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

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.

Cutaneous burn injury represents a major risk factor for the development of traumatic ectopic bone formation following blast-related extremity injury

Blast-related traumatic heterotopic ossification (tHO) impacts clinical outcomes in combat-injured patients, leading to delayed wound healing, inflammatory complications, and reduced quality of life. Blast injured patients often have significant burns. This study investigated whether a partial thickness thermal burn injury exacerbates blast-related tHO in a clinically relevant polytrauma animal model. Adult male Sprague Dawley rats were subjected to an established model involving a whole-body blast overpressure exposure (BOP), complex extremity trauma followed by hind limb amputation (CET) followed by the addition of a 10 % total body surface area (TBSA) second degree thermal burn (BU). Micro-CT scans on post-operative day 56 showed a significant increase in HO volume in the CET + BU as compared to the CET alone injury group (p < .0001; 22.83 ± 3.41 mm3 vs 4.84 ± 5.77 mm3). Additionally, CET + BU concomitant with BOP significantly increased HO (p < .0001; 34.95 ± 7.71 mm3) as compared to CET + BU alone, confirming BOP has a further synergistic effect. No HO was detectable in rats in the absence of CET. Serum analysis revealed similar significant elevated (p < .0001) levels of pro-inflammatory markers (Cxcl1 and Il6) at 6 h post-injury (hpi) in the CET + BU and BOP + CET + BU injury groups as compared to naïve baseline values. Real-time qPCR demonstrated similar levels of chondrogenic and osteogenic gene expression in muscle tissue at the site of injury at 168 hpi in both the CET + BU and BOP+CET + BU injury groups. These results support the hypothesis that a 10 % TBSA thermal burn markedly enhances tHO following acute musculoskeletal extremity injury in the presence and absence of blast overpressure. Furthermore, the influence of BOP on tHO cannot be accounted for either in regards to systemic inflammation induced from remote injury or inflammatory-osteo-chondrogenic expression changes local to the musculoskeletal trauma, suggesting that another mechanism beyond BOP and BU synergistic effects are at play. Therefore, these findings warrant future investigations to explore other mechanisms by which blast and burn influence tHO, and testing prophylactic measures to mitigate the local and systemic inflammatory effects of these injuries on development of HO.

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.

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

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

A Quantitative and Qualitative Literature Analysis of the Orthopedic Surgeons' Experience: Reflecting on 20 Years in the Global War on Terror

INTRODUCTION

After over 20 years of war in the Middle East, orthopedic injuries have been among the most prevalent combat-related injuries, accounting for 14% of all surgical procedures at Role 2/3 (R2/R3) facilities according to the DoD Trauma Registry. To further delineate the role of the deployed orthopedic surgeon on the modern battlefield, a retrospective review was performed highlighting both quantitative and qualitative analysis factors associated with orthopedic surgical care during the war in the Middle East.

METHODS

A retrospective review was conducted of orthopedic surgeons in the Middle East from 2001 to 2021. A comprehensive literature search was conducted using the PubMed and Embase databases using a two-reviewer strategy. Articles were compiled and reviewed using Covidence. Inclusion criteria included journal articles focusing on orthopedic injuries sustained during the Global War on Terror (GWoT) in an adult U.S. Military population. In the event of a conflict, a third author would determine the relevance of the article. For the remaining articles, a full-text review was conducted to extract relevant predetermined quantitative data, and the Delphi consensus method was then utilized to highlight relevant qualitative themes.

