020) on day 3. Mechanical testing revealed the mean energy to failure was significantly higher for OVX-VT at 37.6 N mm (SD 8.4) and 71.9 N mm (SD 30.7) compared with OVX at 5.76 N mm (SD 7.1) (p = 0.010) and 17.7 N mm (SD 11.5) (p = 0.030) at week 2 and week 6, respectively.

Conclusion

Metaphyseal fracture healing is enhanced by LMHFV, and one of the important molecular pathways it acts on is fibrinolysis. LMHFV is a promising intervention for osteoporotic metaphyseal fracture healing. The improved mechanical properties, acceleration of fracture healing, and safety justify its role into translation to future clinical studies.

Cite this article: Bone Joint Res 2021;10(1):41–50.

The role of gut microbiota in bone homeostasis

Aims

The effect of the gut microbiota (GM) and its metabolite on bone health is termed the gut-bone axis. Multiple studies have elucidated the mechanisms but findings vary greatly. A systematic review was performed to analyze current animal models and explore the effect of GM on bone.

Methods

Literature search was performed on PubMed and Embase databases. Information on the types and strains of animals, induction of osteoporosis, intervention strategies, determination of GM, assessment on bone mineral density (BMD) and bone quality, and key findings were extracted.

Results

A total of 30 studies were included, of which six studies used rats and 24 studies used mice. Osteoporosis or bone loss was induced in 14 studies. Interventions included ten with probiotics, three with prebiotics, nine with antibiotics, two with short-chain fatty acid (SCFA), six with vitamins and proteins, two with traditional Chinese medicine (TCM), and one with neuropeptide Y1R antagonist. In general, probiotics, prebiotics, nutritional interventions, and TCM were found to reverse the GM dysbiosis and rescue bone loss.

Conclusion

Despite the positive therapeutic effect of probiotics, prebiotics, and nutritional or pharmaceutical interventions on osteoporosis, there is still a critical knowledge gap regarding the role of GM in rescuing bone loss and its related pathways.

Cite this article: Bone Joint Res 2021;10(1):51–59.

Efficacy of low-magnitude high-frequency vibration (LMHFV) on musculoskeletal health of participants on wheelchair: a study protocol for a single-blinded randomised controlled study

BACKGROUND

Osteoporosis is an age-related disease with progressive loss of bone, leading to fragile bone. It is one of the major health issues in older adults and causes medical, social and economic impacts globally. Patients with osteoporosis have high risk of osteoporotic fractures. Low-magnitude high-frequency vibration (LMHFV) is a non-invasive biophysical intervention providing whole-body mechanical stimulation. Previous studies showed that LMHFV is beneficial to muscle strength, postural control, balancing ability, new bone formation, spinal bone mineral density (BMD) and blood circulation. During the LMHFV treatment, older adults need to stand upright on the platform for 20 min/day. However, some physically weak elderlies with poor musculoskeletal ability cannot stand for a long period. Therefore, the design of vibration platform is modified for the disabled patients to treat at sitting position and the efficacy of LMHFV on this group of elderlies will be verified. It is hypothesised that new design of LMHFV is beneficial to wheelchair users in terms of vertebral BMD, muscle health and musculoskeletal functions.

METHODS

This study is a single-blinded randomised controlled trial to investigate the effect of LMHFV on vertebral BMD, muscle health, balancing ability and functional ability in wheelchair users (mainly on wheelchair for outdoor activities). Healthy elderlies aged 65 years or above with walking difficulties and using wheelchair are eligible. Exclusion criteria are those: (1) who cannot stand and walk independently, (2) who have vibration treatment before, (3) with malignancy, (4) with acute fractures or severe osteoarthritis, (5) with cardiovascular concern such as with pacemaker in situ, (6) with chronic inflammatory conditions known to affect muscle metabolism such as rheumatoid arthritis and (7) with high frequency of physical activities, such as participants who participated in regular exercise five times a week or more. Recruited participants will be randomised to either LMHFV or control group. Participant assigned to LMHFV group will receive LMHFV (35 Hz, 0.3g (g=gravitational acceleration), 20 min/day, at least three times/week) for 6 months. The primary outcome is BMD at the lumbar spine to be assessed by dual-energy X-ray absorptiometry that is clinically recommended for the diagnosis of osteoporosis. All primary and secondary outcome assessments for all groups will be performed in the investigators' institute at baseline and 6 months post treatment.

