Neurological heterotopic ossification: Current understanding and future directions

The Role of Neuromodulation and Potential Mechanism in Regulating Heterotopic Ossification

Heterotopic ossification (HO) is a pathological process characterized by the aberrant formation of bone in muscles and soft tissues. It is commonly triggered by traumatic brain injury, spinal cord injury, and burns. Despite a wide range of evidence underscoring the significance of neurogenic signals in proper bone remodeling, a clear understanding of HO induced by nerve injury remains rudimentary. Recent studies suggest that injury to the nervous system can activate various signaling pathways, such as TGF-β, leading to neurogenic HO through the release of neurotrophins. These pathophysiological changes lay a robust groundwork for the prevention and treatment of HO. In this review, we collected evidence to elucidate the mechanisms underlying the pathogenesis of HO related to nerve injury, aiming to enhance our understanding of how neurological repair processes can culminate in HO.

Delayed femoral artery injury caused by heterotopic ossification: a rare case report and review of the literature

BACKGROUND

Arterial injury caused by heterotopic ossification (HO) following fractures is rarely reported, yet it can have catastrophic consequences. This case report presents a unique instance of femoral artery injury and hematoma organization, occurring a decade after intramedullary nail fixation for a femoral shaft fracture complicated by HO.

CASE PRESENTATION

A 56-year-old male presented with right femoral artery injury and organized hematoma, a decade after suffering bilateral femoral shaft fractures with mild head injury in a traffic accident. He had received intramedullary nailing for the right femoral shaft fracture and plate fixation for the left side in a local hospital. Physical examination revealed two firm, palpable masses with clear boundaries, limited mobility, and no tenderness. Peripheral arterial pulses were intact. Radiography demonstrated satisfactory fracture healing, while a continuous high-density shadow was evident along the inner and posterior aspect of the right thigh. Computed tomography angiography identified a large mixed-density mass (16.8 × 14.8 × 20.7 cm) on the right thigh's medial side, featuring central calcification and multiple internal calcifications. The right deep femoral artery coursed within this mass, with a smaller lesion noted on the posterior thigh. Surgical consultation with a vascular surgeon led to planned intervention. The smaller mass was completely excised, but the larger one partially, as it encased the femoral artery. The inability to remove all HO was due to excessive bleeding. Postoperatively, the patient experienced no complications, and one-year follow-up revealed a favorable recovery with restoration of full right lower limb mobility.

CONCLUSION

This case underscores the potential gravity of vascular injury associated with heterotopic ossification. Surgeons should remain vigilant regarding the risk of vascular injury during HO excision.

Angiogenesis in heterotopic ossification: From mechanisms to clinical significance

Heterotopic ossification (HO) refers to the formation of pathologic bone in nonskeletal tissues (including muscles, tendons or other soft tissues). HO typically occurs after a severe injury and can occur in any part of the body. HO lesions are highly vascularized. Angiogenesis, which is the formation of new blood vessels, plays an important role in the pathophysiology of HO. Surgical resection is considered an effective treatment for HO. However, it is difficult to completely remove new vessels, which can lead to the recurrence of HO and is often accompanied by significant problems such as intraoperative hemorrhage, demonstrating the important role of angiogenesis in HO. Here, we broadly summarize the current understanding of how angiogenesis contributes to HO; in particular, we focus on new insights into the cellular and signaling mechanisms underlying HO angiogenesis. We also review the development and current challenges associated with antiangiogenic therapy for HO.

A case report of heterotopic ossifications in abdominal incision scar

INTRODUCTION

Heterotopic ossification (HO) develops when bone formation appears in soft tissues, usually after an injury or major surgery. Timely and accurately diagnosing of this rare event is essential due to the possibility of misdiagnosis as a maintained foreign body, infection, incisional neoplastic recurrence, and metastatic or primary neoplasms.

CASE PRESENTATION

In this study, we present a 57-year-old man who was operated for peritonitis due to perforated appendicitis, and an asymptomatic HO was accidentally found on an incisional line of previous open prostatectomy about 5 years earlier due to benign prostatic hyperplasia. A bone density lesion was seen in the fascia and on the incisional scar of previous surgery.

DISCUSSION

HO rarely occurs within an abdominal incision due to surgery. It is reported only within vertical midline incisions and mainly within the first year after the operation. Imaging confirms the diagnosis of HO in previous abdominal surgery scars, which reveals dense vertical calcification along the previous incisional scar. In the case of HO, the exclusive effective management is the entire surgical excision with primary closure, and NSAIDs are the preventive choices.

CONCLUSION

HO should be considered in patients presenting with discomfort or palpable mass or even asymptomatic patients with previous abdominal surgeries besides considering relative history such as surgical complications or neoplasms.

Trauma patient heterotopic ossification diagnosis is associated with increased hospital length of stay

BACKGROUND

Traumatic heterotopic ossification (tHO) refers to the development of extra-skeletal bone in muscle and soft tissues following tissue insult secondary to surgery or trauma. This presents a persistent clinical concern associated with significant patient morbidity and expense to diagnose and treat. Traumatic HO is a substantial barrier to rehabilitation for trauma-injured patients. As such, the development of tHO after burn and other trauma is hypothesised to prolong inpatient length of stay (LOS) and thus increase health care costs.

OBJECTIVE

To investigate the association between an inpatient tHO diagnosis and hospital LOS in trauma patients.

METHODS

A retrospective audit of trauma patients over a 14-year period was completed using data from four WA hospitals. Burn and neurological trauma patients diagnosed with tHO as an inpatient (tHO+) and control subjects (tHO-), matched (1:3) by age, gender, and injury severity factors, were identified using medical diagnostic codes. Data relating to patient and injury-related determinants of LOS from tHO+ and tHO- subjects were analysed to model the association of tHO on total hospital length of stay.

RESULTS

188 identified patients were hospitalised due to traumatic injury; 47 patients with tHO following burn injury (n = 17), spinal cord injury (n = 13) and traumatic brain injury (n = 17), and 141 control patients. Those who developed tHO during hospitalisation had a significantly higher median LOS than matched trauma patients who did not develop tHO (142 days vs. 61 days). Multivariate regression analyses identified the following independent predictive factors of a prolonged hospital LOS: tHO diagnosis, mechanical ventilation hours, injury to the hip region and thigh area, other ossification disorder, pressure injury, admission to intensive care unit and deep vein thrombosis. Trauma patients diagnosed with tHO during their hospital admission stayed 1.6 times longer than trauma patients matched for injury severity without a tHO diagnosis (IRR 1.56, 95% CI 1.35-1.79, p<0.001).

CONCLUSION

Traumatic heterotopic ossification is an independent explanatory factor for increased hospital LOS in patients following burns, spinal cord, and traumatic brain injury. Early diagnosis may assist in reducing the impact of tHO on acute hospital stay after trauma.

