Heterotopic ossification following combat-related trauma

Heterotopic Ossifications Following Intramedullary Stabilization of Femoral Fractures in Polytraumatized Patients

INTRODUCTION

Heterotopic ossifications (HOs) are a well-known complication following total hip arthroplasty. Yet only little is known about the development of HOs following a femoral fracture and intramedullary stabilization in polytraumatized patients. Thus, the present study aimed to investigate whether the development of HOs is being observed more frequently in patients suffering polytrauma compared to those with single-extremity trauma.

MATERIALS AND METHODS

The retrospective outcome study was conducted at our level I trauma center. All patients admitted from 2010 to 2020 were included if they (1) presented with multiple injuries (≥2 body regions), (2) had an Injury Severity Score ≥16, (3) suffered a femoral fracture, and (4) were treated with intramedullary stabilization. Furthermore, a control group was established to match the polytrauma group (sex, age), who were suffering from single-extremity trauma (femoral fracture) which was treated with intramedullary stabilization. Subsequently, X-rays of the hip were performed and evaluated for up to one-year post-trauma.

RESULTS

Our study group consisted of 36 patients in total (91.7% male; mean age 39.4 ± 17.4 years, range: 18-82 years). The polytrauma (PT) group included 12 patients (mean age 39.5 years, median ISS 28), whereas the control group (single-extremity-trauma) included 24 patients (mean age 39.3 years). We documented HOs in nine (75%) patients in the PT group vs. five (20.8%) patients in the single-extremity group (p = 0.03).

CONCLUSION

In this study, we were able to demonstrate that heterotopic ossifications are being observed significantly more frequently in patients suffering from polytrauma in comparison to patients with single-extremity trauma following intramedullary stabilization after a femoral fracture.

Case report: Focal heterotopic ossification in paravertebral muscles as a cause of neurogenic lameness in a dog

This case report describes a 17-month-old Pudelpointer with recurring motor impairment localized to the left thoracic limb. A neurological exam highlighted lameness in that limb, accompanied by pre-scapular swelling. Radiographs and magnetic resonance imaging detected an osseous structure in soft tissues close to the fifth cervical vertebra, and subsequent surgery uncovered adjacent cervical spinal nerve impingement. Histology of the bony structure revealed heterotopic ossification in paravertebral muscles. Mild bone re-formation at the operating site was detected after a 2-year period, but the patient was asymptomatic. This article reports the first case of heterotopic ossification with spinal nerve entrapment in a dog and adds a new differential diagnosis to the causes of neurogenic lameness in dogs.

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.

Exosome MiR-21-5p Upregulated by HIF-1α Induces Adipose Stem Cell Differentiation to Promote Ectopic Bone Formation

Heterotopic bone occurs after burns, trauma and major orthopedic surgery, which cannot be completely cured by current treatments. The development of new treatments requires more in-depth research into the mechanism of HO. Available evidence suggests that miR-21-5p plays an important role in bone formation. However, its mechanism in traumatic HO is still unclear. First, we identified exosomes extracted from L6 cells using TEM observation of the structure and western blotting detection of the surface marker CD63. Regulation effect of HIF-1α to miR-21-5p was confirmed by q-PCR assay. Then we co-cultured L6 cells with ASCs and performed alizarin red staining and ALP detection. Overexpression of miR-21-5p upregulated BMP4, p-smad1/5/8, OCN and OPN, which suggests the BMP4-smad signaling pathway may be involved in miR-21-5p regulation of osteogenic differentiation of ASCs. Finally in vivo experiments showed that miR-21-5p exosomes promoted ectopic formation in traumatized mice. This study confirms that HIF-1α could modulate miR-21-5p exosomes to promote post-traumatic ectopic bone formation by inducing ASCs cell differentiation. Our study reveals the mechanisms of miR-21-5p in ectopic ossification formation after trauma.

Heterotopic Ossification Formation in Military Beneficiaries Following Hip- and Pelvic-Level Amputations

INTRODUCTION

Traumatic hip and pelvic level amputations are uncommon but devastating injuries and associated with numerous complications that can significantly affect quality of life for these patients. While heterotopic ossification (HO) formation has been reported at rates of up to 90% following traumatic, combat-related amputations, previous studies included few patients with more proximal hip and pelvic level amputations.

MATERIALS AND METHODS

We conducted a retrospective review of the Military Health System medical record and identified patients with both traumatic and disease-related hip- and pelvic-level amputations performed between 2001 and 2017. We reviewed the most recent pelvis radiograph at least 3 months following amputation to determine bony resection level and the association between HO formation and reason for amputation (trauma versus disease related).

RESULTS

Of 93 patients with post-amputation pelvis radiographs available, 66% (n = 61) had hip-level amputations and 34% (n = 32) had a hemipelvectomy. The median duration from the initial injury or surgery to the most recent radiograph was 393 days (interquartile range, 73-1,094). HO occurred in 75% of patients. Amputation secondary to trauma was a significant predictor of HO formation (χ2 = 24.58; P < .0001); however, there was no apparent relationship between the severity of HO and traumatic versus non-traumatic etiology (χ2 = 2.92; P = .09).

CONCLUSIONS

Amputations at the hip were more common than pelvic-level amputations in this study population, and three-fourths of hip- and pelvic-level amputation patients had radiographic evidence of HO. The rate of HO formation following blast injuries and other trauma was significantly higher compared with patients with non-traumatic amputations.

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.

