Heterotopic Ossification: Basic-Science Principles and Clinical Correlates

Radiation Prophylaxis for Hip Salvage Surgery in Cerebral Palsy: Can We Reduce the Incidence of Heterotopic Ossification?

BACKGROUND

Heterotopic ossification (HO) is a well-recognized complication of proximal femoral resection (PFR) surgery in children with cerebral palsy (CP). Although single-dose radiation prophylaxis (SDRP) has been shown to be effective at lowering the rates of HO following adult total hip arthroplasty; there has been limited study examining the efficacy of SDRP for HO prevention in children with CP undergoing PFR. The purpose of this study was to assess the efficacy of SDRP in children with CP undergoing PFR.

METHODS

This retrospective case control series identified all patients from one tertiary children's hospital undergoing PFHR. Patients were dichotomized into (1) SDRP and (2) non-SDRP groups. In SDRP, radiation was delivered preoperatively at a dose of 7.5 Gy utilizing a 6 MV photon beam. The incidence of HO in the SDRP cohort was compared to historic data using binomial testing. The size of HO lesions was compared using Wilcoxon signed-rank test. McCarthy, Brooker, and Anatomic Classifications of HO were compared using repeated measures logistic regression.

RESULTS

Twenty-three patients (mean age, 15.5) and 35 hips (17 SDRP, 18 Non-SDRP) were included in the analysis. There were 17 females and 6 males in the cohort with the majority classified as GMFCS V, 21/23 (91%). HO was seen in 6 of the SDRP cohort (6/17, 35%) and 15 of the non-SDRP cohort (15/18, 83%) (P=0.015). The average size of HO at maturity was 282.7 mm in the SDRP cohort compared with 1221.5 mm in the Non-SDRP cohort (P=0.026). Radiation treatment was associated with a 938.9 mm decrease in HO size at maturity (P= 0.026). Multivariate repeated measures logistic regression analysis found that non-SDRP hips had 13 times higher odds of developing HO (P=0.015). There were no significant differences in infection rates between the 2 cohorts and there were no radiation-associated complications.

CONCLUSIONS

Short-term follow up demonstrates that SDRP is a safe and efficacious intervention in decreasing the incidence and size of HO in children with CP undergoing PFR.

LEVELS OF EVIDENCE

Level III-Case control cohort study.

Trauma-Induced Nanohydroxyapatite Deposition in Skeletal Muscle is Sufficient to Drive Heterotopic Ossification

Heterotopic ossification (HO), or the pathologic formation of bone within soft tissues, is a significant complication following severe injuries as it impairs joint motion and function leading to loss of the ability to perform activities of daily living and pain. While soft tissue injury is a prerequisite of developing HO, the exact molecular pathology leading to trauma-induced HO remains unknown. Through prior investigations aimed at identifying the causative factors of HO, it has been suggested that additional predisposing factors that favor ossification within the injured soft tissues environment are required. Considering that chondrocytes and osteoblasts initiate physiologic bone formation by depositing nanohydroxyapatite crystal into their extracellular environment, we investigated the hypothesis that deposition of nanohydroxyapatite within damaged skeletal muscle is likewise sufficient to predispose skeletal muscle to HO. Using a murine model genetically predisposed to nanohydroxyapatite deposition (ABCC6-deficient mice), we observed that following a focal muscle injury, nanohydroxyapatite was robustly deposited in a gene-dependent manner, yet resolved via macrophage-mediated regression over 28 days post injury. However, if macrophage-mediated regression was inhibited, we observed persistent nanohydroxyapatite that was sufficient to drive the formation of HO in 4/5 mice examined. Together, these results revealed a new paradigm by suggesting the persistent nanohydroxyapatite, referred to clinically as dystrophic calcification, and HO may be stages of a pathologic continuum, and not discrete events. As such, if confirmed clinically, these findings support the use of early therapeutic interventions aimed at preventing nanohydroxyapatite as a strategy to evade HO formation.

Determining the effective timing of an open arthrolysis for post-traumatic elbow stiffness: a retrospective cohort study

Background

Following trauma, the elbow is the most susceptible to restricted motion among all joints. Open arthrolysis is often performed for post-traumatic elbow stiffness if that stiffness does not improve with non-operative management. However, the optimal timing for performing an open arthrolysis remains controversial. The purpose of this study was to compare the outcome (elbow motion and function) and the rate of complications among patients who had undergone early, median and late release procedures to establish an optimal time interval following the injury, after which, an effective open arthrolysis can be performed.

Methods

In this retrospective cohort study, we included total 133 patients, who had undergone open arthrolysis for post-traumatic elbow stiffness. The subjects were divided into 3 groups, with 31 patients in the early release group (arthrolysis performed at 6–10 months after injury), 78 patients in the median release group (at 11–20 months), and 24 patients in the late release group (at > 20 months). The release procedure in all patients was performed by the same surgeon, using the same technique. The general data, functional performance, and complications, if any, were retrospectively documented for all patients and statistically analysed.

Results

The demographic data and disease characteristics of all patients were comparable at baseline. Postoperatively, no significant differences were found among the three groups with respect to the range of motion (p = 0.067), Mayo Elbow Performance Score (p = 0.350) and its ratings (p = 0.329), visual analog scale score for pain (p = 0.227), Dellon classification for ulnar nerve symptoms (p = 0.497), and each discrete complication (all p values > 0.05).

Conclusions

At the final follow-up, our results showed no significant difference in the postoperative elbow motion capacities, functional scores and the rates of complications among patients who had undergone an early, median, and late release. Therefore, we have recommended that an early arthrolysis would be preferable due to its multiple advantages, and the conventionally observed interval of > 1 year after the injury, could be shortened.

Level of evidence

Level III; Retrospective Cohort Design; Therapeutic Study.

Coordinating Tissue Regeneration Through Transforming Growth Factor-β Activated Kinase 1 Inactivation and Reactivation

Aberrant wound healing presents as inappropriate or insufficient tissue formation. Using a model of musculoskeletal injury, we demonstrate that loss of transforming growth factor-β activated kinase 1 (TAK1) signaling reduces inappropriate tissue formation (heterotopic ossification) through reduced cellular differentiation. Upon identifying increased proliferation with loss of TAK1 signaling, we considered a regenerative approach to address insufficient tissue production through coordinated inactivation of TAK1 to promote cellular proliferation, followed by reactivation to elicit differentiation and extracellular matrix production. Although the current regenerative medicine paradigm is centered on the effects of drug treatment ("drug on"), the impact of drug withdrawal ("drug off") implicit in these regimens is unknown. Because current TAK1 inhibitors are unable to phenocopy genetic Tak1 loss, we introduce the dual-inducible COmbinational Sequential Inversion ENgineering (COSIEN) mouse model. The COSIEN mouse model, which allows us to study the response to targeted drug treatment ("drug on") and subsequent withdrawal ("drug off") through genetic modification, was used here to inactivate and reactivate Tak1 with the purpose of augmenting tissue regeneration in a calvarial defect model. Our study reveals the importance of both the "drug on" (Cre-mediated inactivation) and "drug off" (Flp-mediated reactivation) states during regenerative therapy using a mouse model with broad utility to study targeted therapies for disease. Stem Cells 2019;37:766-778.