Healing an ischial tuberosity pressure ulcer in a patient with neurogenic heterotopic ossification: a case report

Neurogenic heterotopic ossification (NHO) is widely recognised as an aberrant bone formation in soft tissue following central nervous system injury. It is most frequently associated with pain and limited movement, especially in the hip. However, it may be neglected in patients with paraplegia with a pressure ulcer (PU). We report the case of an 18-year-old male patient who presented with a hard-to-heal ischial tuberosity PU and who had undergone three operations at other hospitals during the previous six months, which had failed to repair the PU. There was a history of paraplegia as a consequence of spinal cord injury two years previously. Computed tomography and three-dimensional reconstruction showed massive heterotopic ossification (HO) in the wound bed and around the right hip. Histological findings were consistent with a diagnosis of HO. The HO around the wound was completely excised, negative pressure wound therapy was used to promote granulation, and a gluteus maximus musculocutaneous flap was used to cover the wound. We conclude that for patients with paraplegia, with a hard-to-heal PU, it should be determined whether it is associated with NHO. Surgical resection of HO surrounding the wound and improving the microcirculation are critical for repair and reconstruction of these PUs.

Evaluation of the accuracy of diagnostic coding and clinical documentation for traumatic heterotopic ossification diagnoses in Western Australian hospitals

BACKGROUND

Traumatic heterotopic ossification (tHO) refers to the pathological formation of ectopic bone in soft tissues that can occur following burn, neurological ororthopaedic trauma. As completeness and accuracy of medical diagnostic coding can vary based on coding practices and depend on the institutional culture of clinical documentation, it is important to assess diagnostic coding in that local context. To the authors' knowledge, there is no prior study evaluating the accuracy of medical diagnostic coding or specificity of clinical documentation for tHO diagnoses across Western Australia (WA) trauma centres or across the full range of inciting injury and surgical events.

OBJECTIVE

To evaluate and compare the clinical documentation and the diagnostic accuracy of ICD-10-AM coding for tHO in trauma populations across 4 WA hospitals.

METHODS

A retrospective data search of the WA trauma database was conducted to identify patients with tHO admitted to WA hospitals following burn, neurological or orthopaedic trauma. Patient demographic and tHO diagnostic characteristics were assessed for all inpatient and outpatient tHO diagnoses. The frequency and distribution of M61 (HO-specific) and broader, musculoskeletal (non-specific) ICD-10-AM codes were evaluated for tHO cases in each trauma population.

RESULTS

HO-specific M61 ICD-10-AM codes failed to identify more than a third of true tHO cases, with a high prevalence of non-specific HO codes (19.4 %) and cases identified via manual chart review (25.4 %). The sensitivity of M61 codes for correctly diagnosing tHO after burn injury was 50 %. ROC analysis showed that M61 ICD-10-AM codes as a predictor of a true positive tHO diagnosis were a less than favourable method (AUC=0.731, 95 % CI=0.561-0.902, p = 0.012). Marked variability in clinical documentation for tHO was identified across the hospital network.

CONCLUSION

Coding inaccuracies may, in part, be influenced by insufficiencies in clinical documentation for tHO diagnoses, which may have implications for future research and patient care. Clinicians should consistently employ standardised clinical terminology from the point of care to increase the likelihood of accurate medical diagnostic coding for tHO diagnoses.

Interorgan communication in neurogenic heterotopic ossification: the role of brain-derived extracellular vesicles

Brain-derived extracellular vesicles participate in interorgan communication after traumatic brain injury by transporting pathogens to initiate secondary injury. Inflammasome-related proteins encapsulated in brain-derived extracellular vesicles can cross the blood‒brain barrier to reach distal tissues. These proteins initiate inflammatory dysfunction, such as neurogenic heterotopic ossification. This recurrent condition is highly debilitating to patients because of its relatively unknown pathogenesis and the lack of effective prophylactic intervention strategies. Accordingly, a rat model of neurogenic heterotopic ossification induced by combined traumatic brain injury and achillotenotomy was developed to address these two issues. Histological examination of the injured tendon revealed the coexistence of ectopic calcification and fibroblast pyroptosis. The relationships among brain-derived extracellular vesicles, fibroblast pyroptosis and ectopic calcification were further investigated in vitro and in vivo. Intravenous injection of the pyroptosis inhibitor Ac-YVAD-cmk reversed the development of neurogenic heterotopic ossification in vivo. The present work highlights the role of brain-derived extracellular vesicles in the pathogenesis of neurogenic heterotopic ossification and offers a potential strategy for preventing neurogenic heterotopic ossification after traumatic brain injury. Brain-derived extracellular vesicles (BEVs) are released after traumatic brain injury. These BEVs contain pathogens and participate in interorgan communication to initiate secondary injury in distal tissues. After achillotenotomy, the phagocytosis of BEVs by fibroblasts induces pyroptosis, which is a highly inflammatory form of lytic programmed cell death, in the injured tendon. Fibroblast pyroptosis leads to an increase in calcium and phosphorus concentrations and creates a microenvironment that promotes osteogenesis. Intravenous injection of the pyroptosis inhibitor Ac-YVAD-cmk suppressed fibroblast pyroptosis and effectively prevented the onset of heterotopic ossification after neuronal injury. The use of a pyroptosis inhibitor represents a potential strategy for the treatment of neurogenic heterotopic ossification.

Post-laparotomy heterotopic ossification of the xiphoid process: A case report

BACKGROUND

Heterotopic ossification (HO) represents all types of extraskeletal ossification in the body. It occurs in various areas, including the skin, subcutaneous tissue, muscle, and joints. Surgical excision is recommended for symptomatic HO. Postoperative radiotherapy, oral nonsteroidal anti-inflammatory drugs, and topical sealants, such as bone wax, have been recommended as preventive measures. As HO is rare in occurrence, these recommendations are based on personal experiences, and there is a lack of information on individualized treatments depending on its location.

CASE SUMMARY

A 62-year-old male was admitted for symptomatic HO along a laparotomy scar. Surgical excision was performed for an 11 cm-sized ossification originating from the xiphoid process, and bone wax was applied to the excisional margin. However, the surgical wound failed to heal. After several weeks of saline-soaked gauze dressing, delayed wound closure was performed. The patient was finally discharged eight weeks after the excision. Because HO can occur in various areas of the body, a treatment strategy that may be effective for some may not be for others. Bone wax has been used as a topical sealant over excisional margins in the shoulder, elbow, and temporomandibular joints. However, in our case, its application on an abdominal surgical wound delayed its primary healing intention. The valuable lesson was that, when choosing a treatment method for HO based on available research data, its location must be considered.

CONCLUSION

Complete excision should be the priority treatment option for symptomatic HO along the laparotomy scar. Bone wax application is not recommended.

Fibrocyte: A missing piece in the pathogenesis of fibrous epulis

OBJECTIVES

To explore the role of fibrocytes in the recurrence and calcification of fibrous epulides.

METHODS

Different subtypes of fibrous epulides and normal gingival tissue specimens were first collected for histological and immunofluorescence analyses to see if fibrocytes were present and whether they differentiated into myofibroblasts and osteoblasts upon stimulated by transforming growth factor-β1 (TGF-β1). Electron microscopy and elemental analysis were used to characterize the extracellular microenvironment in different subtypes of fibrous epulides. Human peripheral blood mononuclear cells (PBMCs) were subsequently isolated from in vitro models to mimic the microenvironment in fibrous epulides to identify whether TGF-β1 as well as the calcium and phosphorus ion concentration in the extracellular matrix (ECM) of a fibrous epulis trigger fibrocyte differentiation.

