Intravenous disodium etidronate therapy in spinal cord injury patients with heterotopic ossification

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

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

When the Nervous System Turns Skeletal Muscles into Bones: How to Solve the Conundrum of Neurogenic Heterotopic Ossification

PURPOSE OF REVIEW

Neurogenic heterotopic ossification (NHO) is the abnormal formation of extra-skeletal bones in periarticular muscles after damage to the central nervous system (CNS) such as spinal cord injury (SCI), traumatic brain injury (TBI), stroke, or cerebral anoxia. The purpose of this review is to summarize recent developments in the understanding of NHO pathophysiology and pathogenesis. Recent animal models of NHO and recent findings investigating the communication between CNS injury, tissue inflammation, and upcoming NHO therapeutics are discussed.

RECENT FINDINGS

Animal models of NHO following TBI or SCI have shown that NHO requires the combined effects of a severe CNS injury and soft tissue damage, in particular muscular inflammation and the infiltration of macrophages into damaged muscles plays a key role. In the context of a CNS injury, the inflammatory response to soft tissue damage is exaggerated and persistent with excessive signaling via substance P-, oncostatin M-, and TGF-β1-mediated pathways. This review provides an overview of the known animal models and mechanisms of NHO and current therapeutic interventions for NHO patients. While some of the inflammatory mechanisms leading to NHO are common with other forms of traumatic and genetic heterotopic ossifications (HO), NHOs uniquely involve systemic changes in response to CNS injury. Future research into these CNS-mediated mechanisms is likely to reveal new targetable pathways to prevent NHO development in patients.

Myositis ossificans in the diabetic foot: a review of the literature with an illustrative case series

Objective

Myositis ossificans is a rare non-neoplastic form of heterotopic ossification most commonly described after trauma or surgery, in the diabetic foot.

Design

We provide a review of the literature including three illustrative cases.

Participants

Individuals presenting to the foot clinic.

Setting

Single centre, tertiary multidisciplinary specialist diabetes foot clinic.

Results

We review the literature surrounding Myositis ossificans, and describe three cases of Myositis ossificans following foot surgery in people with diabetes. All of the imaging was consistent with the descriptions of Myositis ossificans reported elsewhere in large muscle groups. These are the first reports of Myositis ossificans occurring in the feet of people with diabetes.

Conclusions

Myositis ossificans has only very rarely been described in the foot and, as far as we are aware, never in people with diabetes. Given that the prevalence of diabetes is increasing, and the foot problems requiring surgery are also rising, we suggest that clinicians should be more aware of this condition because it may occur more frequently.

Neurological heterotopic ossification: Current understanding and future directions

Neurological heterotopic ossification (NHO) involves the formation of bone in soft tissue following a neurological condition, of which the most common are brain and spinal cord injuries. NHO often forms around the hip, knee and shoulder joints, causing severe pain and joint deformation which is associated with significant morbidity and reduced quality of life. The cellular and molecular events that initiate NHO have been the focus of an increasing number of human and animal studies over the past decade, with this work largely driven by the need to unearth potential therapeutic interventions to prevent the formation of NHO. This review provides an overview of the present understanding of NHO pathogenesis and pathobiology, current treatments, novel therapeutic targets, potential biomarkers and future directions.

Association of vitamin D deficiency, secondary hyperparathyroidism, and heterotopic ossification in spinal cord injury

Our objective was to explore the relationship between low vitamin D, secondary hyperparathyroidism, and heterotopic ossification (HO) in patients with spinal cord injury (SCI). Ninety-six subjects with acute or chronic motor complete SCI participated. Levels of serum vitamin D25(OH), calcium, and intact parathyroid hormone (PTH) were collected, and information regarding nutritional patterns and fracture history was obtained from subjects. Evidence of current or previous HO was ascertained through chart review. Of the 96 subjects, 12 were found to have developed HO, 11 with serum vitamin D25(OH) between 5 and 17 ng/mL. Nine subjects exhibited secondary hyperparathyroidism in the range of 72 to 169 pg/mL. Only one subject demonstrated HO in the absence of low vitamin D. However, many subjects with low vitamin D (5-31 ng/mL) did not have hyperparathyroidism or HO. Statistical testing demonstrated a correlation between hyperparathyroidism and HO (p < 0.001) as well as hyperparathyroidism and vitamin D deficiency (<20 ng/mL). Direct correlation between HO and low vitamin D was not observed, but hyperparathyroidism may increase this risk. We believe that those patients who demonstrate low vitamin D and elevated PTH should be screened for HO in addition to beginning vitamin supplementation. Initiating early treatment of low vitamin D to restore therapeutic levels may prevent development of HO.

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.

