Histopathology of periarticular non-hereditary heterotopic ossification

Fulminant Heterotopic Ossification of the Lower Extremity After Gunshot Injury and Blunt Trauma: A Case Report

Traumatic heterotopic ossification (HO) of the lower extremity is relatively rare but is of major importance in clinical practice. They are defined as posttraumatic abnormal formations of bone within soft tissue outside of the skeletal system. This article describes the clinical case of a 31-year-old male patient who suffered 2 traumatic events within 12 months-a gunshot wound in the lumbar spine/gluteal region followed by a severe traumatic brain injury with intracranial hemorrhage in a traffic accident as a pedestrian. Clinically, the patient was bedridden because of complete stiffening of the lumbar spine, both hip joints, and the left knee joint. After preoperative diagnosis, 3 surgical ablations of the HO were performed on both the hip joints and the left knee joint. In addition, physiotherapeutic exercise, postoperative nonsteroidal anti-inflammatory drug administration (25 mg of indomethazine for 6 weeks, 3 times a day), and perioperative radiation with 7 Gy for each operation were advised. After 4 years of follow-up, the patient showed significant improvement. In HO treatment, prophylactic local radiotherapy (pre- and postoperative radiation with a local single dose of 7 Gy) and postoperative administration of nonsteroidal anti-inflammatory drugs are often recommended. For therapeutic purposes, surgical resection is still indicated for pronounced cases.

Cell Senescence in Heterotopic Ossification

The formation of bone outside the normal skeleton, or heterotopic ossification (HO), occurs through genetic and acquired mechanisms. Fibrodysplasia ossificans progressiva (FOP), the most devastating genetic condition of HO, is due to mutations in the ACVR1/ALK2 gene and is relentlessly progressive. Acquired HO is mostly precipitated by injury or orthopedic surgical procedures but can also be associated with certain conditions related to aging. Cellular senescence is a hallmark of aging and thought to be a tumor-suppressive mechanism with characteristic features such as irreversible growth arrest, apoptosis resistance, and an inflammatory senescence-associated secretory phenotype (SASP). Here, we review possible roles for cellular senescence in HO and how targeting senescent cells may provide new therapeutic approaches to both FOP and acquired forms of HO.

Inflammation-Responsive Hydrogel Spray for Synergistic Prevention of Traumatic Heterotopic Ossification via Dual-Homeostatic Modulation Strategy

Traumatic heterotopic ossification (THO) represents one of the most prominent contributors to post-traumatic joint dysfunction, which currently lacks an effective and definitive preventative approach. Inflammatory activation due to immune dyshomeostasis during the early stages of trauma is believed to be critical in initiating the THO disease process. This study proposes a dual-homeostatic modulation (DHM) strategy to synergistically prevent THO without compromising normal trauma repair by maintaining immune homeostasis and inducing stem cell homeostasis. A methacrylate-hyaluronic acid-based hydrogel spray device encapsulating a curcumin-loaded zeolitic imidazolate framework-8@ceric oxide (ZIF-8@CeO2, CZC) nanoparticles (CZCH) is designed. Photo-crosslinked CZCH is used to form hydrogel films fleetly in periosteal soft tissues to achieve sustained curcumin and CeO2 nanoparticles release in response to acidity and reactive oxygen species (ROS) in the inflammatory microenvironment. In vitro experiments and RNA-seq results demonstrated that CZCH achieved dual-homeostatic regulation of inflammatory macrophages and stem cells through immune repolarization and enhanced efferocytosis, maintaining immune cell homeostasis and normal differentiation. These findings of the DHM strategy are also validated by establishing THO mice and rat models. In conclusion, the CZCH hydrogel spray developed based on the DHM strategy enables synergistic THO prevention, providing a reference for a standard procedure of clinical operations.