RESULTS

Fibrous epulides contain fibrocytes that accumulate in the local inflammatory environment and have the ability to differentiate into myofibroblasts or osteoblasts. TGF-β1 promotes fibrocytes differentiation into myofibroblasts in a concentration-dependent manner, while TGF-β1 stimulates the fibrocytes to differentiate into osteoblasts when combined with a high calcium and phosphorus environment.

CONCLUSIONS

Our study revealed fibrocytes play an important role in the fibrogenesis and osteogenesis in fibrous epulis, and might serve as a therapeutic target for the inhibition of recurrence of fibrous epulides.

Surgical Resection of Neurogenic Heterotopic Ossification around Hip Joint in Stroke Patients: A Safety and Outcome Report

Purpose

Resection remains the most reliable treatment for established heterotopic ossification, despite questions regarding its effectiveness due to the potential for complications. This study evaluated the clinical outcomes and complications of neurogenic heterotopic ossification (NHO) resection in stroke patients' ankylosed hips.

Materials and Methods

We retrospectively analyzed nine hip NHO resections performed on seven patients from 2010 to 2018. The pre- and postoperative range of motion of the operated hip were compared. Analysis of postoperative complications, including infection, recurrence, iatrogenic fracture, and neurovascular injury was performed.

Results

The mean operative time was 132.78±21.08 minutes, with a mean hemoglobin drop of 3.06±0.82 g/dL within the first postoperative week. The mean duration of postoperative follow-up was 52.08±28.72 months for all patients. Postoperative range of motion showed improvement from preoperative. Flexion and external rotation (mean, 58.89±30.60° and 16.67±18.03°, respectively) showed the greatest gain of motion of the operated hip joint. Postoperative infections resolved in two cases through surgical debridement, and one case required conversion to total hip arthroplasty due to instability. There were no recurrences, iatrogenic fractures, or neurovascular injuries.

Conclusion

Resection is a beneficial intervention for restoring the functional range of motion of the hip in order to improve the quality of life for patients with NHO and neurological disorders. We recommend performance of a minimal resection to achieve a targeted functional arc of motion in order to minimize the risk of postoperative complications.

The genetic background determines material-induced bone formation through the macrophage-osteoclast axis

Osteoinductive materials are characterized by their ability to induce bone formation in ectopic sites. Thus, osteoinductive materials hold promising potential for repairing bone defects. However, the mechanism of material-induced bone formation remains unknown, which limits the design of highly potent osteoinductive materials. Here, we demonstrated a genetic background link among macrophage polarization, osteoclastogenesis and material-induced bone formation. The intramuscular implantation of an osteoinductive material in FVB/NCrl (FVB) mice resulted in more M2 macrophages at week 1, more osteoclasts at week 2 and increased bone formation after week 4 compared with the results obtained in C57BL/6JOlaHsd (C57) mice. Similarly, in vitro, with a greater potential to form M2 macrophages, monocytes derived from FVB mice formed more osteoclasts than those derived from C57 mice. A transcriptomic analysis identified Csf1, Cxcr4 and Tgfbr2 as the main genes controlling macrophage-osteoclast coupling, which were further confirmed by related inhibitors. With such coupling, macrophage polarization and osteoclast formation of monocytes in vitro successfully predicted in vivo bone formation in four other mouse strains. Considering material-induced bone formation as an example of acquired heterotopic bone formation, the current findings shed a light on precision medicine for both bone regeneration and the treatment of pathological heterotopic bone formation.

The treatment challenge of heterotopic ossification in a patient with Parkinson's disease and stroke

OBJECTIVE

Neurogenic heterotopic ossification (HO) is characterized by bone formation in a non-anatomical site. It is usually seen in patients with spinal cord injury and traumatic brain injury. It occurs less frequently in other types of acquired brain injury. Neurogenic HO has only been recorded in a few cases of Parkinson's disease (PD). Its treatment is challenging and may need pain palliation methods. The course and treatment approach of a complicated case with PD and stroke who developed HO of the hip joints during rehabilitation was discussed in this article.

CASE PRESENTATION

A 79-year-old male patient with stroke and PD experienced restriction and pain in both hip joints. Bilateral HO was discovered on a pelvic radiograph. He did not benefit from exercises, transcutaneous electrical nerve stimulation, or indomethacin. Radiotherapy has also been tried to treat HO. Following that, obturator and femoral nerve blocks were used to relieve pain, and pain was reduced and sitting balance improved.

CONCLUSION

HO is a rare complication of PD and stroke that has an adverse effect on the rehabilitation process. Since treatment choices are limited, palliative pain management approaches such as peripheral nerve block may be considered.

Spinal cord injury dysregulates fibro-adipogenic progenitors miRNAs signaling to promote neurogenic heterotopic ossifications

Neurogenic heterotopic ossifications are intramuscular bone formations developing following central nervous system injury. The pathophysiology is poorly understood and current treatments for this debilitating condition remain unsatisfying. Here we explored the role of miRNAs in a clinically relevant mouse model that combines muscle and spinal cord injury, and in patients' cells. We found an osteo-suppressive miRNAs response in injured muscle that was hindered when the spinal cord injury was associated. In isolated fibro-adipogenic progenitors from damaged muscle (cells at the origin of ossification), spinal cord injury induced a downregulation of osteo-suppressive miRNAs while osteogenic markers were overexpressed. The overexpression of selected miRNAs in patient's fibro-adipogenic progenitors inhibited mineralization and osteo-chondrogenic markers in vitro. Altogether, we highlighted an osteo-suppressive mechanism involving multiple miRNAs in response to muscle injury that prevents osteogenic commitment which is ablated by the neurologic lesion in heterotopic ossification pathogenesis. This provides new research hypotheses for preventive treatments.

Rehabilitation Care of the Child with an Acute Severe Traumatic Brain Injury

Children with traumatic brain injury (TBI) represent a unique and evolving population. Recovery and long-term prognosis are variable given the heterogeneity of ages, developmental stages, and types of injuries. This article summarizes important information regarding severe TBI epidemiology, pathophysiology, classification, and acute management. Early and longitudinal involvement of rehabilitation experts, such as pediatric physiatrists, is critical in managing complications and optimizing outcomes.

Managing painful shoulder after neurological injury

Shoulder pain is common after neurological injury and can be disabling, lead to poor functional outcomes and increase care costs. Its cause is multifactoral and several pathologies contribute to the presentation. Astute diagnostic skills and a multidisciplinary approach are required to recognise what is clinically relevant and to implement appropriate stepwise management. In the absence of large clinical trial data, we aim to provide a comprehensive, practical and pragmatic overview of shoulder pain in patients with neurological conditions. We use available evidence to produce a management guideline, taking into account specialty opinions from neurology, rehabilitation medicine, orthopaedics and physiotherapy.

Oncostatin M: Risks and Benefits of a Novel Therapeutic Target for Atherosclerosis

BACKGROUND

Cardiovascular disease (CVD) is a leading cause of death worldwide. It is predicted that approximately 23.6 million people will die from CVDs annually by 2030. Therefore, there is a great need for an effective therapeutic approach to combat this disease. The European Cardiovascular Target Discovery (CarTarDis) consortium identified Oncostatin M (OSM) as a potential therapeutic target for atherosclerosis. The benefits of modulating OSM - an interleukin (IL)-6 family cytokine - have since been studied for multiple indications. However, as decades of high attrition rates have stressed, the success of a drug target is determined by the fine balance between benefits and the risk of adverse events. Safety issues should therefore not be overlooked.

