Osteoporosts is a disease characterised by low bone mass and microarchitectural deterioration. of bone tissue leading to enhanced fragility and a consequent increase in fracture risk. In western society, the lifetime risk of a fragility fracture in a 50 year old Caucasian woman is 45% and in a man is 13%. A major question in osteoporosis research is why estrogen withdrawal at the menopause is associated with a decreased effectiveness of the mechanically adaptive response which matches bones' strength to their load-bearing. In both men and women the severity of bone loss is related to levels of bio-available estrogen. The mechanism underlying this association is not known since estrogen levels do not directly control bone mass. In contrast, mechanical loading substantially influences bone mass. Previous work from this laboratory has demonstrated that bone cells' early response to loading involves the estrogen receptor (ER) alpha. Recently, Wnt/b-catenin signalling has also been implicated in the regulation of bone mass through its involvement in bone cells' response to their mechanical environment. The aim of the study in this thesis was to determine whether the Wnt/b-catenin pathway was involved in bone cells' early responses to strain and if so whether the mechanisms of this response also involved the ER. Western blot and immunocytochemical analysis showed that in cells of the ROS 17/2.8 osteoblastic cell line a short period dynamic strain in vitro or lithium chloride (LlCl) treatment, an inhibitor of glycogen synthase kinase-Jf (GSK-3(3)), increased the expression of activated catenin and stimulated nuclear accumulation within 3 hours. Strain and LiCl also induced a significant increase in TCF/LEF mediated transcriptional activity. Estrogen treatment had no influence on the level or distribution of activated b-catenin at the time points studies, or any effect on TCF/LEF mediated activation.

Lower bone mineral density (BMD) and increased fracture risk have recently been linked with elevated homocysteine and/or the metabolically related B-vitamins. The most important genetic determinant of homocysteine is the 677C~ T polymorphism (IT genotype) in methylenetetrahydrofolate reductase (MTHFR) which has been associated with lower BMD. The B-vitamins, folate and riboflavin can modulate the expected phenotype of elevated homocysteine, with riboflavin intervention resulting in a marked lowering of homocysteine levels specifically in those with the TT genotype. The overall aim of this thesis is to investigate the association between the IT genotype, homocysteine, the related B-vitamins and bone health in healthy women and an 'at-risk' patient group. In an observational study of well-nourished postmenopausal women this research showed no evidence of lower BMD in individuals pre-screened for the TT genotype (n = 77) when compared to age-matched heterozygous CT (n = 90) and wild-type CC (n = 84) genotypes. Furthermore, there was no evidence of a gene-nutrient interaction in relation to riboflavin status and BMD among participants with the IT genotype. This project presents the first intervention study to show that riboflavin can lower homocysteine in women pre-screened for the TT genotype, and also that a combination of folic acid and riboflavin is more effective than riboflavin alone. Coeliac disease (CD) is a condition which frequently presents with lower BMD and nutrient malabsorption, particularly folate. A case-control study from this thesis showed that compromised folate status and/or elevated homocysteine may contribute to lower BMD in female CD patients, particularly in untreated patients who have not commenced treatment with a gluten-free diet. In a pilot follow-up study with CD patients there was also a suggestion that lower folate status was associated with a greater rate of bone loss, however this effect appeared to be small compared with the role of vitamin D status. Thus individuals with more compromised B-vitamin status and/or elevated homocysteine, due to inadequate dietary intake or malabsorption may be more at risk of osteoporosis.

