Heterotopic ossification

Role of stem/progenitor cells in reparative disorders

Adult stem cells are activated to proliferate and differentiate during normal tissue homeostasis as well as in disease states and injury. This activation is a vital component in the restoration of function to damaged tissue via either complete or partial regeneration. When regeneration does not fully occur, reparative processes involving an overproduction of stromal components ensure the continuity of tissue at the expense of its normal structure and function, resulting in a “reparative disorder”. Adult stem cells from multiple organs have been identified as being involved in this process and their role in tissue repair is being investigated. Evidence for the participation of mesenchymal stromal cells (MSCs) in the tissue repair process across multiple tissues is overwhelming and their role in reparative disorders is clearly demonstrated, as is the involvement of a number of specific signaling pathways. Transforming growth factor beta, bone morphogenic protein and Wnt pathways interact to form a complex signaling network that is critical in regulating the fate choices of both stromal and tissue-specific resident stem cells (TSCs), determining whether functional regeneration or the formation of scar tissue follows an injury. A growing understanding of both TSCs, MSCs and the complex cascade of signals regulating both cell populations have, therefore, emerged as potential therapeutic targets to treat reparative disorders. This review focuses on recent advances on the role of these cells in skeletal muscle, heart and lung tissues.

Heterotopic ossification in orthopaedic trauma

Heterotopic ossification (HO) can be defined as the pathologic formation of bone in extraskeletal tissues. There has been a substantial amount of recent research on the pathophysiology, prophylaxis, and treatment of HO and traumatic conditions associated with the development of HO. This research has advanced our understanding of this disease and helped to clarify evidence-based approaches to both the prophylaxis and treatment of HO. This article reviews the literature on these topics with a focus on their application in orthopaedic trauma.

Fibroregulation of mesenchymal progenitor cells by BMP-4 after traumatic muscle injury

OBJECTIVES

Traumatized muscle is a complex healing environment containing cells with robust reparative and regenerative potential interacting in a cytokine milieu that influences the function and differentiation of these cells, leading to a spectrum of healing responses. In particular, bone morphogenetic protein-4 (BMP-4) is of interest as a potential modulator of healing because its dysregulation has been associated with fibrosis and heterotopic ossification formation. We propose a descriptive study of altered BMP-4 expression in traumatized muscle tissue and to evaluate its role in the fibroregulatory function of resident mesenchymal progenitor cells (MPCs) at the protein- and gene-expression levels.

METHODS

Protein-level expression of BMP-4 from cells resident in traumatized muscle specimens was evaluated using ELISA and also using sodium dodecyl sulfate-polyacrylamide gel electrophoresis to compare BMP-4 in homogenized muscle tissue specimens. BMP-4, cartilage oligomeric matrix protein (COMP), and osteocalcin expression localization was analyzed via immunohistochemistry. Reverse transcription-polymerase chain reaction was performed to evaluate fibroregulatory gene expression in MPCs after treatment with BMP-4.

RESULTS

BMP-4 was present in all traumatized muscle tissue specimens. Immunohistochemistry demonstrated that traumatized muscle fibers contained greater number of cells expressing BMP-4 in a more disorganized fashion compared with control samples. Reverse transcription-polymerase chain reaction demonstrated that COMP, growth and differentiation factor-10, and integrin beta-2 were up-regulated, whereas tumor necrosis factor-alpha was significantly down-regulated. COMP expression was colocalized in the traumatized muscle tissue with osteocalcin.

CONCLUSIONS

BMP-4 has an effect on MPCs that seems to promote fibrotic tissue formation. These findings suggest that BMP-4, while promoting osteoinduction, may also act on MPCs to promote formation of a fibrotic osteoinductive matrix. Thus, this signaling axis might be a potential target for heterotopic ossification prevention.

Could heterotopic ossification be prevented by varying dietary n-3/n-6 polyunsaturated fatty acid ratio: a novel perspective to its treatment?

Heterotopic ossification (HO) is a common complication following with musculoskeletal trauma and surgical procedures. It usually decreases joint mobility and eventually causes loss of joint function. Despite nonsteroidal anti-inflammatory drugs (NSAIDs), the inhibitor of cyclooxygenase(COX), have been proven to prevent HO effectively via prostaglandin E2 synthesis regulation and modulation of tissue responsiveness to pro-inflammatory signaling, HO prevention is still a matter of debate for clinicians to avoid the side effect of NSAIDs. Interestingly, it is suggested that PGE2 production and pro-inflammatory microenvironment in body could be modified by varying the ratio of the precursor fatty acids in the diet. On account of the effect of dietary (n-6)/(n-3) PUFAs ratio on both COX metabolism and pro-inflammatory cytokines mediated biological responsiveness, we hypothesized lowering dietary (n-6)/(n-3) PUFAs ratio may not only directly reduce the substrate of COX-2 and COX-2 activity, but also partially ameliorate tissue inflammatory responsiveness to cytokines correlated with HO development,exerting an inhibitory effect on PGE2 synthesis to prevent HO formation. The negative role of lowering dietary (n-6)/(n-3) PUFAs ratio on angiogenesis, cytokines-induced apoptosis, inflammatory responsiveness and osteogenesis could also contribute to its action on HO development. If our hypothesis is proved to be corrected, it could be an innovative method to treat HO.

Inflammatory cytokine and chemokine expression is associated with heterotopic ossification in high-energy penetrating war injuries

OBJECTIVE

Heterotopic ossification (HO) develops frequently after modern high-energy penetrating war injuries. The purpose of this prospective study was to identify and characterize the unique cytokine and chemokine profile associated with the development of HO as it pertained to the systemic inflammatory response after penetrating combat-related trauma.

METHODS

Patients with high-energy penetrating extremity wounds were prospectively enrolled. Surgical debridement along with the use of a pulse lavage and vacuum-assisted-closure device was performed every 48-72 hours until definitive wound closure. Wound bed tissue biopsy, wound effluent, and serum were collected before each debridement. Effluent and serum were analyzed for 22 relevant cytokines and chemokines. Tissue was analyzed quantitatively for bacterial colonization. Correlations between specific wound and patient characteristics were also analyzed. The primary clinical outcome measure was the formation of HO as confirmed by radiographs at a minimum of 2 months of follow-up.

