Inflammatory cytokine and chemokine expression is associated with heterotopic ossification in high-energy penetrating war injuries

Intersections of Fibrodysplasia Ossificans Progressiva and Traumatic Heterotopic Ossification

Heterotopic ossification (HO) is a debilitating pathology where ectopic bone develops in areas of soft tissue. HO can develop as a consequence of traumatic insult or as a result of dysregulated osteogenic signaling, as in the case of the orphan disease fibrodysplasia ossificans progressiva (FOP). Traumatic HO (tHO) formation is mediated by the complex interplay of signaling between progenitor, inflammatory, and nerve cells, among others, making it a challenging process to understand. Research into the pathogenesis of genetically mediated HO (gHO) in FOP has established a pathway involving uninhibited activin-like kinase 2 receptor (ALK2) signaling that leads to downstream osteogenesis. Current methods of diagnosis and treatment lag behind pre-mature HO detection and progressive HO accumulation, resulting in irreversible decreases in range of motion and chronic pain for patients. As such, it is necessary to draw on advancements made in the study of tHO and gHO to better diagnose, comprehend, prevent, and treat both.

Role of the NF-kB signalling pathway in heterotopic ossification: biological and therapeutic significance

Heterotopic ossification (HO) is a pathological process in which ectopic bone develops in soft tissues within the skeletal system. Endochondral ossification can be divided into the following types of acquired and inherited ossification: traumatic HO (tHO) and fibrodysplasia ossificans progressiva (FOP). Nuclear transcription factor kappa B (NF-κB) signalling is essential during HO. NF-κB signalling can drive initial inflammation through interactions with the NOD-like receptor protein 3 (NLRP3) inflammasome, Sirtuin 1 (SIRT1) and AMP-activated protein kinase (AMPK). In the chondrogenesis stage, NF-κB signalling can promote chondrogenesis through interactions with mechanistic target of rapamycin (mTOR), phosphatidylinositol-3-kinase (PI3K)/AKT (protein kinase B, PKB) and other molecules, including R-spondin 2 (Rspo2) and SRY-box 9 (Sox9). NF-κB expression can modulate osteoblast differentiation by upregulating secreted protein acidic and rich in cysteine (SPARC) and interacting with mTOR signalling, bone morphogenetic protein (BMP) signalling or integrin-mediated signalling under stretch stimulation in the final osteogenic stage. In FOP, mutated ACVR1-induced NF-κB signalling exacerbates inflammation in macrophages and can promote chondrogenesis and osteogenesis in mesenchymal stem cells (MSCs) through interactions with smad signalling and mTOR signalling. This review summarizes the molecular mechanism of NF-κB signalling during HO and highlights potential therapeutics for treating HO.

Classification and Incidence of Heterotopic Ossifications in Relation to NSAID Prophylaxis after Elbow Trauma

Heterotopic ossification (HO) after elbow trauma can be responsible for significant motion restrictions. The study's primary aim was to develop a new X-ray-based classification for HO of the elbow. This retrospective study analyzed elbow injury radiographs from 138 patients aged 6-85 years (mean 45.9 ± 18) who underwent operative treatment. The new classification was applied at 6 weeks, 12 weeks, and 6 months postoperatively. The severity of HO was graded from 0 to 4 and localization was defined as r (radial), p (posterior), u (ulnar) or a (anterior) by two observers. The patients were categorized based on injury location and use of non-steroidal anti-inflammatory drugs (NSAIDs) for HO prophylaxis. The correlations between the generated data sets were analyzed using Chi-square tests (χ2) with a significance level of p < 0.05. The inter- and intraobserver reliability was assessed using Cohen's Kappa. In 50.7% of the evaluated X-rays, the formation of HO could be detected after 12 weeks, and in 60% after 6 months. The analysis showed a significant correlation between the injury's location and the HO's location after 12 weeks (p = 0.003). The use of an NSAID prophylaxis did not show a significant correlation with the severity of HO. The classification showed nearly perfect inter- (κ = 0.951, p < 0.001) and intrareliability (κ = 0.946, p < 0.001) according to the criteria of Landis and Koch. Based on the presented classification, the dimension and localization of HO in the X-ray image can be described in more detail compared to previously established classifications and, thus, can increase the comparability of results across studies.

Inhibition of focal adhesion kinase 2 results in a macrophage polarization shift to M2 which attenuates local and systemic inflammation and reduces heterotopic ossification after polysystem extremity trauma

Introduction

Heterotopic ossification (HO) is a complex pathology often observed in combat injured casualties who have sustained severe, high energy polytraumatic extremity injuries. Once HO has developed, prophylactic therapies are limited outside of surgical excision. Tourniquet-induced ischemia injury (IR) exacerbates trauma-mediated musculoskeletal tissue injury, inflammation, osteogenic progenitor cell development and HO formation. Others have shown that focal adhesion kinase-2 (FAK2) plays a key role in regulating early inflammatory signaling events. Therefore, we hypothesized that targeting FAK2 prophylactically would mitigate extremity trauma induced IR inflammation and HO formation.

Methods

We tested whether the continuous infusion of a FAK2 inhibitor (Defactinib, PF-573228; 6.94 µg/kg/min for 14 days) can mitigate ectopic bone formation (HO) using an established blast-related extremity injury model involving femoral fracture, quadriceps crush injury, three hours of tourniquet-induced limb ischemia, and hindlimb amputation through the fracture site. Tissue inflammation, infiltrating cells, osteogenic progenitor cell content were assessed at POD-7. Micro-computed tomography imaging was used to quantify mature HO at POD-56.

Results

In comparison to vehicle control-treated rats, FAK2 administration resulted in no marked wound healing complications or weight loss. FAK2 treatment decreased HO by 43%. At POD-7, marked reductions in tissue proinflammatory gene expression and assayable osteogenic progenitor cells were measured, albeit no significant changes in expression patterns of angiogenic, chondrogenic and osteogenic genes. At the same timepoint, injured tissue from FAK-treated rats had fewer infiltrating cells. Additionally, gene expression analyses of tissue infiltrating cells resulted in a more measurable shift from an M1 inflammatory to an M2 anti-inflammatory macrophage phenotype in the FAK2 inhibitor-treated group.

Discussion

Our findings suggest that FAK2 inhibition may be a novel strategy to dampen trauma-induced inflammation and attenuate HO in patients at high risk as a consequence of severe musculoskeletal polytrauma.

Bacterial Lipopolysaccharides Exacerbate Neurogenic Heterotopic Ossification Development

Neurogenic heterotopic ossifications (NHO) are heterotopic bones that develop in periarticular muscles after severe central nervous system (CNS) injuries. Several retrospective studies have shown that NHO prevalence is higher in patients who suffer concomitant infections. However, it is unclear whether these infections directly contribute to NHO development or reflect the immunodepression observed in patients with CNS injury. Using our mouse model of NHO induced by spinal cord injury (SCI) between vertebrae T11 to T13 , we demonstrate that lipopolysaccharides (LPS) from gram-negative bacteria exacerbate NHO development in a toll-like receptor-4 (TLR4)-dependent manner, signaling through the TIR-domain-containing adapter-inducing interferon-β (TRIF/TICAM1) adaptor rather than the myeloid differentiation primary response-88 (MYD88) adaptor. We find that T11 to T13 SCI did not significantly alter intestinal integrity nor cause intestinal bacteria translocation or endotoxemia, suggesting that NHO development is not driven by endotoxins from the gut in this model of SCI-induced NHO. Relevant to the human pathology, LPS increased expression of osteoblast markers in cultures of human fibro-adipogenic progenitors isolated from muscles surrounding NHO biopsies. In a case-control retrospective study in patients with traumatic brain injuries, infections with gram-negative Pseudomonas species were significantly associated with NHO development. Together these data suggest a functional association between gram-negative bacterial infections and NHO development and highlights infection management as a key consideration to avoid NHO development in patients. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Systemic inflammation induced from remote extremity trauma is a critical driver of secondary brain injury