Osteogenic differentiation capacity of human skeletal muscle-derived progenitor cells

Heterotopic ossification (HO) is defined as the formation of ectopic bone in soft tissue outside the skeletal tissue. HO is thought to result from aberrant differentiation of osteogenic progenitors within skeletal muscle. However, the precise origin of HO is still unclear. Skeletal muscle contains two kinds of progenitor cells, myogenic progenitors and mesenchymal progenitors. Myogenic and mesenchymal progenitors in human skeletal muscle can be identified as CD56⁺ and PDGFRα⁺ cells, respectively. The purpose of this study was to investigate the osteogenic differentiation potential of human skeletal muscle-derived progenitors. Both CD56⁺ cells and PDGFRα⁺ cells showed comparable osteogenic differentiation potential in vitro. However, in an in vivo ectopic bone formation model, PDGFRα⁺ cells formed bone-like tissue and showed successful engraftment, while CD56⁺ cells did not form bone-like tissue and did not adapt to an osteogenic environment. Immunohistological analysis of human HO sample revealed that many PDGFRα⁺ cells were localized in proximity to ectopic bone formed in skeletal muscle. MicroRNAs (miRNAs) are known to regulate many biological processes including osteogenic differentiation. We investigated the participation of miRNAs in the osteogenic differentiation of PDGFRα⁺ cells by using microarray. We identified miRNAs that had not been known to be involved in osteogenesis but showed dramatic changes during osteogenic differentiation of PDGFRα⁺ cells. Upregulation of miR-146b-5p and -424 and downregulation of miR-7 during osteogenic differentiation of PDGFRα⁺ cells were confirmed by quantitative real-time RT-PCR. Inhibition of upregulated miRNAs, miR-146b-5p and -424, resulted in the suppression of osteocyte maturation, suggesting that these two miRNAs have the positive role in the osteogenesis of PDGFRα⁺ cells. Our results suggest that PDGFRα⁺ cells may be the major source of HO and that the newly identified miRNAs may regulate osteogenic differentiation process of PDGFRα⁺ cells.

A comparison of heterotopic ossification treatment within the traumatic brain and spinal cord injured population: An evidence based systematic review

BACKGROUND

To compare the treatment of heterotopic ossification (HO) within the traumatic brain and spinal cord injured populations.

METHODS

MEDLINE/Pubmed, CINAHL, EMBASE, and PsycINFO databases were searched for articles addressing treatment of HO post-injury. Articles were constrained to: English language and human subjects. Studies were included if: n ≥ 50% of the subjects had a spinal cord injury (SCI) or a traumatic brain injury (TBI), n ≥ 3 SCI or TBI subjects, and study subjects participated in a treatment or intervention. Study quality, for randomized control trials (RCTs), were assessed using the PEDro assessment scale, while non-RCTs was assessed using the Downs and Black evaluation tool. A modified Sackett scale was used to apply levels of evidence for each intervention.

RESULTS

In total 26 studies (NTBI = 12; NSCI = 14) met inclusion criteria. The majority of studies (10/12) conducted in the TBI population were surgical interventions. Studies conducted with the SCI population investigated diverse pharmacological treatments including: bisphosphonates, non-steroidal anti-inflammatory drugs (NSAIDs) and Warfarin. Non-pharmacological studies investigated the benefits of pulse low-intensity electromagnetic field therapy, surgical excision, and radiotherapy in the treatment of HO.

CONCLUSIONS

Within the SCI literature, NSAIDs showed the greatest efficacy in the prevention of HO when administered early after a SCI, and biphosphonates were found to be the most effective treatment strategy. In the TBI population, surgical excision was the most effective treatment.

A systematic review of the therapeutic interventions for heterotopic ossification after spinal cord injury

STUDY DESIGN

Systematic review.

OBJECTIVE

To conduct a systematic review of the effectiveness of interventions used to prevent and treat heterotopic ossification (HO) after spinal cord injury (SCI).

SETTING

St Joseph's Parkwood Hospital, London, Ontario, Canada.

METHODS

MEDLINE, CINAHL, EMBASE and PsycINFO databases were searched for articles addressing the treatment of HO after SCI. Studies were selected by two reviewers and were only included for analysis if at least 50% of the subjects had an SCI, there were at least three SCI subjects and if the study subjects participated in a treatment or intervention. Study quality was assessed by two independent reviewers using the Downs and Black evaluation tool for all studies, as well as the PEDro assessment scale for randomized control trials only. Levels of evidence were assigned using a modified Sackett scale.

RESULTS

A total of 13 studies met the inclusion criteria. The selected articles were divided into prevention or treatment of post-SCI HO. Nonsteroidal anti-inflammatory drugs (NSAIDs), warfarin, and pulse low-intensity electrogmagnetic field (PLIMF) therapy were reviewed as prophylactic measures. Bisphosphonates, radiotherapy and excision were reviewed as treatments of post-SCI HO.

CONCLUSIONS

Pharmacological treatments of HO after SCI had the highest level of research evidence supporting their use. Of these, NSAIDs showed greatest efficacy in the prevention of HO when administered early after an SCI, whereas bisphosphonates were the intervention with strongest supportive evidence once HO had developed. Of the non-pharmacological interventions, PLIMF was supported by the highest level of evidence; however, more research is needed to fully understand its role.