Background: Low peak bone mass is an important risk factor for osteoporotic fracture. Despite heritability of 50-85%, genetic studies have failed to identify a significant susceptibility locus. With advances in genotyping technologies, a genome-wide association (GWA) approach now allows an unbiased search for genetic determinants. Aim: To perform a GWA study using pooled DNA samples (as the cost of individual genotyping is prohibitive) to identify genetic loci associated with bone accrual in a cohort where all known confounding factors could be accounted for Methods: The Young Hearts 2000 Project carried out an in-depth survey of 1700 Northern Irish secondary school children. PIXI DXA scans of wrist and heel were performed and blood was collected. 1318 subjects had complete data available within separate age/sex groups: 12yr boys and girls, 15yr old boys and girls. BMD measurements were ranked after adjustments for age, BMI and pubertal status. Within each group, 50 subjects with the highest (controls) and 50 subjects with the lowest (cases) corrected BMD scores were selected giving a total of 400. DNA was extracted manually from stored buffy coat and pooled DNA was analysed using Illumina's HumanHap550 Genotyping BeadChip. The raw data for each SNP was compared between high and low BMD pools. Results: Clusters of SNPs that showed the greatest differences between high and low BMD pools were at Chr7 - GRM8, Chr8 - SGCZ, Chr15 - TRPM7 and Chr16 - TRAP1. These differences were confirmed on individual genotyping with p-values<0.05 for the SNPs within GRM8, SGCZ and TRAP 1. The SGCZ region showed the strongest association with BMD across the age groups. The TRAP 1 region was confirmed in replication pools. These genes each have described activity in bone and therefore are reasonable candidates for association with bone accrual and warrant further replication studies.

PCOS is the commonest endocrine disorder amongst women associated with insulin resistance and adverse metabolic outcomes e.g. T2DM, dyslipidemia. TlDM, another metabolic disorder, on the other hand, results from auto immune destruction of insulin- producing pancreatic ~-cells, leading to hyperglycemia and its deleterious effects. The metabolic syndrome is associated with accumulation of visceral AT, which produces cytokines termed 'adipokines' implicated in the pathogenesis of diabetes and atherosclerosis. Circulating and AT omentin-l, an insulin sensitizing adipokine, were decreased in women with PCOS; metformin treatment (6 months) increased circulating omentin-l levels. Insulin and glucose decreased omentin-l production in AT; insulin also decreased circulating omentin-l in vivo. Furthermore, in vitro migration and angiogenesis were increased by serum from PCOS women compared to controls; these effects were attenuated by metformin treatment plausibly through the regulation of omentin-l levels via NF-KB (a pro-inflammatory nuclear transcription factor) and Akt pathways. CRP and VEGF induced in vitro migration and angiogenesis was decreased by omentin-l. In another study, there was a decrease in circulating omentin-l together with an increase in circulating adiponectin (fasting and postprandial), in TlDM subjects. Also, circulating and AT ASAA, a pro-inflammatory adipokine, which antagonizes insulin action, were increased in women with PCOS; metformin treatment (6 months) decreased circulating ASAA levels. Glucose increased ASAA production in AT. ASAA production by macrophages may account for these observations. Finally, circulating HMW and total adiponectin, an anti-inflammatory and insulin sensitizing adipokine, were higher in the morning and lower at night; corresponding NF-KB activities in serum treated endothelial cells were lower in the morning and higher at night. Hyperinsulinemic induction decreased HMW and total adiponectin levels but increased NF-N B activity in serum treated endothelial cells. These studies provide novel insights into the biology of adipokines, inflammation and insulin action pertinent to dysmetabolic states such as PCOS and diabetes.

Osteoporotic fractures in the elderly are a worldwide epidemic and the increasing ageing of the global population means that the economic cost of these fractures will continue to rise. Leading a physically active lifestyle offers one preventative measure, so it is important that the general public knows precisely how to exercise. This thesis describes investigations into the effects of brief, high-impact, unilateral exercise on neuromuscular and bone health, concentrating on defining the optimum weekly frequency of exercise required for healthy but sedentary premenopausal women to maximise their peak bone mass.