Blast exposure, commonly experienced by military personnel, can cause devastating life-threatening polysystem trauma. Despite considerable research efforts, the impact of the systemic inflammatory response after major trauma on secondary brain injury-inflammation is largely unknown. The aim of this study was to identify markers underlying the susceptibility and early onset of neuroinflammation in three rat trauma models: (1) blast overpressure exposure (BOP), (2) complex extremity trauma (CET) involving femur fracture, crush injury, tourniquet-induced ischemia, and transfemoral amputation through the fracture site, and (3) BOP+CET. Six hours post-injury, intact brains were harvested and dissected to obtain biopsies from the prefrontal cortex, striatum, neocortex, hippocampus, amygdala, thalamus, hypothalamus, and cerebellum. Custom low-density microarray datasets were used to identify, interpret and visualize genes significant (p < 0.05 for differential expression [DEGs]; 86 neuroinflammation-associated) using a custom python-based computer program, principal component analysis, heatmaps and volcano plots. Gene set and pathway enrichment analyses of the DEGs was performed using R and STRING for protein-protein interaction (PPI) to identify and explore key genes and signaling networks. Transcript profiles were similar across all regions in naïve brains with similar expression levels involving neurotransmission and transcription functions and undetectable to low-levels of inflammation-related mediators. Trauma-induced neuroinflammation across all anatomical brain regions correlated with injury severity (BOP+CET > CET > BOP). The most pronounced differences in neuroinflammatory-neurodegenerative gene regulation were between blast-associated trauma (BOP, BOP+CET) and CET. Following BOP, there were few DEGs detected amongst all 8 brain regions, most were related to cytokines/chemokines and chemokine receptors, where PPI analysis revealed Il1b as a potential central hub gene. In contrast, CET led to a more excessive and diverse pro-neuroinflammatory reaction in which Il6 was identified as the central hub gene. Analysis of the of the BOP+CET dataset, revealed a more global heightened response (Cxcr2, Il1b, and Il6) as well as the expression of additional functional regulatory networks/hub genes (Ccl2, Ccl3, and Ccl4) which are known to play a critical role in the rapid recruitment and activation of immune cells via chemokine/cytokine signaling. These findings provide a foundation for discerning pathophysiological consequences of acute extremity injury and systemic inflammation following various forms of trauma in the brain.

Association Between Tranexamic Acid Use and Heterotopic Ossification Prevalence After Elbow Trauma Surgery: A Propensity-Score-Matched Cohort Study

BACKGROUND

Heterotopic ossification (HO) is a common complication of elbow trauma that can affect limb mobility. Inflammation is an initiating factor for HO formation. Tranexamic acid (TXA) can reduce the inflammatory response after orthopaedic surgery. However, evidence regarding the effectiveness of TXA use for HO prevention after elbow trauma surgery is lacking.

METHODS

This retrospective observational propensity-score-matched (PSM) cohort study was conducted from July 1, 2019, to June 30, 2021, at the National Orthopedics Clinical Medical Center, Shanghai, People's Republic of China. A total of 640 patients who underwent surgery following elbow trauma were evaluated. The present study excluded patients with an age of <18 years; those with a history of elbow fracture; those with a central nervous system injury, spinal cord injury, burn injury, or destructive injury; and those who had been lost to follow-up. After 1:1 matching on the basis of sex, age, dominant arm, injury type, open injury, comminuted fracture, ipsilateral trauma, time from injury to surgery, and nonsteroidal anti-inflammatory drug use, the TXA group and the no-TXA group comprised 241 patients each.

RESULTS

In the PSM population, the prevalence of HO was 8.71% in the TXA group and 16.18% in the no-TXA group (with rates of 2.07% and 5.80% for clinically important HO, respectively). Logistic regression analyses showed that TXA use was associated with a lower rate of HO (odds ratio [OR], 0.49; 95% CI, 0.28 to 0.86; p = 0.014) than no TXA use, as well as with a lower rate of clinically important HO (OR, 0.34; 95% CI, 0.11 to 0.91; p = 0.044). None of the baseline covariates significantly affected the relationship between TXA use and HO rate (p > 0.05 for all). Sensitivity analyses supported these findings.

CONCLUSIONS

TXA prophylaxis may be an appropriate method for the prevention of HO following elbow trauma.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Inhibition of NF-κB Signaling-Mediated Crosstalk Between Macrophages and Preosteoblasts by Metformin Alleviates Trauma-Induced Heterotopic Ossification

Heterotopic ossification (HO) is a pathological condition that occurs in soft tissues following severe trauma. The exact pathogenesis of HO remains unclear. Studies have shown that inflammation predisposes patients to the development of HO and triggers ectopic bone formation. Macrophages are crucial mediators of inflammation and are involved in HO development. The present study investigated the inhibitory effect and underlying mechanism of metformin on macrophage infiltration and traumatic HO in mice. Our results found that abundant levels of macrophages were recruited to the injury site during early HO progression and that early administration of metformin prevented traumatic HO in mice. Furthermore, we found that metformin attenuated macrophage infiltration and the NF-κB signaling pathway in injured tissue. The monocyte-to-macrophage transition in vitro was suppressed by metformin and this event was mediated by AMPK. Finally, we showed that inflammatory mediator's regulation by macrophages targeted preosteoblasts, leading to elevated BMP signaling, and osteogenic differentiation and driving HO formation, and this effect was blocked after the activation of AMPK in macrophages. Collectively, our study suggests that metformin prevents traumatic HO by inhibiting of NF-κB signaling in macrophages and subsequently attenuating BMP signaling and osteogenic differentiation in preosteoblasts. Therefore, metformin may serve as a therapeutic drug for traumatic HO by targeting NF-κB signaling in macrophages.

Post-traumatic heterotopic ossification in front of the ankle joint for 23 years: A case report and review of literature

BACKGROUND

Heterotopic ossification (HO) refers to the formation of new bone in non-skeletal tissues such as muscles, tendons or other soft tissues. Severe muscle and soft tissue injury often lead to the formation of HO. However, anterior HO of the ankle is rarely reported.

CASE SUMMARY

We report a patient with massive HO in front of the ankle joint for 23 years. In 1998, the patient was injured by a falling object on the right lower extremity, which gradually formed a massive heterotopic bone change in the right calf and dorsum of the foot. The patient did not develop gradual ankle function limitations until nearly 36 mo ago, and underwent resection of HO. Even after 23 years and resection of HO, the ankle joint was still able to move.

CONCLUSION

It is recommended that the orthopedist should be aware of HO and distinguish it from bone tumor.

Development, refinement, and characterization of a nonhuman primate critical care environment

BACKGROUND

Systemic inflammatory response remains a poorly understood cause of morbidity and mortality after traumatic injury. Recent nonhuman primate (NHP) trauma models have been used to characterize the systemic response to trauma, but none have incorporated a critical care phase without the use of general anesthesia. We describe the development of a prolonged critical care environment with sedation and ventilation support, and also report corresponding NHP biologic and inflammatory markers.

METHODS

Eight adult male rhesus macaques underwent ventilation with sedation for 48-96 hours in a critical care setting. Three of these NHPs underwent "sham" procedures as part of trauma control model development. Blood counts, chemistries, coagulation studies, and cytokines/chemokines were collected throughout the study, and histopathologic analysis was conducted at necropsy.

RESULTS

Eight NHPs were intentionally survived and extubated. Three NHPs were euthanized at 72-96 hours without extubation. Transaminitis occurred over the duration of ventilation, but renal function, acid-base status, and hematologic profile remained stable. Chemokine and cytokine analysis were notable for baseline fold-change for Il-6 and Il-1ra (9.7 and 42.7, respectively) that subsequently downtrended throughout the experiment unless clinical respiratory compromise was observed.

CONCLUSIONS

A NHP critical care environment with ventilation support is feasible but requires robust resources. The inflammatory profile of NHPs is not profoundly altered by sedation and mechanical ventilation. NHPs are susceptible to the pulmonary effects of short-term ventilation and demonstrate a similar bioprofile response to ventilator-induced pulmonary pathology. This work has implications for further development of a prolonged care NHP model.

Tourniquet use following blast-associated complex lower limb injury and traumatic amputation promotes end organ dysfunction and amplified heterotopic ossification formation

BACKGROUND

Traumatic heterotopic ossification (tHO) is characterized by ectopic bone formation in extra-skeletal sites leading to impaired wound healing, entrapment of neurovascular structures, pain, and reduced range of motion. HO has become a signature pathology affecting wounded military personnel who have sustained blast-associated traumatic amputations during the recent conflicts in Iraq and Afghanistan and can compound recovery by causing difficulty with prosthesis limb wearing. Tourniquet use to control catastrophic limb hemorrhage prior to surgery has become almost ubiquitous during this time, with the recognition the prolonged use may risk an ischemia reperfusion injury and associated complications. While many factors influence the formation of tHO, the extended use of tourniquets to limit catastrophic hemorrhage during prolonged field care has not been explored.

