Heterotopic ossification: Pathophysiology, clinical features, and the role of radiotherapy for prophylaxis

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Risks of secondary malignancies with heterotopic bone radiation therapy for patients younger than 40 years

Heterotopic ossification (HO) of the bone is defined as a benign condition in which abnormal bone formation occurs in soft tissue. One of the most common prophylactic treatments for HO is radiation therapy (RT). This study retrospectively reviewed 20 patients younger than the age of 40 who received radiation to prevent HO in a single fraction of 7 Gray. The purpose of this study is to assess the risk of a second malignancy in these patients by recreating their treatment fields and contouring organs at risk to estimate the radiation dose absorbed by normal tissues outside the radiation treatment field. Diagnostic computed tomography (CT) scans for each patient were used to recreate treatment fields and to calculate dose to structures of interest. The distance from the field edge to each structure and its depth was recorded. Dose measurements in a water phantom were performed for the range of depths, distances, and field sizes used in the actual treatment plans. Computer-generated doses were compared to estimates based on measurement. The structure dose recorded was the higher dose generated between the 2 methods. Scatter dose was recorded to the rectum, bladder, sigmoid colon, small bowel, ovaries and utero-cervix in female patients, and prostate and gonads in male patients. In some patients, there is considerable dose received by certain organs from scatter because of their proximity to the radiation field. The average dose to the ovarian region was 4.125Gy with a range of 1.085 to 6.228Gy. The risk estimate for these patients ranged from 0.16% to 0.93%. The average total lifetime risk estimate for the bladder in all patients is 0.22% and the average total lifetime risk estimate for the remainder organs in all patients is 1.25%. In conclusions, proper shielding created from multileaf collimators (MLCs), blocks, and shields should always be used when possible.

Prevention of heterotopic ossification: an experimental study using a plasma expander in a murine model

Background

Heterotopic ossification (HO) is a frequent complication following orthopedic and trauma surgery. It often leads to substantial morbidity as many affected patients suffer from pain and joint contractures. Current prophylactic measures include nonsteroidal anti-inflammatory drugs (NSAID) and local radiation. However, several disadvantages such as delayed fracture healing and impaired ossification have been reported. For this reason, a novel approach for prevention of HO was searched for.

We hypothesized that systemic administration of hydroxyethyl starch (HES), a substance known to influence microcirculation, would reduce formation of HO in a murine model.

Methods

A pre-established murine model was used where HO has been shown to develop following Achilles tendon tenotomy. Twenty CD1 mice were randomly assigned to a control (n = 10) or treatment group (n = 10). The treatment group received two intravenous HES injections perioperatively, while the control group underwent tenotomy only. After ten weeks, the mice were euthanized and micro CT scans of the hind limbs were performed. HO was manually identified and quantitatively assessed. A Wilcoxon rank sum test was used for comparison of both groups.

Results

The mean heterotopic bone volume in the control group was significantly larger compared to the HES group (2.276 mm³ vs. 0.271 mm³, p = 0.005). A reduction of mean ectopic bone volume of 88 % was found following administration of HES.

Conclusion

A substantial reduction of HO formation was found following perioperative short-term administration of HES. This work represents a preliminary study, necessitating further studies before drawing ultimate conclusions. However, this simple addition to current prophylactic measures might lead to a more effective prevention of HO in the future.

Influence of Bone and Muscle Injuries on the Osteogenic Potential of Muscle Progenitors: Contribution of Tissue Environment to Heterotopic Ossification

: By using surgical mouse models, this study investigated how the tissue environment influences the osteogenic potential of muscle progenitors (m-progenitors) and potentially contributes to heterotopic ossification (HO). Injury was induced by clamping the gluteus maximus and medius (group M) or osteotomy of greater trochanter (group O) on the right hip, as well as combined muscle injury and osteotomy of greater trochanter (group M+O). The gluteus maximus and medius of the operated hips were harvested at days 1, 3, 5, and 10 for isolation of m-progenitors. The cells were cultured in an osteogenic medium for 3 weeks, and osteogenesis was evaluated by matrix mineralization and the expression of osteogenesis-related genes. The expression of type I collagen, RUNX2 (runt-related transcription factor 2), and osteocalcin by the m-progenitors of group M+O was significantly increased, compared with groups M and O. Osteogenic m-progenitors in group O increased the expression of bone morphogenetic protein 2 and also bone morphogenetic protein antagonist differential screening-selected gene aberrative in neuroblastoma. On histology, there was calcium deposition mostly in the muscles of group M+O harvested at day 10. CD56, representing myogenic progenitors, was highly expressed in the m-progenitors isolated from group M (day 10), but m-progenitors of group M+O (day 10) exhibited the highest expression of platelet-derived growth factor receptor α (PDGFR-α), a marker of muscle-derived mesenchymal stem cells (M-MSCs). The expressions of PDGFR-α and RUNX2 were colocalized in osteogenic m-progenitors. The data indicate that the tissue environment simulated in the M+O model is a favorable condition for HO formation. Most likely, M-MSCs, rather than myogenic progenitors, in the m-progenitors participate in HO formation.

SIGNIFICANCE

The prevalence of traumatic heterotopic ossification (HO) is high in war injury. The pathogenesis of HO is still unknown. This study clarified the contribution of a tissue environment created by bone or muscle injury to the formation of HO. The study also found that muscle-derived mesenchymal stem cells, but not myogenic progenitors, are involved in the formation of HO. The findings of this study could be used to strategize the prevention and treatment of HO.

Proinflammatory T cells and IL-17 stimulate osteoblast differentiation

The local immune response is important to consider when the aim is to improve bone regeneration. Recently T lymphocytes and their associated cytokines have been identified as regulators in fracture callus formation, but it is not known whether T cells affect bone progenitor cells directly. The goal of this in vitro study was to investigate the role of different T cell subsets and their secreted factors on the osteogenic differentiation of human mesenchymal stem cells (MSCs). Significant increases in the alkaline phosphatase activity and the subsequent matrix mineralization by MSCs were found after their exposure to activated T cells or activated T cell-derived conditioned medium. Blocking IFN-γ in the conditioned medium abolished its pro-osteogenic effect, while blocking TGF-β further enhanced osteogenesis. The relative contribution of an anti- or proinflammatory T cell phenotype in MSC osteogenic differentiation was studied next. Enrichment of the fraction of anti-inflammatory regulatory T cells had no beneficial osteogenic effect. In contrast, soluble factors derived from enriched T helper 17 cells upregulated the expression of osteogenic markers by MSCs. IL-17A, and IL-17F, their main proinflammatory cytokines, similarly exhibited strong osteogenic effects when exposed directly to MSCs. IL-17A in particular showed a synergistic action together with bone morphogenetic protein 2. These results indicate that individual T cell subsets, following their activation, affect osteoblast maturation in a different manner through the production of soluble factors. From all T cells, the proinflammatory T cells, including the T helper 17 cells, are most stimulatory for osteogenesis.