Effects of hydrogen peroxide on biological characteristics and osteoinductivity of decellularized and demineralized bone matrices

Due to the similar collagen composition and closely physiological relationship with soft connective tissues, demineralized bone matrices (DBMs) were used to repair the injured tendon or ligament. However, the osteoinductivity of DBMs would be a huge barrier of these applications. Hydrogen peroxide (H₂ O₂ ) has been proved to reduce the osteoinductivity of DBMs. Nevertheless, the biological properties of H₂ O₂ -treated DBMs have not been evaluated completely, while the potential mechanism of H₂ O₂ compromising osteoinductivity is also unclear. Hence, the purpose of this study was to characterize the biological properties of H₂ O₂ -treated DBMs and search for the proof that H₂ O₂ could compromise osteoinductivity of DBMs. Decellularized and demineralized bone matrices (DCDBMs) were washed by 3% H₂ O₂ for 12 h to fabricate the H₂ O₂ -treated DCDBMs (HPTBMs). Similar biological properties including collagen, biomechanics, and biocompatibility were observed between DCDBMs and HPTBMs. The immunohistochemistry staining of bone morphogenetic protein 2 (BMP-2) was negative in HPTBMs. Furthermore, HPTBMs exhibited significantly reduced osteoinductivity both in vitro and in vivo. Taken together, these findings suggest that the BMP-2 in DCDBMs could be the target of H₂ O₂ . HPTBMs could be expected to be used as a promising scaffold for tissue engineering. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Treatment of posttraumatic lumbar interspinous ligament calcification with partial resection of spinous processes and calcified interspinous ligaments: case report

The authors report on the first surgical treatment for traumatic interspinous ligament calcification, with significant radiographic and symptomatic improvements at long-term follow-up. Heterotopic ossification occurs following traumatic injury but does not typically affect the interspinous ligaments. While these ligaments can calcify with age, this is rarely seen in patients younger than 50 years of age. The authors present the unusual case of a 31-year-old man who suffered traumatic fractures of thoracic and lumbar spinous processes. He developed progressive low-back pain that failed to respond to conservative treatments. At presentation, he was neurologically intact. CT scanning demonstrated partial calcification of the interspinous ligaments at L2-3, L3-4, and L4-5 with significant hypertrophy of the spinous processes at those levels. He did not have significant disc pathology, and his symptoms were attributed to the limited range of motion caused by the enlarged spinous processes. Partial resection of the spinous processes and calcified interspinous ligaments was performed to remove the heterotopic bone. The patient was seen in follow-up at 5 months postoperatively for imaging, and he was interviewed at 1 and 2 years postoperatively. He is doing well with significant pain relief and an improved range of motion. His Oswestry Disability Index improved from 25 preoperatively to 18 at 2 years postoperatively.

Heterotopic Ossification: A Comprehensive Review

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

Development and validation of a new elbow-specific scoring system for patients with elbow stiffness: the Shanghai Elbow Dysfunction Score

BACKGROUND

Clinical scoring systems are increasingly important and popular for the evaluation of orthopedic patients. Elbow stiffness commonly causes functional impairment and upper-limb disability. The purpose of this study was to develop and validate a new elbow-specific assessment score to evaluate joint function in patients with elbow stiffness.

METHODS

The new system, the Shanghai Elbow Dysfunction Score (SHEDS), was developed in 3 portions: elbow motion capacities, elbow-related symptoms, and patient satisfaction level. A total of 73 patients with elbow stiffness were prospectively included. Intraclass correlation coefficients and Cronbach α values were calculated for test-retest reliability and internal consistency, respectively. Construct validity was assessed by correlating the SHEDS with previously validated scoring systems. Effect sizes (ES) and standardized response means (SRMs) were calculated for responsiveness.

RESULTS

Positive reliability with an intraclass correlation coefficient of 0.83 and adequate homogeneity with a Cronbach α value of 0.74 were found for the SHEDS. Good to excellent validity using Spearman correlation coefficients (SCCs) were determined for the total (0.51-0.82), motion (0.65-0.89), and symptom (0.35-0.53) scores. Responsiveness was large for the total ES, 3.48; SRM, 2.96), motion (ES, 2.54; SRM, 2.08), and symptom (ES, 1.26; SRM, 1.14) scores. There were no ceiling or floor effects. Significant positive correlations were found between patient satisfaction levels and the final scores (SCC, 0.62), as well as the score changes of the SHEDS (SCC, 0.42).

CONCLUSION

Our results suggest that the newly developed SHEDS is an excellent, comprehensive, valid scoring system to evaluate joint function in patients with elbow stiffness.

Neurotrophin-3 acts on the endothelial-mesenchymal transition of heterotopic ossification in rats

Despite the fact that extensive studies have focused on heterotopic ossification (HO), its molecular mechanism remains unclear. The endothelial-mesenchymal transition (EndMT), which may be partially modulated by neuroendocrine cytokines is thought to play a major role in HO. Neurotrophin-3 (NT-3), which has neuroendocrine characteristics is believed to promote skeletal remodeling. Herein, we suggest that that NT-3 may promote HO formation through regulation of EndMT. Here, we used an in vivo model of HO and an in vitro model of EndMT induction to elucidate the effect and underlying mechanism of NT-3 on EndMT in HO. Our results showed that heterotopic bone and cartilage arose from EndMT and NT-3 promoted HO formation in vivo. Our in vitro results showed that NT-3 up-regulated mesenchymal markers (FSP-1, α-SMA and N-cadherin) and mesenchymal stem cell (MSC) markers (STRO-1, CD44 and CD90) and down-regulated endothelial markers (Tie-1, VE-cadherin and CD31). Moreover, NT-3 enhanced a chondrogenesis marker (Sox9) and osteogenesis markers (OCN and Runx2) via activation of EndMT. However, both EndMT specific inhibitor and tropomyosin-related kinase C (TrkC) specific inhibitor rescued NT-3-induced HO formation and EndMT induction in vivo and in vitro. In conclusion, our findings demonstrate that NT-3 promotes HO formation via modulation of EndMT both in vivo and in vitro, which offers a new potential target for the prevention and therapy of HO.

Osseous Metaplasia of the Cervix: A Rare Transformation Can Mimic a Tumor-Literature Review

Background

The transformation of nonosseous soft tissue into bone is known as osseous metaplasia (OM). This condition most commonly affects the musculoskeletal and central nervous systems and it is a well-known phenomenon in different soft tissue organs. Rarely, OM can affect the uterus, which can extend into the cervix. OM affecting the cervix alone is a more rare condition that has multiple different clinical presentations. The presentation can be similar to that of a tumor in extremely rare cases.

Case Summary

A 23-year-old nulligravida was complaining of irregular vaginal bleeding for one-month duration. Speculum examination revealed a foul-smelling bloody purulent discharge, tender cervix, and a brownish growth located at the posterior cervical lip. A punch biopsy of the growth was performed. Histological examination of the tissue revealed multiple bone fragments with necrosis and an inflammatory exudate. Because of the unusual findings, a repeat biopsy was performed. The biopsy yielded the same findings, which confirmed the diagnosis of osseous metaplasia of the cervix.