Toward higher-performance bionic limbs for wider clinical use

Most prosthetic limbs can autonomously move with dexterity, yet they are not perceived by the user as belonging to their own body. Robotic limbs can convey information about the environment with higher precision than biological limbs, but their actual performance is substantially limited by current technologies for the interfacing of the robotic devices with the body and for transferring motor and sensory information bidirectionally between the prosthesis and the user. In this Perspective, we argue that direct skeletal attachment of bionic devices via osseointegration, the amplification of neural signals by targeted muscle innervation, improved prosthesis control via implanted muscle sensors and advanced algorithms, and the provision of sensory feedback by means of electrodes implanted in peripheral nerves, should all be leveraged towards the creation of a new generation of high-performance bionic limbs. These technologies have been clinically tested in humans, and alongside mechanical redesigns and adequate rehabilitation training should facilitate the wider clinical use of bionic limbs.

Contemporary perspectives on heterotopic ossification

Heterotopic ossification (HO) is the formation of ectopic bone that is primarily genetically driven (fibrodysplasia ossificans progressiva [FOP]) or acquired in the setting of trauma (tHO). HO has undergone intense investigation, especially over the last 50 years, as awareness has increased around improving clinical technologies and incidence, such as with ongoing wartime conflicts. Current treatments for tHO and FOP remain prophylactic and include NSAIDs and glucocorticoids, respectively, whereas other proposed therapeutic modalities exhibit prohibitive risk profiles. Contemporary studies have elucidated mechanisms behind tHO and FOP and have described new distinct niches independent of inflammation that regulate ectopic bone formation. These investigations have propagated a paradigm shift in the approach to treatment and management of a historically difficult surgical problem, with ongoing clinical trials and promising new targets.

Key early proinflammatory signaling molecules encapsulated within circulating exosomes following traumatic injury

Background

Assessment of immune status in critically ill patients is often based on serial tracking of systemic cytokine levels and clinical laboratory values. Exosomes are extracellular vesicles that can be secreted and internalized by cells to transport important cellular cargo in the regulation of numerous physiological and pathological processes. Here, we characterize the early compartmentalization profile of key proinflammatory mediators in serum exosomes in the steady state and following trauma. Adult male Sprague-Dawley rats (91 including naïve) were divided into one of four traumatic injury model groups incorporating whole-body blast, fracture, soft-tissue crush injury, tourniquet-induced ischemia, and limb amputation. Serum was collected at 1, 3, 6, and 24 h, and 3- and 7-day post-injury. Electrochemiluminescence-based immunoassays for 9 key proinflammatory mediators in whole serum, isolated serum exosomes, and exosome depleted serum were analyzed and compared between naïve and injured rats. Serum clinical chemistry analysis was performed to determine pathological changes.

Results

In naïve animals, substantial amounts of IL-1β, IL-10, and TNF-α were encapsulated, IL-6 was completely encapsulated, and CXCL1 freely circulating. One hour after blast injury alone, levels of exosome encapsulated IFN-γ, IL-10, IL-6, IL-13, IL-4, and TNF-α increased, whereas freely circulating and membrane-associated levels remained undetectable or low. Rats with the most severe polytraumatic injuries with end organ complications had the earliest rise and most pronounced concentration of IL-1β, IL-10, TNF-α, and IL-6 across all serum compartments. Moreover, CXCL1 levels increased in relation to injury severity, but remained almost entirely freely circulating at all timepoints.

Conclusion

These findings highlight that conventional ELISA-based assessments, which detect only free circulating and exosome membrane-bound mediators, underestimate the full immunoinflammatory response to trauma. Inclusion of exosome encapsulated mediators may be a better, more accurate and clinically useful early strategy to identify, diagnose, and monitor patients at highest risk for post-traumatic inflammation-associated complications.

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.

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.

Plasmin drives burn-induced systemic inflammatory response syndrome

Severe injuries, such as burns, provoke a systemic inflammatory response syndrome (SIRS) that imposes pathology on all organs. Simultaneously, severe injury also elicits activation of the fibrinolytic protease plasmin. While the principal adverse outcome of plasmin activation in severe injury is compromised hemostasis, plasmin also possesses proinflammatory properties. We hypothesized that, following a severe injury, early activation of plasmin drives SIRS. Plasmin activation was measured and related to injury severity, SIRS, coagulopathy, and outcomes prospectively in burn patients who are not at risk of hemorrhage. Patients exhibited early, significant activation of plasmin that correlated with burn severity, cytokines, coagulopathy, and death. Burn with a concomitant, remote muscle injury was employed in mice to determine the role of plasmin in the cytokine storm and inflammatory cascades in injured tissue distant from the burn injury. Genetic and pharmacologic inhibition of plasmin reduced the burn-induced cytokine storm and inflammatory signaling in injured tissue. These findings demonstrate (a) that severe injury-induced plasmin activation is a key pathologic component of the SIRS-driven cytokine storm and SIRS-activated inflammatory cascades in tissues distant from the inciting injury and (b) that targeted inhibition of plasmin activation may be effective for limiting both hemorrhage and tissue-damaging inflammation following injury.

Three-Dimensional Modeling of the Structural Microenvironment in Post-Traumatic War Wounds

BACKGROUND:

The development of post-traumatic heterotopic ossification (HO) is a common, undesirable sequela in patients with high-energy (war-related) extremity injuries. While inflammatory and osteoinductive signaling pathways are known to be involved in the development and progression of post-traumatic HO, features of the structural microenvironment within which the ectopic bone begins to form remain poorly understood. Thus, increasing our knowledge of molecular and structural changes within the healing wound may help elucidate the pathogenesis of post-traumatic HO and aid in the development of specific treatment and/or prevention strategies.

