Ectopic bone formation in severely combat-injured orthopedic patients -- a hematopoietic niche

Regional distribution prevalence of heterotopic ossification in the elbow joint: a 3D study of patients after surgery for traumatic elbow injury

BACKGROUND

Heterotopic ossification (HO) is a common complication after elbow fracture surgery and can lead to severe upper extremity disability. The radiographic localization of postoperative HO has been reported previously. However, there is no literature examining the distribution of postoperative HO at the three-dimensional (3D) level. This study aimed to investigate 1) the distribution characteristics of postoperative HO and 2) the possible risk factors affecting the severity of postoperative HO at a 3D level.

METHODS

A retrospective review was conducted of patients who presented to our institution with HO secondary to elbow fracture between 13 January 2020 and 16 February 2023. Computed tomography scans of 56 elbows before elbow release surgery were reconstructed in 3D. HO was identified using density thresholds combined with manual identification and segmentation. The elbow joint and HO were divided into six regions according to three planes: the transepicondylar plane, the lateral ridge of the trochlear plane, and the radiocapitellar joint and coronoid facet plane. The differences in the volume of regional HO associated with different initial injuries were analyzed.

RESULTS

Postoperative HO was predominantly present in the medial aspect of the capsule in 52 patients (93%), in the lateral aspect of the capsule in 45 patients (80%), in the medial supracondylar in 32 patients (57%), and in the lateral supracondylar, radial head, and ulnar region in the same number of 28 patients (50%). The median and interquartile range volume of total postoperative HO was 1683 (777-4894) mm3. The median and interquartile range volume of regional postoperative HO were: 584 (121-1454) mm3 at medial aspect of capsule, 207 (5-568) mm3 at lateral aspect of capsule, 25 (0-449) mm3 at medial supracondylar, 1 (0-288) at lateral supracondylar, 2 (0-478) at proximal radius and 7 (0-203) mm3 at the proximal ulna. In the subgroups with Injury Severity Score > or = 16, Gustilo-Anderson II, normal uric acid levels, elevated alkaline phosphatase, and body mass index > or = 24, the median HO volume exceeds that of the respective control groups.

CONCLUSION

The medial aspect of the capsule was the area with the highest frequency and median volume of postoperative HO among all initial elbow injury types. Patients with higher Gustilo-Anderson grade, Injury Severity Score, alkaline phosphatase or Body Mass Index had higher median volume of postoperative HO.

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

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

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

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

Pathogenesis of acquired heterotopic ossification: Risk factors, cellular mechanisms, and therapeutic implications

Heterotopic ossification (HO), including hereditary and acquired HO, is the formation of extraskeletal bone in skeletal muscle and surrounding soft tissues. Acquired HO is often caused by range of motion, explosion injury, nerve injury or burns. Severe HO can lead to pain and limited joint activity, affecting functional rehabilitation and quality of life. Increasing evidence shows that inflammatory processes and mesenchymal stem cells (MSCs) can drive HO. However, explicit knowledge about the specific mechanisms that result in HO and related cell precursors is still limited. Moreover, there are no effective methods to prevent or reduce HO formation. In this review, we provide an update of known risk factors and relevant cellular origins for HO. In particular, we focus on the underlying mechanisms of MSCs in acquired HO, which follow the osteogenic program. We also discuss the latest therapeutic value and implications for acquired HO. Our review highlights the current gaps in knowledge regarding the pathogenesis of acquired HO and identifies potential targets for the prevention and treatment of HO.