METHODS

Utilizing an established pre-clinical model of blast-associated complex lower limb injury and traumatic amputation, we evaluated the effects of tourniquet use on tHO formation. Adult male rats were subjected to blast overpressure exposure, femur fracture, and soft tissue crush injury. Pneumatic tourniquet (250-300 mmHg) applied proximal to the injured limb for 150-min was compared to a control group without tourniquet, before a trans-femoral amputation was performed. Outcome measures were volume to tHO formation at 12 weeks and changes in proteomic and genomic markers of early tHO formation between groups.

RESULTS

At 12 weeks, volumetric analysis with microCT imaging revealed a 70% increase in total bone formation (p = 0.007) near the site of injury compared to rats with no tourniquet time in the setting of blast-injuries. Rats subjected to tourniquet usage had increased expression of danger-associated molecular patterns (DAMPs) and end organ damage as early as 6 h and as late as 7 days post injury. The expressions of pro-inflammatory cytokines and chemokines and osteochondrogenic genes using quantitative RT-PCR similarly revealed increased expression as early as 6 h post injury, and these genes along with hypoxia associated genes remained elevated for 7 days compared to no tourniquet use.

CONCLUSION

These findings suggest that tourniquet induced ischemia leads to significant increases in key transcription factors associated with early endochondral bone formation, systemic inflammatory and hypoxia, resulting in increased HO formation.

Metagenomic features of bioburden serve as outcome indicators in combat extremity wounds

Battlefield injury management requires specialized care, and wound infection is a frequent complication. Challenges related to characterizing relevant pathogens further complicates treatment. Applying metagenomics to wounds offers a comprehensive path toward assessing microbial genomic fingerprints and could indicate prognostic variables for future decision support tools. Wound specimens from combat-injured U.S. service members, obtained during surgical debridements before delayed wound closure, were subjected to whole metagenome analysis and targeted enrichment of antimicrobial resistance genes. Results did not indicate a singular, common microbial metagenomic profile for wound failure, instead reflecting a complex microenvironment with varying bioburden diversity across outcomes. Genus-level Pseudomonas detection was associated with wound failure at all surgeries. A logistic regression model was fit to the presence and absence of antimicrobial resistance classes to assess associations with nosocomial pathogens. A. baumannii detection was associated with detection of genomic signatures for resistance to trimethoprim, aminoglycosides, bacitracin, and polymyxin. Machine learning classifiers were applied to identify wound and microbial variables associated with outcome. Feature importance rankings averaged across models indicated the variables with the largest effects on predicting wound outcome, including an increase in P. putida sequence reads. These results describe the microbial genomic determinants in combat wound bioburden and demonstrate metagenomic investigation as a comprehensive tool for providing information toward aiding treatment of combat-related injuries.

Are there really specific risk factors for heterotopic ossifications? A case report of 'non-risk factor' after total hip replacement

Femoral neck fractures are one of the most common fractures in the elderly population. Due to frequent complications of the fixation of these fractures, patients are more and more often eligible for hip replacement surgery. One of the most frequently mentioned postoperative complication is the formation of heterotopic ossification. This case report describes as a 70-year-old male patient that presented with an old hip fracture accompanied by a mild craniocerebral trauma. The patient underwent total cementless hip arthroplasty followed by rehabilitation. At 8 months after surgery, the patient was diagnosed with Brooker IV° heterotopic ossification in the area of the operated hip joint. Due to the persistent pain and complete loss of mobility in the operated joint, computed tomography imaging was performed and the patient was recommended for a revision surgery. The procedure was performed 14 months after the original surgical treatment, resulting in a significant improvement in the range of motion and reduction of pain.

Palovarotene inhibits the NF-κB signaling pathway to prevent heterotopic ossification

Heterotopic ossification (HO) is a common disease characterized by pain, dysfunction, and calcification. The mechanisms underlying HO have not been completely elucidated. Palovarotene, a retinoic acid receptor gamma agonist, significantly inhibits the formation of HO in vivo. However, its specific mechanism of action remains unclear. Therefore, we aimed to evaluate the signaling pathways related to the formation of HO as well as the mechanism of Palovarotene action. We constructed in vitro and in vivo models of HO. Osteogenic differentiation of bone mesenchymal stem cells (BMSCs) was observed by alizarin red and alkaline phosphatase staining assays in vitro. X-ray and hematoxylin-eosin staining were performed in vivo. Western blots and reverse transcription-polymerase chain reaction were performed to determine the levels of osteogenic- and inflammation-related genes. Immunofluorescence and immunocytochemistry were used to assess the levels of p65, the core molecule of the nuclear factor kappa-B (NF-κB) signaling pathway. We demonstrated that, in vitro, under inflammatory stimulation, pathological calcium deposition increased in BMSCs. The levels of osteogenesis- and inflammation-related genes were also upregulated, along with an enhanced expression of p65. Immunofluorescence assays revealed that p65 entered the nucleus, thereby stimulating the downstream effectors of the NF-κB pathway. The above trends were reversed after Palovarotene treatment. In conclusion, the NF-κB signaling pathway played an important role in HO and Palovarotene could alleviate HO by blocking the NF-κB cascade. Our results may provide a theoretical basis for Palovarotene in the treatment of HO. Further studies on the side effects of Palovarotene are warranted in the future.

Wound fluid sampling methods for proteomic studies: A scoping review

Understanding why some wounds are hard to heal is important for improving care and developing more effective treatments. The method of sample collection used is an integral step in the research process and thus may affect the results obtained. The primary objective of this study was to summarise and map the methods currently used to sample wound fluid for protein profiling and analysis. Eligible studies were those that used a sampling method to collect wound fluid from any human wound for analysis of proteins. A search for eligible studies was performed using MEDLINE, Embase and CINAHL Plus in May 2020. All references were screened for eligibility by one reviewer, followed by discussion and consensus with a second reviewer. Quantitative data were mapped and visualised using appropriate software and summarised via a narrative summary. After screening, 280 studies were included in this review. The most commonly used group of wound fluid collection methods were vacuum, drainage or use of other external devices, with surgical wounds being the most common sample source. Other frequently used collection methods were extraction from absorbent materials, collection beneath an occlusive dressing and direct collection of wound fluid. This scoping review highlights the variety of methods used for wound fluid collection. Many studies had small sample sizes and short sample collection periods; these weaknesses have hampered the discovery and validation of novel biomarkers. Future research should aim to assess the reproducibility and feasibility of sampling and analytical methods for use in larger longitudinal studies.

Palovarotene Can Attenuate Heterotopic Ossification Induced by Tendon Stem Cells by Downregulating the Synergistic Effects of Smad and NF-κB Signaling Pathway following Stimulation of the Inflammatory Microenvironment

Heterotopic ossification (HO) is defined as the formation of bone tissues outside the bones, such as in the muscles. Currently, the mechanism of HO is still unclear. Tendon stem cells (TSCs) play important roles in the occurrence and development of HO. The inflammatory microenvironment dominated by macrophages also plays an important role in the course of HO. The commonly used clinical treatment methods, such as nonsteroidal anti-inflammatory drugs and radiotherapy, have relatively large side effects, and more efficient treatment methods are needed in clinical practice. Under physiological conditions, retinoic acid receptor (RAR) signal transduction pathway inhibits osteogenic progenitor cell aggregation and chondrocyte differentiation. We focus on palovarotene, a retinoic acid γ-receptor activator, showing an inhibitory effect on HO mice, but the specific mechanism is still unclear. This study was aimed at exploring the specific molecular mechanism of palovarotene by blocking osteogenic differentiation and HO formation of TSCs in vitro and in vivo in an inflammatory microenvironment. We constructed a coculture model of TCSs and polarized macrophages, as well as overexpression and knockdown models of the Smad signaling pathway of TCSs. In addition, a rat model of HO, which was constructed by Achilles tendon resection, was also established. These models explored the role of inflammatory microenvironment and Smad signaling pathways in the osteogenic differentiation of TSCs which lead to HO, as well as the reversal role played by palovarotene in this process. Our results suggest that, under the stimulation of inflammatory microenvironment and trauma, the injured site was in an inflammatory state, and macrophages were highly concentrated in the injured site. The expression of osteogenic and inflammation-related proteins, as well as Smad proteins, was upregulated. Osteogenic differentiation was performed in TCSs. We also found that TCSs activated Smad and NF-κB signaling pathways, which initiated the formation of HO. Palovarotene inhibited the aggregation of osteogenic progenitor cells and macrophages and attenuated HO by blocking Smad and NF-κB signaling pathways. Therefore, palovarotene may be a novel HO inhibitor, while other drugs or antibodies targeting Smad and NF-κB signaling pathways may also prevent or treat HO. The expressions of Smad5, Id1, P65, and other proteins may predict HO formation.