METHODS:

In this study, we performed high-resolution microscopy and biochemical analysis of tissues obtained from traumatic war wounds to characterize changes in the structural microenvironment. In addition, using an electrospinning approach, we modeled this microenvironment to reconstitute a three-dimensional type I collagen scaffold with non-woven, randomly oriented nanofibers where we evaluated the performance of primary mesenchymal progenitor cells.

RESULTS:

We found that traumatic war wounds are characterized by a disorganized, densely fibrotic collagen I matrix that influences progenitor cells adhesion, proliferation and osteogenic differentiation potential.

CONCLUSION:

Altogether, these results suggest that the structural microenvironment present in traumatic war wounds has the potential to contribute to the development of post-traumatic HO. Our findings may support novel treatment strategies directed towards modifying the structural microenvironment after traumatic injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-021-00355-y.

Regenerative Peripheral Nerve Interfaces for the Treatment and Prevention of Neuromas and Neuroma Pain

A neuroma occurs when a regenerating transected peripheral nerve has no distal target to reinnervate. This situation can result in a hypersensitive free nerve ending that causes debilitating pain to affected patients. No techniques to treat symptomatic neuromas have shown consistent results. One novel physiologic solution is the regenerative peripheral nerve interface (RPNI). RPNI consists of a transected peripheral nerve that is implanted into an autologous free skeletal muscle graft. Early clinical studies have shown promising results in the use of RPNIs to treat and prevent symptomatic neuromas. This review article describes the rationale behind the success of RPNIs and its clinical applications.

A self-amplifying loop of YAP and SHH drives formation and expansion of heterotopic ossification

Heterotopic ossification (HO) occurs as a common complication after injury or in genetic disorders. The mechanisms underlying HO remain incompletely understood, and there are no approved prophylactic or secondary treatments available. Here, we identify a self-amplifying, self-propagating loop of Yes-associated protein (YAP)-Sonic hedgehog (SHH) as a core molecular mechanism underlying diverse forms of HO. In mouse models of progressive osseous heteroplasia (POH), a disease caused by null mutations in GNAS, we found that Gnas^-/- mesenchymal cells secreted SHH, which induced osteoblast differentiation of the surrounding wild-type cells. We further showed that loss of Gnas led to activation of YAP transcription activity, which directly drove Shh expression. Secreted SHH further induced YAP activation, Shh expression, and osteoblast differentiation in surrounding wild-type cells. This self-propagating positive feedback loop was both necessary and sufficient for HO expansion and could act independently of Gnas in fibrodysplasia ossificans progressiva (FOP), another genetic HO, and nonhereditary HO mouse models. Genetic or pharmacological inhibition of YAP or SHH abolished HO in POH and FOP and acquired HO mouse models without affecting normal bone homeostasis, providing a previously unrecognized therapeutic rationale to prevent, reduce, and shrink HO.

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

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

Ectopic models recapitulating morphological and functional features of articular cartilage

BACKGROUND

Articular cartilage is an extremely specialized connective tissue which covers all diarthrodial joints. Implantation of chondrogenic cells without or with additional biomaterial scaffolds in ectopic locationsin vivo generates substitutes of cartilage with structural and functional characteristics that are used in fundamental investigations while also serving as a basis for translational studies.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant ectopic models, among which subcutaneous, intramuscular, and kidney capsule transplantation and elaborates on implanted cells and biomaterial scaffolds and on their use to recapitulate morphological and functional features of articular cartilage. Although the absence of a physiological joint environment and biomechanical stimuli is the major limiting factor, ectopic models are an established component for articular cartilage research aiming to generate a bridge between in vitro data and the clinically more relevant translational orthotopic in vivo models when their limitations are considered.

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.

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

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

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.

A microRNA Signature for Impaired Wound-Healing and Ectopic Bone Formation in Humans

BACKGROUND

Heterotopic ossification (HO) is characterized by the abnormal growth of ectopic bone in soft tissues, frequently occurring within the military population because of extensive orthopaedic combat trauma. MicroRNAs (miRNAs) are small noncoding RNAs that act as post-transcriptional regulators of gene expression. We hypothesized that a clinically relevant miRNA signature could be detected in patients following injury that progressed to form HO (HO+) or did not form HO (HO-).

METHODS

Tissue samples were obtained from injured servicemembers during their initial surgical debridements, and miRNA profiling was performed using a real-time miRNA polymerase chain reaction (PCR) array. Primary mesenchymal progenitor cells (MPCs) were harvested from debrided traumatized human muscle tissue, and cells were isolated and cultured in vitro. Mimic miRNAs were transfected into MPCs, followed by downstream in vitro analyses.

RESULTS

The investigation of the miRNA expression profile in the tissue of HO+ compared with HO- patients demonstrated a molecular signature that included the upregulation of miR-1, miR-133a, miR-133b, miR-206, miR-26a, and miR-125b. Transfection of each of these mature miRNAs into MPCs followed by osteogenic induction demonstrated that miR-1, miR-133a, miR-133b, and miR-206 enhanced osteogenic differentiation compared with control treatments. In silico and in vitro analyses identified the transcription factor SOX9 as a candidate downstream target of miR-1 and miR-206 miRNAs.