RESULTS

Thirty-six penetrating extremity war wounds in 24 patients were investigated. The observed rate of HO in the study population was 38%. Of the 36 wounds, 13 (36%) demonstrated HO at a minimum follow-up of 2 months. An elevated injury severity score was associated with the development of HO (P = 0.006). Wound characteristics that correlated with the development of HO included impaired healing (P = 0.005) and bacterial colonization (P < 0.001). Both serum (interleukin-6, interleukin-10, and MCP-1) and wound effluent (IP-10 and MIP-1α) cytokine and chemokine bioprofiles were individually associated and suggestive of the development of HO (P < 0.05).

CONCLUSIONS

A severe systemic and wound-specific inflammatory state as evident by elevated levels of inflammatory cytokines, elevated injury severity score, and bacterial wound colonization is associated with the development of HO. These findings suggest that the development of HO in traumatic combat-related wounds is associated with a hyper-inflammatory systemic response to injury.

LEVEL OF EVIDENCE

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

Blast injuries and heterotopic ossification

Heterotopic ossification (HO) is perhaps the single most significant obstacle to independence, functional mobility, and return to duty for combat-injured veterans of Operation Enduring Freedom and Operation Iraqi Freedom. Recent research into the cause(s) of HO has been driven by a markedly higher prevalence seen in these wounded warriors than encountered in previous wars or following civilian trauma. To that end, research in both civilian and military laboratories continues to shed light onto the complex mechanisms behind HO formation, including systemic and wound specific factors, cell lineage, and neurogenic inflammation. Of particular interest, non-invasive in vivo testing using Raman spectroscopy may become a feasible modality for early detection, and a wound-specific model designed to detect the early gene transcript signatures associated with HO is being tested. Through a combined effort, the goals of early detection, risk stratification, and development of novel systemic and local prophylaxis may soon be attainable.

Heterotopic ossification of the abdominal wall

INTRODUCTION

Heterotopic ossification is a rare, benign condition which occurs when bone develops in tissues that do not normally ossify.

PRESENTATION OF CASE

We herein report the case of a 73-year-old gentleman who underwent a laparotomy for a large splenic flexure tumour considered unresectable at initial intervention. Following delivery of chemotherapy, he was referred for a second opinion and the tumour with adjacent structures was removed at a subsequent laparotomy. A segment of abnormal hard tissue present in the abdominal wall was also excised. Histopathology revealed metaplastic bone deposition.

DISCUSSION

Heterotopic ossification may occur at various sites and is a recognised but exceedingly infrequent sequela of abdominal surgery.

CONCLUSION

This case highlights clinical, aetiological and histopathological features of this rare finding.

Extraskeletal cartilaginous, osseous, and chordoid tumors in children and adolescents

Extraskeletal cartilaginous, osseous, and chordoid tumors are extraordinarily rare in children and adolescents. These lesions are diagnostically challenging due to their rarity and their overlap with metastatic osteosarcoma, reactive or metabolic calcifying and bone-forming masses, various pseudosarcomatous proliferations such as myositis ossificans, and other rare genetic or metabolic disorders. This article reviews the clinicopathologic features and differential diagnosis of extraskeletal cartilaginous, osseous, and chordoid neoplasms in the first two decades of life and highlights the use of diagnostic adjuncts.

Serum leptin levels are associated with the presence of syndesmophytes in male patients with ankylosing spondylitis

The aim of this study is to clarify the association between serum leptin levels and the presence of syndesmophytes in male patients with ankylosing spondylitis (AS). Seventy-two male patients with AS and 20 age-matched healthy male controls were included. Patients were stratified by the presence of syndesmophytes. Serum leptin levels were measured and adjusted for body mass index (BMI). In addition, bone-specific alkaline phosphatase (BALP), osteocalcin, and telopeptide of type I collagen were determined. Patients with syndesmophytes were associated with older age (p < 0.001), longer disease duration (p = 0.003), and higher BMI (p = 0.038). Serum leptin levels and leptin per BMI (leptin/BMI) ratio were not different between AS patients and healthy controls. However, serum leptin/BMI ratio was significantly higher in patients with syndesmophytes compared to those without (p = 0.010). In multivariate analysis, higher serum leptin/BMI ratio remained significantly associated with the presence of syndesmophytes (p = 0.029). Moreover, serum leptin/BMI ratio was positively correlated with serum BALP (γ = 0.279, p = 0.039). However, there was no significant association between serum leptin/BMI ratio and bone mineral density. Serum leptin levels are elevated in male AS patients with syndesmophytes and were found to be correlated with bone formation marker, suggesting a potential role of leptin in new bone formation in AS.

Multipotent progenitors resident in the skeletal muscle interstitium exhibit robust BMP-dependent osteogenic activity and mediate heterotopic ossification

Heterotopic ossification is a debilitating condition that can result from traumatic injury, surgery, or genetic disease. We investigated the cellular origins of heterotopic skeletogenesis in the mouse using lineage tracing and bioassays of heterotopic ossification based on intramuscular transplantation. We identified, characterized, and purified a tissue-resident stem/progenitor cell population that exhibits robust osteogenic potential and represents a major cell-of-origin for heterotopic ossification. These progenitors reside in the interstitium of skeletal muscle and other tissues, and are distinct from the endothelium, which does not exhibit osteogenic activity in response to bone morphogenetic protein 2 (BMP2) stimulation. Intramuscular transplantation, together with clonal analysis in culture, revealed that these progenitors are multipotent, exhibiting the capacity for both BMP-dependent skeletogenic differentiation and spontaneous adipogenic differentiation. Identifying the cells-of-origin responsible for heterotopic ossification provides a potential therapeutic target to treat, mitigate, or prevent this disabling condition.

Bone in the belly: traumatic heterotopic mesenteric ossification

Heterotopic mesenteric ossification is an unusual but important complication in patients who sustain blunt and penetrating abdominal trauma. In this condition, bone formation occurs in the mesenteric and omental fat in response to injury and may result in serious complications such as bowel obstruction and fistula formation. Although a few case reports exist, the radiology literature on this topic is scant. Based on our experience, this entity is under-recognized on imaging studies and often results in diagnostic confusion due to its resemblance to other pathologies such as barium leak and extraskeletal bone-forming neoplasms. This review highlights the imaging features of heterotopic mesenteric ossification with an emphasis on computed tomographic findings. Radiologist awareness of this condition is crucial to avoid misdiagnosis as well as to direct appropriate and timely management.