RESULTS

The initial search yielded 1,226 potentially relevant articles. In all, 40 studies ultimately met the eligibility criteria. With the consultation of previously deployed orthopedic surgeons at the Walter Reed National Military Medical Center, a retrospective thematic analysis of the 40 studies revealed five themes encompassing the orthopedic surgeons experience throughout GWoT. These themes include unique mechanisms of orthopedic injury compared to previous war injuries due to novel weaponry, differences in interventions depending on R2 versus R3 locations, differences in injuries from those seen in civilian settings, the maintained emphasis on humanitarian aspect of an orthopedic surgeon's mission, and lastly relation of pre-deployment training to perceived deployed success of the orthopedic surgeons. From this extensive review, we found that explosive mechanisms of injury were greatly increased when compared to previous conflicts and were the etiology for the majority of orthopedic injuries sustained. With the increase of complex explosive injuries in the setting of improved body armor and overall survival, R2/3 facilities showed an increased demand for orthopedic intervention including debridement, amputations, and external fixation. Combat injuries sustained during the GWoT differ in the complications, management, and complexity when compared to civilian trauma. "Humanitarian" cases made up a significant number of operative cases for the deployed orthopedic surgeon. Lastly, heterogeneous training opportunities were available prior to deployment (fellowship, combat extremity surgical courses, and dedicated pre-deployment training), and the most commonly identified useful training was learning additional soft-tissue coverage techniques.

CONCLUSION

These major themes indicate an emphasis on pre-deployment training and the strategic positioning of orthopedic surgeons to reflect the changing landscape of musculoskeletal trauma care. Moving forward, these authors recommend analyzing the comfort and perceived capability of orthopedic surgeons in these unique military environments to best prepare for a changing operational format and the possibility of future peer-peer conflicts that will likely lead to a lack of medical evacuation and prolonged field care.

Verteporfin attenuates trauma-induced heterotopic ossification of Achilles tendon by inhibiting osteogenesis and angiogenesis involving YAP/β-catenin signaling

Heterotopic ossification occurs as a pathological ossification condition characterized by ectopic bone formation within soft tissues following trauma. Vascularization has long been established to fuel skeletal ossification during tissue development and regeneration. However, the feasibility of vascularization as a target of heterotopic ossification prevention remained to be further clarified. Here, we aimed to identify whether verteporfin as a widely used FDA-approved anti-vascularization drug could effectively inhibit trauma-induced heterotopic ossification formation. In the current study, we found that verteporfin not only dose dependently inhibited the angiogenic activity of human umbilical vein endothelial cells (HUVECs) but also the osteogenic differentiation of tendon stem cells (TDSCs). Moreover, YAP/β-catenin signaling axis was downregulated by the verteporfin. Application of lithium chloride, an agonist of β-catenin, recovered TDSCs osteogenesis and HUVECs angiogenesis that was inhibited by verteporfin. In vivo, verteporfin attenuated heterotopic ossification formation by decelerating osteogenesis and the vessels densely associated with osteoprogenitors formation, which could also be readily reversed by lithium chloride, as revealed by histological analysis and Micro-CT scan in a murine burn/tenotomy model. Collectively, this study confirmed the therapeutic effect of verteporfin on angiogenesis and osteogenesis in trauma-induced heterotopic ossification. Our study sheds light on the anti-vascularization strategy with verteporfin as a candidate treatment for heterotopic ossification prevention.

Negative pressure wound therapy: Where are we in 2022?

The use of negative pressure wound therapy (NPWT) continues to be an important tool for surgeons. As the use and general acceptance of NPWT have grown, so have the indications for its use. These indications have expanded to include soft tissue defects in trauma, infection, surgical wound management, and soft tissue grafting procedures. Many adjuvants have been engineered into newer generations of NPWT devices such as wound instillation of fluid or antibiotics allowing surgeons to further optimize the wound healing environment or aid in the eradication of infection. This review discusses the recent relevant literature on the proposed mechanisms of action, available adjuvants, and the required components needed to safely apply NPWT. The supporting evidence for the use of NPWT in traumatic extremity injuries, infection control, and wound care is also reviewed. Although NPWT has a low rate of complication, the surgeon should be aware of the potential risks associated with its use. Furthermore, the expanding indications for the use of NPWT are explored, and areas for future innovation and research are discussed.