CONCLUSIONS

Our data demonstrated a molecular signature of miRNAs in the soft tissue of wounded servicemembers that was associated with the development of HO, providing novel insights into the underlying molecular mechanisms associated with posttraumatic HO.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Characterizing loads at transfemoral osseointegrated implants

Establishing normative and outlying loads on transfemoral osseointegrated devices will assist development of preclinical mechanical testing strategies to inform manufacturers and government regulators. Therefore, force and moment data from osseointegrated transfemoral transcutaneous implants were collated to better understand baseline load levels. Load data were also collected from other devices including transfemoral socket prostheses, instrumented hip stems, instrumented knee devices, instrumented limb salvage femoral endoprostheses, as well as estimated loads on transfemoral prostheses using data from able-bodied subjects. These additional data were assessed for their ability to bolster the limited osseointegrated device data. Several activities of daily living were investigated to characterize normative loading. Falling events were investigated to characterize outlying loads. Results revealed that limited loading data exist for osseointegrated devices. The most often reported activity was level walking. While these normative data may inform fatigue testing, they may not fully characterize fatigue loads during all activities of daily living. Socket prosthetics and able-bodied individuals may provide supplementary data, but significance is limited by sample sizes. Falling data are sparse, and insufficient data exist for characterizing adverse loads on osseointegrated devices. Future data collection should include more activities of daily living and adverse events to better define osseointegrated device loading profiles.

A Comparison of Contracture Severity at Acute Discharge in Patients With and Without Heterotopic Ossification: A Burn Model System National Database Study

This study assesses the association between heterotopic ossification and upper extremity contracture by comparing goniometric measured active range of motion outcomes of patients with and without heterotopic ossification. Data were obtained from the Burn Model System National Database between 1994 and 2003 for patients more than 18 years with elbow contracture at acute discharge. Absolute losses in elbow range of motion were compared for those with and without radiologic evidence of heterotopic ossification (location undefined) and were further examined by burn size subgroups using Wilcoxon rank-sum test. Differences in elbow range of motion were estimated using regression models, adjusted for demographic and clinical variables. Loss of range of motion of shoulder, wrist, forearm, and hand were also compared. From 407 instances of elbow contracture, the subjects with heterotopic ossification were found to have greater median absolute loss of elbow flexion among all survivors (median 50° [IQR 45°] vs 20° [30°], P < .0001), for the 20 to 40% total body surface area burn subgroup (70° [20°] vs 20° [30°], P = .0008) and for the >40% subgroup (50° [45°] vs 30° [32°], P = .03). The adjusted estimate of the mean difference in the absolute loss of elbow flexion between groups was 23.5° (SE ±7.2°, P = .0013). This study adds to our understanding of the potential effect of heterotopic ossification on upper extremity joint range of motion, demonstrating a significant association between the presence of heterotopic ossification and elbow flexion contracture severity. Further study is needed to determine the functional implications of heterotopic ossification and develop treatment protocols.

Replicating landmine blast loading in cellular in vitro models

Trauma arising from landmines and improvised explosive devices promotes heterotopic ossification, the formation of extra-skeletal bone in non-osseous tissue. To date, experimental platforms that can replicate the loading parameter space relevant to improvised explosive device and landmine blast wave exposure have not been available to study the effects of such non-physiological mechanical loading on cells. Here, we present the design and calibration of three distinct in vitro experimental loading platforms that allow us to replicate the spectrum of loading conditions recorded in near-field blast wave exposure. We subjected cells in suspension or in a three-dimensional hydrogel to strain rates up to 6000 s^-1 and pressure levels up to 45 MPa. Our results highlight that cellular activation is regulated in a non-linear fashion-not by a single mechanical parameter, it is the combined action of the applied mechanical pressure, rate of loading and loading impulse, along with the extracellular environment used to convey the pressure waves. Finally, our research indicates that PO MSCs are finely tuned to respond to mechanical stimuli that fall within defined ranges of loading.

Risk factors for heterotopic ossification in operatively treated proximal humeral fractures

AIMS

Heterotopic ossification (HO) is a potentially devastating complication of the surgical treatment of a proximal humeral fracture. The literature on the rate and risk factors for the development of HO under these circumstances is lacking. The aim of this study was to determine the incidence and risk factors for the development of HO in these patients.

METHODS

A retrospective analysis of 170 patients who underwent operative treatment for a proximal humeral fracture between 2005 and 2016, in a single institution, was undertaken. The mean follow-up was 18.2 months (1.5 to 140). The presence of HO was identified on follow-up radiographs.

RESULTS

The incidence of HO was 15% (n = 26). Our multivariate model revealed that male sex (odds ratio (OR) 3.57, 95% confidence interval (CI) 1.30 to 9.80 compared to female) and dislocation as the initial injury (OR 5.01, 95% CI 1.31 to 19.22) were significantly associated with the formation of HO (p < 0.05) while no significant associations were seen for the age of the patient, the characteristics of the injury, or the type of operative treatment.

CONCLUSION

This retrospective radiological study is the first to investigate the association between the method of surgical treatment for a proximal humeral fracture and the formation of HO postoperatively. We found that male sex and dislocation as the initial injury were risk factors for HO formation, whereas the method of surgical treatment, the age of the patient, and the pattern of the fracture were not predictive of HO formation. While additional studies are needed, these findings can help to identify those at an increased risk for HO formation under these circumstances. Cite this article: Bone Joint J 2020;102-B(4):539-544.

Definitive External Fixation for Anterior Stabilization of Combat-related Pelvic Ring Injuries, With or Without Sacroiliac Fixation

BACKGROUND

Combat-related pelvic ring injuries frequently lead to placement of a temporizing external fixation device for early resuscitation and transport. These injuries are commonly complicated by concomitant polytrauma and extensive soft-tissue injuries, which may preclude early internal fixation and lead to prolonged use of external fixation. To date, few studies have reported on the outcomes of definitive external fixation for combat-related pelvic ring injuries.

