Influence of heterotopic ossification of the hip on bone densitometry: a study in spinal cord injured patients

Triggered metabolism of adenosine triphosphate as an explanation for the chemical heterogeneity of heterotopic ossification

Heterotopic ossification (HO), the pathological formation of bone in soft tissues, is a debilitating condition, as well as one of the few instances of de novo bone formation in adults. Chemical mapping of HO tissue showed distinct islands of calcium phosphate within phosphate-deficient, calcium-rich regions, suggesting a transition to apatitic bone mineral from a non-phosphatic precursor. The transition of amorphous calcium carbonate (ACC), a generally suggested bone-mineral precursor, in physiological conditions was thus investigated. Here, we show that adenosine triphosphate (ATP), present in high amounts in forming bone, stabilised ACC for weeks in physiological conditions and that enzymatic degradation of ATP triggered rapid crystallisation into apatite, through an amorphous calcium phosphate phase. It is suggested that this localised enzymatic degradation could explain the chemical heterogeneity seen in HO and may also represent a pathway to physiological bone mineralisation.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

Neurogenic heterotopic ossification in the upper limb

Neurogenic heterotopic ossifications (NHOs) are periarticular ectopic ossifications that frequently develop after a central nervous system injury, most often a traumatic one. They limit range of motion and cause pain, interfering with limb positioning and function, whether active or passive. Highly described in the lower limbs, NHOs can also develop in the upper limb, with specific characteristics depending on their location. This article provides a summary of the diagnostic and therapeutic management of NHOs in the upper limb, based on the current literature.

Neurological heterotopic ossification following spinal cord injury is triggered by macrophage-mediated inflammation in muscle

Neurological heterotopic ossification (NHO) is the abnormal formation of bone in soft tissues as a consequence of spinal cord or traumatic brain injury. NHO causes pain, ankyloses, vascular and nerve compression and delays rehabilitation in this high-morbidity patient group. The pathological mechanisms leading to NHO remain unknown and consequently there are no therapeutic options to prevent or reduce NHO. Genetically modified mouse models of rare genetic forms of heterotopic ossification (HO) exist, but their relevance to NHO is questionable. Consequently, we developed the first model of spinal cord injury (SCI)-induced NHO in genetically unmodified mice. Formation of NHO, measured by micro-computed tomography, required the combination of both SCI and localized muscular inflammation. Our NHO model faithfully reproduced many clinical features of NHO in SCI patients and both human and mouse NHO tissues contained macrophages. Muscle-derived mesenchymal progenitors underwent osteoblast differentiation in vitro in response to serum from NHO mice without additional exogenous osteogenic stimuli. Substance P was identified as a candidate NHO systemic neuropeptide, as it was significantly elevated in the serum of NHO patients. However, antagonism of substance P receptor in our NHO model only modestly reduced the volume of NHO. In contrast, ablation of phagocytic macrophages with clodronate-loaded liposomes reduced the size of NHO by 90%, supporting the conclusion that NHO is highly dependent on inflammation and phagocytic macrophages in soft tissues. Overall, we have developed the first clinically relevant model of NHO and demonstrated that a combined insult of neurological injury and soft tissue inflammation drives NHO pathophysiology.

Frequency and age effects of secondary health conditions in individuals with spinal cord injury: a scoping review

STUDY DESIGN

Scoping review.

OBJECTIVES

To gain a better understanding of the prevalence, course and association with age of secondary health conditions in individuals with spinal cord injury (SCI).

SETTING

Seattle, Washington, USA.

METHODS

We performed searches of electronic databases for studies published from 1986-2011 that provided information regarding the prevalence, course or associations with age and duration of secondary health conditions in individuals with SCI.

RESULTS

Ninety-two studies were included. The findings indicate that: (1) individuals with SCI experience a number of secondary health conditions, many of which occur at a higher rate in those with SCI than the normative population; (2) the most common conditions or symptoms are pain, bowel and bladder regulation problems, muscle spasms, fatigue, esophageal symptom and osteoporosis; (3) a number of conditions, including cardiovascular disease, diabetes, bone mineral density loss, fatigue and respiratory complications or infections, occur with higher frequency in older individuals or those with longer SCI duration, relative to younger individuals or those with shorter SCI duration; and (4) there is a marked lack of longitudinal research examining the natural course of health conditions in individuals aging with SCI.