A classification method for neurogenic heterotopic ossification of the hip

Background

Existing classifications for heterotopic ossification (HO) do not include all HO types; nor do they consider the anatomy of the involved joint or the neurological injury. Therefore, we performed this study to propose and evaluate a classification according to the location of neurogenic HO and the neurological injury.

Materials and methods

We studied the files of 24 patients/33 hips with brain or spinal cord injury and neurogenic HO of the hip treated with excision, indomethacin, and radiation therapy. We classified patients according to the Brooker classification scheme as well as ours. Four types of neurogenic HO were distinguished according to the anatomical location of HO: type 1, anterior; type 2, posterior; type 3, anteromedial; type 4, circumferential. Subtypes of each type were added based on the neurological injury: a, spinal cord; b, brain injury. Mean follow-up was 2.5 years (1–8 years).

Results

The Brooker classification scheme was misleading—all hips were class III or IV, corresponding to ankylosis, even though only 14 hips had ankylosis. On the other hand, our classification was straightforward and easy to assign in all cases. It corresponded better to the location of the heterotopic bone, and allowed for preoperative planning of the appropriate surgical approach and evaluation of the prognosis; recurrence of neurogenic HO was significantly higher in patients with brain injury (subtype b), while blood loss was higher for patients with anteromedial (type 3) and circumferential (type 4) neurogenic HO.

Conclusions

Our proposed classification may improve the management and evaluation of the prognosis for patients with neurogenic HO.

Pseudotumors and Reactive Lesions

This article discusses reactive or degenerative processes in bone or periosteal soft tissue that occasionally masquerade as neoplasms. Presentation of the clinical, radiologic, and pathologic features of these processes is provided with an emphasis on the avoidance of overdiagnosis. Clinical, radiologic, and pathologic features of pseudotumors are presented in detail. This article approaches these tumor-like lesions in 2 categories: (1) those in the soft tissue next to bone and (2) those inside bones from the aspect of mineralization and calcification.

Adherence to routine use of pharmacological prophylaxis of heterotopic ossification after total hip arthroplasty: results from an Italian multicenter, prospective, observational survey

BACKGROUND

In spite of the proven efficacy of pharmacological prophylaxis of heterotopic ossification following total hip arthroplasty, its routine use is still debated, and no data are available regarding the adherence to its administration in clinical practice.

MATERIALS AND METHODS

In this prospective, observational, multicenter study, 480 consecutive patients operated on for primary total hip arthroplasty during the year 2009 were followed radiographically for 12 months after surgery in order to assess the incidence of periprosthetic heterotopic ossification. Surgeons were free to choose whether to administer pharmacological prophylaxis, and were asked to keep a record of the duration of the prophylaxis (if used) or the reasons for not using it. To facilitate the statistical analysis, all of the participating centers agreed to use only one drug (celecoxib) that had already proven to be effective.

RESULTS

368 patients were administered celecoxib and 112 patients did not receive any prophylaxis. Reported reasons for not administering celecoxib prophylaxis were the surgeon's opinion that prophylaxis was not needed on a routine basis (84/112 patients, 75%), previous history of gastrointestinal bleeding (17.8%), and concomitant cardiorenal pathologies (7.1%). The overall incidence of heterotopic ossification in the celecoxib-treated patients was 23% (no cases of Brooker grade 3 or 4 ossifications), compared to 55% in the untreated patients (Brooker grade 3 and 4: 8.9%). Multivariate analysis showed that celecoxib prophylaxis was the single most important variable when predicting the occurrence of heterotopic ossification.

CONCLUSIONS

This study confirms the efficacy and tolerability of celecoxib for the prophylaxis of heterotopic ossification after total hip arthroplasty, and shows how the surgeon's belief that routine prevention is not required still plays an important role in the determination of this complication, together with the fear of possible unwanted side effects.

Celecoxib inhibits the heterotopic ossification in the rat model with Achilles tenotomy

Celecoxib, a selective cox-2 inhibitor, has been shown to prevent the heterotopic ossification following total hip arthroplasty. However, the effects of celecoxib on heterotopic ossification at other locations remain unclear. This study aimed to investigate the effect of celecoxib on heterotopic ossification in the rat model with Achilles tenotomy. Forty male Sprague-Dawley rats, which were randomly divided into 2 groups (n = 20), underwent midpoint Achilles tenotomy on left legs through a posterior approach under aseptic condition. Experimental group was treated with the saline solution of celecoxib (10 mg/kg) per day, while control group was treated by normal saline (0.9%). At 3, 5 and 10 postoperative weeks, all animals were examined by X-ray to assess new bone formation in the Achilles tendon. At 10 weeks after surgery, all animals were killed and Achilles tendons were taken for hematoxylin-eosin (HE) and immunohistochemical staining. Heterotopic ossification developed in 3 rats (15%) in experimental group and 20 rats (100%) in control group by postoperative 10 weeks. The incidence of heterotopic ossification was significantly lower in experimental group than in control group (P < 0.05). Our findings suggest that celecoxib inhibits HO development in rat model with Achilles tenotomy.

Brief review of models of ectopic bone formation

Ectopic bone formation is a unique biologic entity--distinct from other areas of skeletal biology. Animal research models of ectopic bone formation most often employ rodent models and have unique advantages over orthotopic (bone) environments, including a relative lack of bone cytokine stimulation and cell-to-cell interaction with endogenous (host) bone-forming cells. This allows for relatively controlled in vivo experimental bone formation. A wide variety of ectopic locations have been used for experimentation, including subcutaneous, intramuscular, and kidney capsule transplantation. The method, benefits and detractions of each method are summarized in the following review. Briefly, subcutaneous implantation is the simplest method. However, the most pertinent concern is the relative paucity of bone formation in comparison to other models. Intramuscular implantation is also widely used and relatively simple, however intramuscular implants are exposed to skeletal muscle satellite progenitor cells. Thus, distinguishing host from donor osteogenesis becomes challenging without cell-tracking studies. The kidney capsule (perirenal or renal capsule) method is less widely used and more technically challenging. It allows for supraphysiologic blood and nutrient resource, promoting robust bone growth. In summary, ectopic bone models are extremely useful in the evaluation of bone-forming stem cells, new osteoinductive biomaterials, and growth factors; an appropriate choice of model, however, will greatly increase experimental success.