QUESTIONS/PURPOSES

(1) In patients treated with definitive external fixation after combat-related pelvic ring injuries, how often is the quality of reduction within radiographically acceptable parameters at the end of treatment? (2) What proportion of patients demonstrate local heterotopic ossification after these injuries? (3) What patient- and treatment-related factors are associated with increased complications and pain?

METHODS

We retrospectively studied all patients with pelvic ring injuries treated at a tertiary military referral center from January 2003 to December 2012. In total, 114 patients were identified, 55 of whom maintained an external fixation frame throughout their treatment. During that time, the general indications for definitive external fixation were an open, contaminated pelvic ring injury with a high risk of infection or open urologic injury; confluent abdominal, perineal, and thigh wounds; or comminution of the pubic ramus that would necessitate plate fixation extending up the anterior column in patients with open abdomen or exposure-compromising abdominal wounds. Posterior fixation, either sacroiliac or lumbopelvic, was applied in patients with sacroiliac instability. Of the 55 patients with pelvic ring injuries treated with definitive external fixation (27 open and 28 closed), four underwent hemipelvectomy and construct removal for massive ascending infections and four were lost to follow-up, leaving 47 patients (85%) who were available at a minimum follow-up of 12 months (median 29 months, interquartile range 17-43 months). All 47 patients underwent serial imaging to assess their injury and reduction during treatment. External fixators were typically removed after 12 weeks, except in patients in whom pin-site irritation or infection prompted earlier removal, and all were confirmed to be grossly stable during an examination under anesthesia. Clinical union was defined as the absence of radiographically present fracture lines and stable examination findings under anesthesia when the external fixator was removed. Data on demographics, injury pattern, associated injuries, revision procedures, complications, and final functional outcomes including ambulation status, sexual function, and pain were collected. Pelvic radiographs were reviewed for the initial injury pattern, type of pelvic fixation construct, residual displacement after removal of the frame, and evidence of formation of heterotopic ossification in the pelvis or bilateral hips. Pelvic displacement and diastasis were determined by digital caliper measurement on plain images; malunion was defined as anterior diastasis of the pelvis or vertical incongruity of the hemipelvis greater than 10 mm.

RESULTS

Radiographic malunion after construct removal occurred in eight of 24 patients with open injuries and in five of 23 patients with closed injuries. Heterotopic ossification developed in the pelvis or hips of all 24 patients with open injuries and in two of the 23 patients with closed injuries. In patients with open pelvic ring injuries, concomitant acetabular fractures were associated with pelvic pain at the final follow-up examination (risk ratio 1.9; 95% confidence interval, 1.0-3.5; p = 0.017). No treatment factor resulted in superior functional outcomes. In the closed-injury group, concomitant lower-extremity amputation was associated with improved radiographic final reduction (RR 0.4; 95% CI, 0.2-0.7; p = 0.02). There was no association between radiographic malunion and increased pain (RR 1.9; 95% CI, 0.5-7.0; p = 0.54 for the open group; RR 0.8; 95% CI, 0.7-1.0; p = 0.86 for the closed group).

CONCLUSION

In this series of patients with severe combat-related pelvic ring injuries who were treated anteriorly with definitive external fixation because of a severe soft-tissue injury, high infection risk, or unacceptable physiologic cost of internal fixation, malunion and chronic pelvic pain were less common than previously observed. Prior studies primarily differ in their lack of sacroiliac or lumbopelvic stabilization for posteriorly unstable fracture patterns, likely accounting for much of these differences. There may have been important between-study differences such as extremely severe injuries, concomitant injuries, and study population. Our study also differs because we specifically analyzed a large cohort of patients who sustained open pelvic ring injuries. Future studies should prospectively investigate the ideal construct type and pin material, optimize the length of treatment and assessment of healing, and improve radiographic measures to predict long-term functional outcomes.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Global Excision of Severe Heterotopic Ossification of the Shoulder: A Case Report

CASE

A 21-year-old man sustained a closed glenohumeral fracture/dislocation as a pedestrian struck by a motor vehicle. He was treated nonoperatively and developed severe post-traumatic heterotopic ossification (HO) with near-complete shoulder ankylosis. We present our technique for safe surgical excision.

CONCLUSIONS

Excision led to improvements in motion and quality of life at 1 year postoperatively. Recommendations for successful HO excision around the shoulder include excision after at least 180 days, appropriate preoperative imaging to include cross-sectional imaging and a 3D model, intraoperative fluoroscopy, well-serviced instruments, preparation for iatrogenic fracture and/or neurovascular injury, meticulous hemostasis, postoperative HO prophylaxis, immediate postoperative therapy, and involvement of a multidisciplinary team.

Extensive Circumferential Heterotopic Ossification Discovered at the Base of a Loop Ileostomy

Heterotopic ossification is a rare phenomenon defined by the formation of bone within nonossifying soft tissues. A rare variant of heterotopic ossification is heterotopic mesenteric ossification (HMO), in which there is involvement of the mesentery and surrounding intra-abdominal structures. There are only four previously reported cases of HMO involving an ileostomy. We present a case of HMO affecting an ileostomy which was discovered during elective stoma reversal in a 52-year-old male who required fecal diversion following perineal necrotizing fasciitis.

Impact of oral resuscitation on circulating and splenic leukocytes after burns

BACKGROUND

Hemodynamic aberrations after severe burns are treated with aggressive intravenous (IV) fluid resuscitation however, oral resuscitation has been proposed in resource poor scenarios. Previously we have shown that animals receiving oral fluid following burns were able to recover kidney function. However, immune function such as circulating and splenic immune cell populations after oral or intravenous fluid administration was not examined. Herein, we perform a follow up analysis of splenic tissue and plasma from the previous animal study to examine the splenic response following these resuscitation strategies after burn injury.