CONCLUSIONS

The findings support the conclusion that individuals with SCI show signs of 'premature aging' in different organ systems. Longitudinal research is needed to understand when problems are most likely to emerge, and to develop and test the efficacy of interventions to prevent these health conditions and their negative impact.

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.

[Osteoporosis in spinal cord injury. Screening and treatment. Results of a survey of physical medicine and rehabilitation physician practices in France. Proposals for action to be taken towards the screening and the treatment]

OBJECTIVE

The management of osteoporosis in spinal cord injury that is a recurring issue in daily practice, but unfortunately, no standard protocol is provided by the literature review, either for screening or for a strategy of prevention and even for therapy. We assessed the practices of the physicians in physical medicine and rehabilitation from all over France, with the ultimate aim to propose a consensus for preventive and curative cares of that osteoporosis.

METHODS

A questionnaire was sent to practitioners engaged with spinal cord injury (SCI) patients residing in the center and patients in medical monitoring. The questionnaire consisted mainly of closed questions.

RESULTS

Twenty-six questionnaires are analyzed. The screening for osteoporosis is made routinely by only 19.2% of the practitioners and after a fracture in only 80.2% of the cases. The diagnosis of osteoporosis is based on bone densitometry (DEXA) (96%). Standing still remains a means of prevention for 88% of physicians in the acute phase and for 77% in the chronic phase. Ninety-two percent of practitioners treat at the stage of established osteoporosis.

CONCLUSION

There is generally no standardized management of osteoporosis in practice for SCI patients. The searching for osteoporosis is usually performed after a fracture. All the literature data and results of the questionnaire led us to propose a protocol consisting in a systematic monitoring of the bone mineral density for the screening of osteoporosis, but also a procedure for early diagnosis and for preventive treatment of osteoporosis in the acute phase.

Diagnosis and treatment of osteoporosis in spinal cord injury patients: A literature review

OBJECTIVE

To present an up-to-date literature review of osteoporosis in spinal cord injury (SCI) patients, in view of the seriousness of this complication (with a high risk of fractures) and the complexity of its diagnosis, evaluation and treatment.

METHODS

A Medline search with the following keywords: immobilization osteoporosis, spinal cord injury, bone loss, dual energy X-ray absorptiometry (DEXA), bisphosphonate.

RESULTS

Our analysis of the literature noted a bone metabolism imbalance in SCI patients, with accelerated early bone resorption (particularly during the first 6 months post-injury). Although dual energy X-ray absorptiometry constitutes the "gold standard" diagnostic method, the decrease in bone mineral density only becomes significant 12 months after the injury. Bisphosphonate therapy has proven efficacy. Despite the frequent use of various physical therapies, these methods have not been found to be effective.

CONCLUSION

Although our literature review did not identify any guidelines on the strategy for diagnosing and treating osteoporosis in SCI patients, several findings provide guidance on procedures for early diagnosis and preventive treatment.

Impact of late surgical intervention on heterotopic ossification of the hip after traumatic neurological injury

Heterotopic ossification (HO) of the hip after injury to the central nervous system can lead to joint ankylosis. Surgery is usually delayed to avoid recurrence, even if the functional status is affected. We report a consecutive series of patients with HO of the hip after injury to the central nervous system who required surgery in a single, specialised tertiary referral unit. As was usual practice, they all underwent CT to determine the location of the HO and to evaluate the density of the femoral head and articular surface. The outcome of surgery was correlated with the pre-, peri- and post-operative findings. In all, 183 hips (143 patients) were included of which 70 were ankylosed. A total of 25 peri-operative fractures of the femoral neck occurred, all of which arose in patients with ankylosed hips and were associated with intra-articular lesions in 18 and severe osteopenia of the femoral head in seven. All the intra-articular lesions were predicted by CT and strongly associated with post-operative complications. The loss of the range of movement before ankylosis is a more important factor than the maturity of the HO in deciding the timing of surgery. Early surgical intervention minimises the development of intra-articular pathology, osteoporosis and the resultant complications without increasing the risk of recurrence of HO.