Neurogenic Heterotopic Ossifications Recapitulate Hematopoietic Stem Cell Niche Development Within an Adult Osteogenic Muscle Environment

Hematopoiesis and bone interact in various developmental and pathological processes. Neurogenic heterotopic ossifications (NHO) are the formation of ectopic hematopoietic bones in peri-articular muscles that develop following severe lesions of the central nervous system such as traumatic cerebral or spinal injuries or strokes. This review will focus on the hematopoietic facet of NHO. The characterization of NHO demonstrates the presence of hematopoietic marrow in which quiescent hematopoietic stem cells (HSC) are maintained by a functional stromal microenvironment, thus documenting that NHOs are neo-formed ectopic HSC niches. Similarly to adult bone marrow, the NHO permissive environment supports HSC maintenance, proliferation and differentiation through bidirectional signaling with mesenchymal stromal cells and endothelial cells, involving cell adhesion molecules, membrane-bound growth factors, hormones, and secreted matrix proteins. The participation of the nervous system, macrophages and inflammatory cytokines including oncostatin M and transforming growth factor (TGF)-β in this process, reveals how neural circuitry fine-tunes the inflammatory response to generate hematopoietic bones in injured muscles. The localization of NHOs in the peri-articular muscle environment also suggests a role of muscle mesenchymal cells and bone metabolism in development of hematopoiesis in adults. Little is known about the establishment of bone marrow niches and the regulation of HSC cycling during fetal development. Similarities between NHO and development of fetal bones make NHOs an interesting model to study the establishment of bone marrow hematopoiesis during development. Conversely, identification of stage-specific factors that specify HSC developmental state during fetal bone development will give more mechanistic insights into NHO.

CD34 positive cells isolated from traumatized human skeletal muscle require the CD34 protein for multi-potential differentiation

The CD34 protein is regarded as a marker of stem cells from multiple origins. Recently a mesenchymal progenitor CD34 positive cell identified from traumatized human skeletal muscle demonstrates differentiation capability into vascular endothelial cells, osteoblasts and adipocytes. Here they were treated with a small inhibitory RNA for CD34, which significantly reduced the cellular level of the CD34 protein. These treated cells had a reduced capacity to proliferate, and migrate. They were both unable to differentiation down multiple pathways and to undergo vascular endothelial differentiation as reflected by a lack of expression of VE cadherin, Tie 2 and CD31. Additionally the cells were unable to form tube-like structures in an endothelial tube assay. These treated cells were also unable to undergo osteogenesis, as revealed by lack of alizarin red and alkaline phosphatase staining and were unable to undergo adipogenesis as revealed by lack of oil red O staining. Finally, when CD34 was expressed in cells lacking this protein, the cells were able to undergo vascular endothelial differentiation as revealed by expression of Tie2, VE-cadherin and CD31. These data indicate that in cells derived from traumatized muscle the CD34 protein is required for enhanced proliferation, migration and differentiation down multiple pathways.

Inhibition of Nf-ҝb prevents trauma-induced heterotopic ossification in rat model

PURPOSE

To investigate the pathogenesis and find a better prophylactic method of acquired heterotopic ossification (HO).

MATERIALS AND METHODS

In the first part, we designed the brain-traumatic/burn/tenotomy rat model and testified its efficacy as HO model. 44 rats were randomly divided into experimental group and control group. After operation, the bilateral tendons of 2 rats were collected at the 2^nd, 3^rd, 4^th, 6^th, 8^th, and 10^th weeks to determine the expression levels of p65. Additionally, the remaining rats were exposed to X-Ray examination at the 10th week. In the second part, 124 rats were randomly divided into four groups based on the administration dosage of Ammonium pyrrolidinedithiocarbamate (PDTC). Then, three rats of each group were euthanized every week in the first seven weeks to collect tendon to detect the expression levels of p65 by qRT-PCR and Western Blot. The remaining rats were exposed to X-Ray examination at the 10th week to assess the size of HO before being euthanized for HE staining.

RESULTS

The success rate of Brain-traumatic/Burn/Tenotomy model was 100%. Pharmacologic inhibition of Nf-ҝb signaling pathway by PDTC could significantly reduce the expression levels of p53 and the size of HO, and the reduction was most significant in the 0.6mg dosage group.

CONCLUSIONS

Brain-traumatic/Burn/Tenotomy model was highly reliable HO model. Inhibition of Nf-ҝb signaling pathway by PDTC could significantly reduce HO formation, and the most effective concentration was 6 mg/ml for local injection.