Conclusion

Although osseous metaplasia is a known phenomenon in different soft tissues, it is extremely rare in the uterine cervix and can mimic malignancy. Therefore, clinicians should be aware of it.

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.

Postinfectious heterotopic ossification of the ilium involving the iliacus muscle

Heterotopic ossification in soft tissue or muscle is rare in the pediatric and adolescent age group. Most cases are associated with musculoskeletal injury and trauma to the central nervous system. Here, we describe an adolescent patient without a history of trauma or lesions in the central nervous system who presented with a painful limp with limited motion of the left hip. Investigations indicated unusually large heterotopic ossification extending from the inner aspect of the ilium down to the anterior part of the hip, highly likely to have developed after an unrecognized periacetabular pyomyositis primarily involving the iliacus muscle. Surgical excision was performed successfully without perioperative complications. No recurrence was detected at the final follow-up.

Validation of the Liverpool Elbow Score for evaluation of elbow stiffness

Background

The Liverpool Elbow Score (LES) has been widely used to assess the outcomes of total elbow replacement in various conditions. However, there have been no published validation studies on LES for patients with stiff elbows undergoing arthrolysis. The purpose of this study was to find out whether LES could be equally applied to evaluate joint function in patients with elbow stiffness.

Methods

A total of 63 patients with elbow stiffness were included in this retrospective validation study. The LES combines a nine-item patient-answered questionnaire (PAQ) and a six-item clinical assessment score (CAS), and can also be divided to evaluate two different parameters: elbow motion capacity (EMC) and elbow-related symptoms (ERS). Construct validity was assessed by correlating LES with previously validated scoring systems, and Spearman correlation coefficients (SCCs) were calculated. Effect size (ES) and standardized response mean (SRM) were calculated to determine responsiveness.

Results

There were no ceiling or floor effects in the target population. Good-to-excellent validity was determined based on total score (0.45–0.89), PAQ (0.42–0.88), CAS (0.35–0.60), EMC (0.46–0.86), and ERS (0.36–0.59). High responsiveness (ES/SRM) was observed in total score (2.80/2.24), PAQ (2.34/1.78), CAS (2.90/2.34), EMC (2.92/2.35), and ERS (0.55/0.52).

Conclusion

Our results suggest that the LES is a valid elbow-specific scoring system that can be used to evaluate joint function in patients with elbow stiffness, though some items included had some weakness either.

Hypoxia-selective allosteric destabilization of activin receptor-like kinases: A potential therapeutic avenue for prophylaxis of heterotopic ossification

Heterotopic ossification (HO), the pathological extraskeletal formation of bone, can arise from blast injuries, severe burns, orthopedic procedures and gain-of-function mutations in a component of the bone morphogenetic protein (BMP) signaling pathway, the ACVR1/ALK2 receptor serine-threonine (protein) kinase, causative of Fibrodysplasia Ossificans Progressiva (FOP). All three ALKs (-2, -3, -6) that play roles in bone morphogenesis contribute to trauma-induced HO, hence are well-validated pharmacological targets. That said, development of inhibitors, typically competitors of ATP binding, is inherently difficult due to the conserved nature of the active site of the 500+ human protein kinases. Since these enzymes are regulated via inherent plasticity, pharmacological chaperone-like drugs binding to another (allosteric) site could hypothetically modulate kinase conformation and activity. To test for such a mechanism, a surface pocket of ALK2 kinase formed largely by a key allosteric substructure was targeted by supercomputer docking of drug-like compounds from a virtual library. Subsequently, the effects of docked hits were further screened in vitro with purified recombinant kinase protein. A family of compounds with terminal hydrogen-bonding acceptor groups was identified that significantly destabilized the protein, inhibiting activity. Destabilization was pH-dependent, putatively mediated by ionization of a histidine within the allosteric substructure with decreasing pH. In vivo, nonnative proteins are degraded by proteolysis in the proteasome complex, or cellular trashcan, allowing for the emergence of therapeutics that inhibit through degradation of over-active proteins implicated in the pathology of diseases and disorders. Because HO is triggered by soft-tissue trauma and ensuing hypoxia, dependency of ALK destabilization on hypoxic pH imparts selective efficacy on the allosteric inhibitors, providing potential for safe prophylactic use.

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.

Has the Proportion of Combat-Related Amputations That Develop Heterotopic Ossification Increased?

OBJECTIVES

To determine what proportion of residual limbs formed heterotopic ossification (HO) in amputations sustained by US service members, the injury profile of these amputations, and what effect the number of limb amputations sustained has on resource utilization.

DESIGN

Retrospective review.

SETTING

A tertiary military medical center.

PATIENTS

Four-hundred seventy-one consecutive patients with 714 combat-related amputations were treated at our institution between September 2009 and August 2014. Four-hundred thirty-nine amputations had radiographic follow-up beyond 2 months of injury and met the criteria for study inclusion.

MAIN OUTCOME MEASURE

Formation and grade of HO.

RESULTS

HO was present in 399 of 439 (91%) residual limbs, including 211 of 216 (98%) transfemoral amputations. Dismounted improvised explosive device blast injury resulted in HO development in 346 of 372 (93%) residual limbs compared with 36 of 44 (82%) in mounted improvised explosive device blast injury [P = 0.014; odds ratio (OR) 2.96, 95% confidence interval (CI), 1.25-7.04]. As the number of amputations per patient increased, so too did blood product utilization [including packed red blood cells (P < 0.001), fresh frozen plasma (P < 0.001), and platelets (P < 0.001)]; the number of days on a ventilator (P < 0.001), in the intensive care unit (P < 0.001), and in the hospital (P = 0.007).

CONCLUSIONS

HO prevalence in the traumatic amputations of war wounded has increased compared with earlier studies, which is temporally associated with higher rates of increasingly severe injuries due to dismounted blast.

LEVEL OF EVIDENCE

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

Heterotopic Ossification of the Inferior Pubic Ramus

The hip is a common location for heterotopic ossification after surgical trauma, blunt trauma, or muscle injury. However, the region around the pubic rami is an unusual location for heterotopic bone formation. Here, we present a case of a young, active man in the Armed Forces Reserve with a large heterotopic bone involving the left inferior pubic ramus who underwent surgical excision through an unusual approach via the perineum. The patient had notable pain relief postoperatively and returned to his active duties 1 month after surgery without discomfort or functional limitation.

Histopathology of periarticular non-hereditary heterotopic ossification

In the mature adult skeleton, new bone formation is normally restricted to regeneration of osseous tissue at sites of fracture. However, heterotopic ossification, or the formation of bone outside the normal skeleton, can occur within muscle, adipose, or fibrous connective tissue. Periarticular non-hereditary heterotopic ossification (NHHO) may occur after musculoskeletal trauma, following CNS injury, with certain arthropathies, or following injury or surgery that is often sustained in the context of age-related pathology. The histological mechanism of bone development in these forms of heterotopic ossification has thus far been uncharacterized. We performed a histological analysis of 90 bone specimens from 18 patients with NHHO secondary to defined precipitating conditions, including traumatic brain injury, spinal cord injury, cerebrovascular accident, trauma without neurologic injury, and total hip or knee arthroplasty. All bone specimens revealed normal endochondral osteogenesis at heterotopic sites. We defined the order of sequence progression in NHHO lesion formation as occurring through six distinct histological stages: (1) perivascular lymphocytic infiltration, (2) lymphocytic migration into soft tissue, (3) reactive fibroproliferation, (4) neovascularity, (5) cartilage formation, and (6) endochondral bone formation. This study provides the first systematic evaluation of the predominant histopathological findings associated with multiple forms of NHHO and shows that they share a common mechanism of lesion formation.