Heterotopic Ossification in Hip Arthroscopy

Introduction  Hip arthroscopy is a rising surgical technique due to the increase in hip diseases, especially femoroacetabular impingement. One of the several complications related to such procedures is heterotopic ossifications (HO). The aim of this study is to describe the prevalence of HO after hip arthroscopy in a series of patients with femoroacetabular impingement and to compare its preoperative and intraoperative variables with a matched control group of patients without HO. Methods  All patients who underwent hip arthroscopy for femoroacetabular impingement between 2010 and 2017 with a minimum follow-up of 2 years were included in this analysis. Radiographic examinations were recorded to select cases with HO. A case-control analysis was performed comparing preoperative and intraoperative variables between cases with HO and a matched control group without HO. Results  A total of 700 cases were included in the analysis. HO was found in 15 (2.14%) of subjects. Cases with HO showed more severe cartilage injuries, less cam morphology ratio, and a higher proportion of partial labrectomies than the control group. No significant differences were observed in preoperative hip pain or function between groups. Conclusions  The prevalence of HO after hip arthroscopy in subjects with femoroacetabular impingement was 2.14%. Cases with HO had more severe cartilage injuries, lower ratio of cam morphology, and higher proportion of partial labrectomies than the control cases without HO. Level of Evidence  Level III.

The Kinesin Gene KIF26B Modulates the Severity of Post-Traumatic Heterotopic Ossification

The formation of pathological bone deposits within soft tissues, termed heterotopic ossification (HO), is common after trauma. However, the severity of HO formation varies substantially between individuals, from relatively isolated small bone islands through to extensive soft tissue replacement by bone giving rise to debilitating symptoms. The aim of this study was to identify novel candidate therapeutic molecular targets for severe HO. We conducted a genome-wide scan in men and women with HO of varying severity following hip replacement for osteoarthritis. HO severity was dichotomized as mild or severe, and association analysis was performed with adjustment for age and sex. We next confirmed expression of the gene encoded by the lead signal in human bone and in primary human mesenchymal stem cells. We then examined the effect of gene knockout in a murine model of osseous trans-differentiation, and finally we explored transcription factor phosphorylation in key pathways perturbed by the gene. Ten independent signals were suggestively associated with HO severity, with KIF26B as the lead. We subsequently confirmed KIF26B expression in human bone and upregulation upon BMP2-induced osteogenic differentiation in primary human mesenchymal stem cells, and also in a rat tendo-Achilles model of post-traumatic HO. CRISPR-Cas9 mediated knockout of Kif26b inhibited BMP2-induced Runx2, Sp7/Osterix, Col1A1, Alp, and Bglap/Osteocalcin expression and mineralized nodule formation in a murine myocyte model of osteogenic trans-differentiation. Finally, KIF26B deficiency inhibited ERK MAP kinase activation during osteogenesis, whilst augmenting p38 and SMAD 1/5/8 phosphorylation. Taken together, these data suggest a role for KIF26B in modulating the severity of post-traumatic HO and provide a potential novel avenue for therapeutic translation.

Treatment of Temporomandibular Joint Heterotopic Ossificans: A Novel Protocol With Multimodal Therapy Based on Literature Review and Presentation of a Unique Case Reportc

PURPOSE

The purpose of this study was to create a treatment protocol for cases of heterotopic ossification (HO) of the temporomandibular joint (TMJ), particularly those refractory to current TMJ HO protocols. In addition, we demonstrate the success of this protocol on a unique case of recurrent HO that failed multiple TMJ HO protocols in the setting of an improvised explosive device (IED) blast in a wounded warrior.

METHODS

An electronic literature review was conducted via PubMed and Web of Science. Twenty-five studies were identified to provide supporting evidence for a proposed, up-to-date protocol for the treatment of refractory TMJ HO. The authors present a case report of a wounded warrior with HO ankylosis of bilateral TMJs in the setting of IED blast and demonstrate successful use of our surgical and pharmacotherapeutic protocol.