OBJECTIVE

In this review, a risk/benefit analysis is performed on OSM inhibition in the context of atherosclerosis treatment. First, OSM signaling characteristics and its role in atherosclerosis are described. Next, an overview of in vitro, in vivo, and clinical findings relating to both the benefits and risks of modulating OSM in major organ systems is provided. Based on OSM's biological function and expression profile as well as drug intervention studies, safety concerns of inhibiting this target have been identified, assessed, and ranked for the target population.

CONCLUSION

While OSM may be of therapeutic value in atherosclerosis, drug development should also focus on de-risking the herein identified major safety concerns: tissue remodeling, angiogenesis, bleeding, anemia, and NMDA- and glutamate-induced neurotoxicity. Close monitoring and/or exclusion of patients with various comorbidities may be required for optimal therapeutic benefit.

Effectiveness of Prophylactic Interventions in Neurogenic Heterotopic Ossification (NHO): A Systematic Review

Neurogenic heterotopic ossification (NHO) is the formation of mature lamellar bone in peri-articular tissues following a neurological insult, most commonly traumatic brain injury (TBI) or spinal cord injury (SCI). NHO is a debilitating condition associated with significant morbidity and reduced quality of life. However, its pathophysiology remains poorly understood. While surgery is the mainstay of treatment once NHO has been diagnosed, prophylactic options are limited and not well studied. This review aimed to determine the efficacy of various interventions used in the primary prevention of NHO. We conducted an electronic literature search using five databases (PubMed, Embase, ScienceDirect, Cochrane Library, and Cumulative Index to Nursing and Allied Health Literature (CINAHL)) for records published until April 10, 2022. We identified 2,610 potentially eligible records across all databases. Nine reports met our eligibility criteria and were included in this review. Four were clinical trials (three randomized control trials, one nonrandomized trial), four were observational studies, and one was a systematic review/meta-analysis. The medications/interventions used included: warfarin, pulse low-intensity electromagnetic field therapy (PLIMF), bisphosphonates, and nonsteroidal anti-inflammatory drugs (NSAIDs). We did not find conclusive evidence to recommend the use of bisphosphonates and warfarin in the prevention of NHO. On the contrary, we found NSAIDs and PLIMF as effective prophylactic options based on the results of high-quality randomized control trials. Further prospective randomized studies with prolonged follow-ups are needed to confirm the long-term efficacy of these preventive interventions.

Cancellous bone-like tissue replacement from calcinosis in patients with systemic sclerosis with multiple external root resorption

Calcinosis is frequently observed in patients with systemic sclerosis (SSc). The fundamental treatment of calcinosis has not yet been established. During follow-up, calcinosis in the subcutaneous surface is often spontaneously extracted or remains confined by fibrous tissues. We previously identified a new symptom in SSc patients, multiple external root resorption (MERR), and these patients had calcifications in the nasal spine. Here, we report for the first time that calcinosis at the nasal spine in patients with MERR can be replaced by cancellous bone-like tissue. Patients 1 and 2 were a 62-year-old Japanese female and a 45-year-old Japanese female (respectively) with MERR who had been previously treated for SSc (Patient 1: limited type, positive for anti-centromere antibody; Patient 2: diffuse type, positive for anti-Scl70 and anti-SS-A antibodies). Patient 3 was a 57-year-old female with MERR who had been previously treated for SSc (diffuse type, positive anti-Scl-70 antibody) and underwent denosumab injection for osteoporosis. Cone-beam computed tomography (CBCT) and CT images in the calcifications at the nasal spine in Patient 1 and 2 were replaced with cancellous bone-like tissue, but not in Patient 3. Serum laboratory examination was performed to assess the systemic bone disease. All three patients had normal clinical data within the references, apart from slightly higher 1,25-dihydroxyvitamin D levels in Patient 1. SSc patients with calcinosis in the maxillofacial area need to be examined carefully for bone replacement using CBCT or CT.

Long-term radial extracorporeal shock wave therapy for neurogenic heterotopic ossification after spinal cord injury: A case report

Context: Heterotopic ossification is characterized by abnormal growth of bone in soft tissues. Neurogenic heterotopic ossification is also closely related to central nervous system injuries and has been reported to respond to radial extracorporeal shock wave therapy.Findings: In this case, a radial extracorporeal shock wave therapy (five times per week, lasted for almost one year) was applied to a patient with neurogenic heterotopic ossification on the left hip as a result of spinal cord injury. Throughout the treatment session, the heterotopic ossification lesion was gradually diminished, associated with the increase in joint range of motion, pain mitigation and decrease in serum alkaline phosphatase level.Conclusion/clinical relevance: Long-term radial extracorporeal shock wave therapy offers a promising therapeutic alternative for neurogenic heterotopic ossification.

Impact of Heterotopic Ossification on Functional Recovery in Acute Spinal Cord Injury

Objective: In spinal cord injury (SCI), heterotopic ossification is a frequent secondary complication, commonly associated with limited range of motion of affected joints, which could lead to secondary disability in activities of daily living. Additionally, heterotopic ossifications might challenge the effect of regeneration-promoting therapies on neurological and functional recovery. This study evaluated the impact of heterotopic ossification on clinical recovery within the first year after SCI.

Methods: The study was conducted as a monocentric longitudinal paired cohort study. Recruitment was based on consecutive sampling in the framework of the European Multicenter about Spinal Cord Injury (EMSCI). Recovery profiles were determined using standardized neurological and functional clinical assessments within the 1st year following SCI. All study participants underwent at least two comprehensive standardized neurological and functional clinical examinations according to the International Standards for Neurological Classification of SCI and the Spinal Cord Independence Measure, respectively. Data regarding the diagnosis and treatment of heterotopic ossification were obtained by reviewing the patient medical records. The most similar “digital twin” from the entire EMSCI database were matched in terms of age, acute neurological and functional status to each individual with SCI, and heterotopic ossification.

Results: Out of 25 participants diagnosed with heterotopic ossification, 13 individuals were enrolled and matched to control individuals. Most individuals presented with motor complete injury (75%). Ossifications were most frequently located at the hip joints (92%) and mainly occurred within the first 3 months after SCI. Individuals with heterotopic ossification achieved around 40% less functional improvement over time compared to their matched counterparts, whereas neurological recovery was not altered in individuals with SCI and heterotopic ossification.

Conclusion: Heterotopic ossification—a common complication of SCI—unfavorably affects functional recovery, which in the end is most relevant for the best possible degree of independence in activities of daily living. Upon presentation with heterotopic ossification, neurological improvement achieved through potential restorative therapies might not translate into clinically meaningful functional improvement. Diagnostic algorithms and effective early prevention/treatment options for heterotopic ossification need to be established to ensure the best possible functional outcome.

Clinical Trial Registration: NCT01571531 (https://clinicaltrials.gov).