Vibrational spectroscopy: a tool being developed for the noninvasive monitoring of wound healing

Wound care and management accounted for over 1.8 million hospital discharges in 2009. The complex nature of wound physiology involves hundreds of overlapping processes that we have only begun to understand over the past three decades. The management of wounds remains a significant challenge for inexperienced clinicians. The ensuing inflammatory response ultimately dictates the pace of wound healing and tissue regeneration. Consequently, the eventual timing of wound closure or definitive coverage is often subjective. Some wounds fail to close, or dehisce, despite the use and application of novel wound-specific treatment modalities. An understanding of the molecular environment of acute and chronic wounds throughout the wound-healing process can provide valuable insight into the mechanisms associated with the patient's outcome. Pathologic alterations of wounds are accompanied by fundamental changes in the molecular environment that can be analyzed by vibrational spectroscopy. Vibrational spectroscopy, specifically Raman and Fourier transform infrared spectroscopy, offers the capability to accurately detect and identify the various molecules that compose the extracellular matrix during wound healing in their native state. The identified changes might provide the objective markers of wound healing, which can then be integrated with clinical characteristics to guide the management of wounds.

Capsular management during hip arthroscopy: from femoroacetabular impingement to instability

Advances in the ability to treat various soft-tissue and osseous pathologic conditions of the hip arthroscopically have been predicated on an improved exposure of the pathology of the central, peripheral, and peritrochanteric compartments. The management of the capsule is critical and must allow for an improved exposure without compromising stability and kinematics of the hip. Described approaches have included capsulectomy, limited capsulotomy, extensile capsulotomy, capsular plication, and capsular shift. The selected approach must consider various factors, including symptomatic complaints, underlying hyperlaxity, specific mechanical pathology, and surgical expertise. Universally using a single technique without consideration of the complex mechanical and anatomic factors unique to each patient may result in incomplete treatment of the pathoanatomy or iatrogenic instability. This article reviews the anatomy of the hip capsule and provide a diagnosis-based consideration of capsular management during hip arthroscopy. The senior author's preferred techniques are also presented.

Cytokine expression in muscle following traumatic injury

Heterotopic ossification (HO) occurs at a high frequency in severe orthopaedic extremity injuries; however, the etiology of traumatic HO is virtually unknown. Osteogenic progenitor cells have previously been identified within traumatized muscle. Although the signaling mechanisms that lead to this dysregulated differentiation pathway have not been identified, it is assumed that inflammation and fibrosis, which contribute to an osteoinductive environment, are necessary for the development of HO. The hypothesis of this study was that cytokines related to chronic inflammation, fibrogenesis, and osteogenesis become up-regulated following severe muscle trauma where HO forms. Classification of these cytokines by their differential expression relative to control muscle will provide guidance for further study of the mechanisms leading to HO. Real-time RT-PCR analysis revealed no significant up-regulation of cytokines typically associated with HO (e.g., BMP-4, as observed in the genetic form of HO, fibrodysplasia ossificans progressiva). Instead, the cytokine gene expression profile associated with the traumatized muscle included up-regulation of cytokines associated with osteogenesis and fibrosis (i.e., BMP-1 and TGF-β(1)). Using immunohistochemistry, these cytokines were localized to fibroproliferative lesions, which have previously been implicated in HO. This study identifies other cell and tissue-level interactions in traumatized muscle that should be investigated further to better define the etiology of HO.

Intra- and periarticular heterotopic ossification in the knee after a low-velocity gunshot wound treated with retrograde intramedullary nailing of the femur

This is a case of a 32-year-old man who developed intra- and periarticular heterotopic ossification (HO) after sustaining a low-velocity gunshot wound to the femur treated with intramedullary nailing of the fracture using a retrograde technique. The association between HO after a high-velocity gunshot wounds is well established. In addition, there have been two case reports of intra-articular HO after retrograde intramedullary femoral nailing. However, HO in and around the knee after a low-velocity gunshot wound has not been reported and may be more common than initially thought.

Heterotopic ossification in complex orthopaedic combat wounds: quantification and characterization of osteogenic precursor cell activity in traumatized muscle

BACKGROUND

Heterotopic ossification frequently develops following high-energy blast injuries sustained in modern warfare. We hypothesized that differences in the population of progenitor cells present in a wound would correlate with the subsequent formation of heterotopic ossification.

METHODS

We obtained muscle biopsy specimens from military service members who had sustained high-energy wartime injuries and from patients undergoing harvest of a hamstring tendon autograft. Plastic-adherent cells were isolated in single-cell suspension and plated to assess the prevalence of colony-forming cells. Phenotypic characteristics were assessed with use of flow cytometry. Individual colony-forming units were counted after an incubation period of seven to ten days, and replicate cultures were incubated in lineage-specific induction media. Immunohistochemical staining was then performed to determine the percentage of colonies that had differentiated along an osteogenic lineage. Quantitative real-time reverse-transcription polymerase chain reaction was used to identify changes in osteogenic gene expression.

RESULTS

Injured patients had significantly higher numbers of muscle-derived connective-tissue progenitor cells per gram of tissue (p < 0.0001; 95% confidence interval [CI], 129,930 to 253,333), and those who developed heterotopic ossification had higher numbers of assayable osteogenic colonies (p < 0.016; 95% CI, 12,249 to 106,065). In the injured group, quantitative real-time reverse-transcription polymerase chain reaction performed on the in vitro expanded progeny of connective-tissue progenitors demonstrated upregulation of COL10A1, COL4A3, COMP, FGFR2, FLT1, IGF2, ITGAM, MMP9, PHEX, SCARB1, SOX9, and VEGFA in the patients with heterotopic ossification as compared with those without heterotopic ossification.