Severe heterotopic ossifications after Rockwood type II acromioclavicular joint injury: a case report

INTRODUCTION

Heterotopic ossification (HO) is a benign condition of abnormal bone formation in soft tissue. It is frequently asymptomatic, though it manifests as decreased range of motion in the affected joints that may occur in the shoulder after a substantial traumatic injury and can complicate the functional outcome of the affected upper extremity. However, severe HO is an extremely rare event following acromioclavicular joint (ACJ) injury.

MATERIALS AND METHODS

We are presenting a case of a 29-year-old male patient who had a trauma with resultant Rockwood type II injury. He subsequently complained of left shoulder pain with decreased range of motion 3 years later. HO was diagnosed after X-rays and the severity was assessed with a computerized tomography scan and magnetic resonance imaging. The patient was treated with a combination of pre-operative radiotherapy, surgical excision, mobilization under anesthesia, non-steroidal anti-inflammatory drug (NSAID) therapy and physiotherapy.

RESULTS

At 6-month follow-up, excellent clinical and radiological outcomes were achieved with a Constant score of 92 points, DASH score of 24%, and ASES score 100%, with a full range of motion of the left shoulder. Furthermore, there was no more radiological evidence of HO on plain radiographs.

CONCLUSION

Severe heterotopic ossification after a Rockwood type II ACJ injury in this case was successfully treated with combination of pre-operative radiotherapy, surgical excision and manipulation under anesthesia as well as NSAID therapy and physiotherapy.

Incidence and Clinical Significance of Heterotopic Ossification After Partial Ray Resection

Heterotopic bone growth is a common finding after partial foot amputation that can predispose to recurrent wounds, osteomyelitis, and reamputation. Heterotopic ossification is the formation of excessive mature lamellar bone in the soft tissues adjacent to bone that is exacerbated by trauma or surgical intervention. The relevance of heterotopic ossification is dependent on its anatomic location. Its occurrence as a sequela of partial foot amputation can lead to prominence on the plantar aspect of the foot that can predispose the patient to recurrent neuropathic ulceration or preclude appropriate wound healing. Reulceration puts the high-risk patient who has already undergone local amputation at greater risk of recurrent infection and further amputation. The present study aimed to assess the incidence and risk factors for heterotopic ossification to further evaluate its role in partial foot amputation. A retrospective analysis of 72 consecutive patients who had undergone partial metatarsal resection was performed, with 90% of the cohort having peripheral neuropathy and 88% diabetes mellitus. Our findings revealed a heterotopic ossification incidence of 75% diagnosed radiographically. The initial onset of heterotopic ossification was not appreciated >10 weeks postoperatively. Ten patients (18.5%) exhibited heterotopic ossification-associated ulceration. The incidence of heterotopic ossification was 30% less in patients with peripheral vascular disease. These results indicate that heterotopic ossification is a common sequela of partial ray resection in an already high-risk patient population. The perioperative use of pharmacologic or radiation prophylaxis in an attempt to minimize amputation-related morbidity should be considered.

Echinomycin did not affect the safety of fracture healing: an experimental pilot study on a murine femur fracture model

Background

There is a need for effective drugs in the prevention and treatment of heterotopic ossifications (HO) after fractures. Echinomycin has been shown to prevent formation of HO in an animal model. However, before it may be considered as an option against HO, it needs to be studied whether it prevents fracture healing similar to non-steroidal anti-inflammatory drugs (NSAIDS). Therefore, the hypothesis was that echinomycin prevents fracture healing and callus formation.

Methods

In an experimental murine pilot study, standard blunt femur fractures were induced and retrograde intramedullary compression fixation of the femur was performed. The treatment group (n = 8) received echinomycin (0.3 mg/kg body weight) and the control group (n = 8) did not receive echinomycin. The fractures and implant positions were verified by conventional X-rays immediately postoperatively. As the primary outcome variable, fracture healing (osseous consolidation) was evaluated by conventional X-rays and micro-computed tomography (CT) scans after ten weeks and graded as healed, partial or complete pseudarthrosis. The secondary outcome, callus formation, was graded semi-quantitatively from 0 (mostly absent) to 3 (maximum).

Results

Fracture healing was present in all living cases after ten weeks concerning the treatment group. Partial pseudarthrosis was seen in two cases, one in the treatment and another one in the control group. Complete pseudarthrosis was seen in one case of the control group after an open fracture. Callus formation was similar in both groups with a mean grade of 1.5 within each group. Two cases of the treatment group died.

Conclusion

As a novel finding, echinomycin did not inhibit fracture healing or callus formation in this in vivo murine standard femur fracture model pilot study. Further studies involving a larger number of cases, quantitative assessment with CT scans and histopathological analysis are needed before generalizing the results of this pilot study.