Macrophage-Derived TGF-β and VEGF Promote the Progression of Trauma-Induced Heterotopic Ossification

Heterotopic ossification (HO) is a pathological bone formation process caused by musculoskeletal trauma. HO is characterized by aberrant endochondral ossification and angiogenesis. Our previous studies have indicated that macrophage inflammation is involved in traumatic HO formation. In this study, we found that macrophage infiltration and TGF-β signaling activation are presented in human HO. Depletion of macrophages effectively suppressed traumatic HO formation in a HO mice model, and macrophage depletion significantly inhibited the activation of TGF-β/Smad2/3 signaling. In addition, the TGF-β blockade created by a neutralizing antibody impeded ectopic bone formation in vivo. Notably, endochondral ossification and angiogenesis are attenuated following macrophage depletion or TGF-β inhibition. Furthermore, our observations on macrophage polarization revealed that M2 macrophages, rather than M1 macrophages, play a critical role in supporting HO development by enhancing the osteogenic and chondrogenic differentiation of mesenchymal stem cells. Our findings on ectopic bone formation in HO patients and the mice model indicate that M2 macrophages are an important contributor for HO development, and that inhibition of M2 polarization or TGF-β activity may be a potential method of therapy for traumatic HO.

The role of miRNA and lncRNA in heterotopic ossification pathogenesis

Heterotopic ossification (HO) is the formation of bone in non-osseous tissues, such as skeletal muscles. The HO could have a genetic or a non-genetic (acquired) background, that is, it could be caused by musculoskeletal trauma, such as burns, fractures, joint arthroplasty (traumatic HO), or cerebral or spinal insult (neurogenetic HO). HO formation is caused by the differentiation of stem or progenitor cells induced by local or systemic imbalances. The main factors described so far in HO induction are TGFβ1, BMPs, activin A, oncostatin M, substance P, neurotrophin-3, and WNT. In addition, dysregulation of noncoding RNAs, such as microRNA or long noncoding RNA, homeostasis may play an important role in the development of HO. For example, decreased expression of miRNA-630, which is responsible for the endothelial-mesenchymal transition, was observed in HO patients. The reduced level of miRNA-421 in patients with humeral fracture was shown to be associated with overexpression of BMP2 and a higher rate of HO occurrence. Down-regulation of miRNA-203 increased the expression of runt-related transcription factor 2 (RUNX2), a crucial regulator of osteoblast differentiation. Thus, understanding the various functions of noncoding RNAs can reveal potential targets for the prevention or treatment of HO.

Does drainage affect development of heterotopic ossification after total hip arthroplasty?

OBJECTIVE

To investigate the effect of drainage on heterotopic ossification (HO) after total hip arthroplasty (THA) and to evaluate other postoperative complications and joint dysfunction between patients with and without drainage.

METHODS

In this retrospective cohort study, the medical records of patients who underwent THA from 2017 to 2019 were reviewed. The patients were divided into a drainage group and non-drainage group. Standard preoperative anteroposterior and lateral radiographs were assessed by senior radiologists for HO analysis. Clinical indicators included the hemoglobin concentration, superficial infection, blood transfusion, hematoma formation, hip range of motion (ROM), erythrocyte sedimentation rate, C-reactive protein concentration, dressing changes, visual analogue scale score, and Harris Hip Score (HHS).

RESULTS

The incidence of HO was significantly higher in the drainage than non-drainage group (32.0% vs. 16.3%). The presence of severe HO (Brooker grade III or IV) was also different between the groups. Patients in the non-drainage group had smaller ROM early after surgery, but the final ROM and HHS did not differ significantly between the groups.

CONCLUSIONS

The rate and degree of HO after THA were significantly different between patients with and without drainage. There is no added advantage of closed suction drainage over no drainage in primary THA.

Comparative proteomic analysis identifies differentially expressed proteins and reveals potential mechanisms of traumatic heterotopic ossification progression

Background

Traumatic Heterotopic Ossification (tHO) is one of complications of elbow fractures to the detriment of patients' rehabilitation, and the severity of tHO corresponds to the size of ectopic bone. It has yet to be elucidated which proteins and pathways underlying the progression of tHO, and biomarkers to predict the severity of tHO at early stage of the disease also need further investigation.

Methods

In this study, a new rat model with distinct volume of ectopic bone was established first. Then a data-independent acquisition proteomics approach was used to investigate injured site tissues sequentially obtained from these rats (2, 7, 14, and 28 days post-injury). Differentially expressed analysis, functional annotation and co-expression analysis and protein-protein interaction network were performed to explore the pathways and hub proteins in the tHO progression. Clinical samples from a nest case-control study were used to validate the selected proteins for predicting the severity of tHO.