CONCLUSIONS

Our study suggests that the number of connective-tissue progenitor cells is increased in traumatized tissue. Furthermore, wounds in which heterotopic ossification eventually forms have a higher percentage of connective-tissue progenitor cells committed to osteogenic differentiation than do wounds in which heterotopic ossification does not form. The early identification of heterotopic ossification-precursor cells and target genes in severe wounds not only may be an effective prognostic tool with which to assess whether heterotopic ossification will develop in a wound, but may also guide the future development of individualized prophylactic measures.

Aspirin decreases heterotopic ossification after hip resurfacing

BACKGROUND

Heterotopic ossification (HO) is a concern for patients undergoing hip surgery, especially surface replacement arthroplasty (SRA) who tend to be younger, more active, and anticipate good motion. It is unclear, however, whether HO occurs more frequently after SRA than traditional total hip arthroplasty (THA) and whether aspirin influences the risk.

QUESTIONS/PURPOSES

We therefore determined the incidence of HO after hip resurfacing compared with THA and determined whether aspirin influenced the incidence or severity of HO.

METHODS

Retrospectively we compared three patient cohorts: SRA with aspirin (176 hips; 160 patients), SRA with warfarin (60 hips; 57 patients), and THA with warfarin (240 hips; 222 patients). All patients satisfied the same selection criteria and all surgeries were performed through the posterolateral approach using spinal anesthesia. HO was classified using the technique of Brooker et al. comparing the preoperative, immediate postoperative, and 6- to 12-month followup radiographs (minimum, 1 year; mean, 2.7 years).

RESULTS

In the SRA with aspirin group, HO was detected in four of 151 hips (2.6%; two Grade I; one Grade II; one Grade III); in the SRA with warfarin group, eight of 46 hips (17.4%) had HO with four hips (8.7%) having severe HO (Grade III). All 12 patients with HO in both SRA groups were male. The HO incidence and severity was less for the SRA patients treated with aspirin compared with those treated with warfarin. In the THA with warfarin control group, HO was detected in five of 189 hips (2.6%; two Grade I; three Grade II). The HO incidence and severity were the same between the THA with warfarin and the SRA with aspirin cohorts.

CONCLUSIONS

The risk of HO is greater in SRA than in THA in patients treated with warfarin postoperatively; aspirin appears to decrease the incidence and severity of HO after hip resurfacing surgery to a similar level as total hip arthroplasty.

Does a plastic drape reduce incidence of heterotopic ossification after hip resurfacing?

BACKGROUND

High rates of heterotopic ossification have been associated with hip resurfacing as compared to THA. Bone debris from femoral head reamings is cited as one of the risk factors linked to increased rates of heterotopic ossification.

QUESTIONS/PURPOSES

We therefore asked whether (1) the incidence of heterotopic ossification differed with and without the use of a plastic drape used to collect bone debris and (2) any of a number of variables (age, gender, diagnosis, previous hip surgery, operative time, and blood loss) related to the occurrence of HO.

METHODS

We retrospectively reviewed 136 hip resurfacings performed using one of two techniques: Group 1 contained 64 hip resurfacings performed using a sterile drape around the femoral neck while reaming the femoral head to collect bone debris; Group 2 contained 72 hip resurfacings carried out with manually removing bone debris and utilizing a pulse lavage. Data were collected with respect to diagnosis, gender, previous surgery, postoperative complications, operative time, and blood loss to rule out confounding variables. The amount of heterotopic ossification was measured radiographically in hips after undergoing resurfacing arthroplasty. The minimum followup was 6 months (mean, 15 months; range, 6-27 months).

RESULTS

No patient had heterotopic ossification of clinical importance and none had resection of the heterotopic ossification. Group 1 had a lower overall incidence of minor heterotopic ossification (32%) than Group 2 (58%). Risk factors linked to heterotopic ossification include male gender and operative time.

CONCLUSIONS

The use of a plastic drape to collect bone debris from femoral head reamings decreased the incidence of heterotopic ossification in resurfacing arthroplasty of the hip.

Late symptomatic heterotopic ossification of the patellar tendon after medial parapatellar intramedullary nailing of the tibia

This article describes a case of a 21-year old man who presented with symptomatic heterotopic ossification of the patellar tendon 3.5 years postinjury. The patient sustained an open tibia fracture during a fall and was treated by reamed intramedullary nailing through a medial paratendinous approach. Radiographic evidence of heterotopic ossification in the patellar tendon was first noted at the 4-week follow-up. He presented at 3.5 years postinjury with new-onset anterior knee pain and reported no interval trauma to the knee. Radiographs revealed a well-circumscribed area of calcification within the patellar tendon, which was excised within 2 weeks. On excision, the patient's symptoms had resolved. This case is unique because the patellar tendon was not violated at initial or subsequent surgeries, and because of the delayed presentation of heterotopic bone within the patellar tendon. To date, there have been only 3 reported cases of heterotopic ossification of the patellar tendon after intramedullary nailing of the tibia. We present a case of late symptomatic heterotopic ossification of the patellar tendon after medial paratendinous intramedullary nailing of an open tibia shaft fracture.

Postoperative Bowel Perforation due to Heterotopic Ossification (Myositis Ossificans Traumatica): A Case Report and Review of the Literature

Heterotopic ossification (HO) is the ectopic development of normal bone within soft tissue that can occur after traumatic injury. It is uncommon and may be missed or misdiagnosed, which can lead to complications. We report the case of an 84-year-old male with a previous history of a laparotomy who underwent resection of an intra-abdominal tumor through a midline incision. On postoperative day six, the patient was taken to the operating room, as succus was draining from the incision. Upon re-exploration, sharp bone-like material was found in the wound directly adjacent to an enterotomy. Pathology confirmed mature lamellar bone and the diagnosis of HO. This is the first report of postoperative intestinal perforation secondary to HO in a midline wound. We report this case to encourage accurate reporting of HO and its morbidity and complications for the benefit of appropriate surgical planning and epidemiologic tracking of outcomes.