Cell death, clearance and immunity in the skeletal muscle

The skeletal muscle is an immunologically unique tissue. Leukocytes, virtually absent in physiological conditions, are quickly recruited into the tissue upon injury and persist during regeneration. Apoptosis, necrosis and autophagy coexist in the injured/regenerating muscles, including those of patients with neuromuscular disorders, such as inflammatory myopathies, dystrophies, metabolic and mitochondrial myopathies and drug-induced myopathies. Macrophages are able to alter their function in response to microenvironment conditions and as a consequence coordinate changes within the tissue from the early injury throughout regeneration and eventual healing, and regulate the activation and the function of stem cells. Early after injury, classically activated macrophages ('M1') dominate the picture. Alternatively activated M2 macrophages predominate during resolution phases and regulate the termination of the inflammatory responses. The dynamic M1/M2 transition is increasingly felt to be the key to the homeostasis of the muscle. Recognition and clearance of debris originating from damaged myofibers and from dying stem/progenitor cells, stromal cells and leukocytes are fundamental actions of macrophages. Clearance of apoptotic cells and M1/M2 transition are causally connected and represent limiting steps for muscle healing. The accumulation of apoptotic cells, which reflects their defective clearance, has been demonstrated in various tissues to prompt autoimmunity against intracellular autoantigens. In the muscle, in the presence of type I interferon, apoptotic myoblasts indeed cause the production of autoantibodies, lymphocyte infiltration and continuous cycles of muscle injury and regeneration, mimicking human inflammatory myopathies. The clearance of apoptotic cells thus modulates the homeostatic response of the skeletal muscle to injury. Conversely, defects in the process may have deleterious local effects, guiding maladaptive tissue remodeling with collagen and fat accumulation and promoting autoimmunity itself. There is strong promise for novel treatments based on new knowledge of cell death, clearance and immunity in the muscle.

Effect of Naproxen Prophylaxis on Heterotopic Ossification Following Hip Arthroscopy: A Double-Blind Randomized Placebo-Controlled Trial

BACKGROUND

Heterotopic ossification (HO) is a known complication of hip arthroscopy. Our objective was to determine the effect of postoperative naproxen therapy on the development of HO following arthroscopic surgery for femoroacetabular impingement.

METHODS

Between August 2011 and April 2013, 108 eligible patients were enrolled and randomized to take naproxen or a placebo for three weeks postoperatively. Radiographs were made at routine follow-up visits for one year following surgery. The primary outcome measure was the development of HO, as classified with the Brooker criteria and two-dimensional measurements on radiographs made at least seventy-five days postoperatively (average, 322 days). The primary analysis, performed with a Fisher exact test, compared the proportion of subjects with HO between the treatment and control groups. A single a priori interim analysis was planned at the midpoint of the study.

RESULTS

Our data safety and monitoring board stopped this study when the interim analysis showed that the stopping criterion had been met for demonstration of efficacy of the naproxen intervention. The prevalence of HO was 46% (twenty-two of the forty-eight in the final analysis) in the placebo group versus 4% (two of forty-eight) in the naproxen group (p < 0.001). Medication compliance was 69% overall, but it did not differ between the naproxen and placebo groups. Minor adverse reactions to the study medications were reported in 42% of the patients taking naproxen versus 35% of those taking the placebo (p = 0.45).

CONCLUSIONS

In this trial, prophylaxis with naproxen was effective in reducing the prevalence of HO without medication-related morbidity.

[The principles of pharmacotherapy of poststroke shoulder pain]

AIM

To analyze the results of examination and treatment of patients with poststroke shoulder pain.

MATERIAL AND METHODS

The study included 213 patients who have had a stroke, including 16.4% patients with poststroke shoulder pain in early recovery period and 35.9% patients with poststroke shoulder pain in late recovery period. Therapeutic efficacy of amitriptyline, lidocaine (intravenously), pregabalin, tizanidine and non-steroid anti-inflammatory drugs was assessed.

RESULTS AND CONCLUSION

Dysfunction of nervous system plays the main role in this pain syndrome. The efficacy of the drugs in the early/late recovery period was estimated as follows: nonsteroidal anti-inflammatory drugs - 33%/12%, amitriptyline - 24%/42%, gabapentin - 10%/13%, lidocaine - 95%/100%, tizanidine - 29%/33%. Seventy-six percent of patients were free of pain after treatment using a regimen suggested by the authors.

Current therapeutic strategies of heterotopic ossification--a survey amongst orthopaedic and trauma departments in Germany

Background

Heterotopic ossification (HO) is a complication after tissue trauma, fracture and surgery (i.e. total hip arthroplasty). Prophylaxis is the most effective therapy. If HO formations become symptomatic and limit patients’ quality of life, revision surgery is indicated and is usually combined with a perioperative oral prophylaxis (NSAIDs) and/or irradiation. However, a long-term use of NSAIDs can induce gastro-intestinal or cardiac side-effects and possible bony non-unions during fracture healing. Subject of this study was to assess the current status of HO prophylaxis after injuries or fractures and to evaluate current indications and strategies for excision of symptomatic HO.

Methods

Between 2013 and 2014, a questionnaire was sent to 119 orthopaedic and trauma surgery departments in Germany. Participation was voluntary and all acquired data was given anonymously.

Results

The cumulative feedback rate was 71 %. Trauma and orthopaedic surgery departments in Germany recommend oral HO prophylaxis after acetabulum and femoral neck fractures, elbow dislocation, and fracture or dislocation of the radial head. Pain upon movement and an increasing loss of range of motion in the affected joint are considered to be clear indications for HO surgery. A partial removal of ROM-limiting HO formations was also considered important. The vast majority of all departments include perioperative oral HO prophylaxis and/or irradiation if surgical HO removal is planned. The choice and duration of NSAIDs is highly variable.

Conclusion

HO is of clinical significance in current traumatology and orthopaedics. Certain fractures and injuries are prone to HO, and prophylactic measures should be taken. The respondents in this survey assessed current therapeutic strategies for HO formations similarly. These concepts are in line with the literature. However, the duration of perioperative oral HO prophylaxis varied greatly among the specialist centres. This is significant as a long-term use of NSAIDs fosters a potential risk for the patients’ safety and could influence the clinical outcome. National and international guidelines need to be developed to further reduce HO rates and improve patients’ safety in trauma and orthopaedic surgery.

Incidence and risk factors for heterotopic ossification after total hip arthroplasty: a meta-analysis

BACKGROUND

This study aims to quantitatively summarize risk factors associated with heterotopic ossification after total hip arthroplasty.

METHODS

The computerized and additional manual searches were performed in Medline, Embase, CNKI, and Cochrane central database (all through March 2014) for potential studies. Studies eligible had to meet the quality assessment criteria by Newcastle-Ottawa Scale and to evaluate the risk factors for heterotopic ossification after total hip arthroplasty. Two reviewers independently extracted the relevant data and any disagreement was solved by consensus. Stata11.0 was used to perform all the statistical analyses.