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.

High Osteogenic Potential of Adipose- and Muscle-derived Mesenchymal Stem Cells in Spinal-Ossification Model Mice

STUDY DESIGN

Basic experiments in a mouse model of ossification of the posterior longitudinal ligament (OPLL).

OBJECTIVE

To assess the osteogenic potential of mesenchymal stem cells (MSCs) obtained from muscle and adipose tissue in Tiptoe-walking (ttw) mice, in which cervical OPLL compresses the spinal cord and causes motor and sensory dysfunction.

SUMMARY OF BACKGROUND DATA

In humans, MSCs have been implicated in the pathogenesis of cervical OPLL. Cervical OPLL in ttw mice causes chronic compression of the spinal cord. Few studies have compared the MSC osteogenic potential with behavioral changes in an OPLL animal model.

METHODS

We compared the osteogenic potential and behavioral characteristics of MSCs from ttw mice (4 to 20 weeks old) with those from control wild-type mice (without hyperostosis). Ligament ossification was monitored by micro-computed tomography and pathology; tissues were double stained with fluorescent antibodies against markers for MSCs (CD45 and CD105), at 8 weeks. The Basso Mouse Scale was used to assess motor function, and heat and mechanical tests to assess sensory function. The osteogenic potential of adipose and muscle MSCs was assessed by Alizarin Red S absorbance, staining for osteogenic mineralization, and real-time quantitative polymerase chain reaction for osteogenesis-related genes.

RESULTS

Spinal-ligament ossification began in ttw mice at 8 weeks of age, and the ossified area increased with age. Immunofluorescence staining identified MSCs in the ossification area. The ttw mice became hyposensitive at 8 weeks of age, and Basso Mouse Scale scores showed motor-function deficits starting at 12 weeks of age. Alizarin Red S staining for mineralization showed a higher osteogenic potential in the adipose- and muscle-derived MSCs from ttw mice than from wild-type mice at 4, 8, and 20 weeks of age. Real-time quantitative polymerase chain reaction showed that ttw MSCs strongly expressed osteogenesis-related genes.

CONCLUSION

MSCs derived from muscle and adipose tissue in ttw mice had a high osteogenic potential.

LEVEL OF EVIDENCE

N/A.

Macrophage-derived oncostatin M contributes to human and mouse neurogenic heterotopic ossifications

Neurogenic heterotopic ossification (NHO) is the formation of ectopic bone generally in muscles surrounding joints following spinal cord or brain injury. We investigated the mechanisms of NHO formation in 64 patients and a mouse model of spinal cord injury-induced NHO. We show that marrow from human NHOs contains hematopoietic stem cell (HSC) niches, in which mesenchymal stromal cells (MSCs) and endothelial cells provide an environment supporting HSC maintenance, proliferation, and differentiation. The transcriptomic signature of MSCs from NHOs shows a neuronal imprinting associated with a molecular network required for HSC support. We demonstrate that oncostatin M (OSM) produced by activated macrophages promotes osteoblastic differentiation and mineralization of human muscle-derived stromal cells surrounding NHOs. The key role of OSM was confirmed using an experimental model of NHO in mice defective for the OSM receptor (OSMR). Our results provide strong evidence that macrophages contribute to NHO formation through the osteogenic action of OSM on muscle cells within an inflammatory context and suggest that OSM/OSMR could be a suitable therapeutic target. Altogether, the evidence of HSCs in ectopic bones growing at the expense of soft tissue in spinal cord/brain-injured patients indicates that inflammation and muscle contribute to HSC regulation by the brain-bone-blood triad.

