Low-Intensity Pulsed Ultrasound Alleviates Hypoxia-Induced Chondrocyte Damage in Temporomandibular Disorders by Modulating the Hypoxia-Inducible Factor Pathway

Comparison of the effects of acupuncture methods on the temporomandibular disorder: A network meta-analysis

OBJECTIVES

A network meta-analysis (NMA) was applied to compare the therapeutic effect of different acupuncture methods on temporomandibular disorder (TMD).

MATERIALS AND METHODS

A computer retrieval was carried out in the English databases of Cochrane, PubMed, Embase and Web of Science, as well as the Chinese databases of CNKI, Wanfang and VIP for randomized controlled trials on the effect of acupuncture on TMD, with a retrieval deadline of January 21, 2024. Data analysis was conducted using R software and Bayesian method. The pain score served as the primary outcome measure, with the mouth opening as the secondary outcome measure.

RESULTS

Thirty-five articles were included in the analysis, involving 1937 TMD patients. The NMA results suggested that DN-PT had the best effect on relieving pain and improving mouth opening. (Description of all abbreviations in Supplementary Material S3).

CONCLUSIONS

Based on the available evidence, the results of the NMA suggest that DN-PT is most effective in relieving TMD pain and increasing mouth opening. However, due to the fact that some acupuncture therapies are only reported in a small number of research reports, this may lead to an increase in the randomness of the results and a decrease in the reliability.

Enhancing the therapeutic efficacy of gefitinib on subcutaneously transplanted SKOV3 ovarian cancer tumors in nude mice via ultrasound‑stimulated microbubble cavitation

The present study aimed to explore the effect of ultrasound-stimulated microbubble cavitation (USMC) on drug concentration and therapeutic efficacy of oral gefitinib in treating subcutaneously transplanted SKOV3 ovarian cancer tumors in nude mice. The present study employed the VINNO70 ultrasonic diagnostic and treatment integrated machine for USMC therapy. Firstly, the mechanical index was set at 0.25, and the therapeutic efficacy of USMC treatment was assessed at intervals of 5, 10 and 20 min. Briefly, 72 nude mice were randomized into the following four groups (n=18/group): Control group, USMC5 min group, USMC10 min group and USMC20 min group, and the therapeutic response to USMC treatment was evaluated by comparing pre-and post-intervention effects. Additionally, the combined therapeutic efficacy of USMC and gefitinib was investigated by randomly dividing 96 tumor-bearing mice into the following four groups (n=24/group): Control group, USMC group, gefitinib group and USMC + gefitinib group. Contrast-enhanced ultrasound, hematoxylin and eosin staining, western blotting, immunofluorescence staining, TUNEL staining, ELISA and liquid chromatography-mass spectrometry were performed in the present study. The results showed that USMC combined with gefitinib had the best treatment effect; the tumor inhibition rate was higher than that of gefitinib alone and the overall survival time was prolonged. In addition, the drug concentration in the tumor tissue obtained from the USMC + gefitinib group was revealed to be ~1.4 times higher than that detected in the group treated with gefitinib alone. The experimental results also confirmed that the strongest tumor inhibition rate and longest overall survival time was observed in the USMC + gefitinib group, followed by the gefitinib group and USMC group. STAT3 is an important signaling transducer and transcription factor, which, when phosphorylated, can lead to abnormal cell proliferation and malignant transformation. In addition, the upregulation of phosphorylated (p)-STAT3 is consider a reason for the poor efficacy of gefitinib in treating ovarian cancer. The present study revealed that ultrasound microbubble therapy could overcome this side effect. In conclusion, USMC improved the effects of oral gefitinib on subcutaneously transplanted SKOV3 ovarian cancer tumors in nude mice and increased drug penetration. In addition, USMC overcame the gefitinib-induced side effect of upregulated STAT3 phosphorylation and reduced the expression levels of p-STAT3 in the tumor.