Impact of trochanteric heterotopic ossification on measurement of femoral bone density following cemented total hip replacement

During a study of bone mineral density changes around cemented femoral implants, we recognized heterotopic ossification occurring regularly in a position anterior to the greater trochanter and proximal femur. The aim of this study was to describe the incidence, distribution, and effect of this ossification on periprosthetic DXA scans following primary cemented total hip replacement. One hundred eleven patients underwent postoperative DXA examinations measuring changes in bone mineral density with heterotopic ossification identified and localized on standard radiographs with confirmation using DXA subtraction imaging. Male gender and age within the male group were significantly associated with occurrence of heterotopic ossification (p = 0.003 and 0.046, respectively). Femoral stem type, weight, and body mass index had no significant effect (p = 0.525, 0.372, and 0.243, respectively). Examining the Gruen zones in all patients suggested a median (plus interquartile range) zone 1 density drop of 4% (-12% to +7%). When separated and analyzed for the effect of heterotopic ossification, the 45 patients with heterotopic ossification showed a 2-year density gain of +6% (-5% to +15%), whereas those without heterotopic ossification showed a loss of 8% (-14% to 0%), a significant difference (p < 0.001). Zone 2 also showed a significant difference (p = 0.048). We therefore recommend that affected zones should be identified and excluded from analysis at all time points. Without this precaution, researchers risk underestimating periprosthetic bone loss in their studies and reporting misleading conclusions.

Physiological effects of lower extremity functional electrical stimulation in early spinal cord injury: lack of efficacy to prevent bone loss

STUDY DESIGN

Controlled, repeat-measures study.

OBJECTIVES

To determine if functional electrical stimulation (FES) can affect bone atrophy in early spinal cord injury (SCI), and the safety, tolerance and feasibility of this modality in bone loss remediation.

SETTING

Spinal Injuries Units, Royal Adelaide Hospital and Hampstead Rehabilitation Centre, South Australia.

METHODS

Patients with acute SCI (ASIA A-D) were allocated to FES (n=23, 28+/-9 years, C4-T10, 13 Tetra) and control groups (CON, n=10, 31+/-11 years, C5-T12, four Tetra). The intervention group received discontinuous FES to lower limb muscles (15 min sessions to each leg twice daily, over a 5-day week, for 5 months). Dual energy X-ray absorptiometry (DEXA) measured total body bone mineral density (tbBMD), hip, spine BMD and fat mass (FM) within 3 weeks, and 3 and 6 months postinjury.

RESULTS

FES and CON groups' tbBMD differed significantly at 3 months postinjury (P<0.01), but not thereafter. Other DEXA measures (hip, spine BMD, FM) did not differ between groups at any time. No adverse events were identified.

CONCLUSION

Electrically stimulated muscle activation was elicited, and tetanic effects were reproducible; however, there were no convincing trends to suggest that FES can play a clinically relevant role in osteoporosis prevention (or subsequent fracture risk) in the recently injured patient. The lack of an osteogenic response in paralysed extremities to electrically evoked exercise during subacute and rehabilitation/recovery phases cannot be fully explained, and may warrant further evaluation.

Bone loss and muscle atrophy in spinal cord injury: epidemiology, fracture prediction, and rehabilitation strategies

Individuals with spinal cord injury (SCI) often experience bone loss and muscle atrophy. Muscle atrophy can result in reduced metabolic rate and increase the risk of metabolic disorders. Sublesional osteoporosis predisposes individuals with SCI to an increased risk of low-trauma fracture. Fractures in people with SCI have been reported during transfers from bed to chair, and while being turned in bed. The bone loss and muscle atrophy that occur after SCI are substantial and may be influenced by factors such as completeness of injury or time postinjury. A number of interventions, including standing, electrically stimulated cycling or resistance training, and walking exercises have been explored with the aim of reducing bone loss and/or increasing bone mass and muscle mass in individuals with SCI. Exercise with electrical stimulation appears to increase muscle mass and/or prevent atrophy, but studies investigating its effect on bone are conflicting. Several methodological limitations in exercise studies with individuals with SCI to date limit our ability to confirm the utility of exercise for improving skeletal status. The impact of standing or walking exercises on muscle and bone has not been well established. Future research should carefully consider the study design, skeletal measurement sites, and the measurement techniques used in order to facilitate sound conclusions.