Inhibition of Mammalian Target of Rapamycin Signaling with Rapamycin Prevents Trauma-Induced Heterotopic Ossification

A pressing clinical need exists for 63% to 65% of combat-wounded service members and 11% to 20% of civilians who develop heterotopic ossification (HO) after blast-related extremity injury and traumatic injuries, respectively. The mammalian target of rapamycin pathway is a central cellular sensor of injury. We evaluated the prophylactic effects of rapamycin, a selective inhibitor of mammalian target of rapamycin signaling, on HO formation in a rat model of blast-related, polytraumatic extremity injury. Rapamycin was administered intraperitoneally daily for 14 days at 0.5 mg/kg or 2.5 mg/kg. Ectopic bone formation was monitored by micro-computed tomography and confirmed by histologic examination. Connective tissue progenitor cells, platelet-derived growth factor receptor-α-positive cells, and α-smooth muscle actin-positive blood vessels were assayed at postoperative day 7 by colony formation and immunofluorescence. Early gene expression changes were determined by low-density microarray. There was significant attenuation of 1) total new bone and soft tissue ectopic bone with 0.5 mg/kg (38.5% and 14.7%) and 2.5 mg/kg rapamycin (90.3% and 82.9%), respectively, 2) connective tissue progenitor cells, 3) platelet-derived growth factor receptor-α-positive cells, 4) α-smooth muscle actin-positive blood vessels, and 5) of key extracellular matrix remodeling (CD44, Col1a1, integrins), osteogenesis (Sp7, Runx2, Bmp2), inflammation (Cxcl5, 10, IL6, Ccl2), and angiogenesis (Angpt2) genes. No wound healing complications were noted. Our data demonstrate the efficacy of rapamycin in inhibiting blast trauma-induced HO by a multipronged mechanism.

Targeted stimulation of retinoic acid receptor-γ mitigates the formation of heterotopic ossification in an established blast-related traumatic injury model

Heterotopic ossification (HO) involves formation of endochondral bone at non-skeletal sites, is prevalent in severely wounded service members, and causes significant complications and delayed rehabilitation. As common prophylactic treatments such as anti-inflammatory drugs and irradiation cannot be used after multi-system combat trauma, there is an urgent need for new remedies. Previously, we showed that the retinoic acid receptor γ agonist Palovarotene inhibited subcutaneous and intramuscular HO in mice, but those models do not mimic complex combat injury. Thus, we tested Palovarotene in our validated rat trauma-induced HO model that involves blast-related limb injury, femoral fracture, quadriceps crush injury, amputation and infection with methicillin-resistant Staphylococcus aureus from combat wound infections. Palovarotene was given orally for 14days at 1mg/kg/day starting on post-operative day (POD) 1 or POD-5, and HO amount, wound dehiscence and related processes were monitored for up to 84days post injury. Compared to vehicle-control animals, Palovarotene significantly decreased HO by 50 to 60% regardless of when the treatment started and if infection was present. Histological analyses showed that Palovarotene reduced ectopic chondrogenesis, osteogenesis and angiogenesis forming at the injury site over time, while fibrotic tissue was often present in place of ectopic bone. Custom gene array data verified that while expression of key chondrogenic and osteogenic genes was decreased within soft tissues of residual limb in Palovarotene-treated rats, expression of cartilage catabolic genes was increased, including matrix metalloproteinase-9. Importantly, Palovarotene seemed to exert moderate inhibitory effects on wound healing, raising potential safety concerns related to dosing and timing. Our data show for the first time that Palovarotene significantly inhibits HO triggered by blast injury and associated complications, strongly indicating that it may prevent HO in patients at high risk such as those sustaining combat injuries and other forms of blast trauma.

Trauma-induced heterotopic bone formation and the role of the immune system: A review

Extremity trauma, spinal cord injuries, head injuries, and burn injuries place patients at high risk of pathologic extraskeletal bone formation. This heterotopic bone causes severe pain, deformities, and joint contractures. The immune system has been increasingly implicated in this debilitating condition. This review summarizes the various roles immune cells and inflammation play in the formation of ectopic bone and highlights potential areas of future investigation and treatment. Cell types in both the innate and adaptive immune system such as neutrophils, macrophages, mast cells, B cells, and T cells have all been implicated as having a role in ectopic bone formation through various mechanisms. Many of these cell types are promising areas of therapeutic investigation for potential treatment. The immune system has also been known to also influence osteoclastogenesis, which is heavily involved in ectopic bone formation. Chronic inflammation is also known to have an inhibitory role in the formation of ectopic bone, whereas acute inflammation is necessary for ectopic bone formation.