Heterotopic Ossification: Clinical Features, Basic Researches, and Mechanical Stimulations

Heterotopic ossification (HO) is defined as the occurrence of extraskeletal bone in soft tissue. Although this pathological osteogenesis process involves the participation of osteoblasts and osteoclasts during the formation of bone structures, it differs from normal physiological osteogenesis in many features. In this article, the primary characteristics of heterotopic ossification are reviewed from both clinical and basic research perspectives, with a special highlight on the influence of mechanics on heterotopic ossification, which serves an important role in the prophylaxis and treatment of HO.

Lymphocytes Are Not Required for Neurogenic Heterotopic Ossification Development after Spinal Cord Injury

Neurogenic heterotopic ossifications (NHOs) are incapacitating complications of traumatic brain and spinal cord injuries (SCI) that manifest as abnormal bone formation in periarticular muscles. Using a unique model of NHO after SCI in genetically unmodified mice, we have previously established that the innate immune system plays a key driving role in NHO pathogenesis. The role of adaptive immune cells in NHO pathogenesis, however, remains unexplored in this model. Here we established that B lymphocytes were reduced in the spleen and blood after SCI and increased in muscles of mice in which NHO develops, whereas minimal changes in T cell frequencies were noted. Interestingly, Rag1^-/- mice lacking mature T and B lymphocytes, developed NHO, similar to wild-type mice. Finally, mice that underwent splenectomy before SCI and muscle damage also developed NHO to the same extent as non-splenectomized SCI controls. Overall, our findings show that functional T and B lymphocytes have minimal influence or dispensable contributions to NHO development after experimental SCI in mice.

Engineered osteoclasts as living treatment materials for heterotopic ossification therapy

Osteoclasts (OCs), the only cells capable of remodeling bone, can demineralize calcium minerals biologically. Naive OCs have limitations for the removal of ectopic calcification, such as in heterotopic ossification (HO), due to their restricted activity, migration and poor adhesion to sites of ectopic calcification. HO is the formation of pathological mature bone within extraskeletal soft tissues, and there are currently no reliable methods for removing these unexpected calcified plaques. In the present study, we develop a chemical approach to modify OCs with tetracycline (TC) to produce engineered OCs (TC-OCs) with an enhanced capacity for targeting and adhering to ectopic calcified tissue due to a broad affinity for calcium minerals. Unlike naive OCs, TC-OCs are able to effectively remove HO both in vitro and in vivo. This achievement indicates that HO can be reversed using modified OCs and holds promise for engineering cells as "living treatment agents" for cell therapy.

Future Perspectives in Spinal Cord Repair: Brain as Saviour? TSCI with Concurrent TBI: Pathophysiological Interaction and Impact on MSC Treatment

Traumatic spinal cord injury (TSCI), commonly caused by high energy trauma in young active patients, is frequently accompanied by traumatic brain injury (TBI). Although combined trauma results in inferior clinical outcomes and a higher mortality rate, the understanding of the pathophysiological interaction of co-occurring TSCI and TBI remains limited. This review provides a detailed overview of the local and systemic alterations due to TSCI and TBI, which severely affect the autonomic and sensory nervous system, immune response, the blood-brain and spinal cord barrier, local perfusion, endocrine homeostasis, posttraumatic metabolism, and circadian rhythm. Because currently developed mesenchymal stem cell (MSC)-based therapeutic strategies for TSCI provide only mild benefit, this review raises awareness of the impact of TSCI-TBI interaction on TSCI pathophysiology and MSC treatment. Therefore, we propose that unravelling the underlying pathophysiology of TSCI with concomitant TBI will reveal promising pharmacological targets and therapeutic strategies for regenerative therapies, further improving MSC therapy.

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.

Beyond the Brain: Peripheral Interactions after Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and disability, and there are currently no pharmacological treatments known to improve patient outcomes. Unquestionably, contributing toward a lack of effective treatments is the highly complex and heterogenous nature of TBI. In this review, we highlight the recent surge of research that has demonstrated various central interactions with the periphery as a potential major contributor toward this heterogeneity and, in particular, the breadth of research from Australia. We describe the growing evidence of how extracranial factors, such as polytrauma and infection, can significantly alter TBI neuropathology. In addition, we highlight how dysregulation of the autonomic nervous system and the systemic inflammatory response induced by TBI can have profound pathophysiological effects on peripheral organs, such as the heart, lung, gastrointestinal tract, liver, kidney, spleen, and bone. Collectively, this review firmly establishes TBI as a systemic condition. Further, the central and peripheral interactions that can occur after TBI must be further explored and accounted for in the ongoing search for effective treatments.

Potential genes and pathways associated with heterotopic ossification derived from analyses of gene expression profiles

Background

Heterotopic ossification (HO) represents pathological lesions that refer to the development of heterotopic bone in extraskeletal tissues around joints. This study investigates the genetic characteristics of bone marrow mesenchymal stem cells (BMSCs) from HO tissues and explores the potential pathways involved in this ailment.

Methods

Gene expression profiles (GSE94683) were obtained from the Gene Expression Omnibus (GEO), including 9 normal specimens and 7 HO specimens, and differentially expressed genes (DEGs) were identified. Then, protein–protein interaction (PPI) networks and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed for further analysis.

Results

In total, 275 DEGs were differentially expressed, of which 153 were upregulated and 122 were downregulated. In the biological process (BP) category, the majority of DEGs, including EFNB3, UNC5C, TMEFF2, PTH2, KIT, FGF13, and WISP3, were intensively enriched in aspects of cell signal transmission, including axon guidance, negative regulation of cell migration, peptidyl-tyrosine phosphorylation, and cell-cell signaling. Moreover, KEGG analysis indicated that the majority of DEGs, including EFNB3, UNC5C, FGF13, MAPK10, DDIT3, KIT, COL4A4, and DKK2, were primarily involved in the mitogen-activated protein kinase (MAPK) signaling pathway, Ras signaling pathway, phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) signaling pathway, and Wnt signaling pathway. Ten hub genes were identified, including CX3CL1, CXCL1, ADAMTS3, ADAMTS16, ADAMTSL2, ADAMTSL3, ADAMTSL5, PENK, GPR18, and CALB2.

Conclusions

This study presented novel insight into the pathogenesis of HO. Ten hub genes and most of the DEGs intensively involved in enrichment analyses may be new candidate targets for the prevention and treatment of HO in the future.

Multi-center observational study on occurrence and related clinical factors of neurogenic heterotopic ossification in patients with disorders of consciousness

Aims: to assess occurrence and clinical correlates of neurogenic heterotopic ossifications (NHO) in patients with prolonged disorder of consciousness (DoC).Design: multi-center cross-sectional observational study.Setting: 23 intensive neurorehabilitation units.Subjects: 287 patients with prolonged disorder of consciousness (DoC; 150 in vegetative state, VS, and 128 in minimally conscious state, MCS) of different etiology (vascular = 125, traumatic = 83, anoxic = 56, others = 14).Main Measures: clinical evidence of NHO confirmed by standard radiological and/or sonographic evaluation; Coma Recovery Scale-Revised; Disability Rating Scale (DRS); Early Rehabilitation Barthel Index; presence of ventilator support, spasticity, bone fractures and paroxysmal sympathetic hyperactivity.Results: 31 patients (11.2%) presented NHO. Univariate analyses showed that NHO was associated with VS diagnosis, traumatic etiology, high DRS category and total score, and high occurrence of limb spasticity and bone fractures. A cluster-corrected binary logistic regression model (excluding spasticity available in a subset of patients) showed that only lower DRS total score and presence of bone fractures were independently associated with NHO.Conclusions: NHO are relatively frequent in patients with DoC, and are independently associated with functional disability, bone fractures and spasticity. These findings contribute to identifying patients with DoC prone to develop NHO and requiring special interventions to improve functional recovery.

