Heterotopic ossification

Angiogenesis in heterotopic ossification: From mechanisms to clinical significance

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

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

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

From inflammation to bone formation: the intricate role of neutrophils in skeletal muscle injury and traumatic heterotopic ossification

Neutrophils are emerging as an important player in skeletal muscle injury and repair. Neutrophils accumulate in injured tissue, thus releasing inflammatory factors, proteases and neutrophil extracellular traps (NETs) to clear muscle debris and pathogens when skeletal muscle is damaged. During the process of muscle repair, neutrophils can promote self-renewal and angiogenesis in satellite cells. When neutrophils are abnormally overactivated, neutrophils cause collagen deposition, functional impairment of satellite cells, and damage to the skeletal muscle vascular endothelium. Heterotopic ossification (HO) refers to abnormal bone formation in soft tissue. Skeletal muscle injury is one of the main causes of traumatic HO (tHO). Neutrophils play a pivotal role in activating BMPs and TGF-β signals, thus promoting the differentiation of mesenchymal stem cells and progenitor cells into osteoblasts or osteoclasts to facilitate HO. Furthermore, NETs are specifically localized at the site of HO, thereby accelerating the formation of HO. Additionally, the overactivation of neutrophils contributes to the disruption of immune homeostasis to trigger HO. An understanding of the diverse roles of neutrophils will not only provide more information on the pathogenesis of skeletal muscle injury for repair and HO but also provides a foundation for the development of more efficacious treatment modalities for HO.

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.

Heterotopic hip ossification resection: monocentric experiences of associated factors, outcomes, and complications

PURPOSE

The exponential increase in total hip arthroplasty (THA) has led to acute and chronic surgery-related complications. Common chronic and local complications are represented by hip ossification (HO). The aim of our study was to assess the clinical and radiological correlates of patients undergoing surgical removal of heterotopic ossifications after THA and the possible association between HO and prosthetic joint infection.

METHODS

Data of 26 patients who underwent surgical removal of periprosthetic calcifications after THA from 2000 to 2022 were analyzed and compared with characteristics of 156 subjects without HO.

RESULTS

The preoperative radiographs of patients showed a high-grade Brooker, 3 or 4, later reduced to 1 or 2 in the postoperative radiographs. Ten (38.5%) patients underwent radiotherapy prophylaxis, administered as a single dose 24 h before surgery. In 19 (73%) patients, pharmacological prophylaxis with indomethacin was added in the 30 postoperative days. Only one patient who underwent radiotherapy had a recurrence, while new ossifications were found in three patients without prophylaxis (11.5%). Intraoperative cultures were performed for suspected periprosthetic infection in 8 study group patients. In logistic regression, the presence of HO was significantly and inversely associated with the ASA score (OR = 0.27, 95% CI = 0.09-0.82; P = 0.021) after adjusting.

CONCLUSION

Surgical HO removal in symptomatic patients with high-grade disease produces good clinical and radiographic results. Radiotherapy was a good perioperative and preventive strategy for recurrence, also associated with NSAIDs and COX-2 inhibitors.

Myositis Ossificans Traumatica of Bilateral Sternocleidomastoid Muscles After Chiropractor Adjustment: A Case Report

A woman in her 20s with a past medical history of surgical debulking of a right neck mass presented to the hospital for persistent and worsening right shoulder pain. The shoulder pain was associated with trismus and back and neck pain. A CT scan of the neck with contrast revealed post-surgical changes with increased heterotopic ossification throughout the surgical site extending to the supraclavicular soft tissues and the left sternocleidomastoid muscle, suggesting muscle ossification. A biopsy was performed, and the patient was diagnosed with myositis ossificans (MO). Initial treatment began with the administration of steroids and analgesics. She was scheduled for a follow-up with orthopedics, rheumatology, and genetics, but she was lost for follow-up. MO is a very rare medical condition usually associated with trauma, and in our patient, the symptoms started after a chiropractic adjustment.

Heterotopic Ossification and Platelet-Rich Plasma in Core Muscle Injuries: A Single-Institution Experience Over 6 Years

BACKGROUND

A 2015 study of platelet-rich plasma (PRP) for groin injuries in National Football League (NFL) players alerted the authors to the possibility that PRP is associated with heterotopic ossification (HO). The current study of athletes seen between 2014 and 2019 provides a more comprehensive analysis of that observation.

PURPOSE/HYPOTHESIS

This report describes the early results of groin surgery for athletes who had experienced failed PRP therapy performed by different practitioners and with an assortment of PRP techniques. The primary goal of this cohort study was to determine short-term clinical outcomes after surgery of PRP-treated patients. It was hypothesized that previous PRP treatment would be associated with the presence of HO among patients with core muscle injuries (CMIs).

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

All athletes seen at 1 institution and identified at their first visit as having received PRP for a CMI were followed and compared with patients with a CMI who had not previously received PRP. Although in many cases HO was observed on clinical examination or imaging, HO was identified intraoperatively in all surgical cases and confirmed pathologically. Successful surgery was defined as return to play at previously high levels of performance or greater as determined by the athletes' own assessments. All patients who had received PRP were followed for ≥2 years.

RESULTS

Among 3642 patients with a new CMI seen between 2014 and 2019, 68 (1.9%) patients developed HO within the core muscles and/or adjacent soft tissues. Of the 68 patients, 60 (88.2%) were men, and the mean age was 34.5 years. Of the 68 patients, 62 (91.2%) were athletes and 44 (64.7%) had been treated previously with PRP. HO was observed in 24 (0.7%) patients without previous PRP treatment. Three athletes who received PRP retired early from sports because of HO and scar issues. In total, 22 of 28 (78.6%) NFL players who received PRP developed HO, compared with 0 (0%) of 28 randomly selected, age-, position-, and injury-matched NFL players. After surgical repair, 3-month success rates were 67.9% and 96.4%, respectively, in the PRP and non-PRP groups (P = .006). By 6 months postoperatively, PRP-treated patients were back to similarly high success rates compared with the non-PRP cohort. Scar tissue issues played a prominent role in the relative delay in definitive success.

CONCLUSION

The present, more comprehensive study confirms the previous preliminary analysis that treating CMIs with PRP may be associated with HO.

Myositis ossificans in the pediatric population: a systematic scoping review

Introduction

Circumscribed or pseudomalignant myositis ossificans (MO) is a rare and benign condition characterized by heterotopic bone formation in soft tissues. The clinical presentation of MO, imaging investigations, histological findings, and treatment strategies are unclear, especially in the pediatric population.

Materials and methods

A literature search was conducted in PubMed, Scopus, and Google Scholar electronic databases to identify original articles and reviews in English or French of traumatic and non-traumatic MO. Studies were selected by 2 independent reviewers following the PRISMA recommendation and descriptive data were extracted. We harvest in each case the sex, age at diagnosis, location, presence of initial trauma, pre-emptive diagnosis, modalities of imagery used, realized biopsy, treatment performed, and type of follow-up.