RESULTS

Based on the literature review, our proposed protocol consists of pharmacotherapy with celecoxib and etidronate, with weekly forced dilation (brisement) and home physical therapy with the TheraBite Jaw Motion Rehab System. Surgically, the TMJ should be treated with two-stage reconstruction using initial polymethyl methacrylate spacers and subsequent total joint reconstruction with custom prostheses, fat grafting, and 3-dimensional-navigated total resection of HO. This protocol was successfully utilized in our patient's refractory HO ankylosed TMJ secondary to IED blast, and the patient's maximal incisal opening was regained and has remained stable 2 years after surgery without recurrent HO.

CONCLUSIONS

Our method for treatment in this case deviated from the standard TMJ Concepts HO protocol in that it included multimodal pharmacotherapy with celecoxib and etidronate. Based on our literature review and experience, we advise that clinicians utilize our protocol for the management of all craniofacial HO cases, particularly in cases of recurrent HO that fail conventional therapies and/or involving high-order blast trauma.

Unraveling an Innate Mechanism of Pathological Mineralization-Regulated Inflammation by a Nanobiomimetic System

Pathological mineralization (PTM) often occurs under inflammation and affects the prognosis of diseases, such as atherosclerosis and cancers. However, how the PTM impacts inflammation has not been well explored. Herein, poly lactic-co-glycolic acid (PLGA)/gelatin/hydroxyapatite (HA) electrospun nanofibers are rationally designed as an ideal PTM microenvironment biomimetic system for unraveling the role of PTM on inflammation. The results demonstrate that the inflammatory response decreases continuously during the process of mineralization. When mature macromineralization forms, the inflammation almost completely disappears. Mechanistically, the PTM formation is mediated by matrix proteins, local high calcium, and cell debris (nuclei), or actively regulated by the lysosomal/plasma membrane components secreted by macrophages. These inflammatory inducible factors (calcium, cell debris, etc.) can be "buried" through PTM process, resulting in reduced immune responses. Overall, the present study demonstrates that PTM is an innate mechanism of inflammation subsidence, providing valuable insight into understanding the action of mineralization on inflammation.

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

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

Targeting local lymphatics to ameliorate heterotopic ossification via FGFR3-BMPR1a pathway

Acquired heterotopic ossification (HO) is the extraskeletal bone formation after trauma. Various mesenchymal progenitors are reported to participate in ectopic bone formation. Here we induce acquired HO in mice by Achilles tenotomy and observe that conditional knockout (cKO) of fibroblast growth factor receptor 3 (FGFR3) in Col2⁺ cells promote acquired HO development. Lineage tracing studies reveal that Col2⁺ cells adopt fate of lymphatic endothelial cells (LECs) instead of chondrocytes or osteoblasts during HO development. FGFR3 cKO in Prox1⁺ LECs causes even more aggravated HO formation. We further demonstrate that FGFR3 deficiency in LECs leads to decreased local lymphatic formation in a BMPR1a-pSmad1/5-dependent manner, which exacerbates inflammatory levels in the repaired tendon. Local administration of FGF9 in Matrigel inhibits heterotopic bone formation, which is dependent on FGFR3 expression in LECs. Here we uncover Col2⁺ lineage cells as an origin of lymphatic endothelium, which regulates local inflammatory microenvironment after trauma and thus influences HO development via FGFR3-BMPR1a pathway. Activation of FGFR3 in LECs may be a therapeutic strategy to inhibit acquired HO formation via increasing local lymphangiogenesis.

Different types of mesenchymal progenitors participate in ectopic bone formation. Here, the authors show Col2⁺ lineage cells adopt a lymphatic endothelium cell fate, which regulates local inflammatory microenvironment after trauma, thus influencing heterotopic ossification (HO) development via a FGFR3-BMPR1a pathway.