METHODS

Eighteen anesthetized Yorkshire swine receiving 40%TBSA contact burns were randomized to receive either: (1) no fluids (Fluid Restricted; negative control), (2) 70 mL/kg/d Oral Rehydration Salt solution (Oral), or (3) 2 mL/kg/%TBSA/d of lactated Ringer's solution IV. Blood was drawn for blood cell analysis, and CT scans were performed before and 48 h post-burn, at which point spleens were harvested for histological, Western blot, and RT-PCR analyses.

RESULTS

Splenic artery diameter decreased by -0.97 ± 0.14 mm in fluid-restricted animals, while IV led to an increase of 0.68 ± 0.30 mm. No significant differences were detected in white and red pulp. IV fluids reduced the population of splenic monocytes (CD163; P = 0.001) and neutrophils (MPO protein; P = 0.13), as well as cytokines IL-8 (P = 0.003), IFN-γ (P = 0.11) and TNFα (P = 0.05). Additionally, withholding IV fluids consistently decreased the expression of FoxP3, CCR6, and IL17β in spleen, suggesting a shift in T-cell phenotype with IV resuscitation.

CONCLUSIONS

The route of fluid administration has a minor influence on the changes in circulating and splenic leukocytes post-burn in the acute phase. Further research is needed to help guide resuscitation approaches using immunologic markers of splenic function following burns.

Heterotopic ossification: radiological and pathological review

Background Heterotopic Ossification (HO) is a common condition referring to ectopic bone formation in soft tissues. It has two major etiologies, acquired (more common) and genetic. The acquired form is closely related to tissue trauma. The exact pathogenesis of this disease remains unclear; however, there is ongoing research in prophylactic and therapeutic treatments that is promising. Conclusions Due to HO potential to cause disability, it is so important to differentiate it from other causes in order to establish the best possible management.

Targeting heterotopic ossification by inhibiting activin receptor‑like kinase 2 function (Review)

Heterotopic ossification (HO) refers to the appearance of osteoblasts in soft tissues under pathological conditions, such as trauma or infection. HO arises in an unpredictable way without any recognizable initiation. Activin receptor-like kinase-2 (ALK2) is a type I cell surface receptor for bone morphogenetic proteins (BMPs). The dysregulation of ALK2 signaling is associated with a variety of diseases, including cancer and HO. At present, the prevention and treatment of HO in the clinic predominantly includes nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates and other drug treatments, low-dose local radiation therapy and surgical resection, rehabilitation treatment and physical therapy. However, most of these therapies have adverse effects. These methods do not prevent the occurrence of HO. The pathogenesis of HO is not being specifically targeted; the current treatment strategies target the symptoms, not the disease. These treatments also cannot solve the fundamental problem of the occurrence of HO. Therefore, scholars have been working to develop targeted therapies based on the pathogenesis of HO. The present review focuses on advances in the understanding of the underlying mechanisms of HO, and possible options for the prevention and treatment of HO. In addition, the role of ALK2 in the process of HO is introduced and the progress made towards the targeted inhibition of ALK2 is discussed. The present study aims to offer a platform for further research on possible targets for the prevention and treatment of HO.

A review on the latest advancements in the non-invasive evaluation/monitoring of dental and trans-femoral implants

Dental implants and transcutaneous prostheses (trans-femoral implants) improve the quality of life of millions of people because they represent the optimal treatments to edentulism and amputation, respectively. The clinical procedures adopted by surgeons to insert these implants are well established. However, there is uncertainty on the outcomes of the post-operation recovery because of the uncertainty associated with the osseointegration process, which is defined as the direct, structural and functional contact between the living bone and the fixture. To guarantee the long-term survivability of dental or trans-femoral implants doctors sometimes implement non-invasive techniques to monitor and evaluate the progress of osseointegration. This may be done by measuring the stability of the fixture or by assessing the quality of the bone-fixture interface. In addition, care providers may need to quantify the structural integrity of the bone-implant system at various moments during the patients recovery. The accuracy of such non-invasive methods reduce recovery and rehabilitation time, and may increase the survival rate of the therapies with undisputable benefits for the patients. This paper provides a comprehensive review of clinically-approved and emerging non-invasive methods to evaluate/monitor the osseointegration of dental and orthopedic implants. A discussion about advantages and limitations of each method is provided based on the outcomes of the cases presented. The review on the emerging technologies covers the developments of the last decade, while the discussion about the clinically approved systems focuses mostly on the latest (2017-2018) findings. At last, the review also provides some suggestions for future researches and developments in the area of implant monitoring.

In vivo model of human post-traumatic heterotopic ossification demonstrates early fibroproliferative signature

Background

The relationship between the tissue injury healing response and development of heterotopic ossification (HO) is poorly understood. Here we compare a rat blast model and human traumatized muscle from a blast injury to study the early signatures of osteogenesis and fibrosis during the formation of HO.

Methods

Rat and human tissues were characterized using histology, scanning electron microscopy, immunohistochemistry, as well as gene and protein expression analysis. Additionally, animals and humans were assessed radiographically for HO formation following injury.

Results

Markers of bone formation were dramatically increased in tissue samples from both humans and rats, and both displayed increased fibroproliferative regions within the injured tissues and elevated expression of markers of tissue fibrosis such as TGF-β1, Fibronectin, SMAD3 and PAI-1. Markers of inflammation and fibrosis (ACTA, TNFα, BMP1 and BMP3) were elevated at the RNA level in both rat and human samples. By day 42, bone formation in the rat blast model appeared similar in radiographs compared to human patients who progressed to develop post-traumatic HO.