Results

Sixty pediatric cases of MO were identified between 2002 and 2023. Twenty-three patients (38.3%) were diagnosed with idiopathic/pseudomalignant and 37 patients (61.7%) with circumscribed. The mean age at diagnosis was 9.5 years (range 0.2-17 years), with a male-to-female ratio of 1:1. The initial pre-emptive diagnosis was neoplasia in 13 patients (21.7%). The biopsy was percutaneous in 9 patients (15%) and incisional in 7 patients (11.7%). Histological analysis was achieved in 35 cases (57%). Surgical excision was the first line treatment in 46.7% of patients, and non-surgical in the remaining patients. The follow-up strategy was clinical in 16 patients (26.7%) or based on imaging investigation in 23 patients (38.3%).

Discussion

Although MO in children is described as a rare pathology, identifying the benignity of the condition is essential to avoid unnecessary invasive treatment and to avoid delaying the treatment of a potentially life-threatening entity. It seems that there is no consensus established concerning the proper imaging for diagnosis. Clinicians should acknowledge that the absence of a triggering trauma tends to direct the investigation and the management toward a surgical attitude. Conservative management is key, however, surgical excision can be proposed on matured lesions on a case-by-case basis. The absence of recurrence is not excluded. Therefore, a close clinical follow-up is suggested for all cases. The true benefit of a radiological is questioned in a question known to be self-resolving.

Chemoprophylaxis for heterotopic ossification following hip arthroscopy: A systematic review

INTRODUCTION

Heterotopic ossification (HO) is a known complication diagnosed following hip arthroscopy.

PURPOSE/HYPOTHESIS

This study sought to review the current literature on chemoprophylaxis for HO following hip arthroscopy and to describe what agents and doses are being utilized.

STUDY DESIGN

Systematic Review.

METHODS

A systematic review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines on the use of chemoprophylactic medications for HO prevention following hip arthroscopy. Mechanical and radiation prophylaxis were not included in the current analysis.

RESULTS

A total of 203 studies were identified, of which 15 were included with 6463 patients. There was one randomized control trial (RCT) and 4 additional comparative studies. The most commonly utilized chemoprophylactic agents were the following: naproxen (n ​= ​8), celecoxib (n ​= ​3), indomethacin (n ​= ​3), aspirin (n ​= ​1), etoricoxib (n ​= ​1), and etodolac (n ​= ​1), and non-specific non-steroidal anti-inflammatory drugs (NSAIDs) (n ​= ​1). Naproxen was either given at a dose of 500 ​mg once or twice daily for 2-4 weeks. RCTs and additional comparative studies showed significant HO prevention using chemoprophylactic agents following hip arthroscopy.

CONCLUSIONS

HO is a known and common complication following hip arthroscopy. The current systematic review found significant heterogeneity across the literature with respect to specific chemoprophylactic agents and their dosing regimens aimed to reduce the incidence and severity of HO following hip arthroscopy. Additionally, this review demonstrates that most studies that utilize chemoprophylaxis use NSAIDs with successful reduction in the incidence of HO.

LEVEL OF EVIDENCE

Level IV Evidence.

Palovarotene Action Against Heterotopic Ossification Includes a Reduction of Local Participating Activin A-Expressing Cell Populations

Heterotopic ossification (HO) consists of extraskeletal bone formation. One form of HO is acquired and instigated by traumas or surgery, and another form is genetic and characterizes fibrodysplasia ossificans progressiva (FOP). Recently, we and others showed that activin A promotes both acquired and genetic HO, and in previous studies we found that the retinoid agonist palovarotene inhibits both HO forms in mice. Here, we asked whether palovarotene's action against HO may include an interference with endogenous activin A expression and/or function. Using a standard mouse model of acquired HO, we found that activin A and its encoding RNA (Inhba) were prominent in chondrogenic cells within developing HO masses in untreated mice. Single-cell RNAseq (scRNAseq) assays verified that Inhba expression characterized chondroprogenitors and chondrocytes in untreated HO, in addition to its expected expression in inflammatory cells and macrophages. Palovarotene administration (4 mg/kg/d/gavage) caused a sharp inhibition of both HO and amounts of activin A and Inhba transcripts. Bioinformatic analyses of scRNAseq data sets indicated that the drug had reduced interactions and cross-talk among local cell populations. To determine if palovarotene inhibited Inhba expression directly, we assayed primary chondrocyte cultures. Drug treatment inhibited their cartilaginous phenotype but not Inhba expression. Our data reveal that palovarotene markedly reduces the number of local Inhba-expressing HO-forming cell populations. The data broaden the spectrum of HO culprits against which palovarotene acts, accounting for its therapeutic effectiveness. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Do Clinical Parameters Reflect Local Bone Metabolism in Heterotopic Ossification After Septic or Aseptic THA?

BACKGROUND

Heterotopic ossification (HO) is a common complication after THA. Although current research primarily focuses on treatment and prevention, little is known about the local bone metabolism of HO and clinical contributing factors.

QUESTIONS/PURPOSES

We aimed to assess bone remodeling processes in HO using histomorphometry, focusing on the effects of inflammation and prior NSAID treatment. Specifically, we asked: (1) Are HO specimens taken from patients with periprosthetic joint infection (PJI) more likely to exhibit active bone modeling and remodeling than specimens taken at the time of revision from patients without infection? (2) Do clinical or inflammatory serum and synovial parameters reflect the microstructure of and remodeling in both HO entities? (3) Is NSAID treatment before revision surgery associated with altered local bone mineralization or remodeling properties?

METHODS

Between June 2021 and May 2022, we screened 395 patients undergoing revision THA at two tertiary centers in Germany. Of those, we considered all patients with radiographic HO as potentially eligible. Based on that, 21% (83 of 395) were eligible; a further 43 were excluded because of an inability to remove the implant intraoperatively (16 patients), insufficient material (11), comorbidities with a major effect on bone metabolism (10), or bone-specific drugs (six), leaving 10% (40) for analysis in this retrospective, comparative study. HO specimens were collected during aseptic (25 patients: 18 male, seven female, mean age 70 ± 11 years, mean BMI 29 ± 4 kg/m 2 ) and septic (15 patients: 11 male, four female, mean age 69 ± 9 years, mean BMI 32 ± 9 kg/m 2 ) revision THA at a mean of 6 ± 7 years after primary implantation and a mean age of 70 ± 9 years at revision. Septic origin (PJI) was diagnosed based on the 2018 International Consensus Meeting criteria, through a preoperative assessment of serum and synovial parameters. To specify the local bone microstructure, ossification, and cellular bone turnover, we analyzed HO specimens using micro-CT and histomorphometry on undecalcified sections. Data were compared with those of controls, taken from femoral neck trabecular bone (10 patients: five female, five male, mean age 75 ± 6 years, mean BMI 28 ± 4 kg/m 2 ) and osteophytes (10 patients: five female, five male, mean age 70 ± 10 years, mean BMI 29 ± 7 kg/m 2 ). The time between primary implantation and revision (time in situ), HO severity based on the Brooker classification, and serum and synovial markers were correlated with HO microstructure and parameters of cellular bone turnover. In a subgroup of specimens of patients with NSAID treatment before revision, osteoid and bone turnover indices were evaluated and compared a matched cohort of specimens from patients without prior NSAID treatment.