RESULTS

Fourteen studies involving 6468 cases with total hip arthroplasty and 1939 heterotopic ossification (HOs) (30.0 %) were eligible and included in this meta-analysis. Our meta-analysis identified the significant increased risk factors for HO were male gender [odds ratio (OR) 2.11; 95 % confidence interval (CI) 1.80-2.48)], cemented implant (OR 1.48; 95 % CI 1.00-2.17), bilateral operations (OR 1.74; 95 % CI 1.24-2.45), ankylosing spondylitis (OR 1.90; 95 % CI 1.07-3.37) and ankylosed hip (OR 9.85; 95 % CI 2.61-37.24). Rheumatoid arthritis was protective for the development of HO (OR 0.51; 95 % CI 0.33-0.80). The other variables including age, use of NSAIDs, femoral neck fracture, previous hip fracture, hypertrophic osteoarthritis and osteophytes were identified not as the risk factors for development of HO (P > 0.05).

CONCLUSION

Patients involved with the above-mentioned medical conditions should be carefully paid close attention by surgeons to reduce HO after total hip arthroplasty.

LEVEL OF EVIDENCE

Level II, meta-analysis.

Influence of transcutaneous electrical stimulation on heterotopic ossification: an experimental study in Wistar rats

Heterotopic ossification (HO) is a metaplastic biological process in which there is newly formed bone in soft tissues, resulting in joint mobility deficit and pain. Different treatment modalities have been tried to prevent HO development, but there is no consensus on a therapeutic approach. Since electrical stimulation is a widely used resource in physiotherapy practice to stimulate joint mobility, with analgesic and anti-inflammatory effects, its usefulness for HO treatment was investigated. We aimed to identify the influence of electrical stimulation on induced HO in Wistar rats. Thirty-six male rats (350-390 g) were used, and all animals were anesthetized for blood sampling before HO induction, to quantify the serum alkaline phosphatase. HO induction was performed by bone marrow implantation in both quadriceps of the animals, which were then divided into 3 groups: control (CG), transcutaneous electrical nerve stimulation (TENS) group (TG), and functional electrical stimulation (FES) group (FG) with 12 rats each. All animals were anesthetized and electrically stimulated twice per week, for 35 days from induction day. After this period, another blood sample was collected and quadriceps muscles were bilaterally removed for histological and calcium analysis and the rats were killed. Calcium levels in muscles showed significantly lower results when comparing TG and FG (P<0.001) and between TG and CG (P<0.001). Qualitative histological analyses confirmed 100% HO in FG and CG, while in TG the HO was detected in 54.5% of the animals. The effects of the muscle contractions caused by FES increased HO, while anti-inflammatory effects of TENS reduced HO.

Proinflammatory Mediators Enhance the Osteogenesis of Human Mesenchymal Stem Cells after Lineage Commitment

Several inflammatory processes underlie excessive bone formation, including chronic inflammation of the spine, acute infections, or periarticular ossifications after trauma. This suggests that local factors in these conditions have osteogenic properties. Mesenchymal stem cells (MSCs) and their differentiated progeny contribute to bone healing by synthesizing extracellular matrix and inducing mineralization. Due to the variation in experimental designs used in vitro, there is controversy about the osteogenic potential of proinflammatory factors on MSCs. Our goal was to determine the specific conditions allowing the pro-osteogenic effects of distinct inflammatory stimuli. Human bone marrow MSCs were exposed to tumor necrosis factor alpha (TNF-α) and lipopolysaccharide (LPS). Cells were cultured in growth medium or osteogenic differentiation medium. Alternatively, bone morphogenetic protein 2 (BMP-2) was used as osteogenic supplement to simulate the conditions in vivo. Alkaline phosphatase activity and calcium deposition were indicators of osteogenicity. To elucidate lineage commitment-dependent effects, MSCs were pre-differentiated prior treatment. Our results show that TNF-α and LPS do not affect the expression of osteogenic markers by MSCs in the absence of an osteogenic supplement. In osteogenic differentiation medium or together with BMP-2 however, these mediators highly stimulated their alkaline phosphatase activity and subsequent matrix mineralization. In pre-osteoblasts, matrix mineralization was significantly increased by these mediators, but irrespective of the culture conditions. Our study shows that inflammatory factors potently enhance the osteogenic capacity of MSCs. These properties may be harnessed in bone regenerative strategies. Importantly, the commitment of MSCs to the osteogenic lineage greatly enhances their responsiveness to inflammatory signals.

Postencephalitic bilateral heterotopic ossification of the hip in a pediatric patient

Heterotrophic ossification has been defined as abnormal formation of mature lamellar bone in soft tissues. Neurogenic heterotopic ossification has been well described in adults. However, it is uncommon in the pediatric population, where it has been noted to recede in some cases. There are very few reports of postmeningitis bilateral involvement of the hip. We describe a case of bilateral heterotopic ossification of hip in a 13-year-old female. The patient had a history of encephalitis, prolonged vegetative state, and intubation for 6 weeks. The patient had fixed deformities of both hips in 30° of flexion and 30° of external rotation. A diagnosis of Brooker stage 4 heterotopic ossification was made. The patient underwent a staged procedure for excision of the heterotopic mass. Postoperatively, the patient was administered radiotherapy and indomethacin for 6 weeks. At the 2-year follow-up, there was no recurrence and both the hips were mobile with full range of motion. The patient was satisfied with the result. The incidence of heterotopic ossification is less than that observed in the adult population and alkaline phosphatase levels are not significantly elevated unlike in adults. To our knowledge, there is no reported case of postencephalitic bilateral anterior heterotopic ossification of the hip in a pediatric patient treated with excision successfully. Postencephalitic heterotopic ossification in children is an uncommon condition. This condition can be treated successfully with surgical excision, combined postoperative protocol of radiotherapy, indomethacin, and immediate postoperative mobilization of the joint.

Heterotopic Ossification: Basic-Science Principles and Clinical Correlates

➤ Heterotopic ossification occurs most commonly after joint arthroplasty, spinal cord injury, traumatic brain injury, blast trauma, elbow and acetabular fractures, and thermal injury.➤ The conversion of progenitor cells to osteogenic precursor cells as a result of cell-mediated interactions with the local tissue environment is affected by oxygen tension, pH, availability of micronutrients, and mechanical stimuli, and leads to heterotopic ossification.➤ Radiation and certain nonsteroidal anti-inflammatory medications are important methods of prophylaxis against heterotopic ossification.➤ Well-planned surgical excision can improve patient outcomes regardless of the joint involved or the initial cause of injury.➤ Future therapeutic strategies are focused on targeted inhibition of local factors and signaling pathways that catalyze ectopic bone formation.