The western world faces an explosion in the number of patients who will fracture their proximal humerus (PH) as a result of the rapidly changing demographics and the increase in osteoporosis. In 1998 there were 110 000 PH fractures in the United Kingdom (UK) and epidemiological studies indicate that the PH fracture incidence is increasing. Scant evidence exists to the optimum management and rehabilitation of these fractures and the aims of the study were to investigate the effect of an accelerated rehabilitation programme on patients' recovery. A Randomised Controlled Trial (RCT) comparing two rehabilitation programmes (n=86) with patients who sustained two-part fractures of the proximal humerus was performed. Patients were randomised to receive immediate physiotherapy within one week (Group A) or delayed physiotherapy (Group B) after 3 weeks immobilisation. Assessment was at 8, 16 and 52 weeks with the Constant Shoulder Score (CSS), Short form generic health survey (SF-36) and Croft Shoulder Disability Questionnaire (CSDQ). Additional reassessment was undertaken at two years. Regression analysis modelling was conducted to identify the risk factors for developed long-term shoulder disability. At the primary outcome point (16 weeks) Group A experienced less pain (p < 0.01) and had greater shoulder function (p < 0.001) compared to Group B. At 52 weeks the differences between the Groups had reduced. Overall, Group A experienced less pain as measured with the SF-36 (mean difference 486 Cl 83 to 889, p < 0.01) and improvedshoulder function (mean difference in AUC 6.4 [95% Cl: 2.5 to 10.5], p < 0.002). At one year, shoulder disability (CSDQ) was 42.8% in Group A and 72.5% in Group B (p < 0.01). By two years, shoulder disability in Group A remained unchanged (43.2%), but had reduced in Group B (59.5%). Immediate physiotherapy following a proximal humerus fracture results in faster recovery with maximal functional benefit being achieved at one year and requires fewer treatment sessions (9 versus 14 treatments, Group-A and B respectively). Delayed rehabilitation by three weeks shoulder immobilisation produces a slower recovery. The belief that patients make an excellent recovery after one year is questionable as 25 patients (33.5%) still reported considerable shoulder disability after two years of their injury. Gender (female), age and high levels of social deprivation were identified as risk factors for continued shoulder problems at two years after the fracture. This work suggests that patients who fracture their PH should not be immobilised before referral for physiotherapy as immediate referral to physiotherapy (within 1 week) results in faster recovery and less reported pain. Physiotherapy should be targeted towards those patients who are identified as having a greater risk of developing long-standing problems. Currently, a wide variation in PH fracture management exists in UK hospitals and implementing clinical care pathways will help target finite resources.

The preferred method of assessing the risk of an osteoporosis related fracture is currently a measure of bone mineral density (BMD) by dual energy X-ray absorptiometry (DXA). However, other factors contribute to the overall risk of fracture, including anatomical geometry and the spatial distribution of bone. Finite element analysis can be performed in both two and three dimensions, and predicts the deformation or induced stress when a load is applied to a structure (such as a bone) of defined material composition and shape. The simulation of a mechanical compression test provides a measure of whole bone stiffness (N mm−1). A simulation system was developed to study the sensitivity of BMD, 3D and 2D finite element analysis to variations in geometric parameters of a virtual proximal femur model. This study demonstrated that 3D FE and 2D FE (FEXI) were significantly more sensitive to the anatomical shape and composition of the proximal femur than conventional BMD. The simulation approach helped to analyse and understand how variations in geometric parameters affect the stiffness and hence strength of a bone susceptible to osteoporotic fracture. Originally, the FEXI technique modelled the femur as a thin plate model of an assumed constant depth for finite element analysis (FEA). A better prediction of tissue depth across the bone, based on its geometry, was required to provide a more accurate model for FEA. A shape template was developed for the proximal femur to provide this information for the 3D FE analysis. Geometric morphometric techniques were used to procure and analyse shape information from a set of CT scans of excised human femora. Generalized Procrustes Analysis and Thin Plate Splines were employed to analyse the data and generate a shape template for the proximal femur. 2D Offset and Depth maps generated from the training set data were then combined to model the three-dimensional shape of the bone. The template was used to predict the three-dimensional bone shape from a 2D image of the proximal femur procured through a DXA scan. The error in the predicted 3D shape was measured as the difference in predicted and actual depths at each pixel. The mean error in predicted depths was found to be 1.7mm compared to an average bone depth of 34mm. 3D FEXI analysis on the predicted 3D bone along with 2D FEXI for a stance loading condition and BMD measurement were performed based on 2D radiographic projections of the CT scans and compared to bone stiffness results obtained from finite element analysis of the original 3D CT scans. 3D FEXI provided a significantly higher correlation (R2 = 0.85) with conventional CT derived 3D finite element analysis than achieved with both BMD (R2 = 0.52) and 2D FEXI (R2 = 0.44).