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.

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.

Early Reciprocal Effects in a Murine Model of Traumatic Brain Injury and Femoral Fracture

Traumatic brain injury (TBI) represents a major cause of death and disability in early adulthood. Concomitant extracranial injury such as long bone fracture was reported to exacerbate TBI pathology. However, early reciprocal effects and mechanisms have been barely investigated. To address this issue, C57BL/6N mice were subjected to either the controlled cortical impact (CCI) model of TBI, fracture of the left femur (FF), combined injury (CCI+FF), or sham procedure. Behavioral alterations were monitored until 5 days post injury (dpi), followed by (immuno-)histology, gene and protein expression analyses using quantitative PCR, western blot, and ELISA. We found that CCI+FF mice exhibited increased neurological impairments, reduced recovery, and altered anxiety-related behavior compared to single injury groups. At 5 dpi, cerebral lesion size was not affected by combined injury but exaggerated hippocampal substance loss and increased perilesional astrogliosis were observed in CCI+FF mice compared to isolated CCI. Bone gene expression of the osteogenic markers Runx2, osteocalcin, alkaline phosphatase, and bone sialoprotein was induced by fracture injury but attenuated by concomitant TBI. Plasma concentrations of the biomarkers osteopontin and progranulin were elevated in CCI+FF mice compared to other experimental groups. Taken together, using a murine model of TBI and femoral fracture, we report early reciprocal impairments of brain tissue maintenance, behavioral recovery, and bone repair gene expression. Increased circulating levels of the biomarkers osteopontin and progranulin indicate ongoing tissue inflammation and repair. Our results may have implications for future therapeutic approaches to interfere with the pathological crosstalk between TBI and concomitant bone fracture.

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.

Neurogenic Heterotopic Ossifications Develop Independently of Granulocyte Colony-Stimulating Factor and Neutrophils

Neurogenic heterotopic ossifications (NHOs) are incapacitating heterotopic bones in periarticular muscles that frequently develop following traumatic brain or spinal cord injuries (SCI). Using our unique model of SCI-induced NHO, we have previously established that mononucleated phagocytes infiltrating injured muscles are required to trigger NHO via the persistent release of the pro-inflammatory cytokine oncostatin M (OSM). Because neutrophils are also a major source of OSM, we investigated whether neutrophils also play a role in NHO development after SCI. We now show that surgery transiently increased granulocyte colony-stimulating factor (G-CSF) levels in blood of operated mice, and that G-CSF receptor mRNA is expressed in the hamstrings of mice developing NHO. However, mice defective for the G-CSF receptor gene Csf3r, which are neutropenic, have unaltered NHO development after SCI compared to C57BL/6 control mice. Because the administration of recombinant human G-CSF (rhG-CSF) has been trialed after SCI to increase neuroprotection and neuronal regeneration and has been shown to suppress osteoblast function at the endosteum of skeletal bones in human and mice, we investigated the impact of a 7-day rhG-CSF treatment on NHO development. rhG-CSF treatment significantly increased neutrophils in the blood, bone marrow, and injured muscles. However, there was no change in NHO development compared to saline-treated controls. Overall, our results establish that unlike monocytes/macrophages, neutrophils are dispensable for NHO development following SCI, and rhG-CSF treatment post-SCI does not impact NHO development. Therefore, G-CSF treatment to promote neuroregeneration is unlikely to adversely promote or affect NHO development in SCI patients. © 2020 American Society for Bone and Mineral Research.

Severe Heterotopic Ossification with Proximal Entrapment of the Ulnar Nerve following Primary Anterior Shoulder Dislocation

Heterotopic ossifications (HO) in the shoulder are rare. The effectiveness of conservative treatment is limited, and therefore, symptomatic cases are usually treated surgically. However, there are no guidelines for the surgical treatment of HO. Herein, we report the case of a 45-year-old man with severe HO and proximal entrapment of the ulnar nerve following primary anterior shoulder dislocation without concomitant injuries (e.g., fracture and rotator cuff tears). Surgical intervention was indicated, including resection of HO and neurolysis of the brachial plexus. Nine months after surgery, the patient presented with restored shoulder function, pain relief, and good patient satisfaction. The case shows that the ulnar nerve can also be impaired due to HO following shoulder dislocation.

Pyrophosphate therapy prevents trauma-induced calcification in the mouse model of neurogenic heterotopic ossification

Trauma‐induced calcification is the pathological consequence of complex injuries which often affect the central nervous system and other parts of the body simultaneously. We demonstrated by an animal model recapitulating the calcification of the above condition that adrenaline transmits the stress signal of brain injury to the calcifying tissues. We have also found that although the level of plasma pyrophosphate, the endogenous inhibitor of calcification, was normal in calcifying animals, it could not counteract the acute calcification. However, externally added pyrophosphate inhibited calcification even when it was administered after the complex injuries. Our finding suggests a potentially powerful clinical intervention of calcification triggered by polytrauma injuries which has no effective treatment.

Crosstalk of Brain and Bone-Clinical Observations and Their Molecular Bases

As brain and bone disorders represent major health issues worldwide, substantial clinical investigations demonstrated a bidirectional crosstalk on several levels, mechanistically linking both apparently unrelated organs. While multiple stress, mood and neurodegenerative brain disorders are associated with osteoporosis, rare genetic skeletal diseases display impaired brain development and function. Along with brain and bone pathologies, particularly trauma events highlight the strong interaction of both organs. This review summarizes clinical and experimental observations reported for the crosstalk of brain and bone, followed by a detailed overview of their molecular bases. While brain-derived molecules affecting bone include central regulators, transmitters of the sympathetic, parasympathetic and sensory nervous system, bone-derived mediators altering brain function are released from bone cells and the bone marrow. Although the main pathways of the brain-bone crosstalk remain ‘efferent’, signaling from brain to bone, this review emphasizes the emergence of bone as a crucial ‘afferent’ regulator of cerebral development, function and pathophysiology. Therefore, unraveling the physiological and pathological bases of brain-bone interactions revealed promising pharmacologic targets and novel treatment strategies promoting concurrent brain and bone recovery.

Development of heterotopic ossification after multiple-ligament reconstruction of the knee joint: Incidence and explanatory factor analysis

BACKGROUND

The development of heterotopic ossification (HO) might nullify any benefit of multiple-ligament reconstruction of the knee joint. The purpose of this study was to investigate the incidence and the specific explanatory factors for the development of HO after multiple-ligament reconstruction of the knee joint.