High-frequency spectral ultrasound imaging (SUSI) visualizes early post-traumatic heterotopic ossification (HO) in a mouse model

PURPOSE

Early treatment of heterotopic ossification (HO) is currently limited by delayed diagnosis due to limited visualization at early time points. In this study, we validate the use of spectral ultrasound imaging (SUSI) in an animal model to detect HO as early as one week after burn tenotomy.

METHODS

Concurrent SUSI, micro CT, and histology at 1, 2, 4, and 9weeks post-injury were used to follow the progression of HO after an Achilles tenotomy and 30% total body surface area burn (n=3-5 limbs per time point). To compare the use of SUSI in different types of injury models, mice (n=5 per group) underwent either burn/tenotomy or skin incision injury and were imaged using a 55MHz probe on VisualSonics VEVO 770 system at one week post injury to evaluate the ability of SUSI to distinguish between edema and HO. Average acoustic concentration (AAC) and average scatterer diameter (ASD) were calculated for each ultrasound image frame. Micro CT was used to calculate the total volume of HO. Histology was used to confirm bone formation.

RESULTS

Using SUSI, HO was visualized as early as 1week after injury. HO was visualized earliest by 4weeks after injury by micro CT. The average acoustic concentration of HO was 33% more than that of the control limb (n=5). Spectroscopic foci of HO present at 1week that persisted throughout all time points correlated with the HO present at 9weeks on micro CT imaging.

CONCLUSION

SUSI visualizes HO as early as one week after injury in an animal model. SUSI represents a new imaging modality with promise for early diagnosis of HO.

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.

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.

Cartilage-derived retinoic acid-sensitive protein (CD-RAP): A stage-specific biomarker of heterotopic endochondral ossification (HEO) in fibrodysplasia ossificans progressiva (FOP)

BACKGROUND

Genesis of a cartilaginous scaffold is an obligate precursor to bone formation in heterotopic endochondral ossification (HEO). We tested the hypothesis that cartilage-derived retinoic acid-sensitive protein (CD-RAP) can serve as a plasma biomarker for the pre-osseous cartilaginous stage of HEO. Palovarotene, a retinoic acid receptor-gamma (RARγ) agonist, has been proposed as a possible treatment for fibrodysplasia ossificans progressiva (FOP) and is a potent inhibitor of HEO in mouse models. Current drug development for FOP mandates the identification of stage-specific biomarkers to facilitate the evaluation of clinical trial endpoints.

RESULTS

Here we show in an injury-induced, constitutively-active transgenic mouse model of FOP that CD-RAP levels peaked between day-7 and day-10 during the zenith of histologically-identified chondrogenesis, preceded radiographically apparent HEO, and were diminished by palovarotene. Cross-sectional analysis of CD-RAP levels in plasma samples from FOP patients demonstrated a statistically non-significant trend toward higher levels in the recent flare-up period (three weeks to three months within onset of symptoms). However, in a longitudinal subgroup analysis of patients followed for at least six months after resolution of flare-up symptoms, there was a statistically significant decrease of CD-RAP when compared to levels in the same patients at the time of active or recent exacerbations.

CONCLUSIONS

These data support the further exploration of CD-RAP as a stage-specific biomarker of HEO in FOP.

Circulating osteogentic precursor cells in non-hereditary heterotopic ossification

Non-hereditary heterotopic ossification (NHHO) may occur after musculoskeletal trauma, central nervous system (CNS) injury, or surgery. We previously described circulating osteogenic precursor (COP) cells as a bone marrow-derived type 1 collagen⁺CD45⁺subpopulation of mononuclear adherent cells that are able of producing extraskeletal ossification in a murine in vivo implantation assay. In the current study, we performed a tissue analysis of COP cells in NHHO secondary to defined conditions, including traumatic brain injury, spinal cord injury, cerebrovascular accident, trauma without neurologic injury, and joint arthroplasty. All bone specimens revealed the presence of COP cells at 2-14 cells per high power field. COP cells were localized to early fibroproliferative and neovascular lesions of NHHO with evidence for their circulatory status supported by their presence near blood vessels in examined lesions. This study provides the first systematic evaluation of COP cells as a contributory histopathological finding associated with multiple forms of NHHO. These data support that circulating, hematopoietic-derived cells with osteogenic potential can seed inflammatory sites, such as those subject to soft tissue injury, and due to their migratory nature, may likely be involved in seeding sites distant to CNS injury.

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.

Heterotopic bone induction via BMP signaling: Potential therapeutic targets for fibrodysplasia ossificans progressiva

More than 50years ago, Marshal M. Urist detected "heterotopic bone-inducing activity" in demineralized bone matrix. This unique activity was referred to as "bone morphogenetic protein (BMP)" because it was sensitive to trypsin digestion. Purification of the bone-inducing activity from demineralized bone matrix using a bone-inducing assay in vivo indicated that the original "BMP" consisted of a mixture of new members of the transforming growth factor-β (TGF-β) family. The establishment of new in vitro assay systems that reflect the bone-inducing activity of BMPs in vivo have revealed the functional receptors and downstream effectors of BMPs. Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by progressive heterotopic bone formation in soft tissues similar to the event induced by the transplantation of BMPs in skeletal muscle. In patients with FOP, genetic mutations have been identified in the ACVR1 gene, which encodes the BMP receptor ALK2. The mutations in ALK2 associated with FOP are hypersensitive to type II receptor kinases. Recently, activin A, a non-osteogenic member of the TGF-β family, was identified as the ligand of the mutant ALK2 in FOP, and various types of signaling inhibitors for mutant ALK2 are currently under development to establish effective treatments for FOP.

A case report of mesenteric heterotopic ossification: Histopathologic and genetic findings

Mesenteric heterotopic ossification (MHO) is very rare and occurs in mid- to late-adulthood, usually in the context of prior abdominal surgery. The mechanisms of MHO are unknown. Here we describe the case of a 72-year-old man with MHO. Standard histological staining revealed that MHO occurred through an endochondral process. By comparison to known mutations in genetic conditions of HO such as fibrodysplasia ossificans progressiva (FOP) and progressive osseous heteroplasia (POH), DNA sequencing analysis demonstrated the presence of a commonly occurring heterozygous synonymous polymorphism (c.690G>A; E230E) in the causative gene for FOP (ACVR1/ALK2). However, no frameshift, missense, or nonsense mutations in ACVR1, or in the causative gene for POH (GNAS), were found. Although genetic predisposition may play a role in MHO, our data suggest that mutations which occur in known hereditary conditions of HO are not the primary cause.