Conclusions

Our data demonstrates that a similar early fibrotic response is evident in both the rat blast model and the human tissues following a traumatic injury and demonstrates the relevance of this animal model for future translational studies.

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.

BMP and mTOR signaling in heterotopic ossification: Does their crosstalk provide therapeutic opportunities?

Heterotopic ossification (HO) refers to the pathological formation of ectopic bone in soft tissues, it occurs following severe trauma or in patients with a rare genetic disorder known as fibrodysplasia ossificans progressiva. The pathological process of HO formation is a two-step mechanism: inflammation and destruction of connective tissues, followed by bone formation. The latter is further subdivided into three stages: fibroproliferation/angiogenesis, chondrogenesis, and osteogenesis. Currently, therapeutic options for HO are limited. New potential therapeutics will most likely arise from a more detailed understanding of the signaling pathways implicated in each stage of ectopic bone formation and molecular targets that may be effective at both the early and late stages of HO. Bone morphogenetic protein (BMP) signaling is believed to play a key role in the overall HO process. Recently, the mammalian target of rapamycin (mTOR) signaling pathway has received attention as a critical pathway for chondrogenesis, osteogenesis, and HO. Inhibition of mTOR signaling has been shown to block trauma-induced and genetic HO. Intriguingly, recent studies have revealed crosstalk between mTOR and BMP signaling. Moreover, mTOR has emerged as a factor involved in the early hypoxic and inflammatory stages of HO. We will summarize the current knowledge of the roles of mTOR and BMP signaling in HO, with a particular focus on the crosstalk between mTOR and BMP signaling. We also discuss the activation of AMP activated protein kinase (AMPK) by the most widely used drug for type 2 diabetes, metformin, which exerts a dual negative regulatory effect on mTOR and BMP signaling, suggesting that metformin is a promising drug treatment for HO. The discovery of an mTOR-BMP signaling network may be a potential molecular mechanism of HO and may represent a novel therapeutic target for the pharmacological control of HO.

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.

Failure of Indomethacin and Radiation to Prevent Blast-induced Heterotopic Ossification in a Sprague-Dawley Rat Model

BACKGROUND

Although use of nonsteroidal antiinflammatory drugs and low-dose irradiation has demonstrated efficacy in preventing heterotopic ossification (HO) after THA and surgical treatment of acetabular fractures, these modalities have not been assessed after traumatic blast amputations where HO is a common complication that can arise in the residual limb.

QUESTIONS/PURPOSES

The purpose of this study was to investigate the effectiveness of indomethacin and irradiation in preventing HO induced by high-energy blast trauma in a rat model.

METHODS

Thirty-six Sprague-Dawley rats underwent hind limb blast amputation with a submerged explosive under water followed by irrigation and primary wound closure. One group (n = 12) received oral indomethacin for 10 days starting on postoperative Day 1. Another group (n = 12) received a single dose of 8 Gy irradiation to the residual limb on postoperative Day 3. A control group (n = 12) did not receive either. Wound healing and clinical course were monitored in all animals until euthanasia at 24 weeks. Serial radiographs were taken immediately postoperatively, at 10 days, and every 4 weeks thereafter to monitor the time course of ectopic bone formation until euthanasia. Five independent graders evaluated the 24-week radiographs to quantitatively assess severity and qualitatively assess the pattern of HO using a modified Potter scale from 0 to 3. Assessment of grading reproducibility yielded a Fleiss statistic of 0.41 and 0.37 for severity and type, respectively. By extrapolation from human clinical trials, a minimum clinically important difference in HO severity was empirically determined to be two full grades or progression of absolute grade to the most severe.

RESULTS

We found no differences in mean HO severity scores among the three study groups (indomethacin 0.90 ± 0.46 [95% confidence interval {CI}, 0.60-1.19]; radiation 1.34 ± 0.59 [95% CI, 0.95-1.74]; control 0.95 ± 0.55 [95% CI, 0.60-1.30]; p = 0.100). For qualitative HO type scores, the radiation group had a higher HO type than both indomethacin and controls, but indomethacin was no different than controls (indomethacin 1.08 ± 0.66 [95% CI, 0.67-1.50]; radiation 1.89 ± 0.76 [95% CI, 1.38-2.40]; control 1.10 ± 0.62 [95% CI, 0.70-1.50]; p = 0.013). The lower bound of the 95% CI on mean severity in the indomethacin group and the upper bound of the radiation group barely spanned a full grade and involved only numeric grades < 2, suggesting that even if a small difference in severity could be detected, it would be less than our a priori-defined minimum clinically important difference and any differences that might be present are unlikely to be clinically meaningful.

CONCLUSIONS

This work unexpectedly demonstrated that, compared with controls, indomethacin and irradiation provide no effective prophylaxis against HO in the residual limb after high-energy blast amputation in a rat model. Such an observation is contrary to the civilian experience and may be potentially explained by either a different pathogenesis for blast-induced HO or a stimulus that overwhelms conventional regimens used to prevent HO in the civilian population.

CLINICAL RELEVANCE

HO in the residual limb after high-energy traumatic blast amputation will likely require novel approaches for prevention and management.