METHODS

From January 2011 to June 2016, 72 consecutive patients with knee dislocations received multiple-ligament reconstructions, of which 57 (79%) were available for a minimum follow up of 12 months and were included in this study. Anteroposterior (AP) and lateral radiographs were reviewed for all patients. This knee dislocation cohort was separated into two groups based on the presence or absence of HO for comparisons. In addition, the HO group was divided into three subgroups based on a modified quadrant grading system introduced by the senior author for further evaluation. Multivariate logistic regression analysis was then performed to identify specific explanatory factors predicting development of HO in patients after multiple-ligament reconstructions of the knee joint.

RESULTS

Among the 72 consecutive patients, 57 (79%) were available for the clinical evaluations with an average period of 28.4 months (range, 12-51 months). Twenty-one patients (37%) showed radiological evidence of HO. The HO group (n = 21) showed significantly inferior results of knee flexion angle compared with the non-HO group (n = 36) (HO group vs. non-HO group: 124 ± 13° vs. 132 ± 5°; P<0.01). According to the quadrant grading system, there were seven patients with grade I, nine with grade II, and five with grade III HO. Subgroup analysis further revealed that higher HO grade would lead to lower knee flexion angle. In addition, multivariate regression analysis showed that concomitant posterior cruciate ligament reconstruction was the only independent explanatory factor predicting the development of HO after multiple-ligament reconstruction of the knee joint (P=0.018; odds ratio, 8.75; 95% confidence interval, 1.69-39.7).

CONCLUSION

In this cohort of knee dislocations, the incidence of HO development following multiple-ligament reconstruction was 37%, with grade III HO showing the most inferior range of motion outcome. Moreover, concomitant posterior cruciate ligament reconstruction was the only independent predictor for the development of HO.

A novel rat model of heterotopic ossification after polytrauma with traumatic brain injury

Neurological heterotopic ossification (NHO) is characterized by abnormal bone growth in soft tissue and joints in response to injury to the central nervous system. The ectopic bone frequently causes pain, restricts mobility, and decreases the quality of life for those affected. NHO commonly develops in severe traumatic brain injury (TBI) patients, particularly in the presence of concomitant musculoskeletal injuries (i.e. polytrauma). There are currently no animal models that accurately mimic these combinations of injuries, which has limited our understanding of NHO pathobiology, as well as the development of biomarkers and treatments, in TBI patients. In order to address this shortcoming, here we present a novel rat model that combines TBI, femoral fracture, and muscle crush injury. Young adult male Sprague Dawley rats were randomly assigned into three different injury groups: triple sham-injury, peripheral injury only (i.e., sham-TBI + fracture + muscle injury) or triple injury (i.e., TBI + fracture + muscle injury). Evidence of ectopic bone in the injured hind-limb, as confirmed by micro-computed tomography (μCT), was found at 6-weeks post-injury in 70% of triple injury rats, 20% of peripheral injury rats, and 0% of the sham-injured controls. Furthermore, the triple injury rats had higher ectopic bone severity scores than the sham-injured group. This novel model will provide a platform for future studies to identify underlying mechanisms, biomarkers, and develop evidence based pharmacological treatments to combat this debilitating long-term complication of TBI and polytrauma.

Lollipop Sign - Ossification at Wire Ends after Osteosynthesis?

Introduction:

Heterotopic ossification (HO) is abnormal formation of new bone in the soft tissue. HO occurs outside the normal bone within soft tissues such as muscles and tendons, and histologically, it is no different from skeletal bone. It is still not clear what factors stimulate HO. The soft tissue around the hip joint has been identified as the most common location for HO. Patients with HO usually have no clinical symptoms; however, it can become very painful and lead to severe functional limitations. The standard diagnostic procedure consists of conventional X-ray diagnostics and/or skeletal scintigraphy. Local radiation and nonsteroidal anti-inflammatory drugs are the classical options for treatment and prophylaxis of HO. We describe two pediatric patients with “lollipop-like” HO at the end of Kirschner wires (K-wires, steel) and titanium elastic nails (TENs, titanium).

Case Report:

A 9-year-old girl, 1 year after Salter and Pemberton osteotomy with K-wires, and a 15-year-old boy, 1 year after fracture of the right femur treated by osteosynthesis with TENs, were treated in our department due to HO. The girl did not report any symptoms, while the boy had pain in the location where the ossification had formed. However, examination of the girl’s hip showed that the range of motion in the hip affected by HO was limited in comparison with the opposite unaffected hip.

Conclusion:

To the best of our knowledge, lollipop-like HO around protruding K-wires or TENs has not yet been described. According to literature, HO is mainly located in the pelvic region and at the elbow. Most studies investigating HO describe cases which have occurred after cemented or uncemented hip replacement surgery. In the cases presented here, HO might have been stimulated by repetitive muscle trauma above the protruding K-wire and TENs, the trauma caused by the operation, bone marrow cells dispersed intraoperatively, or by a combination of these and other factors. There are numerous studies on strategies to prevent HO after joint replacement. We suggest “lollipop sign” as a name for this rare type of HO around the end of K-wires/TENs in pediatric patients.

Surgical Management of Shoulder Heterotopic Ossification

The formation of heterotopic ossification around the shoulder is a rare but potentially debilitating condition. It is found most commonly around the hip and is usually associated with an inciting event such as trauma, burn, previous surgery, or traumatic brain/spinal cord injury. The formation of shoulder heterotopic ossification following arthroscopic surgery is very uncommon, with few data pertaining to it in the current literature. Formation of heterotopic ossification in the shoulder after arthroscopic surgery typically occurs around the acromioclavicular joint and in the subacromial space. This location may lead to chronic pain and decreased mobility. The purpose of this article is to describe an arthroscopic technique for excision of heterotopic ossification.

Muscle injury-induced hypoxia alters the proliferation and differentiation potentials of muscle resident stromal cells

Background

Trauma-induced heterotopic ossification (HO) is a complication that develops under three conditions: the presence of an osteogenic progenitor cell, an inducing factor, and a permissive environment. We previously showed that a mouse multipotent Sca1⁺ CD31⁻ Lin⁻ muscle resident stromal cell (mrSC) population is involved in the development of HO in the presence of inducing factors, members of the bone morphogenetic protein family. Interestingly, BMP9 unlike BMP2 causes HO only if the muscle is damaged by injection of cardiotoxin. Because acute trauma often results in blood vessel breakdown, we hypothesized that a hypoxic state in damaged muscles may foster mrSCs activation and proliferation and trigger differentiation toward an osteogenic lineage, thus promoting the development of HO.

Methods

Three- to - six-month-old male C57Bl/6 mice were used to induce muscle damage by injection of cardiotoxin intramuscularly into the tibialis anterior and gastrocnemius muscles. mrSCs were isolated from damaged (hypoxic state) and contralateral healthy muscles and counted, and their osteoblastic differentiation with or without BMP2 and BMP9 was determined by alkaline phosphatase activity measurement. The proliferation and differentiation of mrSCs isolated from healthy muscles was also studied in normoxic incubator and hypoxic conditions. The effect of hypoxia on BMP synthesis and Smad pathway activation was determined by qPCR and/or Western blot analyses. Differences between normally distributed groups were compared using a Student’s paired t test or an unpaired t test.