Long-term Consequences of Traumatic Brain Injury in Bone Metabolism

Traumatic brain injury (TBI) leads to long-term cognitive, behavioral, affective deficits, and increase neurodegenerative diseases. It is only in recent years that there is growing awareness that TBI even in its milder form poses long-term health consequences to not only the brain but to other organ systems. Also, the concept that hormonal signals and neural circuits that originate in the hypothalamus play key roles in regulating skeletal system is gaining recognition based on recent mouse genetic studies. Accordingly, many TBI patients have also presented with hormonal dysfunction, increased skeletal fragility, and increased risk of skeletal diseases. Research from animal models suggests that TBI may exacerbate the activation and inactivation of molecular pathways leading to changes in both osteogenesis and bone destruction. TBI has also been found to induce the formation of heterotopic ossification and increased callus formation at sites of muscle or fracture injury through increased vascularization and activation of systemic factors. Recent studies also suggest that the disruption of endocrine factors and neuropeptides caused by TBI may induce adverse skeletal effects. This review will discuss the long-term consequences of TBI on the skeletal system and TBI-induced signaling pathways that contribute to the formation of ectopic bone, altered fracture healing, and reduced bone mass.

Prevalence and clinical outcomes of heterotopic ossification after ulnar collateral ligament reconstruction

BACKGROUND

Ulnar collateral ligament (UCL) reconstruction has become increasingly popular in elite athletes. However, the prevalence of heterotopic ossification (HO) formation after UCL reconstruction has not yet been reported. We sought to determine the prevalence of HO formation after UCL reconstruction and the clinical outcomes following HO treatment.

MATERIALS AND METHODS

From October 2005 to April 2014, 179 patients underwent primary UCL reconstruction. Of the 179 patients, 161 with a minimum of 2 years of follow-up were retrospectively reviewed to evaluate HO formation and clinical outcomes.

RESULTS

Among 161 patients, HO was detected in 8 cases (5%). Of these 8 patients, 2 were asymptomatic and another 2 complained about transient ulnar neuropathy. The remaining 4 patients had pain; 2 were treated with open excision, and 1 underwent arthroscopic excision. The odds of HO in patients in whom transient ulnar neuropathy develops after UCL reconstruction are 6 times higher than those without transient ulnar neuropathy (odds ratio, 5.957; 95% confidence level, P = .04). Of the 8 patients, 7 returned to the same level or a higher level of competition. HO was found, on average, 5 months (range, 3-9 months) after UCL reconstruction.

CONCLUSION

The prevalence of HO formation was approximately 5% after UCL reconstruction and increased with transient ulnar neuropathy. After UCL reconstruction, the surgeon should carefully observe HO formation, especially in the early stages after the operation. With appropriate treatment, the clinical outcomes of HO treatment after UCL reconstruction are favorable.

Treatment of tibial nonunion with bone defect using a heterotopic ossification as autologous bone graft: literature overview and case report

INTRODUCTION

Nonunion after open fracture of the lower leg is a frequent complication with a prevalence of up to 40%. In cases with major bone defects, revision of the osteosynthesis with bone grafting is commonly performed. Until today, there is no report on treatment of a tibial nonunion with transplantation of a heterotopic ossification.

PRESENTATION OF CASE

We present a case of a 27-year-old male patient, who suffered from a paragliding accident with major injuries. An open fracture of the lower leg (Gustilo-Anderson IIIB) was initially treated with external fixation and vacuum-assisted closure, followed by reamed intramedullary nailing. The tibia resulted in a bone defect situation with nonunion. It was successfully treated with revision, fibular osteotomy and transplantation of a heterotopic ossification, harvested from the ipsilateral hip.

CONCLUSION

In special cases, autologous transplantation of a mature heterotopic ossification is an attractive bone graft option in treating nonunion defects.

Optimization of screw fixation in rat bone with extracorporeal shock waves

Screw fixation in osteoporotic patients is becoming an increasing problem in orthopaedic surgery as deterioration of cortical and cancellous bone hamper biomechanical stability and screw fixation. This might result in delayed weight-bearing or failure of instrumentation. We hypothesized that local peri-operative shock wave treatment can optimize osseointegration and subsequent screw fixation. In eight female Wistar rats, two cancellous and two cortical bone screws were implanted in both femora and tibiae. Immediately after implantation, 3.000 unfocused extracorporeal shock waves (energy flux density 0.3 mJ/mm² ) were applied to one side. The other side served as non-treated internal control. Evaluation of osseointegration was performed after 4 weeks with the use of microCT scanning, histology with fluorochrome labeling, and pull-out tests of the screws. Four weeks after extracorporeal shock wave treatment, treated legs exhibited increased bone formation and screw fixation around cortical screws as compared to the control legs. This was corroborated by an increased pull-out of the shock wave treated cortical screws. The cancellous bone screws appeared not to be sensitive for shock wave treatment. Formation of neocortices after shock wave therapy was observed in three of eight animals. Furthermore, de novo bone formation in the bone marrow was observed in some animals. The current study showed bone formation and improved screw fixation as a result of shock wave therapy. New bone was also formed at locations remote from the screws, hence, not contributing to screw fixation. Further, research is warranted to make shock wave therapy tailor-made for fracture fixation. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:76-84, 2018.

MMP-2 silencing reduces the osteogenic transformation of fibroblasts by inhibiting the activation of the BMP/Smad pathway in ankylosing spondylitis

Ankylosing spondylitis (AS) is a common type of rheumatoid disease, which has recently been demonstrated to be associated with the expression of matrix metalloproteinase (MMP)-2. The aim of the present study was to investigate whether MMP-2 interference reduced the osteogenic differentiation of fibroblasts and to explore the mechanism involved in the differentiation. Fibroblasts from patients with AS were divided into control, mock and small interfering (si)RNA-MMP-2 groups. Cell viability was assessed using the MTT assay. mRNA and protein expression levels of MMP-2, core-binding factor a1 (Cbfa-1) and bone morphogenetic proteins/Smad-signalling molecules (BMP/Smad) were measured using reverse transcription-quantitative polymerase chain reaction and western blotting. The results indicated that cell viability and fibroblast morphology did not differ significantly between healthy volunteers and patients with AS. However, MMP-2 expression levels in AS fibroblasts were substantially higher. MMP-2 gene silencing markedly downregulated the expression of MMP-2 and Cbfa-1, and inhibitied the activation of the BMP/Smad signalling pathway consequent to the reduction in levels of BMP-2, Smad1, Smad4 and Smad1/5/8. The results showed that MMP-2 gene silencing may reduce the osteogenesis of fibroblasts in AS by inhibiting the activation of the BMP/Smad signalling pathway.

Extensive Surgical Wound Lavage Reduces the Incidence and Severity of Heterotopic Ossification in Primary Total Hip Replacement: A Study of 175 Hip Replacements

Purpose

One of the local factors contributing to the formation of heterotopic ossification includes bone debris generated during the surgery. This risk can be partially nullified by use of saline wash. Our research aim was to ascertain if extensive intraoperative lavage can reduce the incidence and severity of heterotopic ossification in primary total hip arthroplasty.

Materials and Methods

A retrospective case control radiological study of 145 patients (175 hip replacements). The control group received minimal intra-operative lavage (<1,000 mL); consisted of 90 primary hip replacements. The index group received extensive saline lavage (>3,000 mL), and included 85 primary hip replacements. Brooker classification was used to grade radiographs at one year for development of heterotopic ossification.