The War after War: Volumetric Muscle Loss Incidence, Implication, Current Therapies and Emerging Reconstructive Strategies, a Comprehensive Review

Volumetric muscle loss (VML) is the massive wasting of skeletal muscle tissue due to traumatic events or surgical ablation. This pathological condition exceeds the physiological healing process carried out by the muscle itself, which owns remarkable capacity to restore damages but only when limited in dimensions. Upon VML occurring, the affected area is severely compromised, heavily influencing the affected a person’s quality of life. Overall, this condition is often associated with chronic disability, which makes the return to duty of highly specialized professional figures (e.g., military personnel or athletes) almost impossible. The actual treatment for VML is based on surgical conservative treatment followed by physical exercise; nevertheless, the results, in terms of either lost mass and/or functionality recovery, are still poor. On the other hand, the efforts of the scientific community are focusing on reconstructive therapy aiming at muscular tissue void volume replenishment by exploiting biomimetic matrix or artificial tissue implantation. Reconstructing strategies represent a valid option to build new muscular tissue not only to recover damaged muscles, but also to better socket prosthesis in terms of anchorage surfaces and reinnervation substrates for reconstructed mass.

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.

Reliability of the Walter Reed Classification for Heterotopic Ossification Severity in Amputees

OBJECTIVE

At this time, there is no validated tool for describing heterotopic ossification (HO) severity or measuring efficacy of therapies after amputation. This study aims to validate the Walter Reed classification system for reliable characterization of HO burden in residual limbs.

DESIGN

Descriptive, Level IV.

SETTING

US Military Trauma Referral Center.

STUDY POPULATION

Five orthopaedic surgeon raters with varying experience levels assessed orthogonal radiographs of 100 randomly selected residual upper and lower limbs after combat-related amputation.

INTERVENTION

A standardized education session on the Walter Reed HO classification system followed by 2 grading sessions, separated by a 2-week waiting period.

MAIN OUTCOME MEASURES

Scores were analyzed for interobserver and intraobserver reliability using weighted Cohen's kappa, intraclass correlation coefficient, and Krippendorff's alpha for ordinal variables.

RESULTS

After the waiting period, 89% of HO was rated the same by observers with an intraobserver kappa = 0.83 (95% confidence interval [CI] 0.75-0.92). Interobserver reliability was evaluated using group-wise comparison among observers, resulting in an overall Krippendorff's alpha = 0.78 (95% CI 0.76-0.80). Using intraclass correlation coefficient, interrater consistency was 0.94 (95% CI 0.91-0.96).

CONCLUSIONS

The Walter Reed HO classification system is substantially reliable for use by raters with any level of orthopaedic training. In addition, it is reliable for evaluation of both through bone and disarticulation type amputations in the upper and lower extremities. However, in 11% of cases, a secondary read may vary, suggesting that this system is useful for understanding HO and developing interventions but may benefit from further refinement, including advanced imaging and clinical correlation.

When the Nervous System Turns Skeletal Muscles into Bones: How to Solve the Conundrum of Neurogenic Heterotopic Ossification

PURPOSE OF REVIEW

Neurogenic heterotopic ossification (NHO) is the abnormal formation of extra-skeletal bones in periarticular muscles after damage to the central nervous system (CNS) such as spinal cord injury (SCI), traumatic brain injury (TBI), stroke, or cerebral anoxia. The purpose of this review is to summarize recent developments in the understanding of NHO pathophysiology and pathogenesis. Recent animal models of NHO and recent findings investigating the communication between CNS injury, tissue inflammation, and upcoming NHO therapeutics are discussed.

RECENT FINDINGS

Animal models of NHO following TBI or SCI have shown that NHO requires the combined effects of a severe CNS injury and soft tissue damage, in particular muscular inflammation and the infiltration of macrophages into damaged muscles plays a key role. In the context of a CNS injury, the inflammatory response to soft tissue damage is exaggerated and persistent with excessive signaling via substance P-, oncostatin M-, and TGF-β1-mediated pathways. This review provides an overview of the known animal models and mechanisms of NHO and current therapeutic interventions for NHO patients. While some of the inflammatory mechanisms leading to NHO are common with other forms of traumatic and genetic heterotopic ossifications (HO), NHOs uniquely involve systemic changes in response to CNS injury. Future research into these CNS-mediated mechanisms is likely to reveal new targetable pathways to prevent NHO development in patients.

