Risk factors for dysbaric osteonecrosis

Atraumatic osteonecrosis of the humeral head: pathophysiology and current concepts of evaluation and treatment

The humeral head is considered the second most common site for osteonecrosis to occur after the femoral head. As seen in the femoral head, the circulatory implications characteristic of this condition are attributable to the interaction between a genetic predisposition and the exposure to certain risk factors. There is no consensus regarding the pathogenesis of osteonecrosis, yet the final common pathway results in disrupted blood supply, increased intraosseous pressure, and bone death. Disease staging using radiography and magnetic resonance imaging is predictive of disease progression and can help the orthopedic surgeon to guide treatment. Although there is a myriad of treatment modalities, there is a lack of high-quality evidence to conclude what is the most appropriate treatment option for each stage of humeral head osteonecrosis. Nonoperative treatment is the preferred option in early-stage disease, and it may prevent disease progression. Nonetheless, in some cases, disease progression occurs despite nonoperative measures, and surgical treatment is required. The purpose of this article is to provide an updated review of the available evidence on risk factors, diagnosis, and treatment of atraumatic humeral head osteonecrosis.

Utility of magnetic resonance spectroscopy and diffusion-weighted imaging for detecting changes in the femoral head in divers with hip pain at risk for dysbaric osteonecrosis

BACKGROUND

Ischemia before the development of dysbaric osteonecrosis (DON) in femoral heads has never been investigated. We assessed whether quantitative magnetic resonance spectroscopy (MRS) and diffusion weighted imaging (DWI) could detect dysbaric changes in divers with hip pain.

METHODS

This IRB-approved exploratory study recruited 17 divers [9 with hip pain (Group 1); 8 asymptomatic (Group 2)] with normal findings on radiographs and conventional magnetic resonance imaging scans were age-, gender- and body-mass-index matched to 17 non-divers as controls (Group 1C, 2C). Apparent diffusion coefficients (ADCs) and MRS spectra were obtained from regions/voxels of interest on the femoral heads of all subjects. LCModel was used to determine water content, lipid composition, and the unsaturation index in bone marrow. Mann-Whitney non-parametric test was used to compare results of quantitative MRS and ADCs of ipsilateral femoral heads between divers and controls.

RESULTS

MRS of the ipsilateral femoral heads revealed higher water (peak: 4.7 ppm) content, lower total lipid fraction (TLF), and higher unsaturation index (UI) of lipids in Group 1 than in Group 2 (water: P=0.040; UI: P=0.022) and Group 1C (water: P=0.027; TLF: P=0.039; UI: P=0.009). In contrast, femoral head ADCs were comparable between divers and controls. Five out of nine symptomatic divers were contacted for follow-up MRS and DWI studies, and the mean difference in water content in the femoral heads of patients with osteonecrosis was also higher than that in patients with symptom relief (osteonecrosis: 0.077±0.130 vs. symptom relief: 0.003±0.010).

CONCLUSIONS

Dysbaric change in the femoral heads of divers with hip pain can be detected using quantitative MRS, which reveals increases in water content and UI of lipids, and a decrease in TLF.

Dysbaric osteonecrosis of the humeral head in a patient with type 2 decompressive sickness

INTRODUCTION

Dysbaric osteonecrosis, albeit rare, have been reported in patients with decompression sickness. We report a patient with dysbaric osteonecrosis, diagnosed 60 days after presenting with decompression sickness.

CASE PRESENTATION

A 38-year-old, previously fit and healthy male, noted his tank running out of air at approximately 40-50 m while diving, surfaced rapidly before losing consciousness. Upon gaining consciousness, he noted loss of power on all four limbs. He completed 26 sessions of hyperbaric oxygen treatment. Magnetic resonance (MR) of the spine noted T2 abnormality in the upper cervical spine, with some involvement of the central grey matter and the remainder of the cord. According to the International Standards for Neurological Classification of Spinal Cord Injury, it was noted clinically that the patient had a T9 neurological level with ASIA impairment scale A. MR imaging (MRI) of the shoulder was performed, 60 days since initial presentation, after the patient complained of shoulder pain, noted non-specific subcortical oedema of the humeral head, which suggested early osteonecrosis.