Management of shoulder pain after a cerebrovascular accident or traumatic brain injury

BACKGROUND

Shoulder pain after a cerebrovascular accident or traumatic brain injury is a common but often under-recognized problem. It is due to a number of causes including inferior subluxation, spasticity, adhesive capsulitis, and heterotopic ossification. Many of these are amenable to surgical intervention.

METHODS

Literature review of current evidence.

RESULTS

This article shows that there are multiple treatment options in this group of patients, and it is important to understand these as clinicians in delivering quality care to this complex group of patients.

CONCLUSION

This review article describes how careful clinical assessment can differentiate between causes of shoulder pain and guide best management.

Troublesome heterotopic ossification and stroke: Features and risk factors. A case control study

PRIMARY OBJECTIVE

To determine the features of stroke-related HO in a large sample of patients and to assess if HO risk is increased by haemorrhagic stroke.

RESEARCH DESIGN

A case control study (risk factor of a rare event using retrospective analysis).

METHODS AND PROCEDURES

Sixty-one patients with stroke-81 troublesome HOs-were included, each was matched with four controls, i.e. 244 patients with no HO after stroke. Matching criteria were age (±3.5 years) and sex. Data recorded were time from stroke to surgery, ischaemic or haemorrhagic stroke and presence of HO risk factors.

MAIN OUTCOMES AND RESULTS

Mean age at time of stroke = 46.02 ± 11.4 years (15.9-76.3) for the case sub-group. Time from stroke to surgery = 23.4 ± 27.8 months (3.6-150.0). There was a significant relationship between haemorrhagic stroke and HO development (OR = 3.01; 95% CI = 1.14-7.98; p < 0.05), but not for ischaemic stroke. This became non-significant when all matching and risk factors were included in the model (adjusted OR = 1.98; 95% CI = 0.60-6.54; p = 0.26).

CONCLUSION

Haemorrhagic stroke appears to increase the risk of HO development. Further studies are required to determine if this risk factor is independent from other comorbid factors.

Radiation therapy for recurrent heterotopic ossification prophylaxis after partial metatarsal amputation

The formation of heterotopic ossification is a relatively common, yet rarely discussed, cause of re-ulceration after previous partial metatarsal amputation. Excessive bone growth at the amputation site has the potential to create an unwanted prominence on the weightbearing surface of the foot, intuitively increasing plantar pressure and placing the neuropathic patient at greater risk of re-ulceration and limb loss. The aim of the present study was to assess the efficacy of single-dose radiation therapy in preventing recurrent heterotopic ossification. The inclusion criteria consisted of a history of clinically relevant heterotopic ossification formation after partial metatarsal amputation with subsequent partial metatarsal amputation for heterotopic ossification resection, followed by prophylactic single-dose radiation therapy. Eleven consecutive patients meeting the inclusion criteria were identified for the present study. Before the intervention, 10 (91%) patients demonstrated formation of mid- to high-grade heterotopic ossification, and 9 (82%) patients exhibited an associated neuropathic ulceration. On follow-up at least 6 weeks after intervention, 2 (18%) patients exhibited low-grade heterotopic ossification reformation that was not clinically relevant and 9 (82%) did not show signs of heterotopic recurrence. Single-dose radiation therapy can help prevent the formation of heterotopic ossification in high-risk patients, acting as an effective adjunct to surgery in minimizing the risk of re-ulceration and re-amputation in the neuropathic patient.

The impact of race on the development of severe heterotopic ossification following acetabular fracture surgery

OBJECTIVES

To determine the association between race on severe heterotopic ossification (HO) following acetabular fracture surgery.

DESIGN

Retrospective case control study.

SETTING

Level I university trauma centre.

METHODS

Two hundred and fifty-three patients who were surgically treated for acetabular fractures were retrospectively evaluated. Postoperative radiographs were evaluated for HO by a blinded musculoskeletal radiologist, and classified based on a modified Brooker classification.

RESULTS

Of the 253 patients that met inclusion and exclusion criteria, 175 (69%) were male and 78 (31%) were female. One hundred and fifty-four (61%) patients were Caucasian, and 99 (39%) were African American (AA). Fifty-five (21%) patients developed severe HO. Of those who developed severe HO, 25 were Caucasian (45%), 30 were African American (55%). Forty-one patients (75%) with severe HO were male, and 14 (25%) were female. No statistical differences (p>0.05) were found between groups in terms of age, days to surgery, GCS at presentation, surgical approach, perioperative HO prophylaxis, or AO/OTA fracture classification. The patient population was then stratified by race, gender, and race/gender. AA were more likely than Caucasians to develop severe HO (odds ratio [OR], 2.24; confidence interval [CI], 1.22-4.11). When gender was considered independent of race, no statistical differences (p>0.05) were observed (OR, 1.40; CI, 0.71-2.75). AA males were much more likely to develop severe HO when compared to Caucasian females (OR, 4.4; CI, 1.38-14.06).

CONCLUSION

Race is associated with different rates of severe HO formation following acetabular fracture surgery. AA patients are significantly more likely to develop severe HO following acetabular fracture surgery when compared to Caucasian patients.

High-dose-rate brachytherapy for the treatment of recalcitrant keloids: a unique, effective treatment protocol

BACKGROUND

Keloids cause aesthetic disfigurement and physical complaints, mainly pain and pruritus. Treatment of these scars is difficult, with high recurrence rates forming the main issue. Surgical excision with adjuvant radiotherapy is considered the most efficacious treatment. At their institution, the authors have been treating keloids with a high-dose-rate brachytherapy procedure for over 10 years, using a protocol with the lowest total radiation dosage known in the literature.

METHODS

This prospective study included 43 patients of all Fitzpatrick skin types, with 67 keloids in total. After extralesional excision, a radiation scheme of 2 × 6 Gy was administered in two fractions: the first within 4 hours after surgery and the second within 24 hours. Scars were measured and recurrence was judged. Scar appearance was evaluated using the Patient and Observer Scar Assessment Scale.