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

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

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

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

Matrine attenuates heterotopic ossification by suppressing TGF-β induced mesenchymal stromal cell migration and osteogenic differentiation

PURPOSE OF THE STUDY

Heterotopic ossification (HO) is a debilitating disease characterized by extraskeletal bone formation. Active TGF-β recruits mesenchymal stromal cells (MSCs), which contribute to trauma-induced HO. Inhibiting TGF-β induced MSC migration and osteogenic differentiation could be a promising treatment for HO. Matrine is an alkaloid from the genus Sophora that can suppress pancreatic and hepatic fibrosis by regulating TGF-β/Smad signaling. We conducted this study to evaluate the effects of matrine on HO and explore the mechanisms, we carried out this study.

MATERIALS AND METHODS

Achilles tendon puncture was performed in C57BL/6J male mice to establish the HO model. Following treatment with matrine for 3, 6, 9, and 15 weeks, mice were sacrificed and tendons were collected. In vivo, micro-CT, hematoxylin and eosin staining, CD73 and CD90 immunofluorescence, and osteocalcin staining were used to evaluate the development of HO. In vitro, a transwell migration assay was used to evaluate MSC migration. Immunohistochemistry, immunofluorescence and western blotting were used to evaluate the TGF-β/Smad2/3 pathway. Real-time PCR was conducted to analyze the transcription of alkaline phosphatase (Alp), runt-related transcription factor-2 (Runx2), osteocalcin (Ocn), osteopontin (Opn), and type I collagen (Col1). ALP activity and alizarin red staining were used to assess MSC osteogenic differentiation.

RESULTS

In vivo, matrine significantly reduced ossification and inhibited HO progression. In vitro, matrine significantly suppressed MSC migration, ALP activity, and mineralization of MSCs. Mechanistically, matrine inhibited TGF-β induced Smad2/3 phosphorylation and transcription of Runx2, Alp, and Ocn after osteoinduction.

CONCLUSIONS

Matrine inhibited HO by suppressing the migration and osteogenic differentiation of TGF-β-induced-MSCsin mice.

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.

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.

The Reduction of Heterotopic Ossification Incidence After Hip Arthroscopy in Patients Treated With Selective Cyclooxygenase 2 Inhibitor (Celecoxib)

PURPOSE

To evaluate the effectiveness of celecoxib, a selective cyclooxygenase 2 inhibitor, in reducing heterotopic ossification (HO) after hip arthroscopic surgery and to evaluate celecoxib's impact on clinical outcomes.

METHODS

We performed a retrospective review of patients who received hip arthroscopy performed by the same surgeon between January 1, 2012, and December 31, 2016. Patients who had an allergy to sulfa drugs, had pre-existing HO or previous surgery on the operative side, or failed to complete radiographic follow-up at 6 months postoperatively were excluded. Patients in the treatment group received 400 mg of celecoxib postoperatively for 6 weeks, whereas the control group received no postoperative celecoxib. The incidence of HO was assessed using anteroposterior radiographs obtained at 6 months, 1 year, and 2 years postoperatively. Patients completed the International Hip Outcome Tool 33 survey, and the proportion of patients who met the minimal clinically important difference, substantial clinical benefit (SCB), and absolute SCB was calculated.

RESULTS

A total of 559 patients were identified. After application of the exclusion criteria, 454 patients were included in the study (211 in control group and 243 in treatment group). The overall incidence of HO was 20.3% (n = 92). The treatment group had a significantly lower incidence of HO at 6 months (P = .006), 1 year (P < .001), and 2 years (P = .008) postoperatively. At 2 years postoperatively, the treatment group had a significantly higher International Hip Outcome Tool 33 score on average: 64.2 versus 57.3 (P = .023). No significant difference in the proportion of patients reaching the minimal clinically important difference, SCB, or absolute SCB was found at any of the postoperative time points.

CONCLUSION

The findings of this study suggest that a prophylactic treatment regimen of 400 mg of celecoxib once daily for 6 weeks significantly reduces the incidence of HO formation after hip arthroscopic surgery; however, it did not impact clinical outcomes.

