Stimulated angiogenesis for fracture healing augmented by low-magnitude, high-frequency vibration in a rat model-evaluation of pulsed-wave doppler, 3-D power Doppler ultrasonography and micro-CT microangiography

Discretizing low-intensity whole-body vibration into bouts with short rest intervals promotes bone defect repair in osteoporotic mice

Continuous administration of low-intensity whole-body vibration (WBV) gradually diminishes bone mechanosensitivity over time, leading to a weakening of its osteogenic effect. We investigated whether discretizing WBV into bouts with short rest intervals was effective in enhancing osteoporotic bone repair. Ten-week-old female mice were ovariectomized and underwent drill-hole defect surgery (Day 0) on the right tibial diaphysis at 11 weeks of age. The mice underwent one of three regimens starting from Day 1 for 5 days/week: continuous WBV at 45 Hz and 0.3 g for 7.5 min/day (cWBV); 3-s bouts of WBV at 45 Hz, 0.3 g followed by 9-s rest intervals, repeated for 30 min/day (repeated bouts of whole-body vibration with short rest intervals [rWBV]); or a sham treatment. Both the cWBV and rWBV groups received a total of 20,250 vibration cycles per day. On either Day 7 or 14 posteuthanasia (n = 6/group/timepoint), the bone and angiogenic vasculature in the defect were computed tomography imaged using synchrotron light. By Day 14, the bone repair was most advanced in the rWBV group, showing a higher bone volume fraction and a more uniform mineral distribution compared with the sham group. The cWBV group exhibited an intermediate level of bone repair between the sham and rWBV groups. The rWBV group had a decrease in large-sized angiogenic vessels, while the cWBV group showed an increase in such vessels. In conclusion, osteoporotic bone repair was enhanced by WBV bouts with short rest intervals, which may potentially be attributed to the improved mechanosensitivity of osteogenic cells and alterations in angiogenic vasculature.

Treadmill exercise promotes bone tissue recovery in rats subjected to high + Gz loads

INTRODUCTION

High + Gz loads, the gravitational forces experienced by the body in hypergravity environments, can lead to bone loss in pilots and astronauts, posing significant health risks.

MATERIALS AND METHODS

To explore the effect of treadmill exercise on bone tissue recovery, a study was conducted on 72 male Wistar rats. These rats were subjected to four weeks of varying levels of periodic high + Gz loads (1G, 8G, 20G) experiments, and were subsequently divided into the treadmill group and the control group. The treadmill group underwent a continuous two-week treadmill experiment, while the control group rested during this period. The mechanical properties, microstructure, and molecular markers of their tibial bone tissue were measured using three-point bending, micro-CT, and PCR.

RESULTS

The results showed that treadmill exercise improved the elastic modulus, ultimate deflection, and ultimate load of rat bone tissue. It also increased the number, density, and volume fraction of bone trabeculae, and decreased their separation. Moreover, treadmill exercise enhanced osteogenesis and inhibited osteoclastogenesis.

CONCLUSION

This study demonstrates that treadmill exercise can promote the recovery of bone tissue in rats subjected to high + Gz loads, providing a potential countermeasure for bone loss in pilots and astronauts.

Hypergravity stimulates mechanical behavior and micro-architecture of tibia in rats

INTRODUCTION

The bone tissue is susceptible to hypergravity (+ G) environment. It is necessary to discuss the extent to which specific + G values are beneficial or detrimental to bone tissue. The objective of this study was to characterize the effects of high + G values on mechanical properties, microstructures, and cellular metabolism of bone.

MATERIALS AND METHODS

30 male Wistar rats aged 12 weeks were randomly divided into 5 groups, and bore different + G (namely + 1G, + 4G, + 8G, + 10G and + 12G) environments respectively for 4 weeks, 5 days each week, and 3 minutes each day. The macro-mechanical parameters, microstructure parameters, and mRNA transcription levels of the tibia were determined through the three-point bending method, micro-CT detection, and q-PCR analysis, respectively.

RESULTS

As the + G value increases, hypergravity becomes increasingly detrimental to the macro-mechanical performance of rat tibia. Concerning the microstructure of cancellous bone, there appears to be a favorable trend at + 4G, followed by a progressively detrimental trend at higher G values. In addition, the mRNA transcription levels of OPG and RANKL show an initial tendency of enhanced bone absorption at +4G, followed by an increase in bone remodeling capacity as G value increases.

CONCLUSION

The higher G values correspond to poorer macro-mechanical properties of the tibia, and a + 4G environment benefits the microstructure of the tibia. At the cellular level, bone resorption is enhanced in the + 4G group, but the bone remodeling capability gradually increases with further increments in G values.

Utilization of Low-Magnitude High-Frequency Vibration (LMHFV) as an Aid in Treating Peri-Implantitis: Case Presentations

Peri-implantitis is an inflammatory process initiating in the soft tissue and then progressing to the hard tissue surrounding dental implants leading to loss of osseous support and potential loss of the implant if not identified early in the process. This process initiates in the soft tissue, which become inflamed spreading to the underlying bone leading to decreases in bone density with subsequent crestal resorption and thread exposure. In the absence of treatment of the peri-implantitis, the bone loss at the osseous implant interface progresses with inflammatory mediated decrease in the bone density that moves apically, eventually leading to mobility of the implant and its failure. Low-magnitude high-frequency vibration (LMHFV) has been shown to improve bone density, stimulate osteoblastic activity, and arrest progression of peri-implantitis with improvement of the bone or graft around the affected implant with or without surgery as part of the treatment. Two cases are presented using LMHFV to augment treatment.

Influence of Low-Intensity Pulsed Ultrasound Parameters on the Bone Mineral Density in Rat Model: A Systematic Review

OBJECTIVE

Bone recovery typically depends on the age of organisms or the prevalence of metabolic disorders such as osteoporosis, which is a metabolic condition characterized by decreased bone strength and bone mineral density (BMD). Therefore, low-intensity pulsed ultrasound (LIPUS), a non-invasive method for osteogenic stimulation, presents promising results. However, heterogeneity in animal study designs is a typical characteristic. Hence, we conducted a systematic review to evaluate the effectiveness of LIPUS in the recovery of experimental bone defects using rat models. We examined the areal and volumetric BMD to identify LIPUS doses to be applied and evaluated the accuracy reported by previous studies.

METHODS

The Virtual Health Library regional portal, PubMed, Embase, EBSCOhost, Scopus and CAPES were reviewed for animal studies that compared fracture treatments based on LIPUS with sham or no treatments using rat models and reported BMD as an outcome. The tool provided by the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) and the Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies (CAMARADES) checklist were used to assess the bias and quality of such studies.

RESULTS

Of the six studies reviewed, the most frequently used LIPUS dose had an ultrasonic frequency of 1.0 MHz, repetition rate of 0.1 kHz and pulse duration of 2000 μs. An intensity (ISATA) of 30 mW/cm2 was the most preferred for bone recovery. However, the BMD could not solely irrefutably evaluate the effectiveness of LIPUS in bone recovery as the results were discordant with each other. The discrepancies in experimental methodologies, low-quality classifications and high risk of bias in the selected studies, however, did not validate the undertaking of a meta-analysis.

CONCLUSION

On the basis of the BMD results, no sufficient evidence was found to recommend the use of LIPUS for bone recovery in rat models. Thus, this systematic review indicates that the accuracy of such reports must be improved to improve their scientific quality to facilitate a transition of LIPUS applications from pre-clinical research to clinic use.