Bedside, Benchtop, and Bioengineering: Physicochemical Imaging Techniques in Biomineralization

The need to quantify physicochemical properties of mineralization spans many fields. Clinicians, mineralization researchers, and bone tissue bioengineers need to be able to measure the distribution, quantity, and the mechanical and chemical properties of mineralization within a wide variety of substrates from injured muscle to electrospun polymer scaffolds and everything in between. The techniques available to measure these properties are highly diverse in terms of their complexity and utility. Therefore it is of the utmost importance that those who intend to use them have a clear understanding of the advantages and disadvantages of each technique and its appropriateness to their specific application. This review provides all of this information for each technique and uses heterotopic ossification and engineered bone substitutes as examples to illustrate how these techniques have been applied. In addition, we provide novel data using advanced techniques to analyze human samples of combat related heterotopic ossification.

Fibrocytes participate in the development of heterotopic ossification

Heterotopic ossification (HO) is a complication of musculoskeletal injury characterized by the formation of mature bone in soft tissues. The etiology of HO is unknown. We investigated the role of bone marrow derived progenitor cells in HO pathophysiology. We isolated the cells from HO specimens by cell explantation. Using flow cytometry and immunofluorescence microscopy, we found that 35 to 65% of the HO cells exhibit a bone marrow derived fibrocyte profile consisting in spindle-shaped morphology associated with type 1 pro-collagen and LSP1 expression. When cultured in osteogenic differentiation medium, active machinery for bone mineralization (high gene expression of Anx2, TNAP, and Pit-1), and calcium/phosphate deposits were found. Interestingly, interferon-alpha 2b significantly reduced the proliferation rate and COL1 gene expression in HO cells. We have characterized a novel subset of bone marrow derived progenitor cells in the HO specimens. The findings from this research study will provide new insights into the development of HO in burn patients.

Identifying the Cellular Mechanisms Leading to Heterotopic Ossification

Heterotopic ossification (HO) is a debilitating condition defined by the de novo development of bone within non-osseous soft tissues, and can be either hereditary or acquired. The hereditary condition, fibrodysplasia ossificans progressiva is rare but life threatening. Acquired HO is more common and results from a severe trauma that produces an environment conducive for the formation of ectopic endochondral bone. Despite continued efforts to identify the cellular and molecular events that lead to HO, the mechanisms of pathogenesis remain elusive. It has been proposed that the formation of ectopic bone requires an osteochondrogenic cell type, the presence of inductive agent(s) and a permissive local environment. To date several lineage-tracing studies have identified potential contributory populations. However, difficulties identifying cells in vivo based on the limitations of phenotypic markers, along with the absence of established in vitro HO models have made the results difficult to interpret. The purpose of this review is to critically evaluate current literature within the field in an attempt identify the cellular mechanisms required for ectopic bone formation. The major aim is to collate all current data on cell populations that have been shown to possess an osteochondrogenic potential and identify environmental conditions that may contribute to a permissive local environment. This review outlines the pathology of endochondral ossification, which is important for the development of potential HO therapies and to further our understanding of the mechanisms governing bone formation.

Bioburden Increases Heterotopic Ossification Formation in an Established Rat Model

BACKGROUND

Heterotopic ossification (HO) develops in a majority of combat-related amputations wherein early bacterial colonization has been considered a potential early risk factor. Our group has recently developed a small animal model of trauma-induced HO that incorporates many of the multifaceted injury patterns of combat trauma in the absence of bacterial contamination and subsequent wound colonization.