RESULTS

Patients with aseptic and septic HO presented with a higher bone volume (BV/TV; aseptic: 0.41 ± 0.15, mean difference 0.20 [95% CI 0.07 to 0.32]; septic: 0.43 ± 0.15, mean difference 0.22 [95% CI 0.08 to 0.36]; femoral neck: 0.21 ± 0.04; both p < 0.001), lower bone mineral density (aseptic: 809 ± 66 mg HA/cm 3 , mean difference -91 mg HA/cm 3 [95% CI -144 to -38]; septic: 789 ± 44 mg HA/cm 3 , mean difference -111 mg HA/cm 3 [95% CI -169 to -53]; femoral neck: 899 ± 20 mg HA/cm 3 ; both p < 0.001), and ongoing bone modeling with endochondral ossification and a higher proportion of woven, immature bone (aseptic: 25% ± 17%, mean difference 25% [95% CI 9% to 41%]; septic: 37% ± 23%, mean difference 36% [95% CI 19% to 54%]; femoral neck: 0.4% ± 0.5%; both p < 0.001) compared with femoral neck specimens. Moreover, bone surfaces were characterized by increased osteoblast and osteoclast indices in both aseptic and septic HO, although a higher density of osteocytes was detected exclusively in septic HO (aseptic: 158 ± 56 1/mm 2 versus septic: 272 ± 48 1/mm 2 , mean difference 114 1/mm 2 [95% CI 65 to 162]; p < 0.001). Compared with osteophytes, microstructure and turnover indices were largely similar in HO. The Brooker class was not associated with any local bone metabolism parameters. The time in situ was negatively associated with bone turnover in aseptic HO specimens (osteoblast surface per bone surface: r = -0.46; p = 0.01; osteoclast surface per bone surface: r = -0.56; p = 0.003). Serum or synovial inflammatory markers were not correlated with local bone turnover in septic HO. Specimens of patients with NSAID treatment before revision surgery had a higher osteoid thickness (10.1 ± 2.1 µm versus 5.5 ± 2.6 µm, mean difference -4.7 µm [95% CI -7.4 to -2.0]; p = 0.001), but there was no difference in other osteoid, structural, or cellular parameters.

CONCLUSION

Aseptic and septic HO share phenotypic characteristics in terms of the sustained increase in bone metabolism, although differences in osteocyte and adipocyte numbers suggest distinct homeostatic mechanisms. These results suggest persistent bone modeling or remodeling, with osteoblast and osteoclast indices showing a moderate decline with the time in situ in aseptic HO. Future studies should use longitudinal study designs to correlate our findings with clinical outcomes (such as HO growth or recurrence). In addition, the molecular mechanisms of bone cell involvement during HO formation and growth should be further investigated, which may allow specific therapeutic and preventive interventions.

CLINICAL RELEVANCE

To our knowledge, our study is the first to systematically investigate histomorphometric bone metabolism parameters in patients with HO after THA, providing a clinical reference for evaluating modeling and remodeling activity. Routine clinical, serum, and synovial markers are not useful for inferring local bone metabolism.

Heterotopic ossification in the knee following retrograde nailing of a femur fracture

BACKGROUND

Heterotopic ossification (HO) is a pathologic bone formation in extra skeletal tissue and articular space. This was an objection to nailing of femur fractures across the knee; however, this has not been the case in many thousands of cases. Nonetheless, we present a patient in who placement of a retrograde nail resulted in calcification in the knee requiring excision.

CASE PRESENTATION

A 42-year-old male presented to the clinic complaining of pain, popping, clicking, and mocking in the right knee, especially in the patellar region. Nine months prior he suffered an ipsilateral femur fracture that was treated with a retrograde intramedullary nail. X-ray and CT scan were used to confirm the presentation of a heterotopic bone mass in the Hoffa area of the right knee. The patient underwent an arthrotomy for excision of the bone mass. The bone mass was excised, but bone in the ACL was not removed. The patient experienced pain relief and improved range of motion following excision.

CONCLUSION

Intraarticular heterotopic ossification is an infrequent event. We present a case of heterotopic ossification in the knee following retrograde nailing. The patient experienced improved symptoms and range of motion after excision of the intraarticular heterotopic bone mass.

Osório CAB, Bitencourt AGV, Makdissi FBA, do Nascimento AG. Myositis Ossificans of the Breast Mimicking Breast Cancer: A Case Report

Myositis ossificans (MO) is an uncommon tumor characterized by a rapidly growing mass following a history of local trauma. Few cases of MO affecting the breast have been reported, and some were misdiagnosed as primary osteosarcoma of the breast or metaplastic breast carcinoma. The following case report presents a patient with a growing breast lump whose core biopsy result was suspicious for breast cancer. MO was diagnosed after analysis of the mastectomy specimen. This case highlights the importance of MO as a differential diagnosis of a growing soft-tissue mass after trauma to avoid unnecessary overtreatment. Keywords: Myositis Ossificans, Osteosarcoma, Breast Cancer, Mastectomy, Heterotopic Ossification © RSNA, 2023.

Enhancer hijacking at the ARHGAP36 locus is associated with connective tissue to bone transformation

Heterotopic ossification is a disorder caused by abnormal mineralization of soft tissues in which signaling pathways such as BMP, TGFβ and WNT are known key players in driving ectopic bone formation. Identifying novel genes and pathways related to the mineralization process are important steps for future gene therapy in bone disorders. In this study, we detect an inter-chromosomal insertional duplication in a female proband disrupting a topologically associating domain and causing an ultra-rare progressive form of heterotopic ossification. This structural variant lead to enhancer hijacking and misexpression of ARHGAP36 in fibroblasts, validated here by orthogonal in vitro studies. In addition, ARHGAP36 overexpression inhibits TGFβ, and activates hedgehog signaling and genes/proteins related to extracellular matrix production. Our work on the genetic cause of this heterotopic ossification case has revealed that ARHGAP36 plays a role in bone formation and metabolism, outlining first details of this gene contributing to bone-formation and -disease.

A rare femoral heterotopic bone formation in a 14th-19th century female skeleton from Constância (Portugal)

OBJECTIVE

This paper aims to: (1) document a rare femoral heterotopic ossification (HO), and (2) discuss its aetiology and impact on the individual's locomotion and daily living activities.

MATERIALS

Adult female skeleton (SG.14-SK.7) from the village of Constância (Portugal), and dated from the 14th-19th centuries CE.

METHODS

The biological profile and the macroscopic analysis of the bone changes were assessed using standardized methods.

RESULTS

The macroscopic analysis revealed a large bony mass (8 cm length) located immediately inferior to the small trochanter of the right femur. The lesion exhibited a compact, tubular appearance located at the site of attachment of the pectineus muscle. No signs of bone fracture were observed.