DISCUSSION

Dysbaric osteonecrosis is rare but remains extremely important to be recognised as a potential complication from decompressive sickness. The increased risk of pathological fractures with dysbaric osteonecrosis plays an important role as it may alter the rehabilitation prescription. One of the unique features of this case, apart from its rarity, was that it was diagnosed 60 days from his initial presentation, when he has passed his acute phase of illness.

Dysbaric osteonecrosis in technical divers: The new 'at-risk' group?

INTRODUCTION

Dysbaric osteonecrosis (DON) in people working under increased atmospheric pressure is well documented. It is generally less common in military and commercial divers than in caisson workers, except in some high-risk groups, such as in many indigenous diving industries where workers have little or no understanding of decompression principles. With the increasing popularity within the recreational diving community of deep air and mixed-gas decompression diving ('technical diving'), it is likely that diving physicians may see an increase in the prevalence of DON in this group in the future.

METHODS

The case report is presented of a technical diving instructor, with a 30-year history of deep diving, who developed bilateral humeral head DON and required a right shoulder hemi-arthroplasty. A focused literature search was also undertaken to identify published cases of DON in recreational divers.

RESULTS

The frequency, duration and depth of exposure to pressure, inadequate decompression, the occurrence of DCS and increasing age have been common features associated with DON in both divers and caisson workers. Many of these features were present in this technical diver.

CONCLUSIONS

Whilst DON is uncommon in recreational air scuba divers, all the above risk factors are present to a greater degree in technical diving. It is suggested that medical review for DON is merited from time to time in this potentially high-risk group of recreational divers.

Frequency of decompression illness among recent and extinct mammals and "reptiles": a review

The frequency of decompression illness was high among the extinct marine "reptiles" and very low among the marine mammals. Signs of decompression illness are still found among turtles but whales and seals are unaffected. In humans, the risk of decompression illness is five times increased in individuals with Patent Foramen Ovale; this condition allows blood shunting from the venous circuit to the systemic circuit. This right-left shunt is characteristic of the "reptile" heart, and it is suggested that this could contribute to the high frequency of decompression illness in the extinct reptiles.

Steroid changes adipokine concentration in the blood and bone marrow fluid

Our previous study has shown that plasminogen activator inhibitor 1 (PAI-1) gene expression and secretion from bone marrow adipocytes increased markedly with dexamethasone administration. The purpose of the present study was to measure the secretion of various adipokines from human bone marrow and blood, and investigate how adipokine secretion changes in a steroid environment. Human blood and bone marrow fluid were collected from a steroid treatment group and a control group during hip replacement surgery, and an enzyme-linked immunosorbent assay (ELISA) was used to measure the adiponectin, leptin, and PAI-1 levels. Adiponectin and leptin showed no significant differences between bone marrow and blood levels, but PAI-1 was significantly higher in bone marrow. The steroid treatment group had higher levels of leptin and PAI-1 in both the blood and bone marrow than the control group. PAI-1 was present at high concentrations in the bone marrow and increased by steroid treatment. High levels of PAI-1 in bone marrow may influence intraosseous hemodynamics and may induce necrotic bone disorders.

Evaluating PAI-1 as a biomarker for stress in diving: human serum total PAI-1 is unaltered after 2 h dry exposures to 280 kPa hyperbaric air

Plasminogen activator inhibitor (PAI-1) is induced in the vasculature and secreted into the vascular lumen in response to inflammation and oxidative stress. We have previously reported a fivefold increase in plasma PAI-1 from rats exposed to 708 kPa hyperbaric air. In the current study we assess the potential of human serum total PAI-1 as a biomarker for stress in compressed air diving. Eleven recreational divers, nine males and two females, completed four 2 h hyperbaric air exposures to 280 kPa in a pressure chamber over a period of 2 weeks. The air pressure corresponds to a diving depth of 18 m in water. Serum was collected before the study and again 3 h 30 min after completion of each hyperbaric exposure. All samples were taken in the afternoon to minimize the contribution of circadian variation. The analysis revealed no change in serum total PAI-1 after hyperbaric exposures within the group of divers (P = 0.064), but significant interindividual differences persisted throughout the study (P < 0.0005). A case of decompression sickness after the third round of hyperbaric exposure did not affect PAI-1. In conclusion, compressed air exposure to 280 kPa does not affect serum total PAI-1, and significant interindividual variation in PAI-1 levels may limit its usefulness as a biomarker. This does, however, not give a complete answer regarding PAI-1 in physiologically stressful dives. Further studies with different exposures and timing are needed for that.