RESULTS

The recurrence rate was 3.1 percent at a mean follow-up of 33.6 months. A significant average scar surface decrease of 56.7 percent was measured (p = 0.01). Complaints of pain and pruritus decreased by 82.9 and 87.2 percent, respectively. Patients were satisfied with the treatment in 88.6 percent of the cases and with the cosmetic result in 77.1 percent. Pigmentation problems were seen in 21.4 percent of the patients, mostly in Fitzpatrick type V and VI/African American individuals.

CONCLUSIONS

The results of this prospective study show a good cosmetic outcome with a low recurrence rate. The unique radiation schedule proves the efficacy and safety of high-dose-rate brachytherapy and suggests the importance of immediate postoperative irradiation. In addition, only one outpatient treatment is required after surgery, enhancing patient convenience.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Outside the inside: a review of soft-tissue abnormalities seen on thoracoabdominal computed tomography

In this review, we illustrate the computed tomographic features of thoracoabdominal soft-tissue abnormalities, which may be easily overlooked and often can provide important information regarding systemic processes. Examples include necrotizing fasciitis, heterotopic ossification, fat necrosis, benign and malignant neoplasms, endometriosis, and collagen vascular disease as well as systemic and congenital pathology.

Risk of radiation-induced malignancy with heterotopic ossification prophylaxis: a case-control analysis

PURPOSE

To determine the risk of radiation-induced malignancy after prophylactic treatment for heterotopic ossification (HO).

METHODS AND MATERIALS

A matched case-control study was conducted within a population-based cohort of 3489 patients treated either for acetabular fractures with acetabular open reduction internal fixation or who underwent total hip arthroplasty from 1990 to 2009. Record-linkage techniques identified patients who were diagnosed with a malignancy from our state health registry. Patients with a prior history of malignancy were excluded from the cohort. For each documented case of cancer, 2 controls were selected by stratified random sampling from the cohort that did not develop a malignancy. Matching factors were sex, age at time of hip treatment, and duration of follow-up.

RESULTS

A total of 243 patients were diagnosed with a malignancy after hip treatment. Five patients were excluded owing to inadequate follow-up time in the corresponding control cohort. A cohort of 238 cases (control, 476 patients) was included. Mean follow-up was 10 years, 12 years in the control group. In the cancer cohort, 4% of patients had radiation therapy (RT), compared with 7% in the control group. Of the 9 patients diagnosed with cancer after RT, none occurred within the field. The mean latency period was 5.9 years in the patients who received RT and 6.6 years in the patients who did not. Median (range) age at time of cancer diagnosis in patients who received RT was 62 (43-75) years, compared with 70 (32-92) years in the non-RT patients. An ad hoc analysis was subsequently performed in all 2749 patients who were not matched and found neither an increased incidence of malignancy nor a difference in distribution of type of malignancy.

CONCLUSION

We were unable to demonstrate an increased risk of malignancy in patients who were treated with RT for HO prophylaxis compared with those who were not.

Cancer risk estimates from radiation therapy for heterotopic ossification prophylaxis after total hip arthroplasty

PURPOSE

Heterotopic ossification (HO) is a frequent complication following total hip arthroplasty. This study was conducted to calculate the radiation dose to organs-at-risk and estimate the probability of cancer induction from radiotherapy for HO prophylaxis.

METHODS

Hip irradiation for HO with a 6 MV photon beam was simulated with the aid of a Monte Carlo model. A realistic humanoid phantom representing an average adult patient was implemented in Monte Carlo environment for dosimetric calculations. The average out-of-field radiation dose to stomach, liver, lung, prostate, bladder, thyroid, breast, uterus, and ovary was calculated. The organ-equivalent-dose to colon, that was partly included within the treatment field, was also determined. Organ dose calculations were carried out using three different field sizes. The dependence of organ doses upon the block insertion into primary beam for shielding colon and prosthesis was investigated. The lifetime attributable risk for cancer development was estimated using organ, age, and gender-specific risk coefficients.

RESULTS

For a typical target dose of 7 Gy, organ doses varied from 1.0 to 741.1 mGy by the field dimensions and organ location relative to the field edge. Blocked field irradiations resulted in a dose range of 1.4-146.3 mGy. The most probable detriment from open field treatment of male patients was colon cancer with a high risk of 564.3 × 10(-5) to 837.4 × 10(-5) depending upon the organ dose magnitude and the patient's age. The corresponding colon cancer risk for female patients was (372.2-541.0) × 10(-5). The probability of bladder cancer development was more than 113.7 × 10(-5) and 110.3 × 10(-5) for males and females, respectively. The cancer risk range to other individual organs was reduced to (0.003-68.5) × 10(-5).

CONCLUSIONS

The risk for cancer induction from radiation therapy for HO prophylaxis after total hip arthroplasty varies considerably by the treatment parameters, organ site in respect to treatment volume and patient's gender and age. The presented risk estimates may be useful in the follow-up studies of irradiated patients.

Roles of nonmyogenic mesenchymal progenitors in pathogenesis and regeneration of skeletal muscle

Adult skeletal muscle possesses a remarkable regenerative ability that is dependent on satellite cells. However, skeletal muscle is replaced by fatty and fibrous connective tissue in several pathological conditions. Fatty and fibrous connective tissue becomes a major cause of muscle weakness and leads to further impairment of muscle function. Because the occurrence of fatty and fibrous connective tissue is usually associated with severe destruction of muscle, the idea that dysregulation of the fate switch in satellite cells may underlie this pathological change has emerged. However, recent studies identified nonmyogenic mesenchymal progenitors in skeletal muscle and revealed that fatty and fibrous connective tissue originates from these progenitors. Later, these progenitors were also demonstrated to be the major contributor to heterotopic ossification in skeletal muscle. Because nonmyogenic mesenchymal progenitors represent a distinct cell population from satellite cells, targeting these progenitors could be an ideal therapeutic strategy that specifically prevents pathological changes of skeletal muscle, while preserving satellite cell-dependent regeneration. In addition to their roles in pathogenesis of skeletal muscle, nonmyogenic mesenchymal progenitors may play a vital role in muscle regeneration by regulating satellite cell behavior. Conversely, muscle cells appear to regulate behavior of nonmyogenic mesenchymal progenitors. Thus, these cells regulate each other reciprocally and a proper balance between them is a key determinant of muscle integrity. Furthermore, nonmyogenic mesenchymal progenitors have been shown to maintain muscle mass in a steady homeostatic condition. Understanding the nature of nonmyogenic mesenchymal progenitors will provide valuable insight into the pathophysiology of skeletal muscle. In this review, we focus on nonmyogenic mesenchymal progenitors and discuss their roles in muscle pathogenesis, regeneration, and homeostasis.