The use of eidronate disodium in the prevention of heterotopic ossification in burn patients

Heterotopic ossification (HO) is a well-known complication of moderate and severe burn injuries. The development and progression of HO in burn patients are poorly understood phenomena at this time. Numerous measures aimed at preventing or minimizing HO have been described, but no definitive prophylactic modality has been found. Biphosphonate compounds are known to inhibit calcification, but previous studies are equivocal regarding their effectiveness in preventing HO in burn patients. We retrospectively reviewed the effect of etidronate disodium (EDHP), a bisphosphonate, on the development of HO in severely burned patients. We found that not only was EDHP ineffective in preventing HO, the group of patients treated with EDHP demonstrated an increased incidence of HO over that seen in a comparison group. This was true after controlling for age, sex, and %TBSA burned. Based on the results of this study, the routine use of etidronate disodium to prevent HO in burn patients cannot be recommended.

[Treatment of neurogenic heterotopic ossifications (NHO) in brain injured patients: review of literature]

This article is a review of the literature about treatment of neurogenic heterotopic ossifications (NHO) in brain injured patients, from analysis of the main data bases (Medline, Embase, Reedoc). In spite of the hope they arouse in the seventies, biphosphonates, including etidronate, have not demonstrated their efficiency to inhibit NHO in clinical practice. In fact a very early diagnosis, with the scintigraphic overactivity of the joint area and the increase of serum alkaline phosphatases, must lead to begin passive motion and postures, and may contribute to save functional range of motion. Yet, when joint stiffness or even ankylosis have led to severe functional disorders, surgery with NHO resection is the only way; it looks more reliable to manage it when NHO is mature, after a delay of more than 12 months after the first signs, but earlier operations have been reported without an enhanced risk of recurrence; this surgery must be associated with continuous passive motion for several weeks; radiation therapy and/or non-steroid anti-inflammatory drugs have been proposed in the immediate after-surgery period, but their role is still discussed.

Heterotopic ossification in childhood and adolescence

Heterotopic ossification, or myositis ossificans, denotes true bone in an abnormal place. The pathogenic mechanism is still unclear. A total of 643 patients (mean age, 9.1 years) admitted for neuropediatric rehabilitation were analyzed retrospectively with respect to the existence of neurogenic heterotopic ossification. The purpose of this study was to obtain information about incidence, etiology, clinical aspect, and consequences for diagnosis and therapy of this condition in childhood and adolescence. Heterotopic ossification was diagnosed in 32 patients (mean age, 14.8 years) with average time of onset of 4 months after traumatic brain injury, near drowning, strangulation, cerebral hemorrhage, hydrocephalus, or spinal cord injury. The sex ratio was not significant. In contrast to what has been found in adult studies, serum alkaline phosphatase was not elevated during heterotopic ossification formation. A persistent vegetative state for longer than 30 days proved to be a significant risk factor for heterotopic ossification. The incidence of neurogenic heterotopic ossification in children seems to be lower than in adults. A genetic predisposition to heterotopic ossification is suspected but not proven. As a prophylactic regimen against heterotopic ossification we use salicylates for those patients in a coma or persistent vegetative state with warm and painful swelling of a joint and consider continuous intrathecal baclofen infusion and botulinum toxin injection for those patients with severe spasticity. We prefer to wait at least 1 year after trauma before excision of heterotopic ossification.

Cyclical etidronate: its effect on bone density in patients with acute spinal cord injury

OBJECTIVE

To compare the effects of a 30-week trial of cyclical etidronate therapy (starting within 6 weeks of spinal cord injury [SCI] and conventional rehabilitation without etidronate treatment on the bone density of the lumbar spine and lower extremities of SCI patients.

DESIGN

Prospective, randomized control trial.

SETTING

Tertiary care, inpatient rehabilitation center.

PATIENTS

Acute SCI, within 6 weeks of injury. Thirteen SCI subjects were recruited; 6 were assigned randomly to receive etidronate and 7 to receive conventional treatment.

INTERVENTION

Etidronate, 800 mg orally, once per day for 2 weeks of 15 weeks, repeated once.

MAIN OUTCOME MEASURES

Dual X-ray absorptiometry of the spine, hip, distal femur, and proximal tibia measured at baseline, 6 months, and 12 months.

RESULTS

A significant interaction between etidronate treatment and ambulatory status over time was observed in the bone density of the patients after SCI (p = .0003). The patients who became ambulatory and received etidronate treatment had a preservation of bone density as compared to all other patients who showed a loss of bone density over time. The loss of bone density occurred in the leg bones, not the spine. Cyclical etidronate treatment was tolerated well without adverse or side effects.

CONCLUSION

Cyclical etidronate is a feasible treatment and may prevent osteoporosis associated with SCI in patients who eventually walk.