CONCLUSIONS

The morphology of the SG.14-SK.7 femoral lesion is compatible with a probable case of myositis ossificans traumatica (MOT), secondary to acute trauma of the pectineus muscle. The underlying trauma episode, such as random accidental and/or occupation-related injury, is unknown. However, it is highly possible that this self-limiting condition significantly impaired the individual's daily life and mobility.

SIGNIFICANCE

Evidence of severe acute muscle trauma is a rare finding compared with HO secondary to bone trauma and other minor muscle injuries. Moreover, no cases of MOT affecting the pectineus muscle have been reported in the paleopathological literature to date.

LIMITATIONS

Although unlikely, a case of neurogenic or burn-related HO cannot be completely disregarded. It was not possible to undertake radiography as part of this study.

SUGGESTIONS FOR FURTHER RESEARCH

The use of imaging techniques to complement the paleopathological description is advised.

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

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

Overexpression of Wild-Type ACVR1 in Fibrodysplasia Ossificans Progressiva Mice Rescues Perinatal Lethality and Inhibits Heterotopic Ossification

Fibrodysplasia ossificans progressiva (FOP) is a devastating disease of progressive heterotopic bone formation for which effective treatments are currently unavailable. FOP is caused by dominant gain-of-function mutations in the receptor ACVR1 (also known as ALK2), which render the receptor inappropriately responsive to activin ligands. In previous studies, we developed a genetic mouse model of FOP that recapitulates most clinical aspects of the disease. In this model, genetic loss of the wild-type Acvr1 allele profoundly exacerbated heterotopic ossification, suggesting the hypothesis that the stoichiometry of wild-type and mutant receptors dictates disease severity. Here, we tested this model by producing FOP mice that conditionally overexpress human wild-type ACVR1. Injury-induced heterotopic ossification (HO) was completely blocked in FOP mice when expression of both the mutant and wild-type receptor were targeted to Tie2-positive cells, which includes fibro/adipogenic progenitors (FAPs). Perinatal lethality of Acvr1^R206H/+ mice was rescued by constitutive ACVR1 overexpression, and these mice survived to adulthood at predicted Mendelian frequencies. Constitutive overexpression of ACVR1 also provided protection from spontaneous abnormal skeletogenesis, and the incidence and severity of injury-induced HO in these mice was dramatically reduced. Analysis of pSMAD1/5/8 signaling both in cultured cells and in vivo indicates that ACVR1 overexpression functions cell-autonomously by reducing osteogenic signaling in response to activin A. We propose that ACVR1 overexpression inhibits HO by decreasing the abundance of ACVR1(R206H)-containing signaling complexes at the cell surface while increasing the representation of activin-A-bound non-signaling complexes comprised of wild-type ACVR1. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

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.

Heterotopic ossification beneath the upper abdominal incision after radical gastrectomy: Two case reports

BACKGROUND

Heterotopic ossification (HO) is a rare clinical phenomenon that refers to bone formation in nonossifying tissues.

CASE SUMMARY

This report presents two cases of HO beneath the upper abdominal median incision after radical gastrectomy. The first patient had postoperative pain below the incision area. There were no signs of anastomotic leakage, and the wound healed. Computed tomography (CT) findings 2 wk postoperatively were negative for HO, but the 6-wk CT showed HO beneath the incision. The patient refused reoperation, and after conservative therapy, the pain was gradually relieved after 2 wk. In the second case, postoperative recovery was uneventful, and HO was only detected on routine follow-up CT after 4 mo. An anti-adhesion membrane was applied beneath the peritoneum in both patients. Our findings suggest that HO beneath the abdominal incision might form at approximately 1 mo postoperatively. It may cause intractable pain; however, reoperation is usually not required.

CONCLUSION

In our cases, we suspect that HO may be related to the use of foreign materials beneath the peritoneum, which needs to be further investigated.

Heterotopic Mesenteric Ossification With Trilineage Hematopoiesis

Heterotopic ossification (HO) histologically refers to extraskeletal bone formation in non-ossifying tissues, most commonly noted in the extremities, buttocks, abdominal wall, and hip joints. HO developing in the mesentery (heterotopic mesenteric ossification, HMO) is very rare, with fewer than 100 cases reported in the literature. It usually occurs in adult male patients with a history of repeated abdominal trauma. So far, only two cases of HMO have been reported with the development of hematopoietic bone marrow. Here, we report the third case of HMO with true trilineage hematopoiesis in a 66-year-old female with suspicious mesenteric-retained foreign material from prior surgical procedures, including hysterectomy for endometrial adenocarcinoma and multiple repairs for incisional hernia.

Palovarotene Can Attenuate Heterotopic Ossification Induced by Tendon Stem Cells by Downregulating the Synergistic Effects of Smad and NF-κB Signaling Pathway following Stimulation of the Inflammatory Microenvironment

Heterotopic ossification (HO) is defined as the formation of bone tissues outside the bones, such as in the muscles. Currently, the mechanism of HO is still unclear. Tendon stem cells (TSCs) play important roles in the occurrence and development of HO. The inflammatory microenvironment dominated by macrophages also plays an important role in the course of HO. The commonly used clinical treatment methods, such as nonsteroidal anti-inflammatory drugs and radiotherapy, have relatively large side effects, and more efficient treatment methods are needed in clinical practice. Under physiological conditions, retinoic acid receptor (RAR) signal transduction pathway inhibits osteogenic progenitor cell aggregation and chondrocyte differentiation. We focus on palovarotene, a retinoic acid γ-receptor activator, showing an inhibitory effect on HO mice, but the specific mechanism is still unclear. This study was aimed at exploring the specific molecular mechanism of palovarotene by blocking osteogenic differentiation and HO formation of TSCs in vitro and in vivo in an inflammatory microenvironment. We constructed a coculture model of TCSs and polarized macrophages, as well as overexpression and knockdown models of the Smad signaling pathway of TCSs. In addition, a rat model of HO, which was constructed by Achilles tendon resection, was also established. These models explored the role of inflammatory microenvironment and Smad signaling pathways in the osteogenic differentiation of TSCs which lead to HO, as well as the reversal role played by palovarotene in this process. Our results suggest that, under the stimulation of inflammatory microenvironment and trauma, the injured site was in an inflammatory state, and macrophages were highly concentrated in the injured site. The expression of osteogenic and inflammation-related proteins, as well as Smad proteins, was upregulated. Osteogenic differentiation was performed in TCSs. We also found that TCSs activated Smad and NF-κB signaling pathways, which initiated the formation of HO. Palovarotene inhibited the aggregation of osteogenic progenitor cells and macrophages and attenuated HO by blocking Smad and NF-κB signaling pathways. Therefore, palovarotene may be a novel HO inhibitor, while other drugs or antibodies targeting Smad and NF-κB signaling pathways may also prevent or treat HO. The expressions of Smad5, Id1, P65, and other proteins may predict HO formation.

[Research progress of traumatic heterotopic ossification]

OBJECTIVE

To review and evaluate the research progress of traumatic heterotopic ossification (HO).

METHODS

The domestic and foreign related research literature on traumatic HO was widely consulted, and its etiology, pathogenesis, pathological progress, diagnosis, prevention, and treatment were summarized.