[Research progress of traumatic heterotopic ossification]

OBJECTIVE

To review and evaluate the research progress of traumatic heterotopic ossification (HO).

METHODS

The domestic and foreign related research literature on traumatic HO was widely consulted, and its etiology, pathogenesis, pathological progress, diagnosis, prevention, and treatment were summarized.

RESULTS

Traumatic HO is often caused by severe trauma such as joint operation, explosion injury, nerve injury, and burn. At present, it is widely believed that the occurrence of traumatic HO is closely related to inflammation and hypoxia. Oral non-steroidal anti-inflammatory drugs and surgery are the main methods to prevent and treat traumatic HO.

CONCLUSION

Nowadays, the pathogenesis of traumatic HO is still unclear, the efficiency of relevant prevention and treatment measures is low, and there is a lack of specific treatment method. In the future, it is necessary to further study the pathogenesis of traumatic HO and find specific prevention and treatment targets.

Macrophages in heterotopic ossification: from mechanisms to therapy

Heterotopic ossification (HO) is the formation of extraskeletal bone in non-osseous tissues. It is caused by an injury that stimulates abnormal tissue healing and regeneration, and inflammation is involved in this process. It is worth noting that macrophages are crucial mediators of inflammation. In this regard, abundant macrophages are recruited to the HO site and contribute to HO progression. Macrophages can acquire different functional phenotypes and promote mesenchymal stem cell (MSC) osteogenic differentiation, chondrogenic differentiation, and angiogenesis by expressing cytokines and other factors such as the transforming growth factor-β1 (TGF-β1), bone morphogenetic protein (BMP), activin A (Act A), oncostatin M (OSM), substance P (SP), neurotrophin-3 (NT-3), and vascular endothelial growth factor (VEGF). In addition, macrophages significantly contribute to the hypoxic microenvironment, which primarily drives HO progression. Thus, these have led to an interest in the role of macrophages in HO by exploring whether HO is a "butterfly effect" event. Heterogeneous macrophages are regarded as the "butterflies" that drive a sequence of events and ultimately promote HO. In this review, we discuss how the recruitment of macrophages contributes to HO progression. In particular, we review the molecular mechanisms through which macrophages participate in MSC osteogenic differentiation, angiogenesis, and the hypoxic microenvironment. Understanding the diverse role of macrophages may unveil potential targets for the prevention and treatment of HO.

NGF-TrkA signaling dictates neural ingrowth and aberrant osteochondral differentiation after soft tissue trauma

Pain is a central feature of soft tissue trauma, which under certain contexts, results in aberrant osteochondral differentiation of tissue-specific stem cells. Here, the role of sensory nerve fibers in this abnormal cell fate decision is investigated using a severe extremity injury model in mice. Soft tissue trauma results in NGF (Nerve growth factor) expression, particularly within perivascular cell types. Consequently, NGF-responsive axonal invasion occurs which precedes osteocartilaginous differentiation. Surgical denervation impedes axonal ingrowth, with significant delays in cartilage and bone formation. Likewise, either deletion of Ngf or two complementary methods to inhibit its receptor TrkA (Tropomyosin receptor kinase A) lead to similar delays in axonal invasion and osteochondral differentiation. Mechanistically, single-cell sequencing suggests a shift from TGFβ to FGF signaling activation among pre-chondrogenic cells after denervation. Finally, analysis of human pathologic specimens and databases confirms the relevance of NGF-TrkA signaling in human disease. In sum, NGF-mediated TrkA-expressing axonal ingrowth drives abnormal osteochondral differentiation after soft tissue trauma. NGF-TrkA signaling inhibition may have dual therapeutic use in soft tissue trauma, both as an analgesic and negative regulator of aberrant stem cell differentiation.

Pharmacological activation of SIRT1 by metformin prevented trauma-induced heterotopic ossification through inhibiting macrophage mediated inflammation

Trauma-induced heterotopic ossification (HO) is the aberrant extra-skeletal bone formation that severely incapacitates patient's daily life. Inflammation is the first stage of this progression, becoming an appealing target of early therapeutic intervention. Metformin, a widely used antidiabetic drug, also poses the therapeutic potential to modulate various inflammatory-related diseases. Therefore, this study aimed to investigate the preventive effect of metformin on trauma-induced HO progression, and unveil the underlying molecular mechanisms. A murine burn/tenotomy model was established to mimic trauma-induced HO in vivo. The anti-inflammation and anti-ossification effects of metformin were evaluated by histological staining and micro-CT. The inhibitory effects of metformin on macrophages activation in vitro were examined by ELISA and qRT-PCR. The underlying molecular mechanisms were further explored by immunofluorescence staining and western-blotting in vivo. Increased macrophages infiltration and inflammatory responses were found at early stage during HO progression. However, metformin dose-dependently attenuated the macrophage-mediated inflammatory responses both in vivo and vitro, which might account for the inhibitory effect of metformin on chondrogenesis and HO formation after trauma. Furthermore, elevated SIRT1 expression and decreased NF-κB p65 acetylation were found in the beneficial effects of metformin. Moreover, similar preventive effects were also found in SRT1720 HCI, a specific SIRT1 activator, while were remarkably reversed after the administration of EX527 (a specific SIRT1 inhibitor) with metformin. Taken together, our results provide a novel evidence that metformin can effectively attenuate trauma-induced HO by mitigating macrophage inflammatory responses through inhibiting NF-κB signaling via SIRT1-dependent mechanisms, which favors future therapeutic investigations for trauma-related disease.

Improved Biocompatible, Flexible Mesh Composites for Implant Applications via Hydroxyapatite Coating with Potential for 3-Dimensional Extracellular Matrix Network and Bone Regeneration

Hydroxyapatite (HA)-coated metals are biocompatible composites, which have potential for various applications for bone replacement and regeneration in the human body. In this study, we proposed the design of biocompatible, flexible composite implants by using a metal mesh as substrate and HA coating as bone regenerative stimulant derived from a simple sol-gel method. Experiments were performed to understand the effect of coating method (dip-coating and drop casting), substrate material (titanium and stainless steel) and substrate mesh characteristics (mesh size, weave pattern) on implant's performance. HA-coated samples were characterized by X-ray diffractometer, transmission electron microscope, field-emission scanning electron microscope, nanoindenter, polarization and electrochemical impedance spectroscopy, and biocompatibility test. Pure or biphasic nanorod HA coating was obtained on mesh substrates with thicknesses varying from 4.0 to 7.9 μm. Different coating procedures and number of layers did not affect crystal structure, shape, or most intense plane reflections of the HA coating. Moduli of elasticity below 18.5 GPa were reported for HA-coated samples, falling within the range of natural skull bone. Coated samples led to at least 90% cell viability and up to 99.5% extracellular matrix coverage into a 3-dimensional network (16.4% to 76.5% higher than bare substrates). Fluorescent imaging showed no antagonistic effect of the coatings on osteogenic differentiation. Finer mesh size enhanced coating coverage and adhesion, but a low number of HA layers was preferable to maintain open mesh areas promoting extracellular matrix formation. Finally, electrochemical behavior studies revealed that, although corrosion protection for HA-coated samples was generally higher than bare samples, galvanic corrosion occurred on some samples. Overall, the results indicated that while HA-coated titanium grade 1 showed the best performance as a potential implant, HA-coated stainless steel 316 with the finest mesh size constitutes an adequate, lower cost alternative.