Low-Intensity Pulsed Ultrasound: A Physical Stimulus with Immunomodulatory and Anti-inflammatory Potential

Ultrasound has expanded into the therapeutic field as a medical imaging and diagnostic technique. Low-intensity pulsed ultrasound (LIPUS) is a kind of therapeutic ultrasound that plays a vital role in promoting fracture healing, wound repair, immunomodulation, and reducing inflammation. Its anti-inflammatory effects are manifested by decreased pro-inflammatory cytokines and chemokines, accelerated regression of immune cell invasion, and accelerated damage repair. Although the anti-inflammatory mechanism of LIPUS is not very clear, many in vitro and in vivo studies have shown that LIPUS may play its anti-inflammatory role by activating signaling pathways such as integrin/Focal adhesion kinase (FAK)/Phosphatidylinositol 3-kinase (PI3K)/Serine threonine kinase (Akt), Vascular endothelial growth factor (VEGF)/endothelial nitric oxide synthase (eNOS), or inhibiting signaling pathways such as Toll-like receptors (TLRs)/Nuclear factor kappa-B (NF-κB) and p38-Mitogen-activated protein kinase (MAPK). As a non-invasive physical therapy, the anti-inflammatory and immunomodulatory effects of LIPUS deserve further exploration.

Ultrasound-triggered three dimensional hyaluronic acid hydrogel promotes in vitro and in vivo reprogramming into induced pluripotent stem cells

Cellular reprogramming technologies have been developed with different physicochemical factors to improve the reprogramming efficiencies of induced pluripotent stem cells (iPSCs). Ultrasound is a clinically applied noncontact biophysical factor known for regulating various cellular behaviors but remains uninvestigated for cellular reprogramming. Here, we present a new reprogramming strategy using low-intensity ultrasound (LIUS) to improve cellular reprogramming of iPSCs in vitro and in vivo. Under 3D microenvironment conditions, increased LIUS stimulation shows enhanced cellular reprogramming of the iPSCs. The cellular reprogramming process facilitated by LIUS is accompanied by increased mesenchymal to epithelial transition and histone modification. LIUS stimulation transiently modulates the cytoskeletal rearrangement, along with increased membrane fluidity and mobility to increase HA/CD44 interactions. Furthermore, LIUS stimulation with HA hydrogel can be utilized in application of both human cells and in vivo environment, for enhanced reprogrammed cells into iPSCs. Thus, LIUS stimulation with a combinatorial 3D microenvironment system can improve cellular reprogramming in vitro and in vivo environments, which can be applied in various biomedical fields.

Influence on the temporomandibular joint induced by mandibular malpositioning caused by vertical dimension elevation and occlusal loss in adult rats: An imaging, histological and immunohistochemical study

BACKGROUND

Mandibular malpositioning may result in an abnormal concentration of stresses within the temporomandibular joint (TMJ) in adult rats, which may further lead to a series of pathological changes, such as articular cartilage wear, subchondral bone sclerosis and osteophyte formation. However, the pathological and adaptive changes in condylar cartilage caused by different stress distributions are still controversial.

OBJECTIVE

The aim of this study was to observe the effect of sagittal changes in mandibular position on condylar cartilage by changing the occlusal vertical dimension (OVD) in adult rats.

METHODS

Fifteen-week-old female rats were divided into three groups: control (CON), increased OVD (iOVD) and loss of occlusion (LO) groups. An occlusal plate and tooth extraction were used to establish the animal model. TMJ samples of the experimental and CON groups were observed and investigated by bone morphological, histomorphological and immunohistochemical staining analyses at 3 days, 1 week, 2 weeks, 4 weeks and 8 weeks. Weight curves were plotted.

RESULTS

Micro-computed tomography showed that, compared with the CON group, cartilage destruction followed by repair occurred in both experimental groups, which was similar to the trend observed in haematoxylin-eosin staining. All experimental results for the iOVD group showed an approximately similar time trend. Compared with the iOVD group, the toluidine blue and immunohistochemical staining results in the LO group showed no obvious change trend over time.

CONCLUSION

Compared with occlusal loss, an increase in OVD caused faster and more severe damage to condylar cartilage, and subchondral bone repair occurred later.

Low-intensity pulsed ultrasound reduces alveolar bone resorption during orthodontic treatment via Lamin A/C-Yes-associated protein axis in stem cells

BACKGROUND

The bone remodeling during orthodontic treatment for malocclusion often requires a long duration of around two to three years, which also may lead to some complications such as alveolar bone resorption or tooth root resorption. Low-intensity pulsed ultrasound (LIPUS), a noninvasive physical therapy, has been shown to promote bone fracture healing. It is also reported that LIPUS could reduce the duration of orthodontic treatment; however, how LIPUS regulates the bone metabolism during the orthodontic treatment process is still unclear.