Bioinformatics analysis combined with molecular dynamics simulation validation to elucidate the potential molecular mechanisms of Jianshen Decoction for treatment of osteoporotic fracture

Osteoporotic fracture (OPF) is a prevalent skeletal disease in the middle-aged and elderly. In clinical practice, Jianshen Decoction (JSD) has been used to treat OPFs. However, the specific effective components and mechanisms of JSD on OPF have not been explored. Therefore, this study used bioinformatics analysis combined with molecular dynamics simulation validation to explore the molecular mechanism of JSD treatment of OPF. Public databases (TCMSP, Batman TCM) were used to find the effective active components and corresponding target proteins of JSD (screening conditions: OB ≥ 30%, drug-likeness ≥ 0.18, half-life ≥ 4). Differentially expressed genes (DEGs) related to OPF lesions were obtained based on the gene expression omnibus database (screening conditions: adjust P value < .01, | log2 FC | ≥ 1.0). The BisoGenet plug-in and the CytoNCA plug-in of Cytoscape were used to derive the potential core target proteins of JSD in the treatment of OPF. The JSD active ingredient target interaction network and the JSD-OPF target protein core network were constructed using the Cytoscape software. In addition, the R language Bioconductor package and clusterProfiler package were used to perform gene ontology (GO)/Kyoto Encylopedia Of Genes And Genome (KEGG) enrichment analysis on core genes to explain the biological functions and signal pathways of core proteins. Finally, molecular docking and molecular dynamics simulations were carried out through PyMOL, AutoDockTools 1.5.6, Vina, LeDock, Discovery Studio (DS) 2019, and other software to verify the binding ability of drug active ingredients and core target proteins. A total of 245 targets and 70 active components were identified. Through protein-protein interaction (PPI) network construction, 39 core targets were selected for further research. GO/KEGG enrichment analysis showed that the DNA-binding transcription factor binding, RNA polymerase II-specific DNA-binding transcription factor binding, MAPK signaling pathway, and ErbB signaling pathway were mainly involved. The results of molecular docking and molecular dynamics simulations supported the good interaction between MYC protein and Quercetin/Stigmasterol. In this study, bioinformatics, molecular docking, and molecular dynamics simulations were used for the first time to clarify the active components, molecular targets, and key biological pathways of JSD in the treatment of OPF, providing a theoretical basis for further research.

Temporal Pattern of micro-CT Angiography Vascular Parameters and VEGF mRNA Expression in Fracture Healing: a Radiograph and Molecular Comparison

Angiogenesis plays an important role in fracture healing with vascular endothelial growth factor (VEGF) as the main protein involved. Micro-computed tomography (CT) angiography may be used to analyze this revascularization with several parameters such as number of branches, total volume, and diameter. This systematic review is aimed to assess available studies on the temporal pattern of vascular imaging on micro-CT angiographs, especially in terms of the number of branches, total volume, and diameter as well as the temporal pattern of VEGF mRNA expression as the molecular comparison during bone fracture healing. This review was conducted according to the PRISMA guidelines. Electronic database searches were performed using PubMed, ProQuest, ScienceDirect, EBSCOhost, Taylor & Francis Online, and hand searching. The search strategy and keywords were adjusted to each database using the Boolean operators and other available limit functions to identify most relevant articles based on our inclusion and exclusion criteria. Screening and filtration were done in several stages by removing the duplicates and analyzing each title, abstract, and full-text in all included entries. Data extraction was done for syntheses to summarize the temporal pattern of each parameter. A total of 28 articles were eligible and met all criteria, 11 articles were synthesized in its angiograph's analysis, 16 articles were synthesized in its VEGF mRNA expression analysis, and 1 article had both parameters analyzed. The overall temporal pattern of both three micro-CT angiographic parameters and VEGF mRNA expression was in line qualitatively. The number of branches, total volume, and diameter of the blood vessels in micro-CT angiography showed an exponential rise at week 2 and decline at week 3 of fracture healing, with the VEGF mRNA expression concurrently showing a consistent pattern in the phase.

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.

Low-Intensity Pulsed Ultrasound Stimulation for Bone Fractures Healing: A Review

Low-intensity pulsed ultrasound (LIPUS) is a developing technology, which has been proven to improve fracture healing process with minimal thermal effects. This noninvasive treatment accelerates bone formation through various molecular, biological, and biomechanical interactions with tissues and cells. Although LIPUS treatment has shown beneficial effects on different bone fracture locations, only very few studies have examined its effects on deeper bones. This study provides an overview on therapeutic ultrasound for fractured bones, possible mechanisms of action, clinical evidences, current limitations, and its future prospects.

Melatonin alleviates hydrogen peroxide induced oxidative damage in MC3T3-E1 cells and promotes osteogenesis by activating SIRT1

Oxidative stress is an important contributor to the development of osteoporosis. Melatonin, an indoleamine secreted by the pineal gland, has antioxidant properties. This study aims to explore whether melatonin can promote bone formation and elucidate the mechanisms underlying this process. In this study, we used an in vitro hydrogen peroxide (H₂O₂)-induced oxidative stress model in MC3T3-E1 cells and an in vivo ovariectomized osteoporotic bone defect model in rats to explore the protective effects of melatonin against osteoporotic bone defects along with the mechanism underlying these effects. We found that melatonin significantly increased alkaline phosphatase activity, mineralization capacity, and the expression of BMP2, RUNX2, and OPN in MC3T3-E1 cells treated with H₂O₂. Furthermore, melatonin was found to activate SIRT1, SIRT3 and inhibit p66Shc, reduce the intracellular reactive oxygen species levels, stabilize mitochondria, reduce malondialdehyde levels, increase superoxide dismutase activity, and reduce apoptosis in MC3T3-E1 cells treated with H₂O₂. Intriguingly, these effects could be reversed by the SIRT1 inhibitor EX527. In vivo experiments confirmed that melatonin improves the microstructure and bone mineral density of the distal femoral bone trabecula and promotes bone formation. Meanwhile, melatonin activated SIRT1, inhibited p66Shc and increased SIRT3 expression. Taken together, our findings showed that melatonin can restrain oxidative damage in MC3T3-E1 cells and promote osteogenesis by activating SIRT1 which regulate the activity of SIRT3 and inhibit the expression of p66Shc, suggesting that melatonin could be a potential therapeutic agent for osteoporosis-related bone metabolic diseases.

Estrogen Receptor α Signaling in Osteoblasts is Required for Mechanotransduction in Bone Fracture Healing

Biomechanical stimulation by whole-body low-magnitude high-frequency vibration (LMHFV) has demonstrated to provoke anabolic effects on bone metabolism in both non-osteoporotic and osteoporotic animals and humans. However, preclinical studies reported that vibration improved fracture healing and bone formation in osteoporotic, ovariectomized (OVX) mice representing an estrogen-deficient hormonal status, but impaired bone regeneration in skeletally healthy non-OVX mice. These effects were abolished in general estrogen receptor α (ERα)-knockout (KO) mice. However, it remains to be elucidated which cell types in the fracture callus are targeted by LMHFV during bone healing. To answer this question, we generated osteoblast lineage-specific ERα-KO mice that were subjected to ovariectomy, femur osteotomy and subsequent vibration. We found that the ERα specifically on osteoblastic lineage cells facilitated the vibration-induced effects on fracture healing, because in osteoblast lineage-specific ERα-KO (ERαfl/fl; Runx2Cre) mice the negative effects in non-OVX mice were abolished, whereas the positive effects of vibration in OVX mice were reversed. To gain greater mechanistic insights, the influence of vibration on murine and human osteogenic cells was investigated in vitro by whole genome array analysis and qPCR. The results suggested that particularly canonical WNT and Cox2/PGE2 signaling is involved in the mechanotransduction of LMHFV under estrogen-deficient conditions. In conclusion, our study demonstrates a critical role of the osteoblast lineage-specific ERα in LMHFV-induced effects on fracture healing and provides further insights into the molecular mechanism behind these effects.