Results

Sixty-six patients in control group had heterotopic ossification, with six showing a significant grade (grade 3 or 4). Thirty-five patients in the index group had heterotopic ossification with no incidence of severe grade. Majority patients in the index group showed a predominantly grade 1 heterotopic ossification; 28 out of 35, as compared to 37 out of 66 in control group. There was a statistically significant difference in the incidence (P<0.05) as well as severity of heterotopic ossification between the groups (P<0.05).

Conclusion

We conclude that use of extensive lavage during total hip replacement reduces the incidence as well as severity of heterotopic ossification.

Relationship between heterotopic ossification and traumatic brain injury: Why severe traumatic brain injury increases the risk of heterotopic ossification

Heterotopic ossification (HO) is a pathological phenomenon in which ectopic lamellar bone forms in soft tissues. HO involves many predisposing factors, including congenital and postnatal factors. Postnatal HO is usually induced by fracture, burn, neurological damage (brain injury and spinal cord injury) and joint replacement. Recent studies have found that patients who suffered from bone fracture combined with severe traumatic brain injury (S-TBI) are at a significantly increased risk for HO occurrence. Thus, considerable research focused on the influence of S-TBI on fracture healing and bone formation, as well as on the changes in various osteogenic factors with S-TBI occurrence. Brain damage promotes bone formation, but the exact mechanisms underlying bone formation and HO after S-TBI remain to be clarified. Hence, this article summarises the findings of previous studies on the relationship between S-TBI and HO and discusses the probable causes and mechanisms of HO caused by S-TBI. The translational potential of this article: A better understanding of the probable causes of traumatic brain injury-induced HO can provide new perspectives and ideas in preventing HO and may support to design more targeted therapies to reduce HO or enhance the bone formation.

Early local delivery of vancomycin suppresses ectopic bone formation in a rat model of trauma-induced heterotopic ossification

Heterotopic ossification (HO) is a debilitating sequela of high-energy injuries. It frequently requires surgical excision once symptomatic and there is no practical prophylaxis for combat-injured patients. In this study, we examined the effect of local vancomycin powder on HO formation in a small animal model of blast-related, post-traumatic HO. Male Sprague-Dawley rats were subjected to a polytraumatic extremity injury and amputation with or without methicillin-resistant Staphylococcus aureus infection. Animals were randomized to receive a single local application of vancomycin (20 mg/kg) at the time of injury (POD-0, n = 34) or on postoperative day-3 (POD-3, n = 11). Quantitative volumetric measurement of ectopic bone was calculated at 12-weeks post-injury by micro-CT. Bone marrow and muscle tissues were also collected to determine the bacterial burden. Blood for serum cytokine analysis was collected at baseline and post-injury. Vancomycin treatment on POD-0 suppressed HO formation by 86% and prevented bone marrow and soft tissue infections. We concurrently observed a marked reduction histologically in nonviable tissue, chronic inflammatory cell infiltrates, bone infection, fibrous tissue, and areas of bone necrosis within this same cohort. Delayed treatment was significantly less efficacious. Neither treatment had a marked effect on the production of pro-inflammatory cytokines. Our study demonstrates that local vancomycin treatment at the time of injury significantly reduces HO formation in both the presence and absence of infection, with decreased efficacy if not given early. These findings further support the concept that the therapeutic window for prophylaxis is narrow, highlighting the need to develop early treatment strategies for clinical management. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2397-2406, 2017.

Contribution of Implanted, Genetically Modified Muscle Progenitor Cells Expressing BMP-2 to New Bone Formation in a Rat Osseous Defect

Because muscle contains osteoprogenitor cells and has a propensity to form bone, we have explored its utility in healing large osseous defects. Healing is achieved by the insertion of muscle fragments transduced with adenovirus encoding BMP-2 (Ad.BMP-2). However, it is not known whether the genetically modified muscle contributes osteoprogenitor cells to healing defects or merely serves as a local source of BMP-2. This question is part of the larger debate on the fate of progenitor cells introduced into sites of tissue damage to promote regeneration. To address this issue, we harvested fragments of muscle from rats constitutively expressing GFP, transduced them with Ad.BMP-2, and implanted them into femoral defects in wild-type rats under various conditions. GFP⁺ cells persisted within defects for the entire 8 weeks of the experiments. In the absence of bone formation, these cells presented as fibroblasts. When bone was formed, GFP⁺ cells were present as osteoblasts and osteocytes and also among the lining cells of new blood vessels. The genetically modified muscle thus contributed progenitor cells as well as BMP-2 to the healing defect, a property of great significance in light of the extensive damage to soft tissue and consequent loss of endogenous progenitors in problematic fractures.

Mechanical Stress by Spasticity Accelerates Fracture Healing After Spinal Cord Injury

Accelerated fracture healing in patients with spinal cord injuries (SCI) is often encountered in clinical practice. However, there is no distinct evidence in the accelerated fracture healing, and the mechanisms of accelerated fracture healing in SCI are poorly understood. We aimed to determine whether SCI accelerated fracture healing in morphology and strength, to characterize the healing process with SCI, and to clarify the factors responsible for accelerated fracture healing. In total, 39 male Wistar rats were randomly divided into healthy control without intervention, SCI only, fracture with SCI, botulinum toxin (BTX) A-treated fracture with SCI, and propranolol-treated fracture with SCI groups. These rats were assessed with computed microtomography, histological, histomorphological, immunohistological, and biomechanical analyses. Both computed microtomography and histological analyses revealed the acceleration of a bony union in animals with SCI. The strength of the healed fractures after SCI recovered to the same level as that of intact bones after SCI, while the healed bones were weaker than the intact bones. Immunohistology revealed that SCI fracture healing was characterized by formation of callus with predominant intramembranous ossification and promoting endochondral ossification. The accelerated fracture healing after SCI was attenuated by BTX injection, but did not change by propranolol. We demonstrated that SCI accelerate fracture healing in both morphology and strength. The accelerated fracture healing with SCI may be due to predominant intramembranous ossification and promoting endochondral ossification. In addition, our results also suggest that muscle contraction by spasticity accelerates fracture healing after SCI.

Heterotopic Ossification Encountered During a Complex Ventral Hernia Repair: Case Report and Literature Review

Introduction: Heterotopic ossification involves the formation of trabecular bone outside of its usual anatomic location. While it is a well-known entity in orthopedic and spinal injury literature, it has also been observed after midline laparotomy and severe burns. Methods/Case Report: We present a case of a 69-year-old man who presented for ventral hernia repair after a prolonged postoperative course following colectomy involving an open abdomen with eventual closure with skin grafting. Results: Two large calcified objects were encountered during the excision of the skin graft from the small intestine and during the component separation. They had grown into the anterior fascia and rectus muscle and interdigitated between loops of the small bowel. After careful resection of the 2 calcified objects, a ventral hernia repair with a component separation was successfully performed. Pathology was consistent with heterotopic ossification. After 18 months, there was no clinical evidence of recurrence. Discussion: Heterotopic ossification is not frequently encountered during ventral hernia repairs, but its presence can complicate repair. Resection is the only option in the context of hernia repair. If recognized preoperatively, waiting up to a year for the bone to mature before excision has been suggested, but there is minimal data to support this. Consultation with a general surgeon is also advised in case the calcified tissue involves the underlying viscera.