Osteoporosis is a metabolic skeletal disease characterized by low bone mass, depleted micro-architecture and reduced strength. The public health costs of osteoporosis relate almost entirely to the fractures that are the clinical manifestation of the disease and it presents a significant cause of morbidity in today’s ageing population. Oestrogen deficiency during the menopause is the primary causative factor for postmenopausal osteoporosis and although much is known about the pathophysiology of the disease, including dysregulated bone cell function whereby more bone is digested than is formed; the underlying mechanisms involved have not yet been delineated. Recent studies have suggested that although overall strength is decreased following osteoporotic bone loss, the remaining bone tissue is stronger and stiffer, suggesting an alteration in bone tissue composition. Bisphosphonates are among drug treatments administered to tackle bone loss, however the incidence of osteoporotic fractures still remains high. Furthermore, the precise effect of drug treatment on bone tissue mineralisation is unknown. The global aim of this thesis is to discern the alterations in the quantity and distribution of bone mineral during osteoporosis. Specifically, it is sought to test the hypotheses that bone mineral distribution is altered at a tissue level following oestrogen deficiency and bisphosphonate treatment and that oestrogen depletion alters normal mineralisation and mechano-responsiveness of bone cells. Quantitative backscattered imaging (qBEI) on a scanning electron microscope was used to examine individual bone trabeculae from the proximal femur of ovariectomised sheep (oestrogen deficient state), aged matched control sheep and sheep treated with the bisphosphonate Zoledronic acid. It was found that oestrogen deficiency caused significantly higher mineral heterogeneity within trabeculae (site speficic within the femur) and along a common osteoporotic fracture line. Bone mineralisation was diminished with prolonged oestrogen deficiency and conversely was higher in older healthy sheep compared to younger control sheep. Furthermore, significantly lower mineral heterogeneity was found in OVX sheep treated with Zoledronic acid compared to untreated OVX sheep. These results indicate that changes in bone tissue mineralisation during oestrogen deficiency may be a contributing factor for reduced mechanical strength during osteoporosis, while drug induced increased homogeneity may contribute to the ability of Zoledronic acid to prevent fracture occurrence during oestrogen deficiency. The next study aimed to delineate the mechanisms responsible for such altered mineral distribution. Osteoblast and osteocyte cells were pre-treated with oestrogen and the effects of oestrogen deficiency were evaluated by subsequently withdrawing oestrogen from cells, or blocking oestrogen receptors using an oestrogen antagonist, fulvestrant. Specifically, alkaline phosphatase expression was investigated using p-nitrophenyl