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.

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.

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.

Influence of Low-Magnitude High-Frequency Vibration on Bone Cells and Bone Regeneration

Bone is a mechanosensitive tissue for which mechanical stimuli are crucial in maintaining its structure and function. Bone cells react to their biomechanical environment by activating molecular signaling pathways, which regulate their proliferation, differentiation, and matrix production. Bone implants influence the mechanical conditions in the adjacent bone tissue. Optimizing their mechanical properties can support bone regeneration. Furthermore, external biomechanical stimulation can be applied to improve implant osseointegration and accelerate bone regeneration. One promising anabolic therapy is vertical whole-body low-magnitude high-frequency vibration (LMHFV). This form of vibration is currently extensively investigated to serve as an easy-to-apply, cost-effective, and efficient treatment for bone disorders and regeneration. This review aims to provide an overview of LMHFV effects on bone cells in vitro and on implant integration and bone fracture healing in vivo. In particular, we review the current knowledge on cellular signaling pathways which are influenced by LMHFV within bone tissue. Most of the in vitro experiments showed that LMHFV is able to enhance mesenchymal stem cell (MSC) and osteoblast proliferation. Furthermore, osteogenic differentiation of MSCs and osteoblasts was shown to be accelerated by LMHFV, whereas osteoclastogenic differentiation was inhibited. Furthermore, LMHFV increased bone regeneration during osteoporotic fracture healing and osseointegration of orthopedic implants. Important mechanosensitive pathways mediating the effects of LMHFV might be the Wnt/beta-catenin signaling pathway, the estrogen receptor (ER) signaling pathway, and cytoskeletal remodeling.

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.

Mechanotransduction in osteogenesis

Bone is one of the most highly adaptive tissues in the body, possessing the capability to alter its morphology and function in response to stimuli in its surrounding environment. The ability of bone to sense and convert external mechanical stimuli into a biochemical response, which ultimately alters the phenotype and function of the cell, is described as mechanotransduction. This review aims to describe the fundamental physiology and biomechanisms that occur to induce osteogenic adaptation of a cell following application of a physical stimulus. Considerable developments have been made in recent years in our understanding of how cells orchestrate this complex interplay of processes, and have become the focus of research in osteogenesis. We will discuss current areas of preclinical and clinical research exploring the harnessing of mechanotransductive properties of cells and applying them therapeutically, both in the context of fracture healing and de novo bone formation in situations such as nonunion.

Cite this article: Bone Joint Res 2019;9(1):1–14.

Vibration acceleration promotes endochondral formation during fracture healing through cellular chondrogenic differentiation

Vibration acceleration through whole body vibration has been reported to promote fracture healing. However, the mechanism responsible for this effect remains unclear. Purpose of this study was to determine whether vibration acceleration directly affects cells around the fracture site and promotes endochondral ossification. Four-week-old female Wistar Hannover rats were divided into two groups (vibration [V group] and control [C group]). The eighth ribs on both sides were cut vertically using scissors. From postoperative day 3 to 11, vibration acceleration using Power Plate^® (30 Hz, low amplitude [30-Low], 10 min/day) was applied in the V group. Mature calluses appeared earlier in the V group than in the C group by histological analysis. The GAG content in the fracture callus on day 6 was significantly higher in the V group than in the C group. The mRNA expressions of SOX-9, aggrecan, and Col-II in the fracture callus on day 6 and Col-X on day 9 were significantly higher in the V group than in the C group. For in vitro analysis, four different conditions of vibration acceleration (30 or 50 Hz with low or high amplitude [30-Low, 30-High, 50-Low, and 50-High], 10 min/day) were applied to a prechondrogenic cell (ATDC5) and an undifferentiated cell (C3H10T1/2). There was no significant difference in cell proliferation between the control and any of the four vibration conditions for both cell lines. For both cell lines, alcian blue staining was greater under 30-Low and 50-Low conditions than under control as well as 30-High and 50-High conditions on days 7 and 14. Vibration acceleration under 30-L condition upregulated chondrogenic gene expressions of SOX-9, aggrecan, Col-II, and Col-X. Low-amplitude vibration acceleration can promote endochondral ossification in the fracture healing in vivo and chondrogenic differentiation in vitro.

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.

Review of Animal Models of Comorbidities in Fracture-Healing Research

There is clinical evidence that patient-specific comorbidities like osteoporosis, concomitant tissue injury, and ischemia may strongly interfere with bone regeneration. However, underlying mechanisms are still unclear. To study these mechanisms in detail, appropriate animal models are needed. For decades, bone healing has been studied in large animals, including dogs, rabbits, pigs, or sheep. However, large animal models display a limited ability to study molecular pathways and cellular functions. Therefore in recent years, mice and rats have become increasingly popular as a model organism for fracture healing research due to the availability of molecular analysis tools and transgenic models. Both large and small animals can be used to study comorbidities and risk factors, modelling the human clinical situation. However, attention has to be paid when choosing an appropriate model due to species differences between large animals, rodents, and humans. This review focuses on large and small animal models for the common comorbidities ischemic injury/reduced vascularization, osteoporosis, and polytrauma, and critically discusses the translational and molecular aspects of these models. Here, we review material which was presented at the workshop "Animal Models of Comorbidities in Fracture Healing Research" at the 2019 ORS Annual Meeting in Austin Texas. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2491-2498, 2019.

Therapeutic effects of whole-body vibration on fracture healing in ovariectomized rats: a systematic review and meta-analysis

OBJECTIVE

Whole-body vibration (WBV), providing cyclic mechanical stimulation, has been used to accelerate fracture healing in preclinical studies. This study aimed to summarize and evaluate the effects of WBV on bone healing in ovariectomized rat models and then analyze its potential effects on fractures in human postmenopausal osteoporosis.

METHODS

PubMed, EMBASE, Web of Science, China National Knowledge Infrastructure, VIP, SinoMed, and WanFang databases were searched from their inception date to September 2017, and an updated search was conducted in January 2018. Studies that evaluated the effects of WBV on bone healing compared with control groups in ovariectomized rats were included. Two authors selected studies, extracted data, and assessed the methodological quality. Meta-analyses were performed when the same outcomes were reported in two or more studies.

RESULTS

Nine eligible studies were selected. In treatment groups, callus areas were significantly improved in the first 3 weeks, normalized total bone volume and total tissue volume values increased dramatically at 8 weeks, and the mechanical tests showed a significant difference at the end point of the study.

CONCLUSIONS

This study suggested that WBV could accelerate callus formation in the early phase of bone healing, promote callus mineralization and maturity in the later phase, and restore mechanical properties of bones.

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.