Results

The Achilles Tenotomy (AT) induced significantly larger sizes of ectopic bone compared to Partial Achilles Tenotomy (PAT) in rat models. A total of 3547 quantifiable proteins were screened for differential expression analysis among the AT, PAT and control groups. The hierarchical clustering and expression pattern analysis revealed more apparent difference in the pathways such as oxidative phosphorylation, mitochondrial function, and sirtuin signaling between AT and PAT group at the early stage (2 dpi) of tHO. The co-expression analysis identified five hub proteins, UBA1, EIF3E, RPL17, RPL27, and RPS28. qPCR assay, immunoblot assay and immunohistochemistry assay verified that these proteins had higher expression level in the tissue samples of clinically relevant HO patients and clinically irrelevant HO patients than HO negative patients.

Conclusion

The new established animal model and proteome profile could serve as a solid foundation for the comprehensive investigation of the progression of traumatic heterotopic ossification. And the identified 5 proteins (UBA1, EIF3E, RPL17, RPL27, and RPS28) may serve as potential biomarkers to predict the severity of tHO.

The translational potential of this article

The proteins identified in this study may be the potential biomarkers and therapeutic targets for predicting and treating the tHO at early stage.

Impact of heterotopic ossification following lumbar total disk replacement: a systematic review

Background context

Lumbar total disc replacement (TDR) is an alternative to lumbar fusion in the treatment of lower back pain and reduces the risk of adjacent segment degeneration. Heterotopic ossification (HO) has been identified as a common complication following lumbar TDR.

Purpose

This systematic review aims to determine the prevalence, risk factors and clinical and radiological impact of HO following lumbar TDR.

Study Design

Systematic Review.

Methods

MEDLINE, Scopus, PubMed and Cochrane Central were searched for articles that referred to lumbar TDR and HO. The hits were assessed against inclusion and exclusion criteria. Data from each included study was extracted and analysed with respect to the study aims.

Results

Twenty-six studies were included in this review and the pooled prevalence of HO was estimated to be between 13.2% (participants) and 15.3% (vertebral levels). TDR clinical outcomes were not found to be reduced by HO and there was insufficient data to identify a given impact upon radiological outcomes. Age and follow up time were identified as potential risk factors for HO.

Conclusions

This review was hampered by inconsistencies in the reporting of HO across the studies. We therefore recommend that a set of guidelines should be produced to aid future researchers and reduce the risk of bias.

Single-Cell Integration Analysis of Heterotopic Ossification and Fibrocartilage Developmental Lineage: Endoplasmic Reticulum Stress Effector Xbp1 Transcriptionally Regulates the Notch Signaling Pathway to Mediate Fibrocartilage Differentiation

INTRODUCTION

Regeneration of fibrochondrocytes is essential for the healing of the tendon-bone interface (TBI), which is similar to the formation of neurogenic heterotopic ossification (HO). Through single-cell integrative analysis, this study explored the homogeneity of HO cells and fibrochondrocytes.

METHODS

This study integrated six datasets, namely, GSE94683, GSE144306, GSE168153, GSE138515, GSE102929, and GSE110993. The differentiation trajectory and key transcription factors (TFs) for HO occurrence were systematically analyzed by integrating single-cell RNA (scRNA) sequencing, bulk RNA sequencing, and assay of transposase accessible chromatin seq. The differential expression and enrichment pathways of TFs in heterotopically ossified tissues were identified.

RESULTS

HO that mimicked pathological cells was classified into HO1 and HO2 cell subsets. Results of the pseudo-temporal sequence analysis suggested that HO2 is a differentiated precursor cell of HO1. The analysis of integrated scRNA data revealed that ectopically ossified cells have similar transcriptional characteristics to cells in the fibrocartilaginous zone of tendons. The modified SCENIC method was used to identify specific transcriptional regulators associated with ectopic ossification. Xbp1 was defined as a common key transcriptional regulator of ectopically ossified tissues and the fibrocartilaginous zone of tendons. Subsequently, the CellPhoneDB database was completed for the cellular ligand-receptor analysis. With further pathway screening, this study is the first to propose that Xbp1 may upregulate the Notch signaling pathway through Jag1 transcription. Twenty-four microRNAs were screened and were found to be potentially associated with upregulation of XBP1 expression after acute ischemic stroke.

CONCLUSION

A systematic analysis of the differentiation landscape and cellular homogeneity facilitated a molecular understanding of the phenotypic similarities between cells in the fibrocartilaginous region of tendon and HO cells. Furthermore, by identifying Xbp1 as a hub regulator and by conducting a ligand-receptor analysis, we propose a potential Xbp1/Jag1/Notch signaling pathway.