phosphate (pNPP), proliferation by assessing DNA content, calcium production using alizarin red assay and apoptosis by measuring for caspase 3/7 activity. Although mineral production was significantly increased by oestrogen pre-treatment, a further increase in mineral production and apoptosis were observed following oestrogen withdrawal from cells. These observations increase our understanding of the mechanisms controlling bone formation and bone cell death and may aid in the development of enhanced therapeutics for the treatment of osteoporosis. The final study of this thesis aimed to determine if the mechano-biological response of osteoblasts is impaired during oestrogen deficiency and whether changes in bone mineralisation may be related to altered bone formation in response to mechanical stimulation. Osteoblasts were pre-treated with oestrogen and subsequently oestrogen was withdrawn from cell cultures and their responses under fluid shear stress were evaluated. Firstly, daily loading cycles, using an orbital rotator, were applied to cells and mineralisation and cell viability (using alamar blue assay) were assessed after 7 and 14 days. In a separate experiment, following 2 and 7 days of oestrogen withdrawal, osteoblasts were exposed to 2 hours of shear stress in a custom designed parallel plate bioreactor. PGE2 was quantified in cell culture conditioned media using an immunoassay kit. It was found that orbital fluid flow induced shear stress significantly increased mineral production by bone cells and that under an applied shear stress, mineral production was decreased during oestrogen withdrawal. It was also observed that mechanical loading and oestrogen are required in unison to promote mineral production. PGE2 release was significantly increased with applied laminar flow, but was decreased by oestrogen withdrawal. Together, these studies provide evidence that bone cells become accustomed to levels of circulating oestrogen and that diminished oestrogen causes osteocyte apoptosis, increased osteoblast mineralisation and altered mechano-sensitivity. These changes might explain the decreased mean concentrations of mineral, together with increased mineral heterogeneity, from our earlier in vivo studies. Therefore, the results of the thesis provide a unique insight into why the tightly coupled mechanisms of matching bone’s structure and composition to the loads it experiences are disrupted when levels of circulating oestrogen are depleted.

Η οστεοπόρωση αποτελεί την πιο συχνή μεταβολική διαταραχή των οστών που οδηγεί σε αυξημένη ευθραυστότητα αυτών και κατά συνέπεια σε χαμηλής ενέργειας κατάγματα. Τα συνηθέστερα οστεοπορωτικά κατάγματα συμβαίνουν στην περιοχή της πηχεοκαρπικής άρθρωσης, στους σπονδύλους καθώς και στο ισχίο, οστά δηλαδή στα οποία η αναλογία σπογγώδους και φλοιώδους οστού είναι συγκεκριμένη. Λόγω του μεγέθους του προβλήματος, υπάρχει μεγάλο ενδιαφέρον για την εκτίμηση της οστεοπόρωσης και κατ’ επέκταση τη πρόβλεψη του κινδύνου κατάγματος. Μια σειρά από