DISCUSSION

This study aims to investigate the effects of LMHFV on wheelchair users. The findings of this study will help to confirm the efficacy of LMHFV on vertebral BMD, muscle health, balancing ability and functional outcomes in wheelchair using elderlies. LMHFV therapy is an intervention strategy that is easy to implement at the community healthcare level or individually at home that has previously been proven to reduce fall risk and muscle strength at the lower limb. The ultimate goal is to improve their bone and muscle quality of wheelchair users, as well as enhancing their quality of life.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov (NCT04180267).

Influence of bone defect position and span in 3-point bending tests: experimental and finite element analysis

Three-point bending test is the most common mechanical test used for quantifying the biomechanical quality of bone tissue and bone healing in small animals. However, there is a lack of standardization for evaluation of bone repair by cortical perforation. The aim of this study was to determine the influence of bone defect position in the proximal metaphysis of rat tibias during load application and different span configuration on the three-point bending test outcomes. Cortical defects with 1.6 mm diameter were created at a standardized location on the medial surface of 60 tibias of male Wistar rats. The animals were euthanized 7 days after surgery. Five specimens were used to create 3D models for finite element analysis using high-resolution micro-CT images. Two spans (6 and 10mm) and three positions of the bone defect in relation to the load application (upward, frontal and downward) were evaluated experimentally (n = 10) and in finite element analysis (n = 5). Maximum load (N) and stiffness (N/mm) were statistically analyzed with 2-way ANOVA and Tukey test (α = 0.05). The results demonstrated that span and orientation of the bone defect significantly influenced the fracture pattern, stress distribution and force versus displacement relation. Therefore, reliable outcome can be achieved creating the bone defect at 8 mm from the extremity of the proximal epiphysis; placing a 10 mm distance span and downward facing defect position to allow a better distribution of stress and more fracture patterns that reached the bone defect target area with less intra-group variability.

A novel mouse model to study fracture healing of the proximal femur

The majority of fractures, especially in elderly and osteoporotic patients, occurs in metaphyseal bone. However, only a few experimental models exist to study metaphyseal bone healing in mice. Currently used mouse models of metaphyseal fracture healing are either based on drill hole defects, lacking adequate biomechanical stimulation at the site of fracture and therefore endochondral ossification in the fracture callus, or are introduced into the distal part of the mouse femur stabilized by a locking plate, which is challenging due to the small specimen size. Therefore, the aim of the current study was to develop a new mouse model to study metaphyseal fracture healing of the proximal femur. We chose a combination between an open osteotomy and a closed intramedullary stabilization. A 24 G needle was inserted into the femur in a closed manner, then an osteotomy was made with a 0.4-mm Gigli wire saw between the third and the lesser trochanter of the femur using an open approach. Fractured femurs were analyzed using microcomputed tomography and histology at days 14 and 21 after surgery. No animals were lost due to surgery or anesthesia. All animals displayed normal limb loading and a physiological gait pattern within the first three days after fracture. We found robust endochondral ossification during the fracture healing process with high expression of late chondrocyte and early osteogenic markers at day 14 (d14). By day 21 (d21), all fractures had a bony bridging score of 3 or more, indicating successful healing. Callus volume significantly decreased from d14 to d21, whereas high numbers of osteoclasts appeared at the fracture callus until d21, indicating that callus remodeling had already started at d21. In conclusion, we successfully developed a novel mouse model to study endochondral fracture healing of the proximal femur. This model might be useful for future studies using transgenic animals to unravel molecular mechanisms of osteoporotic metaphyseal fracture healing.

Inflammatory response in postmenopausal osteoporotic fracture healing

A balanced inflammatory response is important for successful fracture healing. The response of osteoporotic fracture healing is deranged and an altered inflammatory response can be one underlying cause. The objectives of this review were to compare the inflammatory responses between normal and osteoporotic fractures and to examine the potential effects on different healing outcomes. A systematic literature search was conducted with relevant keywords in PubMed, Embase, and Web of Science independently. Original preclinical studies and clinical studies involving the investigation of inflammatory response in fracture healing in ovariectomized (OVX) animals or osteoporotic/elderly patients with available full text and written in English were included. In total, 14 articles were selected. Various inflammatory factors were reported; of those tumour necrosis factor-α (TNF-α) and interleukin (IL)-6 are two commonly studied markers. Preclinical studies showed that OVX animals generally demonstrated higher systemic inflammatory response and poorer healing outcomes compared to normal controls (SHAM). However, it is inconclusive if the local inflammatory response is higher or lower in OVX animals. As for clinical studies, they mainly examine the temporal changes of the inflammatory stage or perform comparison between osteoporotic/fragility fracture patients and normal subjects without fracture. Our review of these studies emphasizes the lack of understanding that inflammation plays in the altered fracture healing response of osteoporotic/elderly patients. Taken together, it is clear that additional studies, preclinical and clinical, are required to dissect the regulatory role of inflammatory response in osteoporotic fracture healing.