Early postoperative heterotopic omental ossification: report of a case

Heterotopic mesenteric ossification (HMO) is an uncommon disorder that may sometimes be misdiagnosed. It can cause bowel or intestinal perforation, which may also lead to serious complications or even death. Heterotopic bone formation in the omentum, which is called heterotopic omental ossification (HOO) and is one type of HMO, is considered to be an exceedingly rare event. To our knowledge, about 29 cases of HMO have been reported in previous studies, of which three were HOO. We herein describe a case of HOO occurring in a 39-year-old Chinese man with no medical history of abdominal surgery. He underwent a left hemicolectomy, which was performed for the treatment of descending colon adenocarcinoma. Two weeks later, he developed a small bowel obstruction associated with multiple foci of heterotopic bone formation within the omentum. He therefore underwent a second surgical procedure for adhesiolysis and a partial omentectomy. The postoperative course was uneventful. He is still alive and disease-free 16 months later.

Myositis ossificans within the intercondylar notch treated arthroscopically

We present a case of intraarticular myositis ossificans in the right knee of a child. Myositis ossificans (MO), though relatively rare in childhood and even more uncommon within a joint, should be included in the differential diagnosis of an intra-articular mass when indicated by the typical clinical, radiographic, and histologic findings. An 11-year-old male presented with a history of trauma to his right knee. Four weeks after the initial injury, an MRI demonstrated evidence of an ACL rupture with a "cystic mass" within the intercondylar notch along the anterior surface of the torn ligament. At subsequent arthroscopy, the mass noted on MRI was removed. The histology was consistent with MO. The authors believe this to be the first case of MO in the intercondylar notch detected by MRI, treated by arthroscopy, and confirmed by histology.

Acceptable outcome following resection of bilateral large popliteal space heterotopic ossification masses in a spinal cord injured patient: a case report

Spinal cord injury is a well-known predisposing factor for development of heterotopic ossification around the joints especially hip and elbow. Heterotopic ossification about the knee is usually located medially, laterally or anteriorly; besides, the knee is generally fixed in flexion. There are only a few reports of heterotopic bone formation at the posterior aspect of the knee (popliteal space) and fixation of both knees in extension; so, there is little experience in operative management of such a problem.Here, we present a 39-years old paraplegic man who was referred to us five years after trauma with a request of above knee amputation due to sever impairment of his life style and adaptive capacity for daily living because of difficulties in using wheelchair. The principle reason for the impairment was fixed full extension of both knees as the result of bilateral large heterotopic ossification masses in popliteal fossae. The bony masses were surgically resected with acceptable outcome. The anatomic position of the ossified masses as well as ankylosis of both knees in full extension, and the acceptable functional outcome of surgery which was done after a long period of five years following injury makes this case unique.

Management of a massive stage IV sacral decubitus ulcer with anterior flap hip disarticulation and myocutaneous gastrocnemius fillet flap in-continuity

Severe sacral decubitus ulcers represent a common and often recalcitrant clinical problem in paralyzed or bedridden patients and require treatment strategies ranging from specialty beds and local wound care to aggressive debridement and local or free tissue flap coverage. This article presents the case of a young soldier who sustained severe injuries as a result of an improvised explosive device blast, including bilateral sciatic nerve injuries, sacrogluteal degloving, and severe left acetabular and femoral head fractures. The patient subsequently developed a recalcitrant stage IV sacral decubitus ulcer, left acetabular protrusio with minimal left lower extremity function, and ankylosis of the posterior right hip due to heterotopic ossification. A novel left anterior (quadriceps-based) hip disarticulation was performed with a double gastrocnemius myocutaneous fillet flap in-continuity. The procedure was successful in providing robust, partially sensate soft tissue coverage for the decubitus ulcer, permitting removal of the bridging posterior heterotopic ossification of the right hip, and removing the left hip for which reconstructive options were limited due to the absence of superior and inferior gluteal nerve function. The patient healed uneventfully and was subsequently able to resume unrestricted positioning for sitting and wheelchair mobilization and became a limited ambulator with a hip disarticulation prosthesis and contralateral ankle-foot orthosis.

Heterotopic ossification in systemic sclerosis

Although myopathy or myositis may occur in systemic sclerosis (SSc) as well as soft tissue calcification, ossification is not a feature of the disease. Here we present an unusual case of extended calcification and, to a lesser degree, ossification of the right gluteal region, lateral thigh, and knee, with associated myopathy and functional impairment. Heterotopic ossification (HO), or myositis ossificans, has not been reported so far in scleroderma patients, making this case, in our opinion, unique and interesting. However, differential diagnosis from other causes of extraskeletal ossification, such as tumours or tumour-like conditions, is required.

Serum after traumatic brain injury increases proliferation and supports expression of osteoblast markers in muscle cells

BACKGROUND

Traumatic brain injury is associated with an increased rate of heterotopic ossification within skeletal muscle, possibly as a result of humoral factors. In this study, we investigated whether cells from skeletal muscle adopt an osteoblastic phenotype in response to serum from patients with traumatic brain injury.

METHODS

Serum was collected from thirteen patients with severe traumatic brain injury, fourteen patients with a long-bone fracture, and ten control subjects. Primary cultures of skeletal muscle cells isolated from patients undergoing orthopaedic surgery were performed and characterized with use of immunofluorescence microscopy, reverse transcription-polymerase chain reaction, and Western blot analysis. Proliferation and osteoblastic differentiation were assessed with use of commercial cell assays, Western blot analysis (for Osterix protein), and the Villanueva bone stain.

RESULTS

All serum-treated cell populations expressed the osteoblast marker Osterix after one week in culture. Cells treated with serum from all study groups in mineralization medium had increased alkaline phosphatase activity and mineralized nodules within the mesenchymal cell subpopulation after three weeks in culture. Serum from patients with traumatic brain injury induced a significant increase (p = 0.02) in the rate of proliferation of primary skeletal muscle cells (1.87 [95% confidence interval, 1.66 to 2.09]) compared with the rate induced by serum from patients with a fracture (1.42 [95% confidence interval, 1.21 to 1.58]) or by serum from controls (1.35 [95% confidence interval, 1.15 to 1.54]).

CONCLUSIONS

Human serum supports the osteoblastic differentiation of cells derived from human skeletal muscle, and serum from patients with severe traumatic brain injury accelerates proliferation of these cells. These findings suggest the early presence of humoral factors following traumatic brain injury that stimulate the expansion of mesenchymal cells and osteoprogenitors within skeletal muscle.