διαφορετικές τεχνικές έχουν αναπτυχθεί για τη μέτρηση διαφόρων σκελετικών περιοχών ως μέσο για την εκτίμηση του κινδύνου κατάγματος. Η απορροφησιομετρία ακτίνων-Χ διπλής ενέργειας (DXA) είναι η τεχνική που χρησιμοποιείται πιο συχνά για την διάγνωση της οστεοπόρωσης μέσω της εκτίμησης της οστικής πυκνότητας BMD. Ωστόσο, στην πραγματικότητα, μόνο το 60% της διακύμανσης της οστικής αντοχής μπορεί να εξηγηθεί από τις διακυμάνσεις της επιφανειακής οστικής πυκνότητας. Στη συγκεκριμένη μελέτη σταθήκαμε κυρίως στην απορροφησιομετρία ακτίνων-Χ διπλής ενέργειας, στην περιφερική ποσοτική υπολογιστική τομογραφία (pQCT) και στην απεικόνιση μαγνητικού συντονισμού (MRI). Κλινικές και πειραματικές μελέτες έχουν δείξει ότι η απεικόνιση μαγνητικού συντονισμού έχει το δυναμικό να είναι μια χρήσιμη μέθοδος για την μελέτη του σπογγώδους οστού. Το τεχνικό υπόβαθρο αυτής της μεθόδου μπορεί να εξηγηθεί από τις διαφορές της μαγνητικής επιδεκτικότητας στην διεπιφάνεια μεταξύ του σπογγώδους οστού και του μυελού των οστών, που οδηγούν σε χωρικές ανομοιογένειες του μαγνητικού πεδίου. Αυτές οι ανομοιογένειες έχουν ως αποτέλεσμα την εκτροπή της συμφασικότητας της εγκάρσιας μαγνήτισης. Αυτό οδηγεί στην μεταβολή της τιμής του Τ2* του μυελού του οστού. Η μεταβολή του Τ2* μαζί με τα χαρακτηριστικά αυτού του χρόνου χαλάρωσης παρέχουν πληροφορίες για την πυκνότητα και την δομή του περιβάλλοντος σπογγώδους οστικού πλέγματος (ms). Οι κύριοι στόχοι της παρούσας μελέτης ήταν: α) Ο προσδιορισμός της ικανότητας των μετρήσεων του ενεργού εγκάρσιου χρόνου χαλάρωσης Τ2* να επιτύχει διάκριση μεταξύ γυναικών με φυσιολογική ή οστεοπορωτική αρχιτεκτονική του σπογγώδους οστού. β) Η συσχέτιση του εγκάρσιου χρόνου χαλάρωσης Τ2* με τους δείκτες aBMD, vBMD και Trabecular Density που λαμβάνεται μέσω των εξετάσεων DXA και pQCT αντίστοιχα. γ) Η εκτίμηση της ακρίβειας των μετρήσεων του Τ2* μαγνητικού συντονισμού σε συγκεκριμένα τμήματα του ανθρώπινου σώματος με πρωτεύοντα στόχο την περιοχή της οσφυϊκής μοίρας και της κνήμης. Μετά από τη σχετική έγκριση των Επιτροπών Βιοηθικής και Έρευνας του Π.Γ.Ν. «Αττικόν» και του Γ.Ν.Α. «ΚΑΤ», στη μελέτη μας συμμετείχαν 15 μετεμμηνοπαυσιακές γυναίκες και 5 υγιείς, οι οποίες αποτέλεσαν την ομάδα ελέγχου. Όλες οι συμμετέχοντες πραγματοποίησαν τις εξετάσεις των pQCT κνήμης και οστικής πυκνότητας ΟΜΣΣ, στα ίδια συστήματα pQCT και DXA του Γ.Ν.Α. «ΚΑΤ». Έπειτα, για την διεξαγωγή της μαγνητικής τομογραφίας ΟΜΣΣ-κνήμης, οι 15 μετεμμηνοπαυσιακές γυναίκες χωρίστηκαν σε δυο ομάδες. Η Α ομάδα αποτελούμενη από 9 μετεμμηνοπαυσιακές γυναίκες, πραγματοποίησε την μαγνητική τομογραφία στον μαγνητικό τομογράφο του Ευγενίδειου Θεραπευτηρίου και αντίστοιχα, η Β ομάδα αποτελούμενη από 6 μετεμμηνοπαυσιακές γυναίκες πραγματοποίησε την μαγνητική τομογραφία στον μαγνητικό τομογράφο του Π.Γ.