Results

The hypoxic state of a severely damaged muscle increased the proliferation and osteogenic differentiation of mrSCs. mrSCs isolated from damaged muscles also displayed greater sensitivity to osteogenic signals, especially BMP9, than did mrSCs from a healthy muscle. In hypoxic conditions, mrSCs isolated from a control muscle were more proliferative and were more prone to osteogenic differentiation. Interestingly, Smad1/5/8 activation was detected in hypoxic conditions and was still present after 5 days, while Smad1/5/8 phosphorylation could not be detected after 3 h of normoxic incubator condition. BMP9 mRNA transcripts and protein levels were higher in mrSCs cultured in hypoxic conditions. Our results suggest that low-oxygen levels in damaged muscle influence mrSC behavior by facilitating their differentiation into osteoblasts. This effect may be mediated partly through the activation of the Smad pathway and the expression of osteoinductive growth factors such as BMP9 by mrSCs.

Conclusion

Hypoxia should be considered a key factor in the microenvironment of damaged muscle that triggers HO.

Electronic supplementary material

The online version of this article (10.1186/s13395-019-0202-5) contains supplementary material, which is available to authorized users.

Inhibition of JAK1/2 Tyrosine Kinases Reduces Neurogenic Heterotopic Ossification After Spinal Cord Injury

Neurogenic heterotopic ossifications (NHO) are very incapacitating complications of traumatic brain and spinal cord injuries (SCI) which manifest as abnormal formation of bone tissue in periarticular muscles. NHO are debilitating as they cause pain, partial or total joint ankylosis and vascular and nerve compression. NHO pathogenesis is unknown and the only effective treatment remains surgical resection, however once resected, NHO can re-occur. To further understand NHO pathogenesis, we developed the first animal model of NHO following SCI in genetically unmodified mice, which mimics most clinical features of NHO in patients. We have previously shown that the combination of (1) a central nervous system lesion (SCI) and (2) muscular damage (via an intramuscular injection of cardiotoxin) is required for NHO development. Furthermore, macrophages within the injured muscle play a critical role in driving NHO pathogenesis. More recently we demonstrated that macrophage-derived oncostatin M (OSM) is a key mediator of both human and mouse NHO. We now report that inflammatory monocytes infiltrate the injured muscles of SCI mice developing NHO at significantly higher levels compared to mice without SCI. Muscle infiltrating monocytes and neutrophils expressed OSM whereas mouse muscle satellite and interstitial cell expressed the OSM receptor (OSMR). In vitro recombinant mouse OSM induced tyrosine phosphorylation of the transcription factor STAT3, a downstream target of OSMR:gp130 signaling in muscle progenitor cells. As STAT3 is tyrosine phosphorylated by JAK1/2 tyrosine kinases downstream of OSMR:gp130, we demonstrated that the JAK1/2 tyrosine kinase inhibitor ruxolitinib blocked OSM driven STAT3 tyrosine phosphorylation in mouse muscle progenitor cells. We further demonstrated in vivo that STAT3 tyrosine phosphorylation was not only significantly higher but persisted for a longer duration in injured muscles of SCI mice developing NHO compared to mice with muscle injury without SCI. Finally, administration of ruxolitinib for 7 days post-surgery significantly reduced STAT3 phosphorylation in injured muscles in vivo as well as NHO volume at all analyzed time-points up to 3 weeks post-surgery. Our results identify the JAK/STAT3 signaling pathway as a potential therapeutic target to reduce NHO development following SCI.

Polyarticular Neurogenic Heterotopic Ossification in a Spinal Cord Injury: A Case Report from Saudi Arabia

A 33-year-old male victim of a motor vehicle accident, who presented with a T12 (thoracic 12 vertebra) burst fracture (ISNCSCI T11 AIS-A: International Standards for Neurological Classification of Spinal Cord Injury T11 ASIA Impairment Scale), was admitted to a rehabilitation hospital. A stage-II left ischial pressure ulcer was also reported. An X-ray of the pelvis revealed bilateral neurogenic heterotopic ossification (NHO) in both hips and knees, which was further confirmed by TC-99m methylene diphosphonate (MDP) bone scintigraphy. Interventions included indomethacin and conservative management. Surgery was not preferred, as NHO was still immature. Moreover, patient transfer and lower body dressing were unaffected by NHO. It is important to consider an early radiological screen in selected high-risk cases for NHO, to minimize the risk of associated complications.

Protein biomarkers of epileptogenicity after traumatic brain injury

Traumatic brain injury (TBI) is a major risk factor for acquired epilepsy. Post-traumatic epilepsy (PTE) develops over time in up to 50% of patients with severe TBI. PTE is mostly unresponsive to traditional anti-seizure treatments suggesting distinct, injury-induced pathomechanisms in the development of this condition. Moderate and severe TBIs cause significant tissue damage, bleeding, neuron and glia death, as well as axonal, vascular, and metabolic abnormalities. These changes trigger a complex biological response aimed at curtailing the physical damage and restoring homeostasis and functionality. Although a positive correlation exists between the type and severity of TBI and PTE, there is only an incomplete understanding of the time-dependent sequelae of TBI pathobiologies and their role in epileptogenesis. Determining the temporal profile of protein biomarkers in the blood (serum or plasma) and cerebrospinal fluid (CSF) can help to identify pathobiologies underlying the development of PTE, high-risk individuals, and disease modifying therapies. Here we review the pathobiological sequelae of TBI in the context of blood- and CSF-based protein biomarkers, their potential role in epileptogenesis, and discuss future directions aimed at improving the diagnosis and treatment of PTE.

Mild Traumatic Brain Injury in Adolescent Mice Alters Skull Bone Properties to Influence a Subsequent Brain Impact at Adulthood: A Pilot Study

Mild traumatic brain injuries (mTBI) are common during adolescence, and limited clinical evidence suggests that a younger age at first exposure to a mTBI may lead to worse long-term outcomes. In this study, we hypothesized that a mTBI during adolescence would predispose toward poorer neurobehavioral and neuropathological outcomes after a subsequent injury at adulthood. Mice received a mild weight drop injury (mTBI) at adolescence (postnatal day 35; P35) and/or at adulthood (P70). Mice were randomized to 6 groups: 'sham' (sham-surgery at P35 only); 'P35' (mTBI at P35 only); 'P35 + sham' (mTBI at P35 + sham at P70); 'sham + P70' (sham at P35 + mTBI at P70); 'sham + sham' (sham at both P35 and P70); or 'P35 + P70' (mTBI at both P35 and P70). Acute apnea and an extended righting reflex time confirmed a mTBI injury at P35 and/or P70. Cognitive, psychosocial, and sensorimotor function was assessed over 1-week post-injury. Injured groups performed similarly to sham controls across all tasks. Immunofluorescence staining at 1 week detected an increase in glial activation markers in Sham + P70 brains only. Strikingly, 63% of Sham + P70 mice exhibited a skull fracture at impact, compared to 13% of P35 + P70 mice. Micro computed tomography of parietal skull bones found that a mTBI at P35 resulted in increased bone volume and strength, which may account for the difference in fracture incidence. In summary, a single mTBI to the adolescent mouse brain did not exacerbate the cerebral effects of a subsequent mTBI in adulthood. However, the head impact at P35 induced significant changes in skull bone structure and integrity. These novel findings support future investigation into the consequences of mTBI on skull bone.