Estrogen receptor α- (ERα), but not ERβ-signaling, is crucially involved in mechanostimulation of bone fracture healing by whole-body vibration

Mechanostimulation by low-magnitude high frequency vibration (LMHFV) has been shown to provoke anabolic effects on the intact skeleton in both mice and humans. However, experimental studies revealed that, during bone fracture healing, the effect of whole-body vibration is profoundly influenced by the estrogen status. LMHFV significantly improved fracture healing in ovariectomized (OVX) mice being estrogen deficient, whereas bone regeneration was significantly reduced in non-OVX, estrogen-competent mice. Furthermore, estrogen receptors α (ERα) and β (ERβ) were differentially expressed in the fracture callus after whole-body vibration, depending on the estrogen status. Based on these data, we hypothesized that ERs may mediate vibration-induced effects on fracture healing. To prove this hypothesis, we investigated the effects of LMHFV on bone healing in mice lacking ERα or ERβ. To study the influence of the ER ligand estrogen, both non-OVX and OVX mice were used. All mice received a femur osteotomy stabilized by an external fixator. Half of the mice were sham-operated or subjected to OVX 4 weeks before osteotomy. Half of each group received LMHFV with 0.3 g and 45 Hz for 20 min per day, 5 days per week. After 21 days, fracture healing was evaluated by biomechanical testing, μCT analysis, histomorphometry and immunohistochemistry. Absence of ERα or ERβ did not affect fracture healing in sham-treated mice. Wildtype (WT) and ERβ-knockout mice similarly displayed impaired bone regeneration after OVX, whereas ERα-knockout mice did not. Confirming previous data, in WT mice, LMHFV negatively affected bone repair in non-OVX mice, whereas OVX-induced compromised healing was significantly improved by vibration. In contrast, vibrated ERα-knockout mice did not display significant differences in fracture healing compared to non-vibrated animals, both in non-OVX and OVX mice. Fracture healing in ERβ-knockout mice was similarly affected by LMHFV as in WT mice. These results suggest that ERα-signaling may be crucial for vibration-induced effects on fracture healing, whereas ERβ-signaling may play a minor role.

Photoacoustic imaging of synovial tissue hypoxia in experimental post-traumatic osteoarthritis

OBJECTIVES

This pilot study aimed to investigate the feasibility of non-invasively assessing synovial tissue hypoxia in vivo using photoacoustic (PA) imaging in a post-traumatic osteoarthritis model and explore its correlation with OA severity.

METHODS

The three-dimensional vasculature structure and oxygenation level of synovial tissues of destabilization of the medial meniscus (DMM)-induced osteoarthritis (OA) mice were longitudinally monitored using PA imaging. Vascular volume/tissue volume (%) and tissue oxygen saturation (sO₂) were validated against results obtained by established Power Doppler (PD) imaging and dynamic changes of inhaled O₂ concentration respectively. PA changes were correlated with the histological grading of cartilage damages.

RESULTS

PA-measurements of vascularity and sO₂ demonstrated a strong correlation with localized blood flow detected by PD imaging (r = 0.506, p < 0.001) and inhaled O₂ concentration. DMM knees exhibited much more vascularity in synovial tissue at 4 months after surgery (median 11.3%, IQR: 10.7-15.5%) than the intact knees at time zero (median:5.1%, IQR:3.8-6.8%, p < 0.001) as well as the sham-operated knees (median: 4%, IQR: 3.75-5.45%, p = 0.017). Paradoxically, synovial tissue sO₂ was significantly lower in DDM knees (median: 37.7%, IQR: 36.4-40.6%) than both the intact (47.1%, IQR: 41.9-49.8% p = 0.001) and sham-operated knees (45.1% IQR: 45.1-52.4%, p = 0.017). The PA-detected synovial tissue hypoxia correlated with the severity of cartilage loss in DMM mice (rho = -0.597, p = 0.031).

CONCLUSION

Here, we demonstrated PA imaging can be implemented for non-invasive imaging of the synovial tissue. Under PA imaging, synovitis in OA was characterized by increased angiogenesis and synovial tissue hypoxia; the latter was associated with the severity of OA.

A systematic review of current osteoporotic metaphyseal fracture animal models

Objectives

The treatment of osteoporotic fractures is a major challenge, and the enhancement of healing is critical as a major goal in modern fracture management. Most osteoporotic fractures occur at the metaphyseal bone region but few models exist and the healing is still poorly understood. A systematic review was conducted to identify and analyse the appropriateness of current osteoporotic metaphyseal fracture animal models.

Materials and Methods

A literature search was performed on the Pubmed, Embase, and Web of Science databases, and relevant articles were selected. A total of 19 studies were included. Information on the animal, induction of osteoporosis, fracture technique, site and fixation, healing results, and utility of the model were extracted.

Results

Fracture techniques included drill hole defects (3 of 19), bone defects (3 of 19), partial osteotomy (1 of 19), and complete osteotomies (12 of 19). Drill hole models and incomplete osteotomy models are easy to perform and allow the study of therapeutic agents but do not represent the usual clinical setting. Additionally, biomaterials can be filled into drill hole defects for analysis. Complete osteotomy models are most commonly used and are best suited for the investigation of therapeutic drugs or noninvasive interventions. The metaphyseal defect models allow the study of biomaterials, which are associated with complex and comminuted osteoporotic fractures.

Conclusion

For a clinically relevant model, we propose that an animal model should satisfy the following criteria to study osteoporotic fracture healing: 1) induction of osteoporosis, 2) complete osteotomy or defect at the metaphysis unilaterally, and 3) internal fixation.

Cite this article: R. M. Y. Wong, M. H. V. Choy, M. C. M. Li, K-S. Leung, S. K-H. Chow, W-H. Cheung, J. C. Y. Cheng. A systematic review of current osteoporotic metaphyseal fracture animal models. Bone Joint Res 2018;7:6–11. DOI: 10.1302/2046-3758.71.BJR-2016-0334.R2.

Low-Magnitude High-Frequency Vibration Accelerated the Foot Wound Healing of n5-streptozotocin-induced Diabetic Rats by Enhancing Glucose Transporter 4 and Blood Microcirculation

Delayed wound healing is a Type 2 diabetes mellitus (DM) complication caused by hyperglycemia, systemic inflammation, and decreased blood microcirculation. Skeletal muscles are also affected by hyperglycemia, resulting in reduced blood flow and glucose uptake. Low Magnitude High Frequency Vibration (LMHFV) has been proven to be beneficial to muscle contractility and blood microcirculation. We hypothesized that LMHFV could accelerate the wound healing of n5-streptozotocin (n5-STZ)-induced DM rats by enhancing muscle activity and blood microcirculation. This study investigated the effects of LMHFV in an open foot wound created on the footpad of n5-STZ-induced DM rats (DM_V), compared with no-treatment DM (DM), non-DM vibration (Ctrl_V) and non-DM control rats (Ctrl) on Days 1, 4, 8 and 13. Results showed that the foot wounds of DM_V and Ctrl_V rats were significantly reduced in size compared to DM and Ctrl rats, respectively, at Day 13. The blood glucose level of DM_V rats was significantly reduced, while the glucose transporter 4 (GLUT4) expression and blood microcirculation of DM_V rats were significantly enhanced in comparison to those of DM rats. In conclusion, LMHFV can accelerate the foot wound healing process of n5-STZ rats.