Neurogenic heterotopic ossification in the upper limb

Neurogenic heterotopic ossifications (NHOs) are periarticular ectopic ossifications that frequently develop after a central nervous system injury, most often a traumatic one. They limit range of motion and cause pain, interfering with limb positioning and function, whether active or passive. Highly described in the lower limbs, NHOs can also develop in the upper limb, with specific characteristics depending on their location. This article provides a summary of the diagnostic and therapeutic management of NHOs in the upper limb, based on the current literature.

Local and Systemic Factors Drive Ectopic Osteogenesis in Regenerating Muscles of Spinal-Cord-Injured Mice in a Lesion-Level-Dependent Manner

Neuroimmune dysfunction is thought to promote the development of several acute and chronic complications in spinal cord injury (SCI) patients. Putative roles for adrenal stress hormones and catecholamines are increasingly being recognized, yet how these adversely affect peripheral tissue homeostasis and repair under SCI conditions remains elusive. Here, we investigated their influence in a mouse model of SCI with acquired neurogenic heterotopic ossification. We show that spinal cord lesions differentially influence muscular regeneration in a level-dependent manner and through a complex multi-step process that creates an osteopermissive environment within the first hours of injury. This cascade of events is shown to critically involve adrenergic signals and drive the acute release of the neuropeptide, substance P. Our findings generate new insights into the kinetics and processes that govern SCI-induced deregulations in skeletal muscle homeostasis and regeneration, thereby aiding the development of sequential therapeutic strategies that can prevent or attenuate neuromusculoskeletal complications in SCI patients.

Neurogenic Heterotopic Ossifications Recapitulate Hematopoietic Stem Cell Niche Development Within an Adult Osteogenic Muscle Environment

Hematopoiesis and bone interact in various developmental and pathological processes. Neurogenic heterotopic ossifications (NHO) are the formation of ectopic hematopoietic bones in peri-articular muscles that develop following severe lesions of the central nervous system such as traumatic cerebral or spinal injuries or strokes. This review will focus on the hematopoietic facet of NHO. The characterization of NHO demonstrates the presence of hematopoietic marrow in which quiescent hematopoietic stem cells (HSC) are maintained by a functional stromal microenvironment, thus documenting that NHOs are neo-formed ectopic HSC niches. Similarly to adult bone marrow, the NHO permissive environment supports HSC maintenance, proliferation and differentiation through bidirectional signaling with mesenchymal stromal cells and endothelial cells, involving cell adhesion molecules, membrane-bound growth factors, hormones, and secreted matrix proteins. The participation of the nervous system, macrophages and inflammatory cytokines including oncostatin M and transforming growth factor (TGF)-β in this process, reveals how neural circuitry fine-tunes the inflammatory response to generate hematopoietic bones in injured muscles. The localization of NHOs in the peri-articular muscle environment also suggests a role of muscle mesenchymal cells and bone metabolism in development of hematopoiesis in adults. Little is known about the establishment of bone marrow niches and the regulation of HSC cycling during fetal development. Similarities between NHO and development of fetal bones make NHOs an interesting model to study the establishment of bone marrow hematopoiesis during development. Conversely, identification of stage-specific factors that specify HSC developmental state during fetal bone development will give more mechanistic insights into NHO.

Novel Lineage-Tracing System to Identify Site-Specific Ectopic Bone Precursor Cells

Heterotopic ossification (HO) is a form of pathological cell-fate change of mesenchymal stem/precursor cells (MSCs) that occurs following traumatic injury, limiting range of motion in extremities and causing pain. MSCs have been shown to differentiate to form bone; however, their lineage and aberrant processes after trauma are not well understood. Utilizing a well-established mouse HO model and inducible lineage-tracing mouse (Hoxa11-CreER^T2;ROSA26-LSL-TdTomato), we found that Hoxa11-lineage cells represent HO progenitors specifically in the zeugopod. Bioinformatic single-cell transcriptomic and epigenomic analyses showed Hoxa11-lineage cells are regionally restricted mesenchymal cells that, after injury, gain the potential to undergo differentiation toward chondrocytes, osteoblasts, and adipocytes. This study identifies Hoxa11-lineage cells as zeugopod-specific ectopic bone progenitors and elucidates the fate specification and multipotency that mesenchymal cells acquire after injury. Furthermore, this highlights homeobox patterning genes as useful tools to trace region-specific progenitors and enable location-specific gene deletion.