Ν. «Αττικόν». Η ομάδα των 5 υγιών ατόμων, πραγματοποίησε την εξέταση και στα δυο συστήματα μαγνητικής τομογραφίας, ώστε να διερευνηθεί το κατά πόσον η ένταση του μαγνητικού πεδίου επηρεάζει τις παραμέτρους που επρόκειτο να υπολογιστούν. Για τον υπολογισμό της οστικής πυκνότητας της οσφυϊκής μοίρας, ελήφθησαν προσθοπίσθιες προβολές της ΟΜΣΣ και πιο συγκεκριμένα των οσφυϊκών σπονδύλων Ο1 – Ο4 και υπολογίστηκε τόσο η μέση τιμή BMD των Ο1 – Ο4, όσο και η τιμή BMD κάθε σπονδύλου ξεχωριστά. Επιπρόσθετα, σε κάθε ασθενή ελήφθησαν υπόψη τα στοιχεία που προκύπτουν από την μελέτη της τομής 4% του μήκους της κνήμης από την κάτω αρθρική επιφάνεια. Η τομή 4% παρέχει πληροφορίες για το σπογγώδες οστό και οι προτεινόμενες παράμετροι που συλλέχθηκαν ήταν η ογκομετρική πυκνότητα του σπογγώδους οστού (trabecular density) και η ολική πυκνότητα οστού (total density, vBMD). Στην απεικόνιση μαγνητικού συντονισμού, ελήφθησαν ακολουθίες πολλαπλών αντηχήσεων (multi echo) και πολλαπλών τομών (multi slice) για την μέτρηση του εγκάρσιου χρόνου χαλάρωσης T2* χωρίς καταστολή λίπους σε εγκάρσιο και στεφανιαίο επίπεδο. Εν συνεχεία, για την εκτίμηση του εγκάρσιου χρόνου χαλάρωσης T2 ελήφθησαν ανατομικές ακολουθίες Τ2 προσανατολισμού χωρίς καταστολή λίπους σε εγκάρσιο και στεφανιαίο επίπεδο. Στην κεντρική τομή που αντιστοιχεί στο 4% του μήκους της κνήμης από την κάτω αρθρική επιφάνεια καθώς και στις κεντρικές τομές των οσφυϊκών σπονδύλων Ο1 – Ο4, σχεδιάστηκαν οι περιοχές ενδιαφέροντος (ROI) σε όλες τις εικόνες διαφορετικών ΤΕ. Εν συνεχεία, με τη χρήση του λογισμικού IDL πραγματοποιήθηκε αλγόριθμος ανάλυσης Levenberg – Marquadt με τον οποίον έγινε ο υπολογισμός των χρόνων Τ2* και Τ2. Τα αποτελέσματα στην παρούσα μελέτη δείχνουν μια σημαντική θετική συσχέτιση των παραμέτρων οστικής πυκνότητας των περιοχών της ΟΜΣΣ και της κνήμης μεταξύ τους, (r= 0.76 – 0.86, p<0.05). Επιπρόσθετα, έγινε συσχέτιση όλων των παραμέτρων της οστικής πυκνότητας με την ηλικία των εξεταζόμενων γυναικών, όπου σημειώθηκαν ικανοποιητικές αρνητικές συσχετίσεις, (r= -0.66 - -0.73, p<0.05). Ακόμα, σημειώθηκε ικανοποιητική θετική συσχέτιση του εγκάρσιου χρόνου χαλάρωσης T2*, ιδιαίτερα για την περιοχή της κνήμης, με την ηλικία των εξεταζόμενων γυναικών (r= 0.59 – 0.67, p<0.05). Για το σύστημα των 3Τ, ο χρόνος Τ2* στην περιοχή της οσφυϊκής μοίρας ήταν μικρότερος στην ομάδα ελέγχου (4,9 ± 0,4 ms) σε σχέση με την ομάδα Β των μετεμμηνοπαυσιακών γυναικών (5,5 ± 0,8 ms). Για τους χρόνους Τ2, η διαφοροποίηση φάνηκε να είναι πιο ξεκάθαρη, καθώς για την ομάδα ελέγχου, ο χρόνος Τ2 ήταν 65,7 ± 2,4 ms, ενώ για την ομάδα Β 84,7 ± 2,7 ms. Για τις μετρήσεις στην περιοχή της κνήμης, οι χρόνοι Τ2* που καταγράφηκαν ήταν 7,8 ± 0,6 ms για την ομάδα ελέγχου και 9,4 ± 0,4 ms για την ομάδα Β και την mFFE ακολουθία. Αντίστοιχα για την shortest ακολουθία οι χρόνοι χαλάρωσης ήταν 9,0 ± 0,5 ms και 10,8 ± 0,4 ms. Ωστόσο, η διαφορά στους χρόνους Τ2 των δυο ομάδων δεν επέτρεψε τον ασφαλή διαχωρισμό τους, με κριτήριο τον χρόνο αυτό. Για το σύστημα του 1.5 Τ, ο χρόνος Τ2* στην περιοχή της οσφυϊκής μοίρας ήταν μικρότερος στην ομάδα ελέγχου (14,0 ± 1,5 ms) σε σχέση με την ομάδα Γ των μετεμμηνοπαυσιακών γυναικών (20,4 ± 1,2 ms). Αντιθέτως, τα αποτελέσματα των χρόνων Τ2, δεν προσέφεραν κάποιο ξεκάθαρο συμπέρασμα. Αναφορικά