QUESTIONS/PURPOSES

We sought to determine if (1) the presence of bioburden (Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus [MRSA]) increases the magnitude of ectopic bone formation in traumatized muscle after amputation; and (2) what persistent effects bacterial contamination has on late microbial flora within the amputation site.

METHODS

Using a blast-related HO model, we exposed 48 rats to blast overpressure, femur fracture, crush injury, and subsequent immediate transfemoral amputation through the zone of injury. Control injured rats (n = 8) were inoculated beneath the myodesis with phosphate-buffered saline not containing bacteria (vehicle) and treatment rats were inoculated with 1 × 10(6) colony-forming units of A baumannii (n = 20) or MRSA (n = 20). All animals formed HO. Heterotopic ossification was determined by quantitative volumetric measurements of ectopic bone at 12-weeks postinjury using micro-CT and qualitative histomorphometry for assessment of new bone formation in the residual limb. Bone marrow and muscle tissue biopsies were collected from the residual limb at 12 weeks to quantitatively measure the bioburden load and to qualitatively determine the species-level identification of the bacterial flora.

RESULTS

At 12 weeks, we observed a greater volume of HO in rats infected with MRSA (68.9 ± 8.6 mm(3); 95% confidence interval [CI], 50.52-85.55) when compared with A baumannii (20.9 ± 3.7 mm(3); 95% CI, 13.61-28.14; p < 0.001) or vehicle (16.3 ± 3.2 mm(3); 95% CI, 10.06-22.47; p < 0.001). Soft tissue and marrow from the residual limb of rats inoculated with A baumannii tested negative for A baumannii infection but were positive for other strains of bacteria (1.33 × 10(2) ± 0.89 × 10(2); 95% CI, -0.42 × 10(2)-3.08 × 10(2) and 1.25 × 10(6) ± 0.69 × 10(6); 95% CI, -0.13 × 10(6)-2.60 × 10(6) colony-forming units in bone marrow and muscle tissue, respectively), whereas tissue from MRSA-infected rats contained MRSA only (4.84 × 10(1) ± 3.22 × 10(1); 95% CI, -1.47 × 10(1)-11.1 × 10(1) and 2.80 × 10(7) ± 1.73 × 10(7); 95% CI, -0.60 × 10(7)-6.20 × 10(7) in bone marrow and muscle tissue, respectively).

CONCLUSIONS

Our findings demonstrate that persistent infection with MRSA results in a greater volume of ectopic bone formation, which may be the result of chronic soft tissue inflammation, and that early wound colonization may be a key risk factor.

CLINICAL RELEVANCE

Interventions that mitigate wound contamination and inflammation (such as early débridement, systemic and local antibiotics) may also have a beneficial effect with regard to the mitigation of HO formation and should be evaluated with that potential in mind in future preclinical studies.

Characterization of discrete subpopulations of progenitor cells in traumatic human extremity wounds

Here we show that distinct subpopulations of cells exist within traumatic human extremity wounds, each having the ability to differentiate into multiple cells types in vitro. A crude cell suspension derived from traumatized muscle was positively sorted for CD29, CD31, CD34, CD56 or CD91. The cell suspension was also simultaneously negatively sorted for either CD45 or CD117 to exclude hematopoietic stem cells. These subpopulations varied in terms their total numbers and their abilities to grow, migrate, differentiate and secrete cytokines. While all five subpopulations demonstrated equal abilities to undergo osteogenesis, they were distinct in their ability to undergo adipogenesis and vascular endotheliogenesis. The most abundant subpopulations were CD29+ and CD34+, which overlapped significantly. The CD29+ and CD34+ cells had the greatest proliferative and migratory capacity while the CD56+ subpopulation produced the highest amounts of TGFß1 and TGFß2. When cultured under endothelial differentiation conditions the CD29+ and CD34+ cells expressed VE-cadherin, Tie2 and CD31, all markers of endothelial cells. These data indicate that while there are multiple cell types within traumatized muscle that have osteogenic differentiation capacity and may contribute to bone formation in post-traumatic heterotopic ossification (HO), the major contributory cell types are CD29+ and CD34+, which demonstrate endothelial progenitor cell characteristics.