Heterotopic ossification of the quadratus lumborum muscle

Heterotopic ossification is a benign process of mature laminar bone formation in the soft tissues. A synonymous term used to describe this pathology in muscle is myositis ossificans. The pathogenesis is unclear, but is likely multifactorial. The basic pathology is thought to be ectopic production of osseous tissue as part of a repair process in response to tissue injury. This report describes a case of heterotopic ossification of the quadratus lumborum muscle as an incidental finding. This case highlights that treatment is based on symptoms and conservative management might be appropriate for the asymptomatic patient.

Palliative hip surgery in severe cerebral palsy: a systematic review

We performed a systematic review of the results of palliative hip surgery in severe cerebral palsy. Individuals with severe cerebral palsy frequently suffer from pain and other impairments because of dislocation or malformation of the hips. When preventive or reconstructive surgery fails, palliative intervention is performed. A number of salvage interventions have been described. We found articles on resection surgery of the femoral head, arthrodesis of the hip joint, and total hip replacement. The published literature does not clearly favor one procedure over the others. The resection arthroplasty technique developed by Castle is reported to yield the best results and fewer complications, and seems to eventually lead to a good outcome.

Radiotherapy for prevention of heterotopic ossification of the elbow: a systematic review of the literature

BACKGROUND

Heterotopic ossification is a pathological process characterized by abnormal formation of bone in nonskeletal tissue. Radiotherapy for heterotopic ossification of the elbow is questionable because of possible adverse effects.

METHODS

A systematic review of the literature was conducted in MEDLINE, Scopus, ISI Web of Science, National Institute for Health and Clinical Excellence, National Guideline Clearinghouse, System for Information on Grey Literature in Europe, ClinicalTrials.gov, Cochrane Central Register of Clinical Trials, and Cochrane Database of Systematic Reviews up to April 2012. All published articles assessing interventions including radiotherapy for prevention of heterotopic ossification in the elbow of adult patients were considered. Information was recorded by the first two authors, and disagreements in interpretation were resolved by consensus.

RESULTS

In total, 27 studies using radiotherapy for elbow heterotopic ossification were identified (1 randomized clinical trial, 1 case-control study, and 25 case reports and case series) in the literature. Most of them used a single dose of 7.0 Gy. The randomized clinical trial was stopped early because of severe adverse effects (pseudarthrosis) caused by radiation. The case-control study showed that radiotherapy did not effectively prevent recurrence of heterotopic ossification. The case reports and case series mentioned only sparse adverse events.

CONCLUSION

The use of radiation therapy for prevention of heterotopic ossification of the elbow is supported by weak evidence.

Computerized tomography-based radiotherapy improves heterotopic ossification outcomes

PURPOSE

To report the impact of computerized tomography (CT) based radiotherapy (RT) on heterotopic ossification (HO) outcomes.

METHODS

This is a single institution, retrospective study of 532 patients who were treated for traumatic acetabular fractures (TAF). All patients underwent open-reduction internal-fixation (ORIF) of the TAF followed by RT for HO prophylaxis. Postoperative RT was delivered within 72h, in a single fraction of 7Gy. The patients were divided into 2 groups based on RT planning: CT (A) vs. clinical setup (B).

RESULTS

At a median follow up of 8years the incidence of HO was 21.6%. Multivariate regression analysis revealed that group (A) vs. (B) had HO incidence of 6.6% vs. 24.6% (p<0.001), respectively. Furthermore, HO Brooker grade ≥3 was observed in 2.2% vs. 10.8% (p=0.007) in group (A) vs. (B), respectively. Thus, the odds of developing HO and Brooker grades ≥3 were 4.7 and 4.5 times higher, respectively, in patients who underwent clinical setup.

CONCLUSION

Our data suggest that using CT based RT allowed more accurate delineation of the tissues and better clinical outcomes. Although CT-based RT is associated with additional cost the efficacy of CT-based RT reduces the risk of HO, thereby decreasing the need for additional surgical interventions.

A postconization hematometra revealed a rare case of endocervical bone metaplasia

BACKGROUND

Hematometra is an unusual occurrence in young women undergoing conization; moreover, osseous metaplasia of the uterine cervix is a very rare event, with 7 cases in the literature. A postconization hematometra due to endocervical ossification is a unique occurrence. The authors report such an event.

CASE

A young woman undergoing conization developed progressive hypoamenorrhea with pelvic pain. Pregnancy test was negative and a transvaginal ultrasound showed an image of suspected hematometra. Diagnostic hysteroscopy showed an endocervical obstruction due to a bone formation of the uterine cervix, which was removed with an office operative hysteroscopy. After surgery, the patient restored normal menstrual cycle. Histological examination revealed a cervical bone metaplasia.

CONCLUSIONS

In premenopausal women undergoing conization, the appearance of a progressive hypoamenorrhea with pelvic pain could suggest a cervical mechanical obstruction that could be an uncommon stenosis. Despite this case represents a very rare event, a postconization hematometra due to an endocervical ossification can be managed with an office operative hysteroscopy.

Preoperative irradiation for the prevention of heterotopic ossification induces local inflammation in humans

Radiation of the hip is an established method to prevent heterotopic ossification (HO) following total hip arthroplasty (THA) but the precise mechanism is unclear. As inflammatory processes are suggested to be involved in the pathogenesis of HO, we hypothesized that the preoperative irradiation impacts local immune components. Therefore, we quantified immune cell populations and cytokines in hematomas resulting from the transection of the femur in two groups of patients receiving THA: patients irradiated preoperatively (THA-X-hematoma: THA-X-H group) in the hip region (7 Gy) in order to prevent HO and patients who were not irradiated (THA-H group) but were postoperatively treated with non-steroidal anti-inflammatory drugs (NSAIDs). Radiation resulted in significantly increased frequencies of T cells, cytotoxic T cells, NKT cells and CD25+CD127- Treg cells, whereas the number of naive CD45RA-expressing cytotoxic T cells was reduced. These results indicate differential immune cell activation, corroborated by our findings of significantly higher concentrations of pro-inflammatory cytokines (e.g., IL-6, IFNγ) and chemokines (e.g., MCP-1, RANTES) in the THA-X-H group as compared to THA-H group. In contrast, the concentration of the angiogenic VEGF was significantly suppressed in the THA-X-H group. We conclude that preoperative irradiation results in significant changes in immune cell composition and cytokine secretion in THA-hematomas, establishing a specific - rather proinflammatory - milieu. This increase of inflammatory activity together with the observed suppression in VEGF secretion may contribute to the prevention of HO.