Quercetin Attenuates Trauma-Induced Heterotopic Ossification by Tuning Immune Cell Infiltration and Related Inflammatory Insult

Heterotopic ossification (HO) is one of the most intractable disorders following musculoskeletal injury and is characterized by the ectopic presence of bone tissue in the soft tissue leading to severe loss of function in the extremities. Recent studies have indicated that immune cell infiltration and inflammation are involved in aberrant bone formation. In this study, we found increased monocyte/macrophage and mast cell accumulation during early HO progression. Macrophage depletion by clodronate liposomes and mast cell stabilization by cromolyn sodium significantly impeded HO formation. Therefore, we proposed that the dietary phytochemical quercetin could also suppress immune cell recruitment and related inflammatory responses to prevent HO. As expected, quercetin inhibited the monocyte-to-macrophage transition, macrophage polarization, and mast cell activation in vitro in a dose-dependent manner. Using a murine burn/tenotomy model, we also demonstrated that quercetin attenuated inflammatory responses and HO in vivo. Furthermore, elevated SIRT1 and decreased acetylated NFκB p65 expression were responsible for the mechanism of quercetin, and the beneficial effects of quercetin were reversed by the SIRT1 antagonist EX527 and mimicked by the SIRT agonist SRT1720. The findings in this study suggest that targeting monocyte/macrophage and mast cell activities may represent an attractive approach for therapeutic intervention of HO and that quercetin may serve as a promising therapeutic candidate for the treatment of trauma-induced HO by modulating SIRT1/NFκB signaling.

High Frequency Spectral Ultrasound Imaging Detects Early Heterotopic Ossification in Rodents

Heterotopic ossification (HO) is a devastating condition in which ectopic bone forms inappropriately in soft tissues following traumatic injuries and orthopedic surgeries as a result of aberrant mesenchymal progenitor cell (MPC) differentiation. HO leads to chronic pain, decreased range of motion, and an overall decrease in quality of life. While several treatments have shown promise in animal models, all must be given during early stages of formation. Methods for early determination of whether and where endochondral ossification/soft tissue mineralization (HO anlagen) develop are lacking. At-risk patients are not identified sufficiently early in the process of MPC differentiation and soft tissue endochondral ossification for potential treatments to be effective. Hence, a critical need exists to develop technologies capable of detecting HO anlagen soon after trauma, when treatments are most effective. In this study, we investigate high frequency spectral ultrasound imaging (SUSI) as a noninvasive strategy to identify HO anlagen at early time points after injury. We show that by determining quantitative parameters based on tissue organization and structure, SUSI identifies HO anlagen as early as 1-week postinjury in a mouse model of burn/tenotomy and 3 days postinjury in a rat model of blast/amputation. We analyze single cell RNA sequencing profiles of the MPCs responsible for HO formation and show that the early tissue changes detected by SUSI match chondrogenic and osteogenic gene expression in this population. SUSI identifies sites of soft tissue endochondral ossification at early stages of HO formation so that effective intervention can be targeted when and where it is needed following trauma-induced injury. Furthermore, we characterize the chondrogenic to osteogenic transition that occurs in the MPCs during HO formation and correlate gene expression to SUSI detection of the HO anlagen.

Alarming Cargo: The Role of Exosomes in Trauma-Induced Inflammation

Severe polytraumatic injury initiates a robust immune response. Broad immune dysfunction in patients with such injuries has been well-documented; however, early biomarkers of immune dysfunction post-injury, which are critical for comprehensive intervention and can predict the clinical course of patients, have not been reported. Current circulating markers such as IL-6 and IL-10 are broad, non-specific, and lag behind the clinical course of patients. General blockade of the inflammatory response is detrimental to patients, as a certain degree of regulated inflammation is critical and necessary following trauma. Exosomes, small membrane-bound extracellular vesicles, found in a variety of biofluids, carry within them a complex functional cargo, comprised of coding and non-coding RNAs, proteins, and metabolites. Composition of circulating exosomal cargo is modulated by changes in the intra- and extracellular microenvironment, thereby serving as a homeostasis sensor. With its extensively documented involvement in immune regulation in multiple pathologies, study of exosomal cargo in polytrauma patients can provide critical insights on trauma-specific, temporal immune dysregulation, with tremendous potential to serve as unique biomarkers and therapeutic targets for timely and precise intervention.

Firearms-related skeletal muscle trauma: pathophysiology and novel approaches for regeneration

One major cause of traumatic injury is firearm-related wounds (i.e., ballistic trauma), common in both civilian and military populations, which is increasing in prevalence and has serious long-term health and socioeconomic consequences worldwide. Common primary injuries of ballistic trauma include soft-tissue damage and loss, haemorrhage, bone fracture, and pain. The majority of injuries are of musculoskeletal origin and located in the extremities, such that skeletal muscle offers a major therapeutic target to aid recovery and return to normal daily activities. However, the underlying pathophysiology of skeletal muscle ballistic trauma remains poorly understood, with limited evidence-based treatment options. As such, this review will address the topic of firearm-related skeletal muscle injury and regeneration. We first introduce trauma ballistics and the immediate injury of skeletal muscle, followed by detailed coverage of the underlying biological mechanisms involved in regulating skeletal muscle dysfunction following injury, with a specific focus on the processes of muscle regeneration, muscle wasting and vascular impairments. Finally, we evaluate novel approaches for minimising muscle damage and enhancing muscle regeneration after ballistic trauma, which may have important relevance for primary care in victims of violence.

Activin A promotes the development of acquired heterotopic ossification and is an effective target for disease attenuation in mice

Heterotopic ossification (HO) is a common, potentially debilitating pathology that is instigated by inflammation caused by tissue damage or other insults, which is followed by chondrogenesis, osteogenesis, and extraskeletal bone accumulation. Current remedies are not very effective and have side effects, including the risk of triggering additional HO. The TGF-β family member activin A is produced by activated macrophages and other inflammatory cells and stimulates the intracellular effectors SMAD2 and SMAD3 (SMAD2/3). Because HO starts with inflammation and because SMAD2/3 activation is chondrogenic, we tested whether activin A stimulated HO development. Using mouse models of acquired intramuscular and subdermal HO, we found that blockage of endogenous activin A by a systemically administered neutralizing antibody reduced HO development and bone accumulation. Single-cell RNA-seq analysis and developmental trajectories showed that the antibody treatment reduced the recruitment of Sox9+ skeletal progenitors, many of which also expressed the gene encoding activin A (Inhba), to HO sites. Gain-of-function assays showed that activin A enhanced the chondrogenic differentiation of progenitor cells through SMAD2/3 signaling, and inclusion of activin A in HO-inducing implants enhanced HO development in vivo. Together, our data reveal that activin A is a critical upstream signaling stimulator of acquired HO in mice and could represent an effective therapeutic target against forms of this pathology in patients.

A review of the biomarkers and in vivo models for the diagnosis and treatment of heterotopic ossification following blast and trauma-induced injuries

Heterotopic ossification (HO) is the process of de novo bone formation in non-osseous tissues. HO can occur following trauma and burns and over 60% of military personnel with blast-associated amputations develop HO. This rate is far higher than in other trauma-induced HO development. This suggests that the blast effect itself is a major contributing factor, but the pathway triggering HO following blast injury specifically is not yet fully identified. Also, because of the difficulty of studying the disease using clinical data, the only sources remain the relevant in vivo models. The aim of this paper is first to review the key biomarkers and signalling pathways identified in trauma and blast induced HO in order to summarize the molecular mechanisms underlying HO development, and second to review the blast injury in vivo models developed. The literature derived from trauma-induced HO suggests that inflammatory cytokines play a key role directing different progenitor cells to transform into an osteogenic class contributing to the development of the disease. This highlights the importance of identifying the downstream biomarkers under specific signalling pathways which might trigger similar stimuli in blast to those of trauma induced formation of ectopic bone in the tissues surrounding the site of the injury. The lack of information in the literature regarding the exact biomarkers leading to blast associated HO is hampering the design of specific therapeutics. The majority of existing blast injury in vivo models do not fully replicate the combat scenario in terms of blast, fracture and amputation; these three usually happen in one insult. Hence, this paper highlights the need to replicate the full effect of the blast in preclinical models to better understand the mechanism of blast induced HO development and to enable the design of a specific therapeutic to supress the formation of ectopic bone.