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

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

Application of a mechanobiological algorithm to investigate mechanical mediation of heterotopic bone in trans-femoral amputees

Heterotopic ossification (HO) is the process of bone formation in tissues that are not usually osseous. It occurs in 60% of those with blast-related amputations. HO can result in reduced range of motion, pain, nerve impingement and can affect prosthesis fitting and is caused by a combination of mechanical, biological, local and systemic factors. As with normal bone formation and remodelling, it is expected that heterotopic bone responds to mechanical stimuli and understanding this relationship can give insight into the pathology. The objective of this research was to investigate whether a physiological 2D computational model that considers both mechanical and biological factors can be used to simulate HO in the residual limb of a trans-femoral amputee. The study found that characteristic morphologies of HO were reproduced by adjusting the loading environment. Significant effects were produced by changing the loading direction on the femur; this is potentially associated with different initial surgical interventions such as muscle myodesis. Also, initial treatment such as negative pressure through a dressing was found to change the shape of heterotopic bone.

A Systems Biology Approach for Studying Heterotopic Ossification: Proteomic Analysis of Clinical Serum and Tissue Samples

Heterotopic ossification (HO) refers to the abnormal formation of bone in soft tissue. Although some of the underlying processes of HO have been described, there are currently no clinical tests using validated biomarkers for predicting HO formation. As such, the diagnosis is made radiographically after HO has formed. To identify potential and novel biomarkers for HO, we used isobaric tags for relative and absolute quantitation (iTRAQ) and high-throughput antibody arrays to produce a semi-quantitative proteomics survey of serum and tissue from subjects with (HO+) and without (HO-) heterotopic ossification. The resulting data were then analyzed using a systems biology approach. We found that serum samples from subjects experiencing traumatic injuries with resulting HO have a different proteomic expression profile compared to those from the matched controls. Subsequent quantitative ELISA identified five blood serum proteins that were differentially regulated between the HO+ and HO- groups. Compared to HO- samples, the amount of insulin-like growth factor I (IGF1) was up-regulated in HO+ samples, whereas a lower amount of osteopontin (OPN), myeloperoxidase (MPO), runt-related transcription factor 2 (RUNX2), and growth differentiation factor 2 or bone morphogenetic protein 9 (BMP-9) was found in HO+ samples (Welch two sample t-test; P < 0.05). These proteins, in combination with potential serum biomarkers previously reported, are key candidates for a serum diagnostic panel that may enable early detection of HO prior to radiographic and clinical manifestations.

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

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

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

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

Neurological heterotopic ossification: Current understanding and future directions

Neurological heterotopic ossification (NHO) involves the formation of bone in soft tissue following a neurological condition, of which the most common are brain and spinal cord injuries. NHO often forms around the hip, knee and shoulder joints, causing severe pain and joint deformation which is associated with significant morbidity and reduced quality of life. The cellular and molecular events that initiate NHO have been the focus of an increasing number of human and animal studies over the past decade, with this work largely driven by the need to unearth potential therapeutic interventions to prevent the formation of NHO. This review provides an overview of the present understanding of NHO pathogenesis and pathobiology, current treatments, novel therapeutic targets, potential biomarkers and future directions.

Heterotopic ossification and the elucidation of pathologic differentiation

Tissue regeneration following acute or persistent inflammation can manifest a spectrum of phenotypes ranging from the adaptive to the pathologic. Heterotopic Ossification (HO), the endochondral formation of bone within soft-tissue structures following severe injury serves as a prominent example of pathologic differentiation; and remains a persistent clinical issue incurring significant patient morbidity and expense to adequately diagnose and treat. The pathogenesis of HO provides an intriguing opportunity to better characterize the cellular and cell-signaling contributors to aberrant differentiation. Indeed, recent work has continued to resolve the unique cellular lineages, and causative pathways responsible for ectopic bone development yielding promising avenues for the development of novel therapeutic strategies shown to be successful in analogous animal models of HO development. This review details advances in the understanding of HO in the context of inciting inflammation, and explains how these advances inform the current standards of diagnosis and treatment.

Depletion of Mast Cells and Macrophages Impairs Heterotopic Ossification in an Acvr1R206H Mouse Model of Fibrodysplasia Ossificans Progressiva

Heterotopic ossification (HO) is a clinical condition that often reduces mobility and diminishes quality of life for affected individuals. The most severe form of progressive HO occurs in those with fibrodysplasia ossificans progressiva (FOP; OMIM #135100), a genetic disorder caused by a recurrent heterozygous gain-of-function mutation (R206H) in the bone morphogenetic protein (BMP) type I receptor ACVR1/ALK2. In individuals with FOP, episodes of HO frequently follow injury. The first sign of active disease is commonly an inflammatory "flare-up" that precedes connective tissue degradation, progenitor cell recruitment, and endochondral HO. We used a conditional-on global knock-in mouse model expressing Acvr1^R206H (referred to as Acvr1^cR206H/+ ) to investigate the cellular and molecular inflammatory response in FOP lesions following injury. We found that the Acvr1 R206H mutation caused increased BMP signaling in posttraumatic FOP lesions and early divergence from the normal skeletal muscle repair program with elevated and prolonged immune cell infiltration. The proinflammatory cytokine response of TNFα, IL-1β, and IL-6 was elevated and prolonged in Acvr1^cR206H/+ lesions and in Acvr1^cR206H/+ mast cells. Importantly, depletion of mast cells and macrophages significantly impaired injury-induced HO in Acvr1^cR206H/+ mice, reducing injury-induced HO volume by ∼50% with depletion of each cell population independently, and ∼75% with combined depletion of both cell populations. Together, our data show that the immune system contributes to the initiation and development of HO in FOP. Further, the expression of Acvr1^R206H in immune cells alters cytokine expression and cellular response to injury and unveils novel therapeutic targets for treatment of FOP and nongenetic forms of HO. © 2017 American Society for Bone and Mineral Research.