•

Lineage tracing, single-cell RNA-seq and single cell ATAC enable cell specific analysis of in vivo cell fate

•

Hoxa11 lineage marks distinct mesenchymal precursors in the zeugopod

•

Hoxa11 lineage mesenchymal precursors undergo an aberrant cell fate change towards ectopic bone and cartilage

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.

A Three-Generation Pedigree of Multifocal Heterotopic Ossification With Bilateral Involvement

Heterotopic ossification (HO) can be classified as nonhereditary HO (NHHO) or hereditary HO (HHO). Hereditary HO includes 2 different forms: fibrodysplasia ossificans progressiva (FOP) and progressive osseous heteroplasia (POH). Each of these disorders is caused by mutations in a single (different) gene. Clinical diagnosis of FOP can be confirmed by sequence analysis of the ACVR1 gene. Fewer than 10 families with autosomal dominant inheritance of FOP have been reported. The authors report clinical manifestations, pedigree analysis, and mutational analysis of the ACVR1 in a 3-generation Chinese family with 4 individuals presenting multifocal and bilateral involvement of HO. Clinical features of affected individuals of the family were not consistent with the classic FOP or atypical FOP. Exon sequencing was performed on every family member and 3 sporadic NHHO patients who did not belong to this family. All family members and 3 sporadic NHHO patients carried 2 hereditary homozygous silent mutations- c.270C>T and c.690G>A-the new and unique mutations in ACVR1. These results may suggest that the affected individuals in this family present a novel FOP-variant syndrome or a new form of HHO. To the authors' knowledge, this is the first well-documented instance of a 3-generation Chinese family with multifocal and bilateral involvement of HO. [Orthopedics. 2021;44(1):e139-e145.].

Bone From Blood: Characteristics and Clinical Implications of Circulating Osteogenic Progenitor (COP) Cells

Circulating osteogenic progenitor (COP) cells are a population of cells in the peripheral blood with the capacity for bone formation, as well as broader differentiation into mesoderm-like cells in vitro. Although some of their biological characteristics are documented in vitro, their role in diseases of the musculoskeletal system remains yet to be fully evaluated. In this review, we provide an overview of the role of COP cells in a number of physiological and pathological conditions, as well as identify areas for future research. In addition, we suggest possible areas for clinical utilization in the management of musculoskeletal diseases. © 2020 American Society for Bone and Mineral Research (ASBMR).

Medial meniscal ossicles: Associated knee MRI findings in a multicenter case-control study

PURPOSE

The purpose of this study was to assess and compare the prevalence of meniscal, ligament and cartilage lesions on knee MRI in a series of age- and sex-matched patients with and without medial meniscal ossicle.

MATERIALS AND METHODS

Forty-two knee MRI examinations obtained in 42 patients (36 men, 6 women; mean age, 42.5±22.2 [SD] years; range: 19-65years) on which a medial meniscal ossicle was present were compared to 42 knee MRI examinations obtained in 42 age- and sex-matched patients (36 men, 6 women; mean age, 41.8±20.6 [SD] years; range: 19-65years) on which no medial meniscal ossicles were present. Two radiologists (R1, R2) blinded to the presence of meniscal ossicle by reading only the fat-saturated intermediate-weighted MR images separately assessed the presence of meniscal, ligament and cartilage lesions on these 84 knee MRI examinations. Prevalence of meniscal and ligament lesions and degree of cartilage degradation at MRI were compared between knees with and those without medial meniscal ossicle.

RESULTS

In knees with medial meniscal ossicle, R1 and R2 detected 33 (79%) and 38 (90%) medial meniscal lesions, respectively that involved the posterior root (n=25/32 for R1/R2), the posterior horn (n=19/14 for R1/R2) or the body (n=8/10 for R1/R2). The prevalence of posterior root tear (60% [25/42]/76% [32/42] for R1/R2) and that of anterior cruciate ligament (ACL) lesions (48% [20/42]/57% [24/42] for R1/R2) as well as the medial cartilage degradation score (3.35±0.87 [SD] for R1 and 3.92±0.78 [SD] for R2) were significantly greater in knees with than in knees without medial meniscal ossicle (root lesions: P<0.01 for both readers; ACL lesions and medial cartilage score: P<0.01 for both readers).