AIM

To investigate the effects of LIPUS on bone remodeling in an orthodontic tooth movement (OTM) model and explore the underlying mechanisms.

METHODS

A rat model of OTM was established, and alveolar bone remodeling and tooth movement rate were evaluated via micro-computed tomography and staining of tissue sections. In vitro, human bone marrow mesenchymal stem cells (hBMSCs) were isolated to detect their osteogenic differentiation potential under compression and LIPUS stimulation by quantitative reverse transcription-polymerase chain reaction, Western blot, alkaline phosphatase (ALP) staining, and Alizarin red staining. The expression of Yes-associated protein (YAP1), the actin cytoskeleton, and the Lamin A/C nucleoskeleton were detected with or without YAP1 small interfering RNA (siRNA) application via immunofluorescence.

RESULTS

The force treatment inhibited the osteogenic differentiation potential of hBMSCs; moreover, the expression of osteogenesis markers, such as type 1 collagen (COL1), runt-related transcription factor 2, ALP, and osteocalcin (OCN), decreased. LIPUS could rescue the osteogenic differentiation of hBMSCs with increased expression of osteogenic marker inhibited by force. Mechanically, the expression of LaminA/C, F-actin, and YAP1 was downregulated after force treatment, which could be rescued by LIPUS. Moreover, the osteogenic differentiation of hBMSCs increased by LIPUS could be attenuated by YAP siRNA treatment. Consistently, LIPUS increased alveolar bone density and decreased vertical bone absorption in vivo. The decreased expression of COL1, OCN, and YAP1 on the compression side of the alveolar bone was partially rescued by LIPUS.

CONCLUSION

LIPUS can accelerate tooth movement and reduce alveolar bone resorption by modulating the cytoskeleton-Lamin A/C-YAP axis, which may be a promising strategy to reduce the orthodontic treatment process.

Potential Effects of NO-Induced Hypoxia-Inducible Factor-1α on Yak Meat Tenderness during Post-Mortem Aging

The objective of this study was to investigate the mechanism underlying nitric oxide (NO)-induced hypoxia-inducible factor-1α (HIF-1α) and its impact on yak muscle tenderness during post-mortem aging. The Longissimus thoracis et lumborum (LTL) muscle of yak were incubated at 4 °C for 0, 3, 6, 9, 12, 24, and 72 h after treatment with 0.9% saline, NO activator, or a combination of the NO activator and an HIF-1α inhibitor. Results indicated that elevated NO levels could increase HIF-1α transcription to achieve stable expression of HIF-1α protein (P < 0.05). Additionally, elevated NO triggered HIF-1α S-nitrosylation, which further upregulated the activity of key glycolytic enzymes, increased glycogen consumption, accelerated lactic acid accumulation, and decreased pH (P < 0.05). These processes eventually improved the tenderness of yak muscle during post-mortem aging (P < 0.05). The results demonstrated that NO-induced activation of HIF-1α S-nitrosylation enhanced glycolysis during post-mortem aging and provided a possible pathway for improving meat tenderness.

Low-intensity pulsed ultrasound in the treatment of masticatory myositis and temporomandibular joint synovitis: A clinical trial

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS) is a non-invasive physical stimulation application for the therapy of articular cartilage injury. This study aimed to explore the therapeutic effects of low-intensity pulsed ultrasound in treating masticatory myositis and synovitis in temporomandibular joint disorders and to establish an evaluation system to evaluate the clinical efficacy.

METHODS

TMD patients who met the inclusion criteria in the temporomandibular joint clinic of the affiliated Stomatological Hospital of Chongqing Medical University from April 3, 2021, to December 2021 were selected. Before the start and after 7 days of LIPUS treatment, the Fricton temporomandibular joint disorder index, Visual Analog Scale (VAS), and Pressure Difference of Precision Manometer (PD) were measured. A paired t-test was used to compare the values of the Fricton index, VAS, and PD before and after treatment in each group. One-way ANOVA analysis of variance was used to compare the differences between groups.