RESULTS

Traumatic HO is often caused by severe trauma such as joint operation, explosion injury, nerve injury, and burn. At present, it is widely believed that the occurrence of traumatic HO is closely related to inflammation and hypoxia. Oral non-steroidal anti-inflammatory drugs and surgery are the main methods to prevent and treat traumatic HO.

CONCLUSION

Nowadays, the pathogenesis of traumatic HO is still unclear, the efficiency of relevant prevention and treatment measures is low, and there is a lack of specific treatment method. In the future, it is necessary to further study the pathogenesis of traumatic HO and find specific prevention and treatment targets.

Aberrant Bone Regulation in Albright Hereditary Osteodystrophy dueto Gnas Inactivation: Mechanisms and Translational Implications

PURPOSE OF REVIEW

This review highlights the impact of Gnas inactivation on both bone remodeling and the development of heterotopic subcutaneous ossifications in Albright hereditary osteodystrophy (AHO). Here we discuss recent advancements in understanding the pathophysiologic mechanisms of the aberrant bone development in AHO as well as potential translational implications.

RECENT FINDINGS

Gnas inactivation can regulate the differentiation and function of not only osteoblasts but also osteoclasts and osteocytes. Investigations utilizing a mouse model of AHO generated by targeted disruption of Gnas have revealed that bone formation and resorption are differentially affected based upon the parental origin of the Gnas mutation. Data suggest that Gnas inactivation leads to heterotopic bone formation within subcutaneous tissue by changing the connective tissue microenvironment, thereby promoting osteogenic differentiation of tissue-resident mesenchymal progenitors. Observed variations in bone formation and resorption based upon the parental origin of the Gnas mutation warrant future investigations and may have implications in the management and treatment of AHO and related conditions. Additionally, studies of heterotopic bone formation due to Gnas inactivation have identified an essential role of sonic hedgehog signaling, which could have therapeutic implications not only for AHO and related conditions but also for heterotopic bone formation in a wide variety of settings in which aberrant bone formation is a cause of significant morbidity.

Heterotopic Ossification After Arthroscopic Procedures: A Scoping Review of the Literature

Background:

Heterotopic ossification (HO) is the formation of bone in soft tissue resultant from inflammatory processes. Lesion formation after arthroscopic procedures is an uncommon but challenging complication. Optimal prophylaxis and management strategies have not been clearly defined.

Purpose:

To present a scoping review of the pathophysiology, risk factors, diagnostic modalities, prophylaxis recommendations, and current treatment practices concerning HO after arthroscopic management of orthopaedic injuries.

Study Design:

Scoping review; Level of evidence, 4.

Methods:

A scoping review via a PubMed search was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines. The search strategy was based on the terms “heterotopic ossification” AND “arthroscopy.” The clinical outcomes review included studies on the arthroscopic management of orthopaedic injuries in which the primary subject matter or a secondary outcome was the development of HO. An analysis of the pathophysiology, diagnostic modalities, and management options was reported.

Results:

A total of 43 studies (33,065 patients) reported on HO after hip arthroscopy, while 21 (83 patients) collectively reported on HO after arthroscopic procedures to the shoulder, elbow, knee, or ankle; however, management techniques were not standardized. Identified risk factors for HO included male sex and mixed impingement pathology, while intraoperative capsular management was not suggested as a contributing factor. Diagnosis of ossification foci was performed using radiography and computed tomography. The rate of HO after hip arthroscopy procedures approached 46% without prophylaxis, and administration of nonsteroidal anti-inflammatory drugs (NSAIDs) decreased occurrence rates to 4% but carries associated risks. External beam radiation has not been exclusively studied for use after arthroscopic procedures.

Conclusion:

HO is a known complication after arthroscopic management of orthopaedic injuries. NSAID prophylaxis has been demonstrated to be effective after hip arthroscopy procedures. Patients with persistent symptoms and mature lesions may be indicated for surgical excision, although variability is present in patient-reported outcome scores postoperatively.

BMP signaling and skeletal development in fibrodysplasia ossificans progressiva (FOP)

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare genetic disease caused by increased BMP pathway signaling due to mutation of ACVR1, a bone morphogenetic protein (BMP) type 1 receptor. The primary clinical manifestation of FOP is extra-skeletal bone formation (heterotopic ossification) within soft connective tissues. However, the underlying ACVR1 mutation additionally alters skeletal bone development and nearly all people born with FOP have bilateral malformation of the great toes as well as other skeletal malformations at diverse anatomic sites. The specific mechanisms through which ACVR1 mutations and altered BMP pathway signaling in FOP influence skeletal bone formation during development remain to be elucidated; however, recent investigations are providing a clearer understanding of the molecular and developmental processes associated with ACVR1-regulated skeletal formation.

Incidence of Heterotopic Ossification with NSAID Prophylaxis Is Low After Open and Arthroscopic Hip Preservation Surgery

Purpose

We evaluate the incidence of heterotopic ossification (HO) development with nonsteroidal anti-inflammatory drug (NSAID) prophylaxis in patients after open and arthroscopic hip preservation surgery.

Methods

A retrospective review identified patients who underwent hip preservation surgery at a single institution within the past 3 years. Patients who underwent hip arthroscopy with or without periacetabular osteotomy (PAO) or femoral osteotomy (FO) were included. Those who did not receive 3-month postoperative radiographs were excluded. The incidence and Brooker classification (BC) of HO in patients taking Naproxen or another NSAID (meloxicam, celecoxib, indomethacin, or aspirin alone) was assessed using AP radiographs available from 3-, 6-, and 12-month follow-up appointments. Univariate analysis was conducted to compare numerical means and categorical data (significance level P = .05).

Results

A total of 328 hips (284 patients) were included. All patients received hip arthroscopy, while 71 patients (21.6%) received concurrent periacetabular osteotomy (PAO; n = 65) or femoral osteotomy (FO; n = 6). Overall, 276 hips (84.4%) received Naproxen for HO prophylaxis. In total, 5 of 328 hips (1.5%) developed HO (4, BC I; 1, BC III). The rate of HO development was significantly higher in males versus females (4 of 121 (3.31%) vs 1 of 207 (.48%), P = .0441). All 5 patients received arthroscopic cam resection and labral repair, and 1 patient also received PAO. Three patients in the Naproxen group (.91%) developed HO, which was not statistically different from those taking a different NSAID (.61%, P = .1797).

Conclusion

The incidence of HO development was low with NSAID prophylaxis after hip preservation surgery.

Are open surgery and total resection good choices for traumatic myositis ossificans in children?

BACKGROUND

Traumatic myositis ossificans is a self-limited, non-neoplastic, ectopic bone formation in the soft tissues caused by trauma. Conservative treatment is the mainstay of management. However, open surgery and complete resection should be considered in patients with limited joint function and constant pain. Herein, we retrospectively analyzed the outcome of open surgical resection in children with myositis ossificans (MO).