Mechanism of traumatic heterotopic ossification: In search of injury-induced osteogenic factors

Heterotopic ossification (HO) is a pathological condition of abnormal bone formation in soft tissue. Three factors have been proposed as required to induce HO: (a) osteogenic precursor cells, (b) osteoinductive agents and (c) an osteoconductive environment. Since Urist's landmark discovery of bone induction in skeletal muscle tissue by demineralized bone matrix, it is generally believed that skeletal muscle itself is a conductive environment for osteogenesis and that resident progenitor cells in skeletal muscle are capable of differentiating into osteoblast to form bone. However, little is known about the naturally occurring osteoinductive agents that triggered this osteogenic response in the first place. This article provides a review of the emerging findings regarding distinct types of HO to summarize the current understanding of HO mechanisms, with special attention to the osteogenic factors that are induced following injury. Specifically, we hypothesize that muscle injury‐induced up‐regulation of local bone morphogenetic protein‐7 (BMP‐7) level, combined with glucocorticoid excess‐induced down‐regulation of circulating transforming growth factor‐β1 (TGF‐β1) level, could be an important causative mechanism of traumatic HO formation.

Proteomic characterization of a trauma-based rat model of heterotopic ossification identifies interactive signaling networks as potential therapeutic targets

Heterotopic ossification (HO) is the formation of ectopic bone in soft tissues observed in patients following blast injuries, orthopedic or head trauma, burns, or in the context of inborn mutations of genes involved in osteogenesis. There is no universally accepted therapy for HO. This study has used global unbiased mass spectrometry proteomic approaches, validated by western immunoblots, to interrogate skeletal muscle tissues obtained from a highly reproducible rat model of trauma induced HO. During early the phase of HO development, statistically significant modulation of proteins within the following pathways was identified: coagulation, cyclic AMP, extracellular matrix, immunity/inflammation, NADH metabolism, TGFβ. These metabolic proteins and pathways have the potential to serve as diagnostic, prognostic, and therapeutic targets for this devastating orthopedic condition that has considerable impact on the patient's quality of life. Furthermore, the findings confirm and extend previous in vitro stromal/stem cell and clinical studies from the field. SIGNIFICANCE: This study confirms and extends the field's understanding of the protein pathways that are modulated in a rat model of trauma induced heterotopic ossification. The identification of specific proteins such as the AP1 transcription factor as well as protein families such as the complement/coagulation pathway and serine protease inhibitors as biomarkers have potential clinical translational value. These outcomes have relevance to the physiological and pathological mineralization processes contributing to the recovery of orthopedic trauma patients.

Macrophage-derived neurotrophin-3 promotes heterotopic ossification in rats

Heterotopic ossification (HO) is a debilitating condition that results from traumatic injuries or genetic diseases, for which the underlying mechanisms remain unclear. Recently, we have demonstrated the expression of neurotrophin-3 (NT-3) and its role in promoting HO formation via mediating endothelial-mesenchymal transition (EndMT) of vascular endothelial cells. The current study investigated the role of NT-3 on the surrounding mesenchymal cells and its potential origin throughout HO formation at injured Achilles tendons in rats. We used an Achilles tenotomy to induce HO formation in vivo and cultured primary tendon-derived stem cells (TDSCs) to investigate the underlying mechanisms mediating the osteogenesis in vitro. Furthermore, RAW264.7 cells were employed to identify the origin of NT-3. The mRNA levels of NGF, BDNF, NT-3, and NT-4 and their tyrosine protein kinase (Trk) receptors as well as p75 receptor were elevated at injury sites. NT-3 and TrkC showed the highest induction. Neutralization of the NT-3-induced effects by the pan-Trk inhibitor GNF5837 reduced the expression of bone/cartilage-related genes while injection of NT-3 promoted HO formation with elevated mRNA of bone/cartilage-related markers at injured sites. In vitro, NT-3 accelerated osteogenic differentiation and mineralization of TDSCs through activation of the ERK1/2 and PI3K/Akt signaling pathways. Moreover, the colocalization of NT-3 and macrophages, including M1 and M2 macrophages, was observed in injured sites throughout HO formation, and in vitro studies demonstrated that activated macrophages mediated the secretion of NT-3. In addition, an increasing concentration of serum or supernatant NT-3 was observed both in vivo and in vitro. Depletion of macrophages with clodronate-loaded liposomes reduced HO formation as well as secretion and mRNA expression of NT-3. Our study suggests that macrophage-derived NT-3 may promote HO formation and osteogenesis of TDSCs via the ERK1/2 and PI3K/Akt signaling pathways, which may provide new insights for the therapeutic directions of HO in the future.

Both Human Hematoma Punctured from Pelvic Fractures and Serum Increase Muscle Resident Stem Cells Response to BMP9: A Multivariate Statistical Approach

Hematoma and skeletal muscles play a crucial role in bone fracture healing. The muscle resident mesenchymal stromal cells (mrSCs) can promote bone formation by differentiating into osteoblasts upon treatment by bone morphogenetic proteins (BMP), such as BMP9. However, the influence of hematoma fracture extracts (Hema) on human mrSC (hmrSC) response to BMP9 is still unknown. We therefore determined the influence of Hema, human healthy serum (HH), and fetal bovine serum (FBS, control) on BMP9-induced osteoblast commitment of hmrSC by measuring alkaline phosphatase activity. Multiplex assays of 90 cytokines were performed to characterize HH and Hema composition and allow their classification by a multivariate statistical approach depending on their expression levels. We confirmed that BMP9 had a greater effect on osteoblastic differentiation of hmrSCs than BMP2 in presence of FBS. The hmrSCs response to BMP9 was enhanced by both Hema and HH, even though several cytokines were upregulated (IL-6, IL-8, MCP-1, VEGF-A and osteopontin), downregulated (BMP9, PDGF) or similar (TNF-alpha) in Hema compared with HH. Thus, hematoma may potentiate BMP9-induced osteogenic differentiation of hmrSCs during bone fracture healing. The multivariate statistical analyses will help to identify the cytokines involved in such phenomenon leading to normal or pathological bone healing.

Heterotopic ossification: a preventable case of gossypiboma in spinal cord injury

OBJECTIVE

Heterotopic ossification is the formation of ectopic bone in soft tissues. It has three established aetiologies: genetic, traumatic and neurogenic. A gossypiboma is defined as a retained foreign body, such as a mass or sponge, usually after a surgical procedure. In this article, we present a unique, preventable case of a patient admitted for newly developed heterotopic ossification in the gluteus maximus muscle caused by a retained piece of foam from negative pressure wound therapy (NPWT). The heterotopic ossification lesion, together with the retained foreign body, was completely excised and reconstructed using a posterior thigh fasciocutaneous advancement flap. This is the first reported case of heterotopic ossification caused by a retained foreign body and may be helpful to better understanding of the aetiology of heterotopic ossification.

Osteoimmunology: A Current Update of the Interplay Between Bone and the Immune System

Immunology, already a discipline in its own right, has become a major part of many different medical fields. However, its relationship to orthopedics and trauma surgery has unfortunately, and perhaps unjustly, been developing rather slowly. Discoveries in recent years have emphasized the immense breadth of communication and connection between both systems and, importantly, the highly promising therapeutic opportunities. Recent discoveries of factors originally assigned to the immune system have now also been shown to have a significant impact on bone health and disease, which has greatly changed how we approach treatment of bone pathologies. In case of bone fracture, immune cells, especially macrophages, are present throughout the whole healing process, assure defense against pathogens and discharge a complex variety of effectors to regulate bone modeling. In rheumatoid arthritis and osteoporosis, the immune system contributes to the formation of the pathological and chronic conditions. Fascinatingly, prosthesis failure is not at all solely a mechanical problem of improper strain but works in conjunction with an active contribution of the immune system as a reaction to irritant debris from material wear. Unraveling conjoined mechanisms of the immune and osseous systems heralds therapeutic possibilities for ailments of both. Contemplation of the bone as merely an unchanging support pillar is outdated and obsolete. Instead it is mandatory that this highly diverse network be incorporated in our understanding of the immune system and hematopoiesis.

Is fibrodysplasia ossificans progressiva an interleukin-1 driven auto-inflammatory syndrome?