RESULTS

After one week of LIPUS treatment, the PI, DI and CMI of the Fricton index in the masticatory myositis (PI: P < 0.001; CMI: P < 0.001; DI: P = 0.2641, ns) and the synovitis group (DI: P < 0.001; CMI: P < 0.001, PI: P = 0.9729, ns) significantly decreased. The VAS of the masticatory myositis group and the synovitis group were significantly reduced (P < 0.001). The PD between the affected and healthy sides of the masticatory myositis group and the synovitis group was significantly reduced (P < 0.001), and the reduction was more evident in the M group.

CONCLUSIONS

LIPUS is effective in pain relief in patients with masticatory myositis and joint synovitis, meanwhile, masticatory myositis was more sensitive to LIPUS. A new comprehensive clinical efficacy evaluation system which includes PV, FI, and VAS was created to better 2 diagnose masticatory myositis and joint synovitis.

Ultrasound-Driven Healing: Unleashing the Potential of Chondrocyte-Derived Extracellular Vesicles for Chondrogenesis in Adipose-Derived Stem Cells

Repairing cartilage defects represents a significant clinical challenge. While adipose-derived stem cell (ADSC)-based strategies hold promise for cartilage regeneration, their inherent chondrogenic potential is limited. Extracellular vesicles (EVs) derived from chondrocytes (CC-EVs) have shown potential in enhancing chondrogenesis, but their role in promoting chondrogenic differentiation of ADSCs remains poorly understood. Moreover, the clinical application of EVs faces limitations due to insufficient quantities for in vivo use, necessitating the development of effective methods for extracting significant amounts of CC-EVs. Our previous study demonstrated that low-intensity ultrasound (LIUS) stimulation enhances EV secretion from mesenchymal stem cells. Here, we identified a specific LIUS parameter for chondrocytes that increased EV secretion by 16-fold. CC-EVs were found to enhance cell activity, proliferation, migration, and 21-day chondrogenic differentiation of ADSCs in vitro, while EVs secreted by chondrocytes following LIUS stimulation (US-CC-EVs) exhibited superior efficacy. miRNA-seq revealed that US-CC-EVs were enriched in cartilage-regeneration-related miRNAs, contributing to chondrogenesis in various biological processes. In conclusion, we found that CC-EVs can enhance the chondrogenesis of ADSCs in vitro. In addition, our study introduces ultrasound-driven healing as an innovative method to enhance the quantity and quality of CC-EVs, meeting clinical demand and addressing the limited chondrogenic potential of ADSCs. The ultrasound-driven healing unleashes the potential of CC-EVs for chondrogenesis possibly through the enrichment of cartilage-regeneration-associated miRNAs in EVs, suggesting their potential role in cartilage reconstruction. These findings hold promise for advancing cartilage regeneration strategies and may pave the way for novel therapeutic interventions in regenerative medicine.

Potential pathological and molecular mechanisms of temporomandibular joint osteoarthritis

Temporomandibular joint osteoarthritis (TMJ OA) is a progressive degenerative disease of the temporomandibular joint (TMJ). The unclear etiology and mechanisms of TMJ OA bring great difficulties to early diagnosis and effective treatment, causing enormous burdens to patients' life and social economics. In this narrative review, we summarized the main pathological changes of TMJ OA, including inflammatory responses, degeneration of extracellular matrix (ECM), abnormal cell biological behaviors (apoptosis, autophagy, and differentiation) in TMJ tissue, and aberrant angiogenesis. All pathological features are closely linked to each other, forming a vicious cycle in the process of TMJ OA, which results in prolonged disease duration and makes it difficult to cure. Various molecules and signaling pathways are involved in TMJ OA pathogenesis, including nuclear factor kappa-B (NF-κB), mitogen-activated protein kinases (MAPKs), extracellular regulated protein kinases (ERKs) and transforming growth factor (TGF)-β signaling pathways et al. One molecule or pathway can contribute to several pathological changes, and the crosstalk between different molecules and pathways can further lead to a complicated condition TMJ OA. TMJ OA has miscellaneous etiology, complex clinical status, depressed treatment results, and poor prognosis. Therefore, novel in-vivo and in-vitro models, novel medicine, materials, and approaches for therapeutic procedures might be helpful for further investigation of TMJ OA. Furthermore, the role of genetic factors in TMJ OA needs to be elucidated to establish more reasonable and effective clinical strategies for diagnosing and treating TMJ OA.