LEVEL OF EVIDENCE

Level III, retrospective, comparative case-control study.

Decellularized Adipose Tissue Hydrogel Promotes Bone Regeneration in Critical-Sized Mouse Femoral Defect Model

Critical-sized bone defects fail to heal and often cause non-union. Standard treatments employ autologous bone grafting, which can cause donor tissue loss/pain. Although several scaffold types can enhance bone regeneration, multiple factors limit their level of success. To address this issue, this study evaluated a novel decellularized human adipose tissue (DAT) hydrogel as an alternative. In this study, DAT hydrogel alone, or in combination with adipose-derived stromal/stem cells (ASC), osteo-induced ASCs (OIASC), and hydroxyapatite were tested for their ability to mediate repair of a critical-sized (3 mm) femoral defect created in C57BL/6 mice. Micro-computed tomography results showed that all DAT hydrogel treated groups significantly enhanced bone regeneration, with OIASC + hydroxyapatite treated group displaying the most robust bone regeneration. Histological analyses revealed that all treatments resulted in significantly higher tissue areas with the relative mineralized tissue area significantly increased at 12 weeks; however, cartilaginous content was lowest among treatment groups with OIASC. Immunohistochemical analyses showed that DAT hydrogel enhanced collagen I and osteopontin expression, while the addition of OIASCs to the hydrogel reduced collagen II levels. Thus, DAT hydrogel promotes bone regeneration in a critical-sized femoral defect model that is further enhanced in the presence of OIASCs and hydroxyapatite.

Multiligamentous Knee Injuries in the Military Tactical Athlete

Multiligament knee injuries pose a significant challenge to military service members looking to return to active duty service. They represent a diverse injury pattern and recovery is often complicated by other ipsilateral extremity trauma and systemic injuries. There is a paucity of high-quality evidence guiding the treatment of these injuries. Despite this, orthopedic surgeons are tasked with a young, active, high demand population looking to maximize their recovery after these complex injuries. We present a synthesis of the available civilian and military literature and provide an evidence-based review with considerations specific to a military population.

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

Biomaterial and stem cell-based strategies for skeletal muscle regeneration

Adult skeletal muscle can regenerate effectively after mild physical or chemical insult. Muscle trauma or disease can overwhelm this innate capacity for regeneration and result in heightened inflammation and fibrotic tissue deposition resulting in loss of structure and function. Recent studies have focused on biomaterial and stem cell-based therapies to promote skeletal muscle regeneration following injury and disease. Many stem cell populations besides satellite cells are implicated in muscle regeneration. These stem cells include but are not limited to mesenchymal stem cells, adipose-derived stem cells, hematopoietic stem cells, pericytes, fibroadipogenic progenitors, side population cells, and CD133⁺ stem cells. However, several challenges associated with their isolation, availability, delivery, survival, engraftment, and differentiation have been reported in recent studies. While acellular scaffolds offer a relatively safe and potentially off-the-shelf solution to cell-based therapies, they are often unable to stimulate host cell migration and activity to a level that would result in clinically meaningful regeneration of traumatized muscle. Combining stem cells and biomaterials may offer a viable therapeutic strategy that may overcome the limitations associated with these therapies when they are used in isolation. In this article, we review the stem cell populations that can stimulate muscle regeneration in vitro and in vivo. We also discuss the regenerative potential of combination therapies that utilize both stem cell and biomaterials for the treatment of skeletal muscle injury and disease. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1246-1262, 2019.

Union Rates and Reported Range of Motion Are Acceptable After Open Forearm Fractures in Military Combatants

BACKGROUND

High-energy open forearm fractures are unique injuries frequently complicated by neurovascular and soft tissue injuries. Few studies have evaluated the factors associated with nonunion and loss of motion after these injuries, particularly in the setting of blast injuries.