Mutation Analysis and Prenatal Exclusion of Fibrodysplasia Ossificans Progressiva in a Chinese Fetus

Aims: Fibrodysplasia ossificans progressiva (FOP) is a rare and severely disabling autosomal dominant disorder characterized by congenital malformations of the great toes and progressive postnatal heterotopic ossification. A point mutation in the activin receptor IA (ACVR1) gene is the cause of FOP. Most of the reported cases of FOP are sporadic and caused by de novo mutations; however, some rare cases can also result from parental germline mosaicism associated with a greater risk of recurrence in successive pregnancies. Therefore, once the pathogenic mutation has been identified in the proband, it is relative cheaper and important to perform prenatal diagnostic tests to exclude the recurrence risk of FOP in subsequent pregnancies. In this study, we first investigated the mutation in the ACVR1 gene in a Chinese FOP patient and then performed prenatal tests to exclude the risk of recurrence in the patient's unborn sibling. Methods: A couple visited our clinic with their 4-year-old son, who was clinically diagnosed with FOP, for genetic counseling. Genetic testing was performed by amplifying all the nine exons of the ACVR1 gene using the conventional polymerase chain reaction. Further, DNA sequencing was used to determine the mutation based on the results of a mutation screening using denaturing high-performance liquid chromatography. Subsequently, a prenatal test was performed using the same technique as that used for the proband. Results: A recurrent single nucleotide mutation c.617 G>A (R206H) of the ACVR1 gene was identified in the patient; however, both the parents had a normal ACVR1 gene. Prenatal tests showed that the fetus did not carry the pathogenic mutation. Conclusion: The results confirmed that a recurrent single nucleotide mutation c.617 G>A (R206H) was the genetic cause of FOP and explored the utility of prenatal testing in excluding the risk of recurrence in the successive pregnancy.

Putative heterotopic ossification progenitor cells derived from traumatized muscle

Heterotopic ossification (HO) is a frequent complication following combat-related trauma, but the pathogenesis of traumatic HO is poorly understood. Building on our recent identification of mesenchymal progenitor cells (MPCs) in traumatically injured muscle, the goal of this study was to evaluate the osteogenic potential of the MPCs in order to assess the role of these cells in HO formation. Compared to bone marrow-derived mesenchymal stem cells (MSCs), a well-characterized population of osteoprogenitor cells, the MPCs exhibited several significant differences during osteogenic differentiation and in the expression of genes related to osteogenesis. Upon osteogenic induction, MPCs showed increased alkaline phosphatase activity, production of a mineralized matrix, and up-regulated expression of the osteoblast-associated genes CBFA1 and alkaline phosphatase. However, MPCs did not appear to reach terminal differentiation as the expression of osteocalcin was not substantially up-regulated. With the exception of a few genes, the osteogenic gene expression profile of traumatized muscle-derived MPCs was comparable to that of the MSCs after osteogenic induction. These findings indicate that traumatized muscle-derived MPCs have the potential to function as osteoprogenitor cells when exposed to the appropriate biochemical environment and are the putative osteoprogenitor cells that initiate ectopic bone formation in HO.

Reactive oxygen and nitrogen species induce protein and DNA modifications driving arthrofibrosis following total knee arthroplasty

Background

Arthrofibrosis, occurring in 3%-4% of patients following total knee arthroplasty (TKA), is a challenging condition for which there is no defined cause. The hypothesis for this study was that disregulated production of reactive oxygen species (ROS) and nitrogen species (RNS) mediates matrix protein and DNA modifications, which result in excessive fibroblastic proliferation.

Results

We found increased numbers of macrophages and lymphocytes, along with elevated amounts of myeloperoxidase (MPO) in arthrofibrotic tissues when compared to control tissues. MPO expression, an enzyme that generates ROS/RNS, is usually limited to neutrophils and some macrophages, but was found by immunohistochemistry to be expressed in both macrophages and fibroblasts in arthrofibrotic tissue. As direct measurement of ROS/RNS is not feasible, products including DNA hydroxylation (8-OHdG), and protein nitrosylation (nitrotyrosine) were measured by immunohistochemistry. Quantification of the staining showed that 8-OHdg was significantly increased in arthrofibrotic tissue. There was also a direct correlation between the intensity of inflammation and ROS/RNS to the amount of heterotopic ossification (HO). In order to investigate the aberrant expression of MPO, a real-time oxidative stress polymerase chain reaction array was performed on fibroblasts isolated from arthrofibrotic and control tissues. The results of this array confirmed the upregulation of MPO expression in arthrofibrotic fibroblasts and highlighted the downregulated expression of the antioxidants, superoxide dismutase1 and microsomal glutathione S-transferase 3, as well as the significant increase in thioredoxin reductase, a known promoter of cell proliferation, and polynucleotide kinase 3'-phosphatase, a key enzyme in the base excision repair pathway for oxidative DNA damage.

Conclusion

Based on our current findings, we suggest that ROS/RNS initiate and sustain the arthrofibrotic response driving aggressive fibroblast proliferation and subsequent HO.

The FOP metamorphogene encodes a novel type I receptor that dysregulates BMP signaling

The ability of mature organisms to stabilize phenotypes has enormous selective advantage across all phyla, but the mechanisms have been largely unexplored. Individuals with fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder of progressive heterotopic ossification, undergo a pathological metamorphosis in which one normal tissue is transformed into another through a highly regulated process of tissue destruction and phenotype reassignment. This disabling metamorphosis is mediated by the FOP metamorphogene, which encodes a mutant bone morphogenetic protein (BMP) type I receptor that exhibits mild constitutive activity during development and severe episodic dysregulation postnatally. The discovery of the FOP metamorphogene reveals a highly conserved target for drug development and identifies a fundamental defect in the BMP signaling pathway that when triggered by injury and inflammation transforms one tissue into another.