The therapeutic effects of low-intensity pulsed ultrasound in musculoskeletal soft tissue injuries: Focusing on the molecular mechanism

Musculoskeletal soft tissue injuries are very common and usually occur during both sporting and everyday activities. The intervention of adjuvant therapies to promote tissue regeneration is of great importance to improving people's quality of life and extending their productive lives. Though many studies have focused on the positive results and effectiveness of the LIPUS on soft tissue, the molecular mechanisms standing behind LIPUS effects are much less explored and reported, especially the intracellular signaling pathways. We incorporated all research on LIPUS in soft tissue diseases since 2005 and summarized studies that uncovered the intracellular molecular mechanism. This review will also provide the latest evidence-based research progress in this field and suggest research directions for future experiments.

Effectiveness and Mechanisms of Low-Intensity Pulsed Ultrasound on Osseointegration of Dental Implants and Biological Functions of Bone Marrow Mesenchymal Stem Cells

Dental implant restoration is the preferred choice for patients with dentition defects or edentulous patients, and obtaining stable osseointegration is the determining factor for successful implant healing. The risk of implant failure during the healing stage is still an urgent problem in clinical practice due to differences in bone quality at different implant sites and the impact of some systemic diseases on bone tissue metabolism. Low-intensity pulsed ultrasound (LIPUS) is a noninvasive physical intervention method widely recognized in the treatment of bone fracture and joint damage repair. Moreover, many studies indicated that LIPUS could effectively promote the osseointegration of dental implants and improve the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). This review is aimed at investigating the research progress on the use of LIPUS in dental implant medicine from three aspects: (1) discuss the promoting effects of LIPUS on osseointegration and peri-implant bone regeneration, (2) summarize the effects and associated mechanisms of LIPUS on the biological functions of BMSCs, and (3) introduce the application and prospects of LIPUS in the clinical work of dental implantation. Although many challenges need to be overcome in the future, LIPUS is bound to be an efficient and convenient therapeutic method to improve the dental implantation success rate and expand clinical implant indications.

The Attenuating Effect of Low-Intensity Pulsed Ultrasound on Hypoxia-Induced Rat Chondrocyte Damage in TMJ Osteoarthritis Based on TMT Labeling Quantitative Proteomic Analysis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease with a complex and multifactorial etiology. An increased intrajoint pressure or weakened penetration can exacerbate the hypoxic state of the condylar cartilage microenvironment. Our group previously simulated the hypoxic environment of TMJOA in vitro. Low-intensity pulsed ultrasound (LIPUS) stimulation attenuates chondrocyte matrix degradation via a hypoxia-inducible factor (HIF) pathway-associated mechanism, but the mode of action of LIPUS is currently poorly understood. Moreover, most recent studies investigated the pathological mechanisms of osteoarthritis, but no biomarkers have been established for assessing the therapeutic effect of LIPUS on TMJOA with high specificity, which results in a lack of guidance regarding clinical application. Here, tandem mass tag (TMT)-based quantitative proteomic technology was used to comprehensively screen the molecular targets and pathways affected by the action of LIPUS on chondrocytes under hypoxic conditions. A bioinformatic analysis identified 902 and 131 differentially expressed proteins (DEPs) in the <1% oxygen treatment group compared with the control group and in the <1% oxygen + LIPUS stimulation group compared with the <1% oxygen treatment group, respectively. The DEPs were analyzed by gene ontology (GO), KEGG pathway and protein-protein interaction (PPI) network analyses. By acting on extracellular matrix (ECM)-associated proteins, LIPUS increases energy production and activates the FAK signaling pathway to regulate cell biological behaviors. DEPs of interest were selected to verify the reliability of the proteomic results. In addition, this experiment demonstrated that LIPUS could upregulate chondrogenic factors (such as Sox9, Collagen Ⅱ and Aggrecan) and increase the mucin sulfate content. Moreover, LIPUS reduced the hydrolytic degradation of the ECM by decreasing the MMP3/TIMP1 ratio and vascularization by downregulating VEGF. Interestingly, LIPUS improved the migration ability of chondrocytes. In summary, LIPUS can regulate complex biological processes in chondrocytes under hypoxic conditions and alter the expression of many functional proteins, which results in reductions in hypoxia-induced chondrocyte damage. ECM proteins such as thrombospondin4, thrombospondin1, IL1RL1, and tissue inhibitors of metalloproteinase 1 play a central role and can be used as specific biomarkers determining the efficacy of LIPUS and viable clinical therapeutic targets of TMJOA.