Synergistic protection of bone vasculature and bone mass by desferrioxamine in osteoporotic mice

It has previously been demonstrated that impaired angiogenesis is associated with metabolic abnormalities in bone in addition to osteoporosis (including postmenopausal osteoporosis). Enhancing vessel formation in bone is therefore a potential clinical therapy for osteoporosis. The present study conducted an in-depth investigation using desferrioxamine (DFO) in an ovariectomy (OVX)-induced osteoporotic mouse model in order to determine the time frame of alteration of bone characteristics and the therapeutic effect of DFO. It was demonstrated that OVX induced instant bone mass loss 1 week following surgery, as expected. In contrast, DFO treatment protected the mice against OVX-induced osteoporosis during the first week, however failed to achieve long-term protection at a later stage. A parallel alteration for cluster of differentiation 31/endomucin double positive vessels (type H vessels) was observed, which have previously been reported to be associated with osteogenesis. DFO administration not only partially prevented bone loss and maintained trabecular bone microarchitecture, however additionally enhanced the type H vessels during the first week post-OVX. The molecular mechanism of how DFO influences type H vessels to regulate bone metabolism needs to be further investigated. However, the findings of the present study provide preliminary evidence to support combined vascular and osseous therapies for osteoporotic patients. Pharmacotherapy may offer a novel target for improving osteoporosis by promoting type H vessel formation, which indicates potential clinical significance in the field of bone metabolism.

Effect of low-intensity whole-body vibration on bone defect repair and associated vascularization in mice

Low-intensity whole-body vibration (LIWBV) may stimulate bone healing, but the involvement of vascular ingrowth, which is essential for bone regeneration, has not been well examined. We thus investigated the LIWBV effect on vascularization during early-stage bone healing. Mice aged 13 weeks were subjected to cortical drilling on tibial bone. Two days after surgery (day 0), mice were exposed daily to sine-wave LIWBV at 30 Hz and 0.1 g peak-to-peak acceleration for 20 min/day (Vib) or were sham-treated (sham). Following vascular casting with a zirconium-based contrast agent on days 6, 9, or 12 and sacrifice, vascular and bone images were obtained by K-edge subtraction micro-CT using synchrotron lights. Bone regeneration advanced more in the Vib group from days 9 to 12. The vascular volume fraction decreased from days 6 to 9 in both groups; however, from days 9 to 12, it was increased in shams, while it stabilized in the Vib group. The vascular volume fraction tended to be or was smaller in the Vib group on days 6 and 12. The vessel number density was higher on day 9 but lower on day 12 in the Vib group. These results suggest that the LIWBV-promoted bone repair is associated with the modulation of vascularization, but additional studies are needed to determine the causality of this association.

Effect of low-magnitude different-frequency whole-body vibration on subchondral trabecular bone microarchitecture, cartilage degradation, bone/cartilage turnover, and joint pain in rabbits with knee osteoarthritis

Backgroud

Whole-body vibration(WBV) has been suggested for the prevention of subchondral bone loss of knee osteoarthritis (OA) . This study examined the effects of different frequency of whole-body vibration on subchondral trabecular bone microarchitecture, cartilage degradation and metabolism of the tibia and femoral condyle bone, and joint pain in an anterior cruciate ligament transection (ACLT)–induced knee osteoarthritisrabbit model.

Method

Ninety adult rabbits were divided into six groups: all groups received unilateral ACLT; Group 1, ACLT only; Group 2, 5 Hz WBV; Group 3, 10 Hz WBV; Group 4, 20 Hz WBV; Group 5, 30 Hz WBV; and Group 6, 40 Hz WBV. Pain was tested via weight-bearing asymmetry. Subchondral trabecular bone microarchitecture was examined using in vivo micro-computed tomography. Knee joint cartilage was evaluated by gross morphology, histology, and ECM gene expression level (aggrecan and type II collagen [CTX-II]). Serum bone-specific alkaline phosphatase, N-mid OC, cartilage oligometric protein, CPII, type I collagen, PIIANP, G1/G2 aggrecan levels, and urinary CTX-II were analyzed.

Results

After 8 weeks of low-magnitude WBV, the lower frequency (10 Hz and 20 Hz) WBV treatment decreased joint pain and cartilage resorption, accelerated cartilage formation, delayed cartilage degradation especially at the 20 Hz regimen. However, the higher frequencies (30 Hz and 40 Hz) had worse effects, with worse limb function and cartilage volume as well as higher histological scores and cartilage resorption. In contrast, both prevented loss of trabeculae and increased bone turnover. No significant change was observed in the 5 Hz WBV group.

Conclusion

Our data demonstrate that the lower frequencies (10 Hz and 20 Hz) of low-magnitude WBV increased bone turnover, delayed cartilage degeneration, and caused a significant functional change of the OA-affected limb in ACLT-induced OA rabbit model but did not reverse OA progression after 8 weeks of treatment.

Mechanical stimulation enhanced estrogen receptor expression and callus formation in diaphyseal long bone fracture healing in ovariectomy-induced osteoporotic rats

Estrogen receptor (ER) in ovariectomy-induced osteoporotic fracture was reported to exhibit delayed expression. Mechanical stimulation enhanced ER-α expression in osteoporotic fracture callus at the tissue level. ER was also found to be required for the effectiveness of vibrational mechanical stimulation treatment in osteoporotic fracture healing.

INTRODUCTION

Estrogen receptor(ER) is involved in mechanical signal transduction in bone metabolism. Its expression was reported to be delayed in osteoporotic fracture healing. The purpose of this study was to investigate the roles played by ER during osteoporotic fracture healing enhanced with mechanical stimulation.

METHODS

Ovariectomy-induced osteoporotic SD rats that received closed femoral fractures were divided into five groups, (i) SHAM, (ii) SHAM-VT, (iii) OVX, (iv) OVX-VT, and (v) OVX-VT-ICI, where VT stands for whole-body vibration treatment and ICI for ER antagonization by ICI 182,780. Callus formation and gene expression were assessed at 2, 4, and 8 weeks postfracture. In vitro osteoblastic differentiation, mineralization, and ER-α expression were assessed.

RESULTS

The delayed ER expression was found to be enhanced by vibration treatment. Callus formation enhancement was shown by callus morphometry and micro-CT analysis. Enhancement effects by vibration were partially abolished when ER was modulated by ICI 182,780, in terms of callus formation capacity at 2-4 weeks and ER gene and protein expression at all time points. In vitro, ER expression in osteoblasts was not enhanced by VT treatment, but osteoblastic differentiation and mineralization were enhanced under estrogen-deprived condition. When osteoblastic cells were modulated by ICI 182,780, enhancement effects of VT were eliminated.

CONCLUSIONS

Vibration was able to enhance ER expression in ovariectomy-induced osteoporotic fracture healing. ER was essential in mechanical signal transduction and enhancement in callus formation effects during osteoporotic fracture healing enhanced by vibration. The enhancement of ER-α expression by mechanical stimulation was not likely to be related to the increased expression in osteoblastic cells but rather to the systemic enhancement in recruitment of ER-expressing progenitor cells through increased blood flow and neo-angiogenesis. This finding might explain the observed difference in mechanical sensitivity of osteoporotic fracture to mechanical stimulation.