CONCLUSION

On MRI examination, knees with a medial meniscal ossicle demonstrate a greater frequency of medial posterior root tear and of ACL lesions and a greater degree of medial femoro-tibial cartilage degradation by comparison with knees without medial ossicle.

Genetic and Acquired Heterotopic Ossification: A Translational Tale of Mice and Men

Heterotopic ossification is defined as an aberrant formation of bone in extraskeletal soft tissue, for which both genetic and acquired conditions are known. This pathologic process may occur in many different sites such as the skin, subcutaneous tissue, skeletal muscle and fibrous tissue adjacent to joints, ligaments, walls of blood vessels, mesentery and other. The clinical spectrum of this disorder is wide: lesions may range from small foci of ossification to massive deposits of bone throughout the body, typical of the progressive genetically determined conditions such as fibrodysplasia ossificans progressiva, to mention one of the most severe and disabling forms. The ectopic bone formation may be regarded as a failed tissue repair process in response to a variety of triggers and evolving towards bone formation through a multistage differentiation program, with several steps common to different clinical presentations and distinctive features. In this review, we aim at providing a comprehensive view of the genetic and acquired heterotopic ossification disorders by detailing the clinical and molecular features underlying the different human conditions in comparison with the corresponding, currently available mouse models.

Neurological heterotopic ossification: novel mechanisms, prognostic biomarkers and prophylactic therapies

Neurological heterotopic ossification (NHO) is a debilitating condition where bone forms in soft tissue, such as muscle surrounding the hip and knee, following an injury to the brain or spinal cord. This abnormal formation of bone can result in nerve impingement, pain, contractures and impaired movement. Patients are often diagnosed with NHO after the bone tissue has completely mineralised, leaving invasive surgical resection the only remaining treatment option. Surgical resection of NHO creates potential for added complications, particularly in patients with concomitant injury to the central nervous system (CNS). Although recent work has begun to shed light on the physiological mechanisms involved in NHO, there remains a significant knowledge gap related to the prognostic biomarkers and prophylactic treatments which are necessary to prevent NHO and optimise patient outcomes. This article reviews the current understanding pertaining to NHO epidemiology, pathobiology, biomarkers and treatment options. In particular, we focus on how concomitant CNS injury may drive ectopic bone formation and discuss considerations for treating polytrauma patients with NHO. We conclude that understanding of the pathogenesis of NHO is rapidly advancing, and as such, there is the strong potential for future research to unearth methods capable of identifying patients likely to develop NHO, and targeted treatments to prevent its manifestation.

Diagnosis of Klippel-Trenaunay syndrome and extensive heterotopic ossification in a patient with a femoral fracture: a case report and literature review

Background

Klippel-Trenaunay syndrome (KTS) is a rare complex vessel malformation syndrome characterized by venous varicosities, capillary malformations, and limb hypertrophy. However, extensive heterotopic ossification (HO) secondary to this syndrome is extremely rare.

Case presentation

We report the case of a patient with previously undiagnosed KTS and extensive HO who presented with a femoral fracture secondary to a motor vehicle accident. Extensive ossification, which leads to compulsive contracture deformity and dysfunction of the leg, was distributed on the flexor muscle side, as revealed by the radiograph. The diagnosis was finally established by combining imaging and histological analysis with classical clinical symptoms. Amputation was performed at the fracture site proximal to the infected necrotic foci. Open management of the fracture was challenging owning to the pervasive ossification and tendency for excessive bleeding. Gene sequencing analysis showed homozygous mutation of FoxO1 gene.

Conclusions

Definitive diagnosis of a combination of KTS and extensive HO requires detailed imaging analysis and pathologic evidence. Mutation of the FoxO1 gene, which regulates bone formation by resistance to oxidative stress in osteoblasts, is a potential factor in the microenvironment of malformed vessels caused by KTS.