METHODS

The data of patients diagnosed with MO between February 2010 and May 2019 were retrospectively analyzed. The clinical data included medical history, physical examination, and laboratory, imaging, and pathological findings. All patients underwent an open surgery and total resection. Radiography findings and joint function were evaluated. Patients with developing complications, such as recurrence and assessing joint function, were followed up. In total, 20 patients (sex, 15 male and 5 female patients; age, 8.1 ± 2.5 years) were included.

RESULTS

MO was located around the elbow, wrist, proximal humerus, and thigh in 13, one, one, and five patients, respectively. All patients were followed up for > 12 months. Two patients had partial recurrence after surgery. One patient with forearm MO had poor elbow function (Broberg-Morrey score of 70). Nineteen patients had good functional outcomes according to the Broberg-Morrey and Cooney methods.

CONCLUSION

Open surgical resection is an effective method for children with MO. The recurrence rate was low when the surgery was performed after the acute stage (1.5 months from disease presentation).

Heterotopic Ossification Negatively Influences Range of Motion After Revision Total Knee Arthroplasty

BACKGROUND

The incidence of heterotopic ossification (HO) after total knee arthroplasty (TKA) varies and is of unclear clinical significance. This study aimed to identify the incidence of HO in patients undergoing revision TKA for either stiffness or aseptic loosening/instability and determine if the presence of HO is associated with inferior absolute range of motion (ROM) and ROM gains.

METHODS

Eighty-seven patients were prospectively enrolled and separated into 2 cohorts to evaluate ROM after revision TKA (2017-2019). Group 1 (N = 40) patients were revised for stiffness, while group 2 (N = 47) patients were revised for either aseptic loosening or instability. Goniometer-measured ROM values were obtained preoperatively and at 6 weeks, 6 months, and 1 year postoperatively. Statistical analysis included a Fisher's exact test to assess for an association between preoperative HO and final ROM at 1 year after revision TKA.

RESULTS

HO was identified on preoperative radiographs in 17 patients (20%). There was a significantly higher rate of preoperative HO in patients revised for stiffness compared to patients revised for instability or loosening (30% vs 11%; P = .03). Five cases of HO qualitatively identified as most clinically severe were associated with lower ROM at each time point compared to the remainder of HO cases in this study cohort (P < .02).

CONCLUSION

The presence of HO is greater in patients undergoing revision TKA for stiffness. Additionally, HO severity appears to have a major effect on preoperative and postoperative ROM trajectory. This information should help guide patient expectations and highlight the need for a comprehensive, standardized classification system for HO.

Post-traumatic myositis ossificans: a benign lesion that simulates malignant bone and soft tissue tumours

Myositis ossificans (MO) is a benign bone formation in an extra-skeletal location. The most common subtype of MO, the post-traumatic, usually develops in young males after a traumatic event or sports injury.MO may simulate malignant bone lesions such as extra-skeletal or surface osteosarcomas, or soft tissue sarcomas such as synovial sarcoma or undifferentiated pleomorphic sarcoma. In the early phase the diagnosis of MO is challenging because imaging and histopathological findings may be non-characteristic.Detailed medical history as well as clinical examination, follow-up imaging studies and histological assessment are crucial for a proper diagnosis. Early and accurate differential diagnosis between MO and malignant soft tissue and bone tumours is important to maximize. Cite this article: EFORT Open Rev 2021;6:572-583. DOI: 10.1302/2058-5241.6.210002.

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

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

The Surgical Management of the Rare Neurogenic Myositis Ossificans of the Hip: A Report of 3 Cases

Introduction:

Myositis ossificans (MO) is a benign non-neoplastic condition in which heterotopic bone formation occurs in soft tissues. Neurogenic MO is one variant of MO where the lesion is a result of neurological disorders, including brain and spinal cord injuries, especially when followed by immobility and spasticity. MO can also be a result of direct trauma or even genetic mutations.

Case Report:

We present three cases of young men (16, 37, and 22-year-old) who developed MO of the hip joint following brain or spinal cord injuries. One of them had also sustained a direct trauma to the affected hip joint at the time of the accident. All three patients presented with inability to walk independently due to diminished range of motion at the affected joint. X-rays and computerized tomography (CT) scans with 3-dimentional (3D) reconstruction suggested the diagnosis of MO, but the serum alkaline phosphatase was within normal limits at the time of presentation. The first case had bilateral involvement with unmistakable separation between the heterotopic bone formation and the frank hip joints on CT. This patient underwent successful staged excision of the ossifications. The second patient had unilateral hip joint involvement with the absence of clear separation between the heterotopic bone formation and the hip joint, thus, underwent total hip replacement for the affected side as excision was not possible. The third patienthad unilateral hip joint involvement and underwent excision of the ossification with dynamic hip screw insertion after sustaining a stable intertrochanteric fracture intraoperatively. Postoperatively, all three patients received physiotherapy and oral indomethacin. Upon recovery, they were able to walk independently with a near-normal range of motion at the hip joint. There was no evidence of recurrence upon follow-up visits, and CT scans in patients I and II. Follow-ups for patient III were not possible as the patient died 1 month after surgery due to pulmonary embolism.

Conclusion:

The surgical management of MO is indicated when non-operative methods fail to provide an adequate range of motion around the hip joint. Pre-operative assessment utilizing 3D-CT scans proved to be essential in dictating the appropriate surgical approach. During post-operative follow-ups, the physiotherapy and oral indomethacin provided additional improvement in outcome and patients’ satisfaction.

Early diagnosis of heterotopic ossification among patients admitted to a neurological Post-Intensive Care Rehabilitation Unit

BACKGROUND

Heterotopic ossification (HO) is defined as the formation of endochondral bone within soft tissue. Non-genetic forms, mainly corresponding to a consequence of bone, brain or spinal cord injury, are the most common. HO leads to important functional limitations and alteration of quality of life. To our knowledge, the time between brain, bone, or spinal cord injury and clinical suspicion of HO has never been studied. By admitting patients with severe neurological disorders, we hypothesized that the prevalence of HO in neurological post-intensive care rehabilitation units (PICRU) might be significant as these patients have recognized risk factors for HO.

AIM

This study aimed to investigate HO among patients admitted to a neurological PICRU with two objectives: 1) to describe the prevalence of HO in PICRU; 2) to assess the time between neurological disorder, clinical suspicion of HO and radiological diagnosis.

DESIGN

A monocentric retrospective cohort study.

SETTING

PICRU in our public university teaching hospital. This inpatient referral department is specifically dedicated to the early discharge from Intensive Care Units (ICU) of patients with severe neurological impairment who need rehabilitation.

POPULATION

We study all patients admitted between April 2016 and January 2019. One hundred twenty-five subjects were admitted for a rehabilitation program after neuro-trauma or stroke. We included all first-time stays in PICRU lasting 7 days or longer.

METHODS

Retrospective data extraction using administrative data from an electronic patient management program was done to select eligible subjects. Included subjects were then identified by a retrospective review of electronic inpatient medical records after patient discharge. Data of interest were collected from these same medical records.