Atypical femoral fractures and current management

With the rapid increase in patients receiving bisphosphonates (BPs) for treating osteoporosis, one of the clinical complications associated with its long-term use is atypical femoral fractures (AFFs). Although the absolute risk for AFFs is low and it was a consensus that AFFs were acceptable compared with the amount of osteoporotic fractures BPs have prevented, epidemiological studies have proved that BPs had a strong association with AFFs and possibly more people were going to suffer from this adverse effect with wide prescriptions of this drug. In addition, AFFs seemed to have impaired ability to heal. Thus, to understand the mechanism(s) behind AFFs is important and desirable for considering preventive measures. This article reviewed the clinical features of AFFs as well as potential underlining pathological characteristics, such as the decreased turnover rate caused by BPs that led to multiple-level alternations, e.g., changes not only at cellular and tissue levels, but also related to changes in bone micro- and macrostructure and organic/inorganic contents, leading to potentially compromised mechanical properties of cortical bone when exposed to prolonged BP therapy. Severely suppressed bone turnover may also be the underlying mechanism for impaired fracture healing in patients with AFFs. The rising concerns about the risk for AFFs in nonosteoporotic patients receiving high-dose BPs to treat cancers were also discussed. Detailed investigation will help develop potential targeted pharmacological treatments such as parathyroid hormone. In addition, potential innovative internal fixation implants were discussed with regard to dynamic and biological fixation for enhancing AFF repair.

Fracture healing in osteoporotic bone

As the world population rises, osteoporotic fracture is an emerging global threat to the well-being of elderly patients. The process of fracture healing by intramembranous ossification or/and endochondral ossification involve many well-orchestrated events including the signaling, recruitment and differentiation of mesenchymal stem cells (MSCs) during the early phase; formation of a hard callus and extracellular matrix, angiogenesis and revascularization during the mid-phase; and finally callus remodeling at the late phase of fracture healing. Through clinical and animal research, many of these factors are shown to be impaired in osteoporotic bone. Animal studies related to post-menopausal estrogen deficient osteoporosis (type I) have shown healing to be prolonged with decreased levels of MSCs and decreased levels of angiogenesis. Moreover, the expression of estrogen receptor (ER) was shown to be delayed in ovariectomy-induced osteoporotic fracture. This might be related to the observed difference in mechanical sensitivity between normal and osteoporotic bones, which requires further experiments to elucidate. In mice fracture models related to senile osteoporosis (type II), it was observed that chondrocyte and osteoblast differentiation were impaired; and that transplantation of juvenile bone marrow would result in enhanced callus formation. Other factors related to angiogenesis and vasculogenesis have also been noted to be impaired in aged models, affecting the degradation of cartilaginous matrixes and vascular invasion; the result is changes in matrix composition and growth factors concentrations that ultimately impairs healing during age-related osteoporosis. Most osteoporotic related fractures occur at metaphyseal sites clinically, and reports have indicated that differences exist between diaphyseal and metaphyseal fractures. An animal model that satisfies three main criteria (metaphyseal region, plate fixation, osteoporosis) is suggested for future research for more comprehensive understanding of the impairment in osteoporotic fractures. Therefore, a metaphyseal fracture or osteotomy that achieves complete discontinuity fixed with metal implants is suggested on ovariectomized aged rodent models.

High-acceleration whole body vibration stimulates cortical bone accrual and increases bone mineral content in growing mice

Whole body vibration (WBV) is a promising tool for counteracting bone loss. Most WBV studies on animals have been performed at acceleration <1g and frequency between 30 and 90Hz. Such WBV conditions trigger bone growth in osteopenia models, but not in healthy animals. In order to test the ability of WBV to promote osteogenesis in young animals, we exposed seven-week-old male mice to vibration at 90Hz and 2g peak acceleration for 15min/day, 5 days/week. We examined the effects on skeletal tissues with micro-computed tomography and histology. We also quantified bone vascularization and mechanosensitive osteocyte proteins, sclerostin and DMP1. Three weeks of WBV resulted in an increase of femur cortical thickness (+5%) and area (+6%), associated with a 25% decrease of sclerostin expression, and 35% increase of DMP1 expression in cortical osteocytes. Mass-structural parameters of trabecular bone were unaltered in femur or vertebra, while osteoclastic parameters and bone formation rate were increased at both sites. Three weeks of WBV resulted in higher blood vessel numbers (+23%) in the distal femoral metaphysis. After 9-week WBV, we have not observed the difference in structural cortical or trabecular parameters. However, the tissue mineral density of cortical bone was increased by 2.5%. Three or nine weeks of 2g/90Hz WBV treatment did not affect longitudinal growth rate or body weight increase under our experimental conditions, indicating that these are safe to use. These results validate a potential of 2g/90Hz WBV to stimulate trabecular bone cellular activity, accelerate cortical bone growth, and increase bone mineral density.

Effect of Low-Magnitude, High-Frequency Vibration Treatment on Retardation of Sarcopenia: Senescence-Accelerated Mouse-P8 Model

Sarcopenia-related falls and fall-related injuries in community-dwelling elderly people garnered more and more interest in recent years. Low-magnitude high-frequency vibration (LMHFV) was proven beneficial to musculoskeletal system and recommended for sarcopenia treatment. This study aimed to evaluate the effects of LMHFV on the sarcopenic animals and explore the mechanism of the stimulatory effects. Senescence-accelerated mouse P8 (SAMP8) mice at month 6 were randomized into control (Ctrl) and vibration (Vib) groups and the mice in the Vib group were given LMHFV (0.3 g, 20 min/day, 5 days/week) treatment. At months 0, 1, 2, 3, and 4 post-treatment, muscle mass, structure, and function were assessed. The potential proliferation capacity of the muscle was also evaluated by investigating satellite cells (SCs) pool and serum myostatin expression. At late stage, the mice in the Vib group showed higher muscle strength (month 4, p = 0.028). Generally, contractibility was significantly improved by LMHFV (contraction time [CT], p = 0.000; half-relaxation time [RT50], p = 0.000). Enlarged cross-sectional area of fiber type IIA was observed in the Vib group when compared with Ctrl group (p = 0.000). No significant difference of muscle mass was observed. The promotive effect of LMHFV on myoregeneration was reflected by suppressed SC pool reduction (month 3, p = 0.000; month 4, p = 0.000) and low myostatin expression (p = 0.052). LMHFV significantly improved the structural and functional outcomes of the skeletal muscle, hence retarding the progress of sarcopenia in SAMP8. It would be a good recommendation for prevention of the diseases related to skeletal muscle atrophy.

LIPUS promotes spinal fusion coupling proliferation of type H microvessels in bone

Low-intensity pulsed ultrasound (LIPUS) has been found to accelerate spinal fusion. Type H microvessels are found in close relation with bone development. We analyzed the role of type H vessels in rat spinal fusion model intervened by LIPUS. It was found LIPUS could significantly accelerate bone fusion rate and enlarge bone callus. Osteoblasts were specifically located on the bone meshwork of the allograft, and were surrounded by type H microvessels. LIPUS could significantly increase the quantity of osteoblasts during spine fusion, which process was coupled with elevated angiogenesis of type H microvessels. Our results suggest that LIPUS may be a noninvasive adjuvant treatment modality in spinal fusion for clinical use. The treatment is recommended for usage for at least one month.

Ultrasound and fragility fracture: is there a role?