Ultrasound is Effective to Treat Temporomandibular Joint Disorder

Background

Temporomandibular joint disorder (TMD) affects millions of people. It is unclear if low intensity ultrasound (US) is effective to treat TMD.

Methods

A total of 160 patients with TMD were enrolled in this study. The subjects were randomized into two groups to receive US therapy or no therapy. Patients in the US group were given US therapy once a day for 5 days per week for 2 consecutive weeks. Before and 4 weeks and 6 months after the treatments, the patients were assessed for pain using visual analog scale (VAS) and the maximum pain-free inter-incisal distance (IID). In addition, mandibular movement (MM), jaw noise (JN), disability index (DI) and craniomandibular index (CMI) were also assessed.

Results

Compared with the patients before the therapy, VAS, IID, MM, JN, DI and CMI in the US group were significantly improved 4 weeks and 6 months after therapy. However, 6 months after the therapy, US group had a recurrence rate of 2.63%.

Conclusion

US therapy can significantly reduce the pain, and improve the functionality of the temporomandibular joint and mouth opening limit for TMD patients, and is therefore recommended for TMD patients.

Evaluating the Effectiveness of Biophysical Methods of Osteogenesis Stimulation: Review

Background. Stimulation of osteogenesis (SO) by biophysical methods has been widely used in practice to accelerate healing or stimulate the healing of fractures with non-unions, since the middle of the XIX century. SO can be carried out by direct current electrostimulation, or indirectly by low-intensity pulsed ultrasound, capacitive electrical coupling stimulation, and pulsed electromagnetic field stimulation. SO simulates natural physiological processes: in the case of electrical stimulation, it changes the electromagnetic potential of damaged cell tissues in a manner similar to normal healing processes, or in the case of low-intensity pulsed ultrasound, it produces weak mechanical effects on the fracture area. SO increases the expression of factors and signaling pathways responsible for tissue regeneration and bone mineralization and ultimately accelerates bone union.The purpose of this review was to present the most up-to-date data from laboratory and clinical studies of the effectiveness of SO.Material and Methods. The results of laboratory studies and the final results of metaanalyses for each of the four SO methods published from 1959 to 2020 in the PubMed, EMBASE, and eLibrary databases are reviewed.Conclusion. The use of SO effectively stimulates the healing of fractures with the correct location of the sensors, compliance with the intensity and time of exposure, as well as the timing of use for certain types of fractures. In case of non-union or delayed union of fractures, spondylodesis, arthrodesis, preference should be given to non-invasive methods of SO. Invasive direct current stimulation can be useful for non-union of long bones, spondylodesis with the risk of developing pseudoarthrosis.

Evaluating the Effectiveness of Biophysical Methods of Osteogenesis Stimulation: Review

Background. Stimulation of osteogenesis (SO) by biophysical methods has been widely used in practice to accelerate healing or stimulate the healing of fractures with non-unions, since the middle of the XIX century. SO can be carried out by direct current electrostimulation, or indirectly by low-intensity pulsed ultrasound, capacitive electrical coupling stimulation, and pulsed electromagnetic field stimulation. SO simulates natural physiological processes: in the case of electrical stimulation, it changes the electromagnetic potential of damaged cell tissues in a manner similar to normal healing processes, or in the case of low-intensity pulsed ultrasound, it produces weak mechanical effects on the fracture area. SO increases the expression of factors and signaling pathways responsible for tissue regeneration and bone mineralization and ultimately accelerates bone union.The purpose of this review was to present the most up-to-date data from laboratory and clinical studies of the effectiveness of SO.Material and Methods. The results of laboratory studies and the final results of metaanalyses for each of the four SO methods published from 1959 to 2020 in the PubMed, EMBASE, and eLibrary databases are reviewed.Conclusion. The use of SO effectively stimulates the healing of fractures with the correct location of the sensors, compliance with the intensity and time of exposure, as well as the timing of use for certain types of fractures. In case of non-union or delayed union of fractures, spondylodesis, arthrodesis, preference should be given to non-invasive methods of SO. Invasive direct current stimulation can be useful for non-union of long bones, spondylodesis with the risk of developing pseudoarthrosis.