Do inflammatory markers portend heterotopic ossification and wound failure in combat wounds?

BACKGROUND

After a decade of war in Iraq and Afghanistan, we have observed an increase in combat-related injury survival and a paradoxical increase in injury severity, mainly because of the effects of blasts. These severe injuries have a devastating effect on each patient's immune system resulting in massive upregulation of the systemic inflammatory response. By examining inflammatory mediators, preliminary data suggest that it may be possible to correlate complications such as wound failure and heterotopic ossification (HO) with distinct systemic and local inflammatory profiles, but this is a relatively new topic.

QUESTIONS/PURPOSES

We asked whether systemic or local markers of inflammation could be used as an objective means, independent of demographic and subjective factors, to estimate the likelihood of (1) HO and/or (2) wound failure (defined as wounds requiring surgical débridement after definitive closure, or wounds that were not closed or covered within 21 days of injury) in patients sustaining combat wounds.

METHODS

Two hundred combat wounded active-duty service members who sustained high-energy extremity injuries were prospectively enrolled between 2008 and 2012. Of these 200 patients, 189 had adequate followups to determine the presence or absence of HO, and 191 had adequate followups to determine the presence or absence of wound failure. In addition to injury-specific and demographic data, we quantified 24 cytokines and chemokines during each débridement. Patients were followed clinically for 6 weeks, and radiographs were obtained 3 months after definitive wound closure. Associations were investigated between these markers and wound failure or HO, while controlling for known confounders.

RESULTS

The presence of an amputation (p < 0.001; odds ratio [OR], 6.1; 95% CI. 1.63-27.2), Injury Severity Score (p = 0.002; OR, 33.2; 95% CI, 4.2-413), wound surface area (p = 0.001; OR, 1.01; 95% CI, 1.002-1.009), serum interleukin (IL)-3 (p = 0.002; OR, 2.41; 95% CI, 1.5-4.5), serum IL-12p70 (p = 0.01; OR, 0.49; 95% CI, 0.27-0.81), effluent IL-3 (p = 0.02; OR, 1.75; 95% CI, 1.2-2.9), and effluent IL-13 (p = 0.006; OR, 0.67; 95% CI, 0.50-0.87) were independently associated with HO formation. Injury Severity Score (p = 0.05; OR, 18; 95% CI, 5.1-87), wound surface area (p = 0.05; OR, 28.7; 95% CI, 1.5-1250), serum procalcitonin ([ProCT] (p = 0.03; OR, 1596; 95% CI, 5.1-1,758,613) and effluent IL-6 (p = 0.02; OR, 83; 95% CI, 2.5-5820) were independently associated with wound failure.

CONCLUSIONS

We identified associations between patients' systemic and local inflammatory responses and wound-specific complications such as HO and wound failure. However, future efforts to model these data must account for their complex, time dependent, and nonlinear nature.

LEVEL OF EVIDENCE

Level II, prognostic study. See the Instructions for Authors for a complete description of levels of evidence.

BMP-9 expression in human traumatic heterotopic ossification: a case report

Background

Heterotopic ossification (HO) is defined as the abnormal formation of mature bone in soft tissue, notably skeletal muscle. The morbidity of HO in polytraumatized patients impacts the functional outcome, impairs rehabilitation, and increases costs due to subsequent surgical interventions.

Case presentation

We present the case of a 34-year-old African male who developed severe HO around his right hip 11 days after a major trauma. Immunohistochemical analyses of resected tissue revealed that several BMPs were expressed in the HO, including highly osteogenic BMP-9.

Conclusions

To the best of our knowledge, this is the first report of local BMP expression, notably BMP-9, in traumatic HO, and suggests that BMP-9, possibly through mrSCs, can contribute to HO formation in soft tissues when a suitable microenvironment is present.