Heterotopic ossification following traumatic brain injury and spinal cord injury

Heterotopic ossification associated with neurologic injury, or neurogenic heterotopic ossification, tends to form at major synovial joints surrounded by spastic muscles. It is commonly associated with traumatic brain or spinal cord injury and with other causes of upper motor neuron lesions. Heterotopic ossification can result in a variety of complications, including nerve impingement, joint ankylosis, complex regional pain syndrome, osteoporosis, and soft-tissue infection. The associated decline in range of motion may greatly limit activities of daily living, such as positioning and transferring and maintenance of hygiene, thereby adversely affecting quality of life. Management of heterotopic ossification is aimed at limiting its progression and maximizing function of the affected joint. Nonsurgical treatment is appropriate for early heterotopic ossification; however, surgical excision should be considered in cases of joint ankylosis or significantly decreased range of motion before complications arise. Patient selection, timing of excision, and postoperative prophylaxis are important components of proper management.

Rarely occurring mutation of ACVR1 gene in Moroccan patient with fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP, MIM 135100) is a rare autosomal dominant disorder characterized by postnatal progressive heterotopic ossification of the connective tissue and congenital malformation of the big toes. Recently, FOP has been associated with a specific mutation of ACVR1, the gene coding for a bone morphogenetic protein type I receptor. We report the case of a Moroccan patient with FOP carrying a rarely occurring mutation of ACVR1 gene.

The Spectrum of Pediatric Fibroblastic and Myofibroblastic Tumors

Fibroblastic and myofibroblastic tumors in neonates, infants, and children provide a diagnostic dilemma in surgical pathology due to their relative rarity and similarity in appearances. These tumors may be congenital or occur early during the first years of life or later during the first and second decades of life. The morphologic, immunocytochemical, ultrastructural, cytogenetic, and molecular features of the more "common" pediatric fibroblastic and myofibroblastic tumors are reviewed. In addition, the importance of a multimodal approach to tumor diagnosis is emphasized, with correlation with treatment and outcome differences among these unique fibroblastic and myofibroblastic tumors. The importance of providing an accurate diagnosis with pediatric fibroblastic and myofibroblastic tumors cannot be overstated, because treatment, prognosis, follow-up, and outcome are based on the initial assessment of these fascinating, but oftentimes, perplexing tumors.

Dysregulation of local stem/progenitor cells as a common cellular mechanism for heterotopic ossification

Heterotopic ossification (HO), the abnormal formation of true marrow-containing bone within extraskeletal soft tissues, is a serious bony disorder that may be either acquired or hereditary. We utilized an animal model of the genetic disorder fibrodysplasia ossificans progressiva to examine the cellular mechanisms underlying HO. We found that HO in these animals was triggered by soft tissue injuries and that the effects were mediated by macrophages. Spreading of HO beyond the initial injury site was mediated by an abnormal adaptive immune system. These observations suggest that dysregulation of local stem/progenitor cells could be a common cellular mechanism for typical HO irrespective of the signal initiating the bone formation.

Mesenchymal progenitor cells derived from traumatized human muscle

Mesenchymal stem cells (MSCs) derived from adult tissues are an important candidate cell type for cell-based tissue engineering and regenerative medicine. Currently, clinical applications for MSCs require additional surgical procedures to harvest the autologous MSCs (i.e. from bone marrow) or commercial allogeneic alternatives. We have recently identified a population of mesenchymal progenitor cells (MPCs) in traumatized muscle tissue that has been surgically debrided from traumatic orthopaedic extremity wounds. The purpose of this study was to evaluate whether MPCs derived from traumatized muscle may provide a clinical alternative to bone-marrow MSCs, by comparing their morphology, proliferation capacity, cell surface epitope profile and differentiation capacity. After digesting the muscle tissue with collagenase, the MPCs were enriched by a direct plating technique. The morphology and proliferation rate of the muscle-derived MPCs was similar to bone-marrow derived MSCs. Both populations expressed cell surface markers characteristic for MSCs (CD 73, CD 90 and CD105), and did not express markers typically absent on MSCs (CD14, CD34 and CD45). After 21 days in specific differentiation media, the histological staining and gene expression of the MPCs and MSCs was characteristic for differentiation into osteoblasts, chondrocytes and adipocytes, but not into myoblasts. Our findings demonstrate that traumatized muscle-derived MPCs exhibit a similar phenotype and resemble MSCs derived from the bone marrow. MPCs harvested from traumatized muscle tissue may be considered for applications in tissue engineering and regenerative medicine following orthopaedic trauma requiring circumferential debridement.

Heterotopic ossification in high-energy wartime extremity injuries: prevalence and risk factors

BACKGROUND

Heterotopic ossification in the extremities remains a common complication in the setting of high-energy wartime trauma, particularly in blast-injured amputees and in those in whom the definitive amputation was performed within the zone of injury. The purposes of this cohort study were to report the experience of one major military medical center with high-energy wartime extremity wounds, to define the prevalence of heterotopic ossification in these patients, and to explore the relationship between heterotopic ossification and other potential independent predictors.

METHODS

We retrospectively reviewed the records and radiographs of all combat-wounded patients admitted to this institution between March 1, 2003, and December 31, 2006. Patients with a minimum of two months of radiographic follow-up who underwent at least one orthopaedic procedure on an extremity constituted our study group; those who underwent at least one orthopaedic procedure but had not had heterotopic ossification develop constituted the control group. Variables recorded for each study subject included age and sex, location and mechanism of injury, method(s) of fracture fixation, number of débridement procedures, duration of negative pressure therapy, location of heterotopic ossification, presence and severity of traumatic brain injury, and Injury Severity Scores.

RESULTS

During the study period, 1213 war-wounded patients were admitted. Of those patients, 243 (157 in the heterotopic ossification group and eighty-six controls) met the inclusion criteria. The observed rate of heterotopic ossification was 64.6%. A significant relationship was detected between heterotopic ossification and the presence (p = 0.006) and severity (p = 0.003) of a traumatic brain injury. Risk factors for the development of heterotopic ossification were found to be an age of less than thirty years (p = 0.007, odds ratio = 3.0), an amputation (p = 0.048, odds ratio = 2.9), multiple extremity injuries (p = 0.002, odds ratio = 3.9), and an Injury Severity Score of >or=16 (p = 0.02, odds ratio = 2.2).

CONCLUSIONS

The prevalence of heterotopic ossification in war-wounded patients is higher than that in civilian trauma. Although trends associated with local wound conditions were identified, the risk factors for the development of heterotopic ossification found in this study suggest that systemic causes predominate.