Osteoporotic fracture is known to have impaired healing capacity and therefore takes longer time to heal, as compared with younger one. The mechanism of impaired osteoporotic fracture healing is multifactorial, where lower responsiveness to mechanical loading is generally believed to be one factor, yet not absolutely confirmed. In recent years, low intensity pulsed ultrasound (LIPUS) is demonstrated to have good efficacy in treating normal fracture healing, as proven by many randomized controlled trials, as well as in vitro and animal evidences. The effects of LIPUS on osteoporotic fracture healing was also validated in an animal study, which revealed that osteoporotic fractured bone of SD rats showed radiologically and biomechanically comparable responses to LIPUS as age-matched normal fracture healing, in terms of callus width, bridging rate, bone volume fraction, and stiffness etc. Gene expression profiling also confirmed that osteoporotic fractured bone responded to LIPUS very well by upregulating Col1 and BMP2 (osteogenesis) at early phase, VEGF (angiogenesis) at middle phase and RANKL (remodeling) at late phase. These confirm that osteoporotic bones respond well to LIPUS as good as normal bone. These findings may be associated with estrogen receptors (ERs), as estrogen depletion is sensed and relayed by ERs and ERs also function as mechano-sensors. A previous study observed a delayed ERs expression pattern in fracture callus of OVX rats, as compared with SHAM rats, which correlated well with the expression pattern of BMP-2 (callus formation-related gene). Hence, the responses of osteoporotic fractured bone to LIPUS may be related to the local ERs expression at fracture callus that needs further experiments to validate.

Low-Magnitude, High-Frequency Vibration Fails to Accelerate Ligament Healing but Stimulates Collagen Synthesis in the Achilles Tendon

Background:

Low-magnitude, high-frequency vibration accelerates fracture and wound healing and prevents disuse atrophy in musculoskeletal tissues.

Purpose:

To investigate the role of low-magnitude, high-frequency vibration as a treatment to accelerate healing of an acute ligament injury and to examine gene expression in the intact Achilles tendon of the injured limb after low-magnitude, high-frequency vibration.

Study Design:

Controlled laboratory study.

Methods:

Complete surgical transection of the medial collateral ligament (MCL) was performed in 32 Sprague-Dawley rats, divided into control and low-magnitude, high-frequency vibration groups. Low-magnitude, high-frequency vibration started on postoperative day 2, and rats received vibration for 30 minutes a day for 12 days. All rats were sacrificed 2 weeks after the operation, and their intact and injured MCLs were biomechanically tested or used for histological analysis. Intact Achilles tendons from the injured limb were evaluated for differences in gene expression.

Results:

Mechanical testing revealed no differences in the ultimate tensile load or the structural stiffness between the control and vibration groups for either the injured or intact MCL. Vibration exposure increased gene expression of collagen 1 alpha (3-fold), interleukin 6 (7-fold), cyclooxygenase 2 (5-fold), and bone morphogenetic protein 12 (4-fold) in the intact Achilles tendon when compared with control tendons (P < .05).

Conclusion:

While no differences were observed in the mechanical or histological properties of the fully transected MCL after low-magnitude, high-frequency vibration treatment, significant enhancements in gene expression were observed in the intact Achilles tendon. These included collagen, several inflammatory cytokines, and growth factors critical for tendons.

Clinical Relevance:

As low-magnitude, high-frequency vibration had no negative effects on ligament healing, vibration therapy may be a useful tool to accelerate healing of other tissues (bone) in multitrauma injuries without inhibiting ligament healing. Additionally, the enhanced gene expression in response to low-magnitude, high-frequency vibration in the intact Achilles tendon suggests the need to further study its potential to accelerate tendon healing in partial injury or repair models.

Vibration stimuli and the differentiation of musculoskeletal progenitor cells: Review of results in vitro and in vivo

Due to the increasing burden on healthcare budgets of musculoskeletal system disease and injury, there is a growing need for safe, effective and simple therapies. Conditions such as osteoporosis severely impact on quality of life and result in hundreds of hours of hospital time and resources. There is growing interest in the use of low magnitude, high frequency vibration (LMHFV) to improve bone structure and muscle performance in a variety of different patient groups. The technique has shown promise in a number of different diseases, but is poorly understood in terms of the mechanism of action. Scientific papers concerning both the in vivo and in vitro use of LMHFV are growing fast, but they cover a wide range of study types, outcomes measured and regimens tested. This paper aims to provide an overview of some effects of LMHFV found during in vivo studies. Furthermore we will review research concerning the effects of vibration on the cellular responses, in particular for cells within the musculoskeletal system. This includes both osteogenesis and adipogenesis, as well as the interaction between MSCs and other cell types within bone tissue.

Systemic and Local Administration of Allogeneic Bone Marrow-Derived Mesenchymal Stem Cells Promotes Fracture Healing in Rats

Mesenchymal stem cells (MSCs) are immune privileged and a cell source for tissue repair. Previous studies showed that there is systemic mobilization of osteoblastic precursors to the fracture site. We hypothesized that both systemic and local administration of allogeneic MSCs may promote fracture healing. Bone marrow-derived MSCs and skin fibroblasts were isolated from GFP Sprague-Dawley rats, cultured, and characterized. Closed transverse femoral fracture with internal fixation was established in 48 adult male Sprague-Dawley rats, which were randomly assigned into four groups receiving PBS injection, MSC systemic injection, fibroblast systemic injection, and MSC fracture site injection; 2 × 10(6) cells were injected at 4 days after fracture. All animals were sacrificed at 5 weeks after fracture; examinations included weekly radiograph, micro-CT, mechanical testing, histology, immunohistochemistry, and double immunofluorescence. The callus size of MSC injection groups was significantly larger among all the groups. Radiographs and 3D reconstruction images showed that the fracture gaps united in the MSC injected groups, while gaps were still seen in the fibroblast and PBS injection groups. The mechanical properties were significantly higher in the MSC injection groups than those in the fibroblast and PBS groups, but no difference was found between the MSC local and systemic injection groups. Immunohistochemistry and double immunofluorescence demonstrated that GFP-positive MSCs were present in the callus in the MSC injection groups at 5 weeks after fracture, and some differentiated into osteoblasts. Quantitative analysis revealed the number of GFP-positive cells in the callus in the MSC systemic injection group was significantly lower than that of the MSC local injection group. The proportion of GFP osteoblasts in GFP-positive cells in the MSC systemic injection group was significantly lower than that of the MSC local injection group. These findings provide critical insight for developing MSC-based therapies, and systemic injection of allogeneic MSCs may be a novel treatment method for promoting fracture repair.

Low-magnitude high-frequency vibration enhances gene expression related to callus formation, mineralization and remodeling during osteoporotic fracture healing in rats

Low magnitude high frequency vibration (LMHFV) has been shown to improve anabolic and osteogenic responses in osteoporotic intact bones and during osteoporotic fracture healing; however, the molecular response of LMHFV during osteoporotic fracture healing has not been investigated. It was hypothesized that LMHFV could enhance osteoporotic fracture healing by regulating the expression of genes related to chondrogenesis (Col-2), osteogenesis (Col-1) and remodeling (receptor activator for nuclear factor- κ B ligand (RANKL) and osteoproteger (OPG)). In this study, the effects of LMHFV on both osteoporotic and normal bone fracture healing were assessed by endpoint gene expressions, weekly radiographs, and histomorphometry at weeks 2, 4 and 8 post-treatment. LMHFV enhanced osteoporotic fracture healing by up-regulating the expression of chondrogenesis-, osteogenesis- and remodeling-related genes (Col-2 at week 4 (p=0.008), Col-1 at week 2 and 8 (p<0.001 and p=0.008) and RANKL/OPG at week 8 (p=0.045)). Osteoporotic bone had a higher response to LMHFV than normal bone and showed significantly better results as reflected by increased expression of Col-2 and Col-1 at week 2 (p<0.001 for all), larger callus width at week 2 (p=0.001), callus area at week 1 and 5(p<0.05 for all) and greater relative area of osseous tissue (p=0.002) at week 8. This study helps to understand how LMHFV regulates gene expression of callus formation, mineralization and remodeling during osteoporotic fracture healing.