BACKGROUND

Fibrodysplasia ossificans progressiva (FOP) is the most catastrophic form of heterotopic ossification, due to ongoing intracellular signaling through the bone morphogenic protein pathway. The paroxysmal appearance of inflammatory lumps and elevated inflammatory markers during flares, suggest that FOP is an auto-inflammatory disease. Based on evidence, demonstrating a role for interleukin-1β (IL-1β) in other forms of heterotopic ossification, we hypothesized that treating FOP patients with anti-IL-1 agents could help lower the rate of FOP paroxysms and/or limit the symptoms and residual lesions.

CASE PRESENTATION

A 13.5-year-old Arab boy was diagnosed with FOP. Treatment with anti-inflammatory drugs did not change the disease course. New lumps appeared in a rate of approximately one every 8 days. Treatment with the anti-IL-1 agents anakinra and canakinumab resulted in significantly lower rate of paroxysms (every 22-25 days, of which almost all involved only 2 existing lumps), as well as shorter duration. High levels of IL-1β were found in the patient's plasma samples, collected during a paroxysm that appeared 8 weeks after the last canakinumab dose. In contrast, IL-1β plasma levels were undetectable in the previous three plasma samples, obtained while he was treated with anti-IL-1 agents.

CONCLUSIONS

Our data demonstrate the efficacy of anti-IL-1 agents in the treatment of a patient with FOP. Results showing the marked increase in IL-1β plasma levels during a paroxysm support a role for IL-1β in the pathogenesis of FOP and further provide the rationale for the use of anti-IL-1 agents in FOP treatment.

Inflammation in Fibrodysplasia Ossificans Progressiva and Other Forms of Heterotopic Ossification

PURPOSE OF REVIEW

Heterotopic ossification (HO) is associated with inflammation. The goal of this review is to examine recent findings on the roles of inflammation and the immune system in HO. We examine how inflammation changes in fibrodysplasia ossificans progressiva, in traumatic HO, and in other clinical conditions of HO. We also discuss how inflammation may be a target for treating HO.

RECENT FINDINGS

Both genetic and acquired forms of HO show similarities in their inflammatory cell types and signaling pathways. These include macrophages, mast cells, and adaptive immune cells, along with hypoxia signaling pathways, mesenchymal stem cell differentiation signaling pathways, vascular signaling pathways, and inflammatory cytokines. Because there are common inflammatory mediators across various types of HO, these mediators may serve as common targets for blocking HO. Future research may focus on identifying new inflammatory targets and testing combinatorial therapies based on these results.

Investigating the incidence and magnitude of heterotopic ossification with and without joints involvement in patients with a limb fracture and mild traumatic brain injury

Objectives

This study seeks to evaluate the incidence rate of heterotopic ossification (HO) formation in patients afflicted by an isolated limb fracture (ILF) and a concomitant mild traumatic brain injury (mTBI).

Methods

The current study is an observational study including ILF patients with or without a concomitant mTBI recruited from an orthopedic clinic of a Level 1 Trauma Hospital. Patients were diagnosed with a mTBI according to the American Congress of Rehabilitation Medicine (ACRM) criteria. Radiographs taken on average 3 months post-trauma were analyzed separately by two distinct specialists for the presence of HO proximally to the fracture site (joints or extra joints). Both raters referred to Brooker's and Della's Valle's classification to establish signs of HO. First, analyses were conducted for the full sample. Secondly, a matched cohort was used in order to control for specific factors, namely age, sex, type of injury, and time elapsed between the accident and the analyzed radiograph.

Results

The full sample included a total of 183 patients with an ILF (94 females; 47.5 years old), of which 50 had a concomitant mTBI and 133 without. Radiographic evidence of HO was significantly higher in patients with an ILF and a mTBI compared to ILF patients (X² = 6.50; p = 0.01). The matched cohort consisted of 94 participants (i.e.; 47 patients from the ILF + mTBI group and 47 patients from the ILF group). Again, ILF + mTBI patients presented significantly higher rates of HO signs in comparison to ILF patients (X² = 3.69; p = 0.04). Presence of HO was associated with prolonged delays to return to work (RTW) only in ILF + mTBI patients (F = 4.055; p = 0.05) but not in ILF patients (F = 0.823; p = 0.37).

Conclusions

Study findings suggest that rates of HO are significantly higher proximally to fracture sites when ILF patients sustain a concomitant mTBI, even after controlling for factors known to influence HO. Moreover, results show that HO is associated with a prolonged RTW only in ILF patients with a concomitant mTBI but not in ILF-only patients. The impact of mTBI on HO formation warrants further attention to detect early signs of HO, to identify shared physiopathological mechanisms and, ultimately, to design targeted therapies.

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Rates of HO are significantly higher in patients with a fracture and a mTBI compared to patients with a fracture only.

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Factors such as sex, age, joint involvement, and surgical procedures were unrelated to the detection of signs of HO

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Presence of HO negatively impacted RTW delays in patients with a concomitant mTBI

Inhibition of Nf-ҝb prevents trauma-induced heterotopic ossification in rat model

PURPOSE

To investigate the pathogenesis and find a better prophylactic method of acquired heterotopic ossification (HO).

MATERIALS AND METHODS

In the first part, we designed the brain-traumatic/burn/tenotomy rat model and testified its efficacy as HO model. 44 rats were randomly divided into experimental group and control group. After operation, the bilateral tendons of 2 rats were collected at the 2^nd, 3^rd, 4^th, 6^th, 8^th, and 10^th weeks to determine the expression levels of p65. Additionally, the remaining rats were exposed to X-Ray examination at the 10th week. In the second part, 124 rats were randomly divided into four groups based on the administration dosage of Ammonium pyrrolidinedithiocarbamate (PDTC). Then, three rats of each group were euthanized every week in the first seven weeks to collect tendon to detect the expression levels of p65 by qRT-PCR and Western Blot. The remaining rats were exposed to X-Ray examination at the 10th week to assess the size of HO before being euthanized for HE staining.

RESULTS

The success rate of Brain-traumatic/Burn/Tenotomy model was 100%. Pharmacologic inhibition of Nf-ҝb signaling pathway by PDTC could significantly reduce the expression levels of p53 and the size of HO, and the reduction was most significant in the 0.6mg dosage group.

CONCLUSIONS

Brain-traumatic/Burn/Tenotomy model was highly reliable HO model. Inhibition of Nf-ҝb signaling pathway by PDTC could significantly reduce HO formation, and the most effective concentration was 6 mg/ml for local injection.

Heterotopic Ossification: A Comprehensive Review

Heterotopic ossification (HO) is a diverse pathologic process, defined as the formation of extraskeletal bone in muscle and soft tissues. HO can be conceptualized as a tissue repair process gone awry and is a common complication of trauma and surgery. This comprehensive review seeks to synthesize the clinical, pathoetiologic, and basic biologic features of HO, including nongenetic and genetic forms. First, the clinical features, radiographic appearance, histopathologic diagnosis, and current methods of treatment are discussed. Next, current concepts regarding the mechanistic bases for HO are discussed, including the putative cell types responsible for HO formation, the inflammatory milieu and other prerequisite “niche” factors for HO initiation and propagation, and currently available animal models for the study of HO of this common and potentially devastating condition. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Demethylation of ITGAV accelerates osteogenic differentiation in a blast-induced heterotopic ossification in vitro cell culture model

Trauma-induced heterotopic ossification is an intriguing phenomenon involving the inappropriate ossification of soft tissues within the body such as the muscle and ligaments. This inappropriate formation of bone is highly prevalent in those affected by blast injuries. Here, we developed a simplified cell culture model to evaluate the molecular events involved in heterotopic ossification onset that arise from the shock wave component of the disease. We exposed three subtypes of human mesenchymal cells in vitro to a single, high-energy shock wave and observed increased transcription in the osteogenic master regulators, Runx2 and Dlx5, and significantly accelerated cell mineralisation. Reduced representation bisulfite sequencing revealed that the shock wave altered methylation of gene promoters, leading to opposing changes in gene expression. Using a drug to target ITGAV, whose expression was perturbed by the shock wave, we found that we could abrogate the deposition of mineral in our model. These findings show how new therapeutics for the treatment of heterotopic ossification can be identified using cell culture models.