RESULTS

Forty-four HO were diagnosed in 24 subjects (24/125; 19%), with a median number of 2 [1; 2] HO per subject. Neurological trauma was the main reason for admission to ICU (89/125; 71%) and half of patients had a traumatic brain injury (TBI) (67/125; 54%). The diagnosis of HO was made in PICRU in 75% of cases. Clinical suspicion of HO (autonomic dysfunction, local inflammatory signs, pain, or reduced joint range of motion) was made 6 [5; 7] weeks after admission to ICU. Radiological confirmation of clinical suspicion or fortuitous diagnosis by imaging (50% of the cases) occurred 8 [7; 12] weeks after admission to ICU. The median time of clinical suspicion or radiological diagnosis was 1 week after admission to PICRU.

CONCLUSIONS

HO is a sub-acute complication which develops in patients admitted to ICU for severe central nervous system disorders as clinical suspicion or radiological confirmation of diagnosis was made within the first week after admission in neurological PICRU (i.e. 6 to 8 weeks after ICU admission).

CLINICAL REHABILITATION IMPACT

As treatment for HO may at least partially improves rehabilitation and quality of life, we recommend a systematic screening in PICRU patients for HO by clinical examination supplemented by imaging in case of suspicion.

Heterotopic ossification in primary total hip arthroplasty using the posterolateral compared to the direct lateral approach

PURPOSE

Total hip arthroplasty (THA) is a successful procedure. However, in time, heterotopic ossification (HO) can form due to, amongst others, soft tissue damage. This can lead to pain and impairment. This study compares the formations of HO between patients who underwent either THA with the posterolateral approach (PA) or with the direct lateral approach (DLA). Our hypothesis is that patients who underwent THA with a PA form less HO compared to THA patients who underwent DLA.

METHODS

In this prospective cohort study, 296 consecutive patients were included who underwent THA. A total of 127 patients underwent THA with the PA and 169 with the DLA. This was dependent on the surgeon's preference and experience. More than 95% of patients had primary osteoarthritis as the primary diagnosis. Clinical outcomes were scored using the Numeric Rating Scale (NRS) and Harris Hip Score (HHS), radiological HO were scored using the Brooker classification. Follow-up was performed at 1 and 6 years postoperatively.

RESULTS

Two hundred and fifty-eight patients (87%) completed the 6-year follow-up. HO formation occurred more in patients who underwent DLA, compared to PA (43(30%) vs. 21(18%), p = 0.024) after 6 years. However, the presence of severe HO (Brooker 3-4) was equal between the DLA and PA (7 vs. 5, p = 0.551). After 6 years the HHS and NRS for patient satisfaction were statistically significant higher after the PA (95.2 and 8.9, respectively) compared to the DLA (91.6 and 8.5, respectively) (p < 0.001 and p = 0.003, respectively). The NRS for load pain was statistically significant lower in the PA group (0.5) compared to the DLA group (1.2) (p = 0.004). The NRS for rest pain was equal: 0.3 in the PA group and 0.5 in the DLA group.

CONCLUSION

THA with the PA causes less HO formation than the DLA.

TRIAL REGISTRATION

Registrated as HipVit trial, NL 32832.100.10, R-10.17D/HIPVIT 1. Central Commission Human-Related research (CCMO) Registry.

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

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

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.

A 2-Week Course of Naproxen for Heterotopic Ossification Prophylaxis Is Effective Following Hip Arthroscopy for Femoroacetabular Impingement

Purpose

To evaluate the effectiveness of 2 weeks of naproxen prophylaxis for heterotopic ossification (HO) after primary hip arthroscopy for femoroacetabular impingement (FAI).

Methods

All consecutive hip arthroscopy cases by a single surgeon from January 1, 2015, to December 31, 2016, were retrospectively reviewed. Cases were included if they met the following criteria: (1) Primary hip arthroscopy, including femoral neck osteoplasty, for FAI; (2) naproxen prophylaxis for 2 weeks’ duration; and (3) radiographic follow-up at a minimum of 3 months postoperatively. Radiographic imaging for each patient was evaluated for the presence of HO, and independent radiology reports were used to confirm patients with HO. Maximal size of HO was measured and classified according to the Brooker criteria. Demographic and operative variables of the patients included in this study who received naproxen prophylaxis for 2 weeks were formally compared with a cohort of patients who received naproxen prophylaxis for 3 weeks in a previous randomized controlled trial.

Results

A total of 185 patients who received naproxen prophylaxis for 2 weeks were included in the study, 5 of whom developed HO (3%). A total of 48 patients who received naproxen prophylaxis for 3 weeks were included for comparison, 2 of whom developed HO (4%). There was no significant difference in the rate of HO formation between 2 weeks and 3 weeks of naproxen prophylaxis (P = .597). All 7 cases of HO were classified as Brooker class 1.

Conclusions

The observed rate of postoperative heterotopic ossification after 2 weeks of naproxen prophylaxis in this study was equivalent to that observed after 3 weeks’ prophylaxis in a previously published study. Two weeks of naproxen prophylaxis may be a sufficient treatment course for the prevention of heterotopic ossification after primary hip arthroscopy for FAI.

Level of Evidence

Level III – Retrospective Comparative Study.

BMP signalling in a mechanical context - Implications for bone biology

Bone Morphogenetic Proteins (BMPs) are extracellular multifunctional signalling cytokines and members of the TGFβ super family. These pleiotropic growth factors crucially promote bone formation, remodeling and healing after injury. Additionally, bone homeostasis is systematically regulated by mechanical inputs from the environment, which are incorporated into the bone cells' biochemical response. These inputs range from compression and tension induced by the movement of neighboring muscle, to fluid shear stress induced by interstitial fluid flow in the canaliculi and in the vascular system. Although BMPs are widely applied in a clinic context to promote fracture healing, it is still elusive how mechanical inputs modulate this signalling pathway, hindering an efficient and side-effect free application of these ligands in bone healing. This review aims to summarize the current understanding in how mechanical cues (tension, compression, shear force and hydrostatic pressure) and substrate stiffness modulate BMP signalling. We highlight the time-dependent effects in modulating immediate early up to long-term effects of mechano-BMP crosstalk during bone formation and remodeling, considering the interplay with other already established mechanosensitive pathways, such as MRTF/SRF and Hippo signalling.

Murine Tissue-Resident PDGFRα+ Fibro-Adipogenic Progenitors Spontaneously Acquire Osteogenic Phenotype in an Altered Inflammatory Environment

Acquired heterotopic ossifications (HO) arising as a result of various traumas, including injury or surgical interventions, often result in pain and loss of motion. Though triggers for HO have been identified, the cellular source of these heterotopic lesions as well as the underlying mechanisms that drive the formation of acquired HO remain poorly understood, and treatment options, including preventative treatments, remain limited. Here, we explore the cellular source of HO and a possible underlying mechanism for their spontaneous osteogenic differentiation. We demonstrate that HO lesions arise from tissue-resident PDGFRα+ fibro/adipogenic progenitors (FAPs) in skeletal muscle and not from circulating bone marrow-derived progenitors. Further, we show that accumulation of these cells in the tissue after damage due to alterations in the inflammatory environment can result in activation of their inherent osteogenic potential. This work suggests a mechanism by which an altered inflammatory cell and FAP interactions can lead to the formation of HO after injury and presents potential targets for therapeutics in acquired HO. © 2020 American Society for Bone and Mineral Research.