Cite this article: Bone Joint Res 2020;9(7):368–385.

The effectiveness of exercises on fall and fracture prevention amongst community elderlies: A systematic review and meta-analysis

Objective

To analyze the effectiveness of exercise interventions on falls and fall-related fracture prevention among community-dwelling elderlies.

Methods

Literature search was conducted in Pubmed and Embase. Keywords used for literature search were “fracture” AND “fall” AND “exercise”. Randomized controlled trials involving community-dwelling elderlies older than 60 years old with physical exercises as intervention were included. A systematic review and meta-analysis was performed. The primary outcomes were falls and fractures.

Results

Twelve studies were included and 4784 participants were involved with a mean age of 75.4. The most common exercise interventions were strength and balance exercises. The results of meta-analysis of 11 studies showed that exercise intervention had beneficial effect on fall prevention (RR = 0.71, 95% CI, 0.62–0.82; I² = 24%, p < 0.0001). The effect was better when exercise intervention applied to women participants (RR = 0.64, 95% CI, 0.49–0.83; I² = 28%, p = 0.00009) compared to men and women participants (RR = 0.75, 95% CI, 0.64–0.89; I² = 24%, p = 0.001). The results of meta-analysis of seven studies showed that physical exercise had significant effect on fracture prevention (RR = 0.54, 95% CI, 0.35–0.83; I² = 25%, p = 0.005). However, the effect was significant when exercise intervention applied to women participants only (RR = 0.37, 95% CI, 0.20–0.67; I² = 0%, p = 0.001) but not significant when exercise intervention applied to both genders (RR = 0.80, 95% CI, 0.58–1.09; I² = 0%, p = 0.15).

Conclusion

Exercise interventions, especially the combination of strength and balance training, were effective in preventing falls. Resistance exercises and jumping exercises were effective for fracture prevention among community-dwelling older population. The effectiveness of exercise interventions on fracture prevention have more significant effect on women. Further studies are needed to test the effectiveness of exercise interventions in men.

Translational potential

The use of effective exercises or biophysical interventions including vibration therapy can be incorporated into Fracture Liaison Services to prevent future fall and fracture.

Can we enhance osteoporotic metaphyseal fracture healing through enhancing ultrastructural and functional changes of osteocytes in cortical bone with low-magnitude high-frequency vibration?

Fragility fractures are related to the loss of bone integrity and deteriorated morphology of osteocytes. Our previous studies have reported that low-magnitude high-frequency vibration (LMHFV) promoted osteoporotic fracture healing. As osteocytes are known for mechanosensing and initiating bone repair, we hypothesized that LMHFV could enhance osteoporotic fracture healing through enhancing morphological changes in the osteocyte lacuna-canalicular network (LCN) and mineralization. A metaphyseal fracture model was established in female Sprague-Dawley rats to investigate changes in osteocytes and healing outcomes from early to late phase post-fracture. Our results showed that the LCN exhibited an exuberant outgrowth of canaliculi in the osteoporotic fractured bone at day 14 after LMHFV. LMHFV upregulated the E11, dentin matrix protein 1 (DMP1), and fibroblast growth factor 23 (FGF23), but downregulated sclerostin (Sost) in osteocytes. Moreover, LMHFV promoted mineralization with significant enhancements of Ca/P ratio, mineral apposition rate (MAR), mineralizing surface (MS/BS), and bone mineral density (BMD) in the osteoporotic group. Consistently, better healing was confirmed by microarchitecture and mechanical properties, whereas the enhancement in osteoporotic group was comparable or even greater than the normal group. This is the first report to reveal the enhancement effect of LMHFV on the osteocytes' morphology and functions in osteoporotic fracture healing.

Fragility fractures and imminent fracture risk in Hong Kong: one of the cities with longest life expectancies

INTRODUCTION

Imminent fracture risk, or fractures within 2 years of an initial fracture, is a pressing issue worldwide. Hong Kong is a city with one of the longest life expectancies. The concern of fragility fractures and the imminent risk of a subsequent fracture is becoming a top priority. The objective of this study was to present the epidemiology of incident fragility fractures of all public acute hospitals and the imminent risk of a subsequent fracture in Hong Kong.

METHODOLOGY

This was a retrospective population-based analysis. Patient records from all acute hospitals in Hong Kong from 1 January 2004 to 31 December 2018 were retrieved for patients ≥ 50 years of age with hip, distal radius, or proximal humerus fractures. Secondary fractures and falls were identified in the subsequent 5 years. Post hoc analysis in recent 2013-2018 period was performed. Overall survival (re-fracture incidence) on age subgroups using Kaplan survival analysis and variables was compared using the log-rank test. Cox proportional hazard regressions, obtaining the hazard ratios (HR) and their respective 95% confidence intervals (CI), were used.