Activin A does not drive post-traumatic heterotopic ossification

Heterotopic ossification (HO), the formation of ectopic bone in soft tissues, has been extensively studied in its two primary forms: post-traumatic HO (tHO) typically found in patients who have experienced musculoskeletal or neurogenic injury and in fibrodysplasia ossificans progressiva (FOP), where it is genetically driven. Given that in both diseases HO arises via endochondral ossification, the molecular mechanisms behind both diseases have been postulated to be manifestations of similar pathways including those activated by BMP/TGFβ superfamily ligands. A significant step towards understanding the molecular mechanism by which HO arises in FOP was the discovery that FOP causing ACVR1 variants trigger HO in response to activin A, a ligand that does not activate signaling from wild type ACVR1, and that is not inherently osteogenic in wild type settings. The physiological significance of this finding was demonstrated by showing that activin A neutralizing antibodies stop HO in two different genetically accurate mouse models of FOP. In order to explore the role of activin A in tHO, we performed single cell RNA sequencing and compared the expression of activin A as well as other BMP pathway genes in tHO and FOP HO. We show that activin A is expressed in response to injury in both settings, but by different types of cells. Given that wild type ACVR1 does not transduce signal when engaged by activin A, we hypothesized that inhibition of activin A will not block tHO. Nonetheless, as activin A was expressed in tHO lesions, we tested its inhibition and compared it with inhibition of BMPs. We show here that anti-activin A does not block tHO, whereas agents such as antibodies that neutralize ACVR1 or ALK3-Fc (which blocks osteogenic BMPs) are beneficial, though not completely curative. These results demonstrate that inhibition of activin A should not be considered as a therapeutic strategy for ameliorating tHO.

The Survey of Cells Responsible for Heterotopic Ossification Development in Skeletal Muscles-Human and Mouse Models

Heterotopic ossification (HO) manifests as bone development in the skeletal muscles and surrounding soft tissues. It can be caused by injury, surgery, or may have a genetic background. In each case, its development might differ, and depending on the age, sex, and patient's conditions, it could lead to a more or a less severe outcome. In the case of the injury or surgery provoked ossification development, it could be, to some extent, prevented by treatments. As far as genetic disorders are concerned, such prevention approaches are highly limited. Many lines of evidence point to the inflammatory process and abnormalities in the bone morphogenetic factor signaling pathway as the molecular and cellular backgrounds for HO development. However, the clear targets allowing the design of treatments preventing or lowering HO have not been identified yet. In this review, we summarize current knowledge on HO types, its symptoms, and possible ways of prevention and treatment. We also describe the molecules and cells in which abnormal function could lead to HO development. We emphasize the studies involving animal models of HO as being of great importance for understanding and future designing of the tools to counteract this pathology.

The effect of celecoxib in traumatic heterotopic ossification around temporomandibular joint in mice

OBJECTIVE

In this study, the role of inflammation in traumatic heterotopic ossification around temporomandibular joint (THO-TMJ), as well as the preventive and treatment effect of celecoxib in THO-TMJ both in vivo and in vitro were explored.

DESIGN

A surgically-induced THO-TMJ mouse model and a co-culture model of ATDC-5 or MC3T3-E1 and RAW-264.7 cells were used in this study for in vivo and in vitro research.

RESULTS

A series of inflammatory factors, such as CD3, CD68, CD20, IL-10, IL-6 and TNF-α, were activated 48 h after trauma in a THO-TMJ model. Local trauma initiated systemic inflammatory responses as well as T cell- and macrophage-mediated local inflammatory responses around TMJ. In addition, expression of COX-2 was significantly elevated. The findings also showed that local injection of celecoxib could effectively alleviate the inflammatory response around TMJ at the early stage of trauma and inhibit the formation of THO-TMJ in vivo. Meanwhile, celecoxib could inhibit chondrogenic differentiation of ATDC-5 and osteogenic differentiation of MC3T3-E1 under inflammatory condition in vitro. Furthermore, celecoxib could inhibit the expression of Bmpr1b in the injured condylar cartilage at the initiation stage of THO-TMJ, which implied that Bmpr1b expressed by the residual condylar cartilage might be related to the pathogenesis of THO-TMJ.

CONCLUSIONS

Inflammation played a crucial role in the pathogenesis of THO-TMJ, and anti-inflammation might be a possible choice to inhibit THO-TMJ, which provided scientific clues for the mechanisms, pharmacotherapy and molecular intervention of THO-TMJ.

Regulation of heterotopic ossification by monocytes in a mouse model of aberrant wound healing

Heterotopic ossification (HO) is an aberrant regenerative process with ectopic bone induction in response to musculoskeletal trauma, in which mesenchymal stem cells (MSC) differentiate into osteochondrogenic cells instead of myocytes or tenocytes. Despite frequent cases of hospitalized musculoskeletal trauma, the inflammatory responses and cell population dynamics that regulate subsequent wound healing and tissue regeneration are still unclear. Here we examine, using a mouse model of trauma-induced HO, the local microenvironment of the initial post-injury inflammatory response. Single cell transcriptome analyses identify distinct monocyte/macrophage populations at the injury site, with their dynamic changes over time elucidated using trajectory analyses. Mechanistically, transforming growth factor beta-1 (TGFβ1)-producing monocytes/macrophages are associated with HO and aberrant chondrogenic progenitor cell differentiation, while CD47-activating peptides that reduce systemic macrophage TGFβ levels and help ameliorate HO. Our data thus implicate CD47 activation as a therapeutic approach for modulating monocyte/macrophage phenotypes, MSC differentiation and HO formation during wound healing.