Dysbaric osteonecrosis: a literature review of pathophysiology, clinical presentation, and management

OBJECTIVE

To perform a general literature review of dysbaric osteonecrosis (DON) to describe its pathophysiology, prevalence in scuba divers, prognosis, and treatment options.

DATA SOURCES

A literature search on PubMed was performed using the term "dysbaric osteonecrosis" yielding 67 results. There was no exclusion based on dates. Articles that mainly dealt with decompression sickness secondary to tunnel work, mining, or airplane travel were not selected. An additional search on PubMed using the terms "(osteonecrosis diving) NOT dysbaric" was performed to identify other publications not picked up in the initial search.

MAIN RESULTS

Dysbaric osteonecrosis is associated with prolonged hyperbaric exposure and rapid decompression that cause nitrogen bubbles to enter the fatty marrow-containing shafts of long bones leading to reduction in blood flow and subsequent osteonecrosis. Patients may present asymptomatically, and typical radiographic findings of DON include: decalcification of bone, cystic lesions, osteosclerotic patterns, nontraumatic fractures, bone islands, and a subchondral crescent sign. Surgical treatment options are comprised of core decompression and free vascularized fibular graft, whereas nonsurgical treatment options consist of monitoring, physical therapy, and bisphosphonate therapy.

CONCLUSIONS

Although the incidence of DON has decreased significantly over the past 2 decades, the lack of timely diagnosis and optimal management keeps DON relevant in the orthopedic and sport medicine community.

The ecological associations of surface-dwelling lizards in Qom Province in the Northwest of Central Plateau of Iran

We used pitfall trapping to investigate the effects of elevation, plant density and soil structure on species diversity and the impact of these habitat factors on lizard habitat selectivity in the Qom Province in the Central Plateau of Iran. From a total of 12 1-ha plots, we captured 363 individuals of 15 species of lizards (six species of Lacertidae, five species of Agamidae, two species of Gekkonidae, one species of Varanidae and one species of Scincidae). A generalized linear model (GLM) determined that elevation was the most important factor impacting species diversity. The highest species diversity was at the intermediate elevation (1289 m). Abundance of 6 out of 15 species showed strong relationships with some habitat factors. These relationships were demonstrated by habitat selectivity index (Ivlev's index). Our result supports other surveys that showed that elevation plays an important role in determining lizard species diversity.

Early genetic responses in rat vascular tissue after simulated diving

Diving causes a transient reduction of vascular function, but the mechanisms behind this are largely unknown. The aim of this study was therefore to analyze genetic reactions that may be involved in acute changes of vascular function in divers. Rats were exposed to 709 kPa of hyperbaric air (149 kPa Po(2)) for 50 min followed by postdive monitoring of vascular bubble formation and full genome microarray analysis of the aorta from diving rats (n = 8) and unexposed controls (n = 9). Upregulation of 23 genes was observed 1 h after simulated diving. The differential gene expression was characteristic of cellular responses to oxidative stress, with functions of upregulated genes including activation and fine-tuning of stress-responsive transcription, cytokine/cytokine receptor signaling, molecular chaperoning, and coagulation. By qRT-PCR, we verified increased transcription of neuron-derived orphan receptor-1 (Nr4a3), plasminogen activator inhibitor 1 (Serpine1), cytokine TWEAK receptor FN14 (Tnfrsf12a), transcription factor class E basic helix-loop-helix protein 40 (Bhlhe40), and adrenomedullin (Adm). Hypoxia-inducible transcription factor HIF1 subunit HIF1-α was stabilized in the aorta 1 h after diving, and after 4 h there was a fivefold increase in total protein levels of the procoagulant plasminogen activator inhibitor 1 (PAI1) in blood plasma from diving rats. The study did not have sufficient power for individual assessment of effects of hyperoxia and decompression-induced bubbles on postdive gene expression. However, differential gene expression in rats without venous bubbles was similar to that of all the diving rats, indicating that elevated Po(2) instigated the observed genetic reactions.