NF-κB/MAPK activation underlies ACVR1-mediated inflammation in human heterotopic ossification

BACKGROUND

Inflammation helps regulate normal growth and tissue repair. Although bone morphogenetic proteins (BMPs) and inflammation are known contributors to abnormal bone formation, how these pathways interact in ossification remains unclear.

METHODS

We examined this potential link in patients with fibrodysplasia ossificans progressiva (FOP), a genetic condition of progressive heterotopic ossification caused by activating mutations in the Activin A type I receptor (ACVR1/ALK2). FOP patients show exquisite sensitivity to trauma, suggesting that BMP pathway activation may alter immune responses. We studied primary blood, monocyte, and macrophage samples from control and FOP subjects using multiplex cytokine, gene expression, and protein analyses; examined CD14+ primary monocyte and macrophage responses to TLR ligands; and assayed BMP, TGF-β activated kinase 1 (TAK1), and NF-κB pathways.

RESULTS

FOP subjects at baseline without clinically evident heterotopic ossification showed increased serum IL-3, IL-7, IL-8, and IL-10. CD14+ primary monocytes treated with the TLR4 activator LPS showed increased CCL5, CCR7, and CXCL10; abnormal cytokine/chemokine secretion; and prolonged activation of the NF-κB pathway. FOP macrophages derived from primary monocytes also showed abnormal cytokine/chemokine secretion, increased TGF-β production, and p38MAPK activation. Surprisingly, SMAD phosphorylation was not significantly changed in the FOP monocytes/macrophages.

CONCLUSIONS

Abnormal ACVR1 activity causes a proinflammatory state via increased NF-κB and p38MAPK activity. Similar changes may contribute to other types of heterotopic ossification, such as in scleroderma and dermatomyositis; after trauma; or with recombinant BMP-induced bone fusion. Our findings suggest that chronic antiinflammatory treatment may be useful for heterotopic ossification.

Primary Pulmonary Thrombus in Combat Casualties: Is Treatment Necessary?

The objective of this study was to describe the natural history of primary pulmonary thrombus (PPT) in combat casualties. This was a retrospective study of casualties treated at a major military treatment facility from 2010 to 2012. Patients with a downrange chest CTwere included. CTs were reviewed by two independent, blinded radiologists to confirm PPTon initial imaging. Follow-up CTs, if obtained, were also independently reviewed to determine the extent of clot burden. Two hundred and forty-nine casualties with a downrange, acceptable quality chest CT were included. 9 per cent (23/249) of patients sustained PPT. Thirty nine per cent (9/23) were initially treated with therapeutic anticoagulation (AC). Conversely, 61 per cent (14/23) arrived to our military treatment facility without AC. Seven arriving without AC-developed pulmonary symptoms during their hospitalization and had interval chest CTs. Of those, three had no evidence of pulmonary thrombus. The other four had subsegmental filling defects and three were started AC whereas one had an IVC (Inferior Vena Cava) filter inserted. In total, 11/23 (48%) PPT patients were managed without AC and discharged without complications. This is the first study attempting to look at PPT natural history. There were no adverse sequelae from managing PPT without AC. Further studies are warranted to further characterize PPT.

Trauma induced heterotopic ossification patient serum alters mitogen activated protein kinase signaling in adipose stem cells

Post-traumatic heterotopic ossification (HO) is the formation of ectopic bone in non-osseous structures following injury. The precise mechanism for bone development following trauma is unknown; however, early onset of HO may involve the production of pro-osteogenic serum factors. Here we evaluated serum from a cohort of civilian and military patients post trauma to determine early induction gene signatures in orthopaedic trauma induced HO. To test this, human adipose derived stromal/stem cells (hASCs) were stimulated with human serum from patients who developed HO following trauma and evaluated for a gene panel with qPCR. Pathway gene analysis ontology revealed that hASCs stimulated with serum from patients who developed HO had altered gene expression in the activator protein 1 (AP1) and AP1 transcriptional targets pathways. Notably, there was a significant repression in FOS gene expression in hASCs treated with serum from individuals with HO. Furthermore, the mitogen-activated protein kinase (MAPK) signaling pathway was activated in hASCs following serum exposure from individuals with HO. Serum from both military and civilian patients with trauma induced HO had elevated downstream genes associated with the MAPK pathways. Stimulation of hASCs with known regulators of osteogenesis (BMP2, IL6, Forskolin, and WNT3A) failed to recapitulate the gene signature observed in hASCs following serum stimulation, suggesting non-canonical mechanisms for gene regulation in trauma induced HO. These findings provide new insight for the development of HO and support ongoing work linking the systemic response to injury with wound specific outcomes.

Palovarotene inhibits connective tissue progenitor cell proliferation in a rat model of combat-related heterotopic ossification

Heterotopic ossification (HO) develops in the extremities of wounded service members and is common in the setting of high-energy penetrating injuries and blast-related amputations. No safe and effective prophylaxis modality has been identified for this patient population. Palovarotene has been shown to reduce bone formation in traumatic and genetic models of HO. The purpose of this study was to determine the effects of Palovarotene on inflammation, progenitor cell proliferation, and gene expression following a blast-related amputation in a rodent model (n = 72 animals), as well as the ability of Raman spectroscopy to detect early HO before radiographic changes are present. Treatment with Palovarotene was found to dampen the systemic inflammatory response including the cytokines IL-6 (p = 0.01), TNF-α (p = 0.001), and IFN-γ (p = 0.03) as well as the local inflammatory response via a 76% reduction in the cellular infiltration at post-operative day (POD)-7 (p = 0.03). Palovarotene decreased osteogenic connective tissue progenitor (CTP-O) colonies by as much as 98% both in vitro (p = 0.04) and in vivo (p = 0.01). Palovarotene treated animals exhibited significantly decreased expression of osteo- and chondrogenic genes by POD-7, including BMP4 (p = 0.02). Finally, Raman spectroscopy was able to detect differences between the two groups by POD-1 (p < 0.001). These results indicate that Palovarotene inhibits traumatic HO formation through multiple inter-related mechanisms including anti-inflammatory, anti-proliferative, and gene expression modulation. Further, that Raman spectroscopy is able to detect markers of early HO formation before it becomes radiographically evident, which could facilitate earlier diagnosis and treatment. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1135-1144, 2018.

Post-Traumatic Heterotopic Ossification: An Old Problem in Need of New Solutions

Heterotopic ossification (HO) is the formation of pathological bone in ectopic sites and it can have serious consequences for functional outcomes. For many years, its main clinical relevance was as a rare complication of elective joint arthroplasty or CNS injury and a number of prophylaxes were developed to mitigate against it in these settings. As a consequence of changes in patterns of wounding and survival in conflicts since the turn of the century, post-traumatic HO has become much more common and case severity has increased. It represents one of the main barriers to rehabilitation in a large cohort of combat-injured patients. However, extant prophylaxes have not been shown to be effective or appropriate in this patient cohort. In addition, the lack of reliable early detection or means of predicting which patients will develop HO is another barrier to effective prevention. This review examines the current state of understanding of post-traumatic HO including the historical context, epidemiology, pathophysiology, clinical issues, currently prophylaxis and detection, management, and potential future approaches. Our aims are to highlight the current lack of effective means of early detection and prevention of HO after major trauma and to stimulate research into novel solutions to this challenging problem. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1061-1068, 2018.

Heterotopic ossification and lessons learned from fifteen years at war: A review of therapy, novel research, and future directions for military and civilian orthopaedic trauma

Heterotopic ossification, the formation of bone in soft tissues, is a common complication of the high-energy extremity trauma sustained in modern armed conflict. In the past 15years, military treatment facilities and aligned laboratories have been in a unique position to study and treat this process due to the high volume of patients with these injuries secondary to blast trauma. The devastating nature of these wounds has limited traditional therapeutic options, necessitating alternative solutions to prophylaxis and initial treatment producing substantial advances in modeling, prophylaxis, detection, and therapy. Specific developments include establishment of an animal model that reproduces the systemic and local tissue injury of blast injuries, the use of molecular assays and predictive modeling in clinical decision making, advances in early detection including Raman spectroscopy, and investigation of prophylactic and therapeutic pharmacotherapy targeting the molecular pathways of aberrant bone formation. In this review article, we will present the literature to date, ongoing studies, and future directions for investigation of heterotopic ossification, with a focus on military-specific research.