Peripheral denervation participates in heterotopic ossification in a spinal cord injury model

We previously reported the development of a new acquired neurogenic HO (NHO) mouse model, combining spinal cord transection (SCI) and chemical muscle injury. Pathological mechanisms responsible for ectopic osteogenesis after central neurological damage are still to be elucidated. In this study, we first hypothesized that peripheral nervous system (PNS) might convey pathological signals from injured spinal cord to muscles in NHO mouse model. Secondly, we sought to determine whether SCI could lead to intramuscular modifications of BMP2 signaling pathways. Twenty one C57Bl6 mice were included in this protocol. Bilateral cardiotoxin (CTX) injection in hamstring muscles was associated with a two-stage surgical procedure, combining thoracic SCI with unilateral peripheral denervation. Volumes of HO (Bone Volume, BV) were measured 28 days after surgery using micro-computed tomography imaging techniques and histological analyses were made to confirm intramuscular osteogenesis. Volume comparisons were conducted between right and left hind limb of each animal, using a Wilcoxon signed rank test. Quantitative polymerase chain reaction (qPCR) was performed to explore intra muscular expression of BMP2, Alk3 and Id1. Nineteen mice survive the complete SCI and peripheral denervation procedure. When CTX injections were done right after surgery (n = 7), bilateral HO were detected in all animals after 28 days. Micro-CT measurements showed significantly increased BV in denervated paws (1.47 mm3 +/- 0.5) compared to contralateral sides (0.56 mm3 +/-0.4), p = 0.03. When peripheral denervation and CTX injections were performed after sham SCI surgery (n = 6), bilateral HO were present in three mice at day 28. Quantitative PCR analyses showed no changes in intra muscular BMP2 expression after SCI as compared to control mice (shamSCI). Peripheral denervation can be reliably added to spinal cord transection in NHO mouse model. This new experimental design confirms that neuro inflammatory mechanisms induced by central or peripheral nervous system injury plays a key role in triggering ectopic osteogenesis.

STING Contributes to Abnormal Bone Formation Induced by Deficiency of DNase II in Mice

OBJECTIVE

Cytosolic DNA sensors detect microbial DNA and promote type I interferon (IFN) and proinflammatory cytokine production through the adaptor stimulator of IFN genes (STING) to resolve infection. Endogenous DNA also engages the STING pathway, contributing to autoimmune disease. This study sought to identify the role of STING in regulating bone formation and to define the bone phenotype and its pathophysiologic mechanisms in arthritic mice double deficient in DNase II and IFN-α/β/ω receptor (IFNAR) (DNase II^-/- /IFNAR^-/- double-knockout [DKO] mice) compared with controls.

METHODS

Bone parameters were evaluated by micro-computed tomography and histomorphometry in DKO mice in comparison with mice triple deficient in STING, DNase II, and IFNAR and control mice. Cell culture techniques were employed to determine the parameters of osteoclast and osteoblast differentiation and function. NanoString and Affymetrix array analyses were performed to identify factors promoting ectopic bone formation.

RESULTS

Despite the expression of proinflammatory cytokines that would be expected to induce bone loss in the skeleton of DKO mice, the results, paradoxically, demonstrated an accumulation of bone in the long bones and spleens, sites of erythropoiesis and robust DNA accrual. In addition, factors promoting osteoblast recruitment and function were induced. Deficiency of STING significantly inhibited bone accrual.

CONCLUSION

These data reveal a novel role for cytosolic DNA sensor pathways in bone in the setting of autoimmune disease. The results demonstrate the requirement of an intact STING pathway for bone formation in this model, a finding that may have relevance to autoimmune diseases in which DNA plays a pathogenic role. Identification of pathways linking innate immunity and bone could reveal novel targets for the treatment of bone abnormalities in human autoimmune diseases.

Acquired heterotopic ossification of the temporomandibular joint

Although the risk factors and diagnosis of heterotopic ossification (HO) are discussed in the orthopedics literature, the etiology of HO, as well as its prevention and management, remain theoretical. Furthermore, there is a lack of information in the literature regarding HO in temporomandibular joint replacement (TMJR). This article provides a qualitative review of information relative to the etiology, diagnosis, and management of HO to inform and encourage further investigation in TMJR. The orthopedic HO literature considered for this qualitative review was drawn from a comprehensive examination of the subject published previously by one of the authors. Using the key words "heterotopic ossification" or "heterotopic bone", citations in the PubMed database from both the dental and oral and maxillofacial surgery literature were reviewed. Based on this, it appears that the etiology, diagnosis, imaging, laboratory testing, risk factors, prophylaxis, and non-surgical and surgical options available for the management of TMJR-related HO are similar to those for orthopedic HO, but further elucidation is required for TMJR. There is a lack of published information in the literature on TMJR. Therefore, using the literature from this review as a foundation, studies should be developed and reported so that alloplastic TMJ surgeons have evidence-based protocols that will lead to the early detection and potential prevention of HO.

Predicting Heterotopic Ossification Early After Burn Injuries: A Risk Scoring System

OBJECTIVE

The purpose of this study is to develop a scoring system that stratifies burn patients at the time of hospital admission according to risk of developing heterotopic ossification (HO).

SUMMARY OF BACKGROUND DATA

HO in burns is an uncommon but severely debilitating problem with a poorly understood mechanism and no fully effective prophylactic measures.

METHODS

Data were obtained from the Burn Model System National Database from 1994 to 2010 (n = 3693). The primary outcome is diagnosis of HO at hospital discharge. Logistic regression analysis was used to determine significant demographic and medical predictors of HO. A risk scoring system was created in which point values were assigned to predictive factors and final risk score is correlated with the percent risk of developing HO. The model was internally and externally validated.

RESULTS

The mean age of the subjects is 42.5 ± 16.0 years, the mean total body surface area (TBSA) burned is 18.5 ± 16.4%, and the population is 74.9% male. TBSA and the need for grafting of the arm, head/neck, and trunk were significant predictors of HO development (P < 0.01). A 13-point risk scoring system was developed using these significant predictors. The model c-statistic is 0.92. The risk scoring system demonstrated evidence of internal and external validity. An online calculator was developed to facilitate translation of knowledge to practice and research.

CONCLUSIONS

This HO risk scoring system identifies high-risk burn patients suitable for diagnostic testing and interventional HO prophylaxis trials.