QUESTIONS/PURPOSES

(1) In military service members with high-energy open forearm fractures, what proportion achieved primary or secondary union? (2) What is the pronation-supination arc of motion as stratified by the presence or absence of heterotopic ossification (HO) and synostosis? (3) What are the risks of heterotopic ossification and synostosis? (4) What factors may be associated with forearm fracture nonunion?

METHODS

A retrospective study of all open forearm fractures treated at a tertiary military referral center from January 2004 to December 2014 was performed. In all, 76 patients were identified and three were excluded, leaving 73 patients for inclusion. All 73 patients had serial radiographs to assess for HO and union. Only 64 patients had rotational range of motion (ROM) data. All patients returned to the operating room at least once after initial irrigation and débridement to ensure the soft tissue envelope was stable before definitive fixation. The indication for repeat irrigation and débridement was determined by clinical appearance. Patient demographics, fracture and soft tissue injury patterns, surgical treatments, neurovascular status at the time of injury, incidence of infection, heterotopic ossification (defined as the presence of heterotopic bone visible on serial radiographs), radioulnar synostosis, bony status after initial definitive treatment (union, nonunion, or amputation), and forearm rotation at final followup were retrospectively obtained from chart review by someone other than the operating surgeon. Seventy-six open forearm fractures in 76 patients were reviewed; 73 patients were examined for osseous union as three went on to early amputation, and 64 patients had forearm ROM data available for analysis. Union was determined by earliest radiology or orthopaedic staff official dictation stating the fracture was healed. Nonunion was defined as the clinical determination by the orthopaedist for a repeat procedure to achieve bony union. Secondary union was defined as union after reoperation to achieve bony union, and final union was defined as overall percentage of patients who were healed at final followup. Of the patients analyzed for union, 20 had less than 1 year of followup, and of these, none had nonunion. Of the patients analyzed for ROM, eight patients had less than 6 months of followup (range, 84-176 days). Of these, one patient had decreased ROM, none had a synostosis, and the remaining had > 140° of motion.

RESULTS

Initial treatment resulted in primary union in 62 of 73 patients (85%); secondary union was achieved in eight of 11 patients (73%); and final union was achieved in 70 of 73 patients (96%). Although pronation-supination arc in patients without HO was 140° ± 35°, a limited pronation-supination arc was primarily associated with synostosis (arc: 40° ± 40°; mean difference from patients without HO: 103° [95% confidence interval {CI}, 77°-129°], p < 0.001); patients with HO but without synostosis had fewer limitations to ROM than those with synostosis (arc: 110° ± 80°, mean difference: 77° [35°-119°], p < 0.001). Heterotopic ossification developed in 40 of 73 patients (55%), including a radioulnar synostosis in 14 patients (19%). Bone loss at the fracture site (relative risk (RR) 6.2; 95% CI, 1.8-21) and healing complicated by infection (RR, 9.9; 95% CI, 4.9-20) were associated with the development of nonunion after initial treatment. Other potential factors such as smoking status, vascular injury, both-bone involvement, need for free flap coverage and blast mechanism were not associated.

CONCLUSIONS

Despite a high-energy mechanism of injury and high rate of soft tissue defects, the ultimate probability of fracture union in our series was high with a low infection risk. Nonunions were associated with bone loss and deep infection. Functional motion was achieved in most patients despite increased burden of HO and synostosis compared with civilian populations. However, if synostosis did not develop, HO itself did not appear to interfere with functional ROM. Future investigations may provide improved decision-making tools for timing of fixation and prophylactic means against HO synostosis.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Cellular plasticity, caspases and autophagy; that which does not kill us, well, makes us different

The ability to regenerate is a fundamental requirement for tissue homeostasis. Regeneration draws on three sources of cells. First and best-studied are dedicated stem/progenitor cells. Second, existing cells may proliferate to compensate for the lost cells of the same type. Third, a different cell type may change fate to compensate for the lost cells. This review focuses on regeneration of the third type and will discuss the contributions by post-transcriptional mechanisms including the emerging evidence for cell-autonomous and non-lethal roles of cell death pathways.