Callus formation is related to the expression ratios of estrogen receptors-alpha and -beta in ovariectomy-induced osteoporotic fracture healing

INTRODUCTION

This study characterizes ovariectomized (OVX)-induced osteoporotic fracture healing with focus on estrogen receptors (ERs). Callus formation plays a critical role in fracture healing, and ERs are well-known mechanosensors in osteogenic pathways. It was hypothesized that callus formation was related to and partially determined by the difference in expression patterns of ERs in both normal and OVX-induced osteoporotic fractures.

METHODS

Closed femoral fracture in SHAM and ovariectomized rats were used in this study. Weekly callus width (CW) and area (CA), endpoint mechanical properties, gene expressions of Col-1, BMP-2, ER-α, ER-β and ER-α:ER-β ratios (ER-ratios), and correlations were assessed at 2, 4 and 8 weeks post-fracture.

RESULTS

CW and CA results confirmed that OVX-induced osteoporotic fracture was delayed at 2-4 weeks with impaired endpoint mechanical properties. Gene expressions of ER-α and ER-β were higher in the SHAM group at week 2 (p < 0.05) and later lowered at week 8; whereas the OVX group showed an opposing trend. Moderate correlation existed between ER-α and BMP-2 (0.545, p = 0.003), and ER-ratio and BMP-2 (0.601, p = 0.001), and BMP-2 to CW and CA (r = 0.709, p = 0.000 and r = 0.588, p = 0.001, respectively). ER-α and ER-β proteins expressions were confirmed by immunohistochemistry at the fracture callus in reparative progenitor cells, osteoblasts- and osteoclasts-like cells.

CONCLUSION

We conclude that the delayed healing rate and impaired callus quality in OVX-induced osteoporotic fracture is related to the delayed expression of ERs. A high ER-α:ER-β ratio favors callus formation.

Distinct frequency dependent effects of whole-body vibration on non-fractured bone and fracture healing in mice

Low-magnitude high-frequency vibration (LMHFV) provokes anabolic effects in non-fractured bone; however, in fracture healing, inconsistent results were reported and optimum vibration conditions remain unidentified. Here, we investigated frequency dependent effects of LMHFV on fracture healing. Twelve-week-old, female C57BL/6 mice received a femur osteotomy stabilized using an external fixator. The mice received whole-body vibrations (20 min/day) with 0.3g peak-to-peak acceleration and a frequency of either 35 or 45 Hz. After 10 and 21 days, the osteotomized femurs and intact bones (contra-lateral femurs, lumbar spine) were evaluated using bending-testing, µ-computed tomography, and histomorphometry. In non-fractured trabecular bone, vibration with 35 Hz significantly increased the relative amount of bone (+28%) and the trabecular number (+29%), whereas cortical bone was not influenced. LMHFV with 45 Hz failed to provoke anabolic effects in trabecular or cortical bone. Fracture healing was not significantly influenced by whole-body vibration with 35 Hz, whereas 45 Hz significantly reduced bone formation (-64%) and flexural rigidity (-34%) of the callus. Although the exact mechanisms remain open, our results suggest that small vibration setting changes could considerably influence LMHFV effects on bone formation in remodeling and repair, and even disrupt fracture healing, implicating caution when treating patients with impaired fracture healing.

Low magnitude high frequency vibration accelerated cartilage degeneration but improved epiphyseal bone formation in anterior cruciate ligament transect induced osteoarthritis rat model

OBJECTIVES

To evaluate the effects of low-magnitude high-frequency vibration (LMHFV) on degenerated articular cartilage and subchondral bone in anterior cruciate ligament transection (ACLT) induced osteoarthritis (OA) rat model.

METHODS

6 months old female Sprague-Dawley rats received ACLT on right knee and randomly divided into treatment and control groups. OA developed 12 weeks after surgery. LMHFV (35 Hz, 0.3 g) treatment was given 20 min/day and 5 days/week. After 6, 12 and 18 weeks, six rats of each group were sacrificed at each time point and the right knees were harvested. OA grading score, distal femur cartilage volume (CV), subchondral bone morphology, elastic modulus of cartilage and functional changes between groups were analyzed.

RESULTS

Increased cartilage degradation (higher OA grading score) and worse functional results (lower duty cycle, regular index and higher limb idleness index) were observed after LMHFV treatment (P = 0.011, 0.020, 0.012 and 0.005, respectively). CV increased after LMHFV treatment (P = 0.019). Subchondral bone density increased with OA progress (P < 0.01). Increased BV/TV, Tb.N and decreased Tb.Sp were observed in distal femur epiphysis in LMHFV treatment group (P = 0.006, 0.018 and 0.011, respectively).

CONCLUSION

LMHFV accelerated cartilage degeneration and caused further functional deterioration of OA affected limb in ACLT-induced OA rat model. In contrast, LMHFV promoted bone formation in OA affected distal femur epiphysis, but did not reverse OA progression.

Imaging techniques for the assessment of fracture repair

Imaging of a healing fracture provides a non-invasive and often instructive reproduction of the fracture repair progress and the healing status of bone. However, the interpretation of this reproduction is often qualitative and provides only an indirect and surrogate measure of the mechanical stability of the healing fracture. Refinements of the available imaging techniques have been suggested to more accurately determine the healing status of bone. Plain radiographs provide the ability to determine the degree of bridging of the fracture gap and to quantify the amount of periosteal callus formation. Absorptiometric measures including dual X-ray absorptiometry and computed tomography provide quantitative information on the amount and the density of newly formed bone around the site of the fracture. To include the effect of spatial distribution of newly formed bone, finite element models of healing fracture can be employed to estimate its load bearing capacity. Ultrasound technology not only avoids radiation doses to the patients but also provides the ability to additionally measure vascularity in the surrounding soft tissue of the fracture and in the fracture itself.

Programmable mechanobioreactor for exploration of the effects of periodic vibratory stimulus on mesenchymal stem cell differentiation

A programmable bioreactor using a voice-coil actuator was developed to enable research on the effects of periodic vibratory stimulus on human and porcine mesenchymal stem cells (MSCs). We hypothesized that low frequency vibrations would result in a cartilage phenotype and higher frequency vibrations would result in a bone phenotype. The mechanical stimulation protocol is adjusted from a computer external to the incubator via a USB cable. Once programmed, the embedded microprocessor and sensor system on the bioreactor execute the protocol independent of the computer. In each test, a sinusoidal stimulus was applied to a culture plate in 1-min intervals with a 15-min rest following each, for a total of 15 h per day for 10 days. Frequencies of 1 and 100 Hz were applied to cultures of both human and porcine umbilical cord–derived MSCs. Chondrogenesis was determined by Alcian blue staining for glycosaminoglycans and an increased differentiation index (ratio of mRNA for collagen II and collagen I). Osteogenic differentiation was indicated with Alizarin red for calcium staining and increased bone morphogenetic protein 2 mRNA. One-hertz stimulation resulted in a cartilage phenotype for both human and porcine MSCs, while 100-Hz stimulation resulted in a bone phenotype.