RESULTS

There is an overall increasing trend of fragility fractures (hip, distal radius, proximal humerus) from 5596 in 2004 to 8465 in 2018. The average cumulative imminent risk of fractures from recent 5 years is 3.87% at 1 year and 6.50% at 2 years. 49.5% of the patients with a secondary fracture occurred within 2 years since the initial major fragility fracture. Post hoc analysis in recent 2013-2018 period (N = 7039) showed male patients were 1.21 times more likely to have further fractures with time (HR = 1.21 (1.02, 1.45), p = 0.03) compared with female patients. Patients over age 95 were 2.01 times higher than patients of age under 75 to have further fracture over time.

CONCLUSIONS

Following an initial fracture, prompt treatment strategies should be adopted to avoid imminent risk of fractures. This window of opportunity in the first 2 years is a golden period to treat osteoporosis and prevent falls. Our post hoc analysis has shown that male patients and patients older than 95 are at even higher risk. Clinicians and allied healthcare professionals should be alert on these patients.

How much do we know about the role of osteocytes in different phases of fracture healing? A systematic review

Background

Although emerging studies have provided evidence that osteocytes are actively involved in fracture healing, there is a general lack of a detailed understanding of the mechanistic pathway, cellular events and expression of markers at different phases of healing.

Methods

This systematic review describes the role of osteocytes in fracture healing from early to late phase. Literature search was performed in PubMed and Embase. Original animal and clinical studies with available English full-text were included. Information was retrieved from the selected studies.

Results

A total of 23 articles were selected in this systematic review. Most of the studies investigated changes of various genes and proteins expression patterns related to osteocytes. Several studies have described a constant expression of osteocyte-specific marker genes throughout the fracture healing cascade followed by decline phase with the progress of healing, denoting the important physiological role of the osteocyte and the osteocyte lacuno-canalicular network in fracture healing. The reports of various markers suggested that osteocytes could trigger coordinated bone healing responses from cell death and expression of proinflammatory markers cyclooxygenase-2 and interleukin 6 at early phase of fracture healing. This is followed by the expression of growth factors bone morphogenetic protein-2 and cysteine-rich angiogenic inducer 61 that matched with the neo-angiogenesis, chondrogenesis and callus formation during the intermediate phase. Tightly controlled regulation of osteocyte-specific markers E11/Podoplanin (E11), dentin matrix protein 1 and sclerostin modulate and promote osteogenesis, mineralisation and remodelling across different phases of fracture healing. Stabilised fixation was associated with the finding of higher number of osteocytes with little detectable bone morphogenetic proteins expressions in osteocytes. Sclerostin-antibody treatment was found to result in improvement in bone mass, bone strength and mineralisation.

Conclusion

To further illustrate the function of osteocytes, additional longitudinal studies with appropriate clinically relevant model to study osteoporotic fractures are crucial. Future investigations on the morphological changes of osteocyte lacuno-canalicular network during healing, osteocyte-mediated signalling molecules in the transforming growth factor-beta-Smad3 pathway, perilacunar remodelling, type of fixation and putative biomarkers to monitor fracture healing are highly desirable to bridge the current gaps of knowledge.The translational potential of this article: This systematic review provides an up-to-date chronological overview and highlights the osteocyte-regulated events at gene, protein, cellular and tissue levels throughout the fracture healing cascade, with the hope of informing and developing potential new therapeutic strategies that could improve the timing and quality of fracture healing in the future.

Mechanisms Underlying Normal Fracture Healing and Risk Factors for Delayed Healing

PURPOSE OF REVIEW

Substantial advances have been made in understanding the biological basis of fracture healing. Yet, it is unclear whether the presence of osteoporosis or prior or current osteoporosis therapy influences the healing process or is associated with impaired healing. This review discusses the normal process of fracture healing and the role of osteoporosis and patient-specific factors in relation to fracture repair.

RECENT FINDINGS

The definitive association of osteoporosis to impaired fracture healing remains inconclusive because of limited evidence addressing this point. eStudies testing anabolic agents in preclinical models of ovariectomized animals with induced fractures have produced mostly positive findings showing enhanced fracture repair. Prospective human clinical trials, although few in number and limited in design and to testing only one anabolic agent, have similarly yielded modestly favorable results. Interest is high for exploring currently available osteoporosis therapies for efficacy in fracture repair. Definitive data supporting their efficacy are essential in achieving approval for this indication.