The efficacy of a multimodal analgesia protocol in preventing heterotopic ossification after acetabular fractures surgery

Background Heterotopic ossification (HO) after joint surgery is always a disturbing problem for patients and surgeons. Prophylaxis is the most effective therapy. Objective To assess the efficacy and safety of a multimodal analgesia protocol that included parecoxib and celecoxib in preventing HO after acetabular fracture surgery. Setting Selecting patients from trauma registry of our hospital. Method We identified 259 patients who had acetabular fracture surgery between January 2008 and December 2014. Hundredsixty-three patients received parecoxib and celecoxib (Group A) and 96 patients received no prophylaxis (Group B). The presence of HO was assessed according to the classification of Brooker et al. at the 12 month postoperative visit. Main outcome measure The differences in HO incidence and severity between the two groups. Results 49 patients (30.0%) developed HO in the Group A and 44(45.8%) in Group B. The difference in total HO incidence between the two groups was significant (P = 0.011 < 0.05, χ² = 6.530, OR 0.508, 95% CI (0.301-0.857). Severe HO (Brooker grade III or IV) developed in 15 patients (9.2%) in Group A and 17 patients (17.7%) in Group B. Brooker grade I + II was 34(20.9%) and 27(28.1%) in each group. The difference in the severity of HO between the two Groups was significant (P = 0.008 < 0.05). Conclusion A short-term administration of parecoxib and celecoxib aids in the prevention of HO after acetabular fractures surgery.

A survey of proteomic biomarkers for heterotopic ossification in blood serum

Background

Heterotopic ossification (HO) is a significant problem for wounded warriors surviving high-energy blast injuries; however, currently, there is no biomarker panel capable of globally characterizing, diagnosing, and monitoring HO progression. The aim of this study was to identify biomarkers for HO using proteomic techniques and blood serum.

Methods

Isobaric tags for relative and absolute quantitation (iTRAQ) was used to generate a semi-quantitative global proteomics survey of serum from patients with and without heterotopic ossification. Leveraging the iTRAQ data, a targeted selection reaction monitoring mass spectrometry (SRM-MS) assay was developed for 10 protein candidates: alkaline phosphatase, osteocalcin, alpha-2 type I collagen, collagen alpha-1(V) chain isoform 2 preprotein, bone sialoprotein 2, phosphatidate phosphatase LPIN2, osteomodulin, protein phosphatase 1J, and RRP12-like protein.

Results

The proteomic survey of serum from both healthy and disease patients includes 1220 proteins and was enriched for proteins involved in the response to elevated platelet Ca⁺², wound healing, and extracellular matrix organization. Proteolytic peptides from three of the ten SRM-MS proteins, osteocalcin preprotein, osteomodulin precursor, and collagen alpha-1(v) chain isoform 2 preprotein from serum, are potential clinical biomarkers for HO.

Conclusions

This study is the first reported SRM-MS analysis of serum from individuals with and without heterotopic ossification, and differences in the serum proteomic profile between healthy and diseased subjects were identified. Furthermore, our results indicate that normal wound healing signals can impact the ability to identify biomarkers, and a multi-protein panel assay, including osteocalcin preproprotein, osteomodulin precursor, and collagen alpha-1(v) chain isoform 2 preprotein, may provide a solution for HO detection and monitoring.

Electronic supplementary material

The online version of this article (doi:10.1186/s13018-017-0567-2) contains supplementary material, which is available to authorized users.

Vascular patterning in human heterotopic ossification

Heterotopic ossification (HO, also termed myositis ossificans) is the formation of extra-skeletal bone in muscle and soft tissues. HO is a tissue repair process gone awry, and is a common complication of surgery and traumatic injury. Medical strategies to prevent and treat HO fall well short of addressing the clinical need. Better characterization of the tissues supporting HO is critical to identifying therapies directed against this common and sometimes devastating condition. The physiologic processes of osteogenesis and angiogenesis are highly coupled and interdependent. However, few efforts have been made to document the vascular patterning within heterotopic ossification. Here, surgical pathology case files of 29 human HO specimens were examined by vascular histomorphometric analysis. Results demonstrate a temporospatial patterning of HO vascularity that depends on the "maturity" of the bony lesion. In sum, human HO demonstrates a time- and space-dependent pattern of vascularization suggesting a coupled pathophysiologic process involving the coordinate processes of osteogenesis and angiogenesis. Further imaging studies may be used to further characterize vasculogenesis within HO and whether anti-angiogenic therapies are a conceivable future therapy for this common condition.

Evaluation of Salivary Cytokines for Diagnosis of both Trauma-Induced and Genetic Heterotopic Ossification

PURPOSE

Heterotopic ossification (HO) occurs in the setting of persistent systemic inflammation. The identification of reliable biomarkers can serve as an early diagnostic tool for HO, especially given the current lack of effective treatment strategies. Although serum biomarkers have great utility, they can be inappropriate or ineffective in traumatic acute injuries and in patients with fibrodysplasia ossificans progressiva (FOP). Therefore, the goal of this study is to profile the cytokines associated with HO using a different non-invasive source of biomarkers.

METHODS

Serum and saliva were collected from a model of trauma-induced HO (tHO) with hind limb Achilles' tenotomy and dorsal burn injury at indicated time points (pre-injury, 48 h, 1 week, and 3 weeks post-injury) and a genetic non-trauma HO model (Nfatc1-Cre/caAcvr1fl/wt ). Samples were analyzed for 27 cytokines using the Bio-Plex assay. Histologic evaluation was performed in Nfatc1-Cre/caAcvr1fl/wt mice and at 48 h and 1 week post-injury in burn tenotomy mice. The mRNA expression levels of these cytokines at the tenotomy site were also quantified with quantitative real-time PCR. Pearson correlation coefficient was assessed between saliva and serum.

RESULTS

Levels of TNF-α and IL-1β peaked at 48 h and 1 week post-injury in the burn/tenotomy cohort, and these values were significantly higher when compared with both uninjured (p < 0.01, p < 0.03) and burn-only mice (p < 0.01, p < 0.01). Immunofluorescence staining confirmed enhanced expression of IL-1β, TNF-α, and MCP-1 at the tenotomy site 48 h after injury. Monocyte chemoattractant protein-1 (MCP-1) and VEGF was detected in saliva showing elevated levels at 1 week post-injury in our tHO model when compared with both uninjured (p < 0.001, p < 0.01) and burn-only mice (p < 0.005, p < 0.01). The Pearson correlation between serum MCP-1 and salivary MCP-1 was statistically significant (r = 0.9686, p < 0.001) Similarly, the Pearson correlation between serum VEGF and salivary VEGF was statistically significant (r = 0.9709, p < 0.05).

CONCLUSION

In this preliminary study, we characterized the diagnostic potential of specific salivary cytokines that may serve as biomarkers for an early-stage diagnosis of HO. This study identified two candidate biomarkers for further study and suggests a novel method for diagnosis in the context of current difficult diagnosis and risks of current diagnostic methods in certain patients.

Chemical, Electrical, and Radiation Injuries

This article reviews the unique challenges presented by chemical, electrical, and radiation injuries. The authors discuss pathophysiology and diagnosis of these injuries and provide recommendations for management.

Heterotopic Ossification in Trauma

Better understanding of the biology of heterotopic ossification (HO) formation will lead to treatment and prevention modalities that can be directed specifically at the cellular level. Early identification of HO precursor cells and target genes may provide prognostic value that guides individualized prophylactic treatment. Better understanding of molecular signaling and proteomics variability will allow surgeons to individualize preemptive treatment to suppress inflammation and formation of HO. Careful surgical technique to avoid muscle damage is important. Damaged muscle should be debrided as a prophylactic measure. Hemostasis and avoidance of a postoperative hematoma may decrease the chance of formation of HO.