Development of a Meniscal Ossicle After a Meniscal Root Repair Augmented with Bone Marrow Aspirate Concentrate: A Case Report

CASE

A 17-year-old boy had persistent knee pain 1 year after medial meniscal root repair augmented with bone marrow aspirate concentrate injection. Radiographs and magnetic resonance imaging (MRI) demonstrated an intrameniscal ossicle which was not present on MRI performed before 6 months. He underwent arthroscopic excision of the meniscal ossicle. At the 7-month follow-up, he had complete relief of his pain.

CONCLUSIONS

It is possible that the meniscal ossicle developed because of osteoinductive cells and cytokines from the injected bone marrow or the drill hole for root repair and should be considered as a possible complication of this procedure.

Heterotopic Ossification in Orthopaedic and Trauma surgery: A Histopathological Ossification Score

Heterotopic Ossification (HO) is a potential long-term complication in orthopaedic surgery. It is commonly classified according to the Brooker classification, which is based on radiological findings. To our knowledge the correlation of histological features to the Brooker grade is unknown as is the association between HO and the indication for revision. The aim of this paper is to analyze the ossification grade of HO tissue in patients undergoing revision hip and knee arthroplasty and to propose a histologically based classification system for HO. We also assess the relationship between the grade of HO and the indication for revision (septic and aseptic revision). From January to May 2019 we collected 50 human HO samples from hip and knee revision arthroplasty cases. These tissue samples were double-blinded and sent for histopathological diagnostic. Based on these results, we developed a classification system for the progression of HO. The grade of ossification was based on three characteristics: Grade of heterotopic ossification (Grade 1–3), presence of necrosis (N0 or N1) and the presence of osteomyelitis (HOES-Score Type 1 to 5). Demographic data as well as surgical details and indication for surgery was prospectively collected from clinical records. Fifty tissue samples were harvested from 44 hips and 6 knee joints. Of these 33 exhibited Grade I ossifications (66%), followed by 11 Grade II (22%) and one Grade III (2%). Necrosis was noted in two tissue samples (4%) and 2 more had osteomyelitis findings according to HOES-Score. Six samples (12%) with radiologically suggestive of HO turned out to be wear-induced synovitis, SLIM Type 1. Of these cases 16 were septic (32%) and 34 aseptic (68%) revisions. Most of the HO tissue samples were classified as a low-grade. High-grade ossification-Score is rare. Higher grades of ossification seem to be associated with septic revision cases. Wear-induced synovitis potentially influences HO development. A histological scoring system for ossification grading can be derived from the data presented in this study.

Resection of heterotopic ossification around the hip after trauma

Traumatic neurological lesions may lead to development of heterotopic ossification. These cases are classified as ‘neurogenic heterotopic ossifications’ (NHOs). The associated neurological lesions can be caused by cranial trauma or spinal cord injury and may sometimes include a local trauma.

NHOs that form around the hip joints are of particular interest because they often cause the patient to avoid the sitting position or the resumption of walking.

Whilst NHO can involve the knee, shoulder and elbow joints, hip-involving NHOs are more numerous, and sometimes develop in close contact with vascular or neurological structures.

Multi-disciplinary clinical examination is fundamental to evaluate patients for surgical intervention and to define the objectives of the surgery. The best investigation to define an NHO mass is a computerized tomography (CT) scan.

Resection is performed to liberate a fused joint to provide functionality, and this need not be exhaustive if it is not necessary to increase the range of motion.

While recurrence does occur post-surgery, a partial resection does not pose a greater risk of recurrence and there are no adjuvant treatments available to reduce this risk.

The greatest risks associated with NHO surgical resection are infection and haematoma; these risks are very high and must be considered when evaluating patients for surgery.

Cite this article: EFORT Open Rev 2019;4 DOI: 10.1302/2058-5241.4.180098

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.