Occupational health issues in marine and freshwater research

Marine and freshwater scientists are potentially exposed to a wide variety of occupational hazards. Depending on the focus of their research, risks may include animal attacks, physiological stresses, exposure to toxins and carcinogens, and dangerous environmental conditions. Many of these hazards have been investigated amongst the general population in their recreational use of the environment; however, very few studies have specifically related potential hazards to occupational exposure. For example, while the incidence of shark and crocodile attacks may invoke strong emotions and the occupational risk of working with these animals is certainly real, many more people are stung by jellyfish or bitten by snakes or dogs each year. Furthermore, a large proportion of SCUBA-related injuries and deaths are incurred by novice or uncertified divers, rather than professional divers using aquatic environments. Nonetheless, marine and freshwater research remains a potentially risky occupation, and the likelihood of death, injury and long-term health impacts still needs to be seriously considered.

Simvastatin suppresses dexamethasone-induced secretion of plasminogen activator inhibitor-1 in human bone marrow adipocytes

Background

Osteonecrosis of the femoral head is a common complication of high-dose glucocorticoid treatment. Intravascular thrombosis is thought to be associated with the ischemic state of the femoral head. Plasminogen activator inhibitor-1 (PAI-1) is an adipokine, which are physiologically active substances secreted from visceral and subcutaneous adipocytes. PAI-1 suppresses fibrinolysis by binding tissue-type plasminogen activator. Several reports have described the relationship between PAI-1 and steroid-induced osteonecrosis of the femoral head, and the preventive effects of lipid-lowering agents (statins) against steroid-induced osteonecrosis of the femoral head. We previously reported that adipokines and dexamethasone induced PAI-1 secretion from bone marrow adipocytes. The purpose of the present study is to examine the effects of simvastatin on PAI-1 secretion from human bone marrow adipocytes in vitro.

Methods

Primary bone marrow adipocytes were extracted from collagenase-treated bone marrow fluid obtained from the femoral necks of 40 patients (6 men, 34 women; age range, 52-81 years) undergoing hip joint replacement surgery. After suspended culture with or without dexamethasone or simvastatin, PAI-1 mRNA expression was assessed by real-time RT-PCR. Total PAI-1 protein secretion in culture medium was assessed by enzyme-linked immunosorbent assay.

Results

PAI-1 mRNA expression was up-regulated by 388% (P = 0.002) with dexamethasone, and down-regulated by 45% (P = 0.002) with simvastatin, as compared to control levels. Dexamethasone increased total PAI-1 secretion by 166% (P = 0.001) and simvastatin decreased total PAI-1 secretion by 64% (P = 0.002). No significant changes were observed in adiponectin mRNA expression and secretion by dexamethasone and simvastatin, while pre-treatment with simvastatin reversed dexamethasone induced PAI-1 secretion by 89%, as compared to control levels.

Conclusion

The present study confirmed the suppressive effects of simvastatin on PAI-1 expression and secretion from bone marrow adipocytes. Furthermore, pre-treatment with simvastatin reversed dexamethasone induced PAI-1 secretion. Simvastatin may thus exhibit preventive effects against steroid-induced osteonecrosis of the femoral head by suppressing PAI-1 secretion.

Characterization of human mesenchymal stem cell secretome at early steps of adipocyte and osteoblast differentiation

Background

It is well established that adipose tissue plays a key role in energy storage and release but is also a secretory organ and a source of stem cells. Among different lineages, stem cells are able to differentiate into adipocytes and osteoblasts. As secreted proteins could regulate the balance between both lineages, we aimed at characterizing the secretome of human multipotent adipose-derived stem cell (hMADS) at an early step of commitment to adipocytes and osteoblasts.

Results

A proteomic approach, using mono-dimensional electrophoresis and tandem mass spectrometry, allowed us to identify a total of 73 proteins at day 0 and day 3 of adipocyte and osteoblast differentiation. Analysis of identified proteins showed that 52 % corresponded to classical secreted proteins characterized by a signal peptide, that 37 % previously described in the extracellular compartment were devoid of signal peptide and that 11 % neither exhibited a signal peptide nor had been previously described extracellularly. These proteins were classified into 8 clusters according to their function. Quantitative analysis has been performed for 8 candidates: PAI-1, PEDF, BIGH3, PTX3, SPARC, ENO1, GRP78 and MMP2. Among them, PAI-1 was detected at day 0 and day 3 of osteoblast differentiation but never in adipocyte secretome. Furthermore we showed that PAI-1 mRNA was down-regulated in the bone of ovariectomized mice.

Conclusion

Given its regulation during the early events of hMADS cell differentiation and its status in ovariectomized mice, PAI-1 could play a role in the adipocyte/osteoblast balance and thus in bone diseases such as osteoporosis.