Heterotopic ossification of the shoulder after central nervous system lesion: indications for surgery and results

BACKGROUND

Heterotopic ossification (HO) of the shoulder after central nervous system damage has seldom been studied.

MATERIALS AND METHODS

We performed a single-center retrospective study from 1993 to 2009 including patients who underwent surgery for troublesome shoulder HO. Demographic data, HO location, surgical approach, preoperative and postoperative shoulder range of motion, etiologies, and postoperative complications were collected from patients' files.

RESULTS

We found 19 shoulder HOs in 16 patients (traumatic brain injury in 11, spinal cord injury in 2, stroke in 1, and cerebral anoxia in 2). The data in 2 files were incomplete and were therefore not used. HO locations around the joint were anteroinferomedial in 4 (21.1%), posteroinferomedial in 5 (26.3%), encircling in 3 (15.8%), superior in 1 (5.3%), and mixed (2 associated HOs that are not encircling) in 6 (31.6%). The surgical approaches were as follows: deltopectoral, 5 (26.3%); Neer, 3 (15.8%); posterior, 5 (26.3%); axillary, 1 (5.3%); Martini, 2 (10.5%); posterior associated with deltopectoral, 2 (10.5%); and Neer (superolateral) associated with deltopectoral, 1 (5.3%). The mean range of motion increased significantly (gain at follow-up of 69°, 60°, and 13° in forward elevation, abduction, and lateral rotation, respectively). Regarding postoperative complications, there was 1 case of capsulitis and 1 reoperation for insufficient excision (because of hemorrhage during surgery). There were no other side effects.

CONCLUSION

Anatomic relations with nerves and vessels, as well as limited range of motion, require a case-by-case surgical approach, a preoperative scan (looking for a gutter), and sometimes, electromyography. Surgical indications depend on the degree of loss of function or hygiene, control of comorbid factors, and discussion with the patient and his or her family.

The influence of pregnancy on heterotopic ossification post-displaced acetabular fractures surgical repair

Pregnancy is associated with maternal bone mineral density loss and modulation of calcium metabolism. We hypothesized that pregnancy may decrease the risk of heterotopic ossification (HO) after trauma. This is a single-institution, University of Mississippi Medical Center, retrospective study investigating the effect of pregnancy on the incidence HO after surgical repair (SR) of displaced acetabular fractures. Between January 1998 and 2010, 257 non-pregnant women (Group A) and 16 pregnant women (Group B) were identified. All the non-pregnant women received radiation therapy (RT) ± indomethacin. None of the pregnant women in group B received any prophylaxis. After a median follow-up of 6.6 years the incidence of HO in all patients was 27% (75/273). In Group A, non-pregnant, women who received RT ± indomethacin, 29% developed HO; HO risk was 0.4. In Group B, 16 pregnant patients, only one developed HO (6%); HO risk was 0.06. Thus, the risk of HO appears to be nearly six-fold higher in non-pregnant women despite prophylactic RT ± indomethacin. Our data suggest that pregnancy may be associated with a reduced risk of HO after SR of displaced acetabular fractures. Further analysis with a larger pregnant patient sample is necessary to confirm this finding.

Heterotopic bone formation about the hip undergoes endochondral ossification: a rabbit model

BACKGROUND

Heterotopic ossification (HO) occurs most commonly after trauma and surgery about the hip and may compromise subsequent function. Currently available animal models describing the cellular progression of HO are based on exogenous osteogenic induction agents and may not reflect the processes following trauma.

QUESTIONS/PURPOSES

We therefore sought to characterize the histologic progression of heterotopic bone formation in an animal model that recapitulates the human condition without the addition of exogenous osteogenic material.

METHODS

We used a rabbit model that included intramedullary instrumentation of the upper femur and ischemic crush injury of the gluteal muscle. Bilateral surgical induction procedures were performed on 30 animals with the intention of inciting the process of HO; no supplemental osteogenic stimulants were used. Three animals were sacrificed at each of 10 predetermined times between 1 day and 26 weeks postoperatively and the progression of tissue maturation was graded histologically using a five-item scale.

RESULTS

Heterotopic bone reliably formed de novo and consistently followed a pathway of endochondral ossification. Chondroid elements were found in juxtaposition with immature woven bone in all sections that contained mature osseous elements.

CONCLUSIONS

These results establish that HO occurs in an animal model mimicking the human condition following surgical trauma about the hip; it is predictable in its histologic progression and follows a pathway of endochondral bone formation.

CLINICAL RELEVANCE

By showing a consistent pathway of endochondral ossification leading to ectopic bone formation, this study provides a basis for understanding the mechanisms by which HO might be mitigated by interventions.

Heterotopic ossification after central nervous system trauma: A current review

Neurogenic heterotopic ossification (NHO) is a disorder of aberrant bone formation affecting one in five patients sustaining a spinal cord injury or traumatic brain injury. Ectopic bone forms around joints in characteristic patterns, causing pain and limiting movement especially around the hip and elbow. Clinical sequelae of neurogenic heterotopic ossification include urinary tract infection, pressure injuries, pneumonia and poor hygiene, making early diagnosis and treatment clinically compelling. However, diagnosis remains difficult with more investigation needed. Our pathophysiological understanding stems from mechanisms of basic bone formation enhanced by evidence of systemic influences from circulating humor factors and perhaps neurological ones. This increasing understanding guides our implementation of current prophylaxis and treatment including the use of non-steroidal anti-inflammatory drugs, bisphosphonates, radiation therapy and surgery and, importantly, should direct future, more effective ones.