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

PURPOSE OF THE STUDY

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Post-stroke bilateral heterotopic ossification: An acute problem with long-lasting consequences

Heterotopic ossification (HO) is a complication of injury to the central nervous system in which production of lamellar bone within the soft tissues occurs resulting in pain, reduced range of motion (ROM) and loss of functional capacity. Heterotopic ossification is rarely seen in stroke patients and mostly affects the paretic side. In this article, we present a case of established bilateral HO of the hips soon after stroke onset. A 77-year-old female patient with a five-month history of stroke presented to our rehabilitation clinic. Physical examination revealed sensorimotor aphasia, right-sided hemiplegia, bilateral painful limited ROM of the hips and left knee contracture. An anteroposterior X-ray of the pelvis revealed previously undiagnosed bilateral HO of the hips. The patient and her relatives declined operative interventions. The patient was discussed in the departmental meeting and it was agreed that she would not be able to partake in an active inpatient rehabilitation program. She was discharged with a home exercise plan. This case highlights the importance of HO, of both the paretic and non-paretic side, being included in the differential diagnosis of post-stroke patients presenting with joint pain and reduced ROM, both acutely and in the long-term. This may aid the timely diagnosis and management of HO, a pathology which has detrimental effects on functionality.

Discovery of os cordis in the cardiac skeleton of chimpanzees (Pan troglodytes)

Cardiovascular diseases, especially idiopathic myocardial fibrosis, is one of the most significant causes of morbidity and mortality in captive great apes. This study compared the structure and morphology of 16 hearts from chimpanzees (Pan troglodytes) which were either healthy or affected by myocardial fibrosis using X-ray microtomography. In four hearts, a single, hyperdense structure was detected within the right fibrous trigone of the cardiac skeleton. High resolution scans and histopathology revealed trabecular bones in two cases, hyaline cartilage in another case and a focus of mineralised fibro-cartilaginous metaplasia with endochondral ossification in the last case. Four other animals presented with multiple foci of ectopic calcification within the walls of the great vessels. All hearts affected by marked myocardial fibrosis presented with bone or cartilage formation, and increased collagen levels in tissues adjacent to the bone/cartilage, while unaffected hearts did not present with os cordis or cartilago cordis. The presence of an os cordis has been described in some ruminants, camelids, and otters, but never in great apes. This novel research indicates that an os cordis and cartilago cordis is present in some chimpanzees, particularly those affected by myocardial fibrosis, and could influence the risk of cardiac arrhythmias and sudden death.

Local injection of a hexametaphosphate formulation reduces heterotopic ossification in vivo

Heterotopic ossification (HO), the pathological formation of ectopic bone, is a debilitating condition which can cause chronic pain, limit joint movement, and prevent prosthetic limb fitting. The prevalence of this condition has risen in the military population, due to increased survivorship following blast injuries. Current prophylaxes, which aim to target the complex upstream biological pathways, are inconsistently effective ​and have a range of side-effects that make them unsuitable for combat-injured personnel. As such, many patients must undergo further surgery to remove the formed ectopic bone. In this study, a non-toxic, U.S. Food and Drug Administration (FDA) -approved calcium chelator, hexametaphosphate (HMP), is explored as a novel treatment paradigm for this condition, which targets the chemical, rather that biological, ​bone formation pathways. This approach allows not only prevention of pathological bone formation ​but also uniquely facilitates reversal, which current drugs cannot achieve. Targeted, minimally invasive delivery is achieved by loading HMP into an injectable colloidal alginate. These formulations significantly reduce ​the length of the ectopic bone formed in a rodent model of HO, with no effect on the adjacent skeletal bone. This study demonstrates the potential of localized dissolution as a new treatment ​and an alternative to surgery ​for pathological ossification and calcification conditions.

Serum uric acid level is associated with the incidence of heterotopic ossification following elbow trauma surgery

BACKGROUND

Heterotopic ossification (HO) is a common complication after surgery for elbow trauma. Uric acid is the end product of purine metabolism and has several physiological and pathogenic roles. However, the relationship between HO and uric acid has not been explored. This retrospective study aimed to assess the relationship between HO and serum uric acid (SUA).

MATERIAL AND METHODS

We retrospectively reviewed data from 155 patients undergoing elbow trauma surgery in our hospital between January 2013 and December 2018. One hundred patients were included according to the inclusion criteria. They were divided into 2 groups according to the presence or absence of HO, and the SUA level was compared between groups using the independent samples t test. The optimal prognostic cutoff value was obtained using the maximum value of the Youden index.

RESULTS

The SUA level was significantly higher in the HO group than in the non-HO group (362.0 ± 87.4 μmol/L vs. 318.3 ± 87.0 μmol/L; P < .05). Using the maximum value of Youden index, 317.5 μmol/L was determined to be the optimal SUA cutoff value for the prediction of HO, with a sensitivity of 68.75% (95% confidence interval [CI], 54.67%-80.05%) and specificity of 55.77% (95% CI, 42.34%-68.40%).

CONCLUSIONS

Our study was the first to find that the high SUA level is a risk factor for HO of the elbow joint after trauma. Moreover, 317.5 μmol/L is the SUA threshold predicting the occurrence and development of HO of the elbow, with high sensitivity and specificity.

Heterotopic Ossification following Total Elbow Arthroplasty in a Patient with Parkinson's Disease: Case Report and Literature Review

Introduction. Heterotopic ossification (HO) usually develops following surgery or trauma. Risk factors for HO following elbow fractures include delay to surgery (>7 days), floating fractures, and elbow subluxation. Systemic risk factors for HO include male sex; concurrent cranial, neurological, or abdominal injury; high-energy trauma; previous development of HO; and contralateral fracture. To date, no studies have reported on Parkinson's disease (PD) as a risk factor for the development of HO. Case Presentation. A 68-year-old female with PD (treated with levodopa-carbidopa) sustained a right closed (OTA type A3) distal humerus fracture and was treated with a total elbow arthroplasty. Postoperatively, development of significant near-ankylosing HO was observed and contributed to significant restriction of elbow motion with activities of daily living. After HO maturation, the osseous growth was excised, and the area irradiated. The patient regained excellent elbow motion with no recurrence of HO. Discussion. A literature review revealed six cases of HO development in PD patients following arthroplasty. Patients with PD have higher serum concentrations of interleukins (IL) and tumor necrosis factor- (TNF-) α. These factors stimulate BMP-2 production which may promote osteogenesis. Levodopa-carbidopa may also influence HO through stimulation of growth hormone and IGF-1. Conclusion. Parkinsonism may promote heterotopic bone growth through the release of osteoinductive factors. HO development may also be mediated by levodopa-carbidopa therapy. Future research should highlight the link between HO and PD and identify if prophylaxis is warranted in PD patients undergoing arthroplasty.