με τις μετρήσεις της κνήμης, παρατηρήθηκαν ικανοποιητικές διαφορές μεταξύ των χρόνων Τ2* των δυο ομάδων και για τις δυο ακολουθίες (mFFE και mFFE shortest). Οι χρόνοι που σημειώθηκαν ήταν 16,7 ± 1,2 ms για την ομάδα ελέγχου και 20,9 ± 1,7 ms για την ομάδα Γ και την mFFE ακολουθία. Αντίστοιχα, για την shortest ακολουθία οι χρόνοι χαλάρωσης ήταν 16,5 ± 1,2 ms και 20,6 ± 1,6 ms. Επίσης, η διαφορά των χρόνων Τ2 των δυο ομάδων ήταν ικανοποιητική, (91,6 ± 2,4 ms για την ομάδα Α και 99,0 ± 2,8 ms για την ομάδα Γ). Συμπερασματικά, η παρούσα μελέτη απέδειξε πως μέσω του φαινομένου της αποκατάστασης μαγνητικού συντονισμού και κατ’ επέκταση της μέτρησης των εγκάρσιων χρόνων αποκατάστασης (χαλάρωσης) T2* και T2, μπορούν να εκτιμηθούν μεταβολές της κατάστασης των οστών που σχετίζονται με την ηλικία και την οστική πυκνότητα, μεταξύ υγιών και μετεμμηνοπαυσιακών γυναικών. / Osteoporosis is the most common metabolic bone disorder leading to increased fragility and consequently to low energy fractures. The most common osteoporotic fractures occur in the wrist joint, the vertebrae and the hip, i.e. bones in which the ratio of trabecular and cortical bone is specific. Because of the problem magnitude, there is great interest in assessing osteoporosis and hence the prediction of the fracture risk. A number of different techniques have been developed to measure different skeletal sites as a tool for assessing the fracture risk. The dual energy X-ray absorptiometry (DXA) is the most frequently used technique for the diagnosis of osteoporosis by evaluating the bone mineral density BMD. However, in reality, only 60% of the variation in bone strength can be explained by variations in areal bone density. In this study, we mainly stood in dual energy X-ray absorptiometry, peripheral quantitative computed tomography (pQCT) and magnetic resonance imaging (MRI). Clinical and experimental studies have shown that magnetic resonance imaging has the potential to be a useful method for the study of trabecular bone. The technical background of this method can be explained by the differences in the magnetic susceptibilities between the inter-surfaces of trabecular bone and bone marrow, leading to spatial inhomogeneities of the magnetic field. These inhomogeneities result in additional dephasing of transverse magnetization. The change in Τ2* together with the characteristics of this relaxation time, provide information on the density and structure of trabecular bone matrix (ms). The main objectives of this study were: a) To determine the ability of the active transverse relaxation time Τ2* measurements, to achieve discrimination between women with normal or osteoporotic trabecular bone architecture. b) The correlation of the transverse relaxation time Τ2* with aBMD, vBMD and Trabecular Density indicators, obtained through DXA and pQCT examinations, respectively. c) The assessment of Τ2* magnetic resonance measurements accuracy in certain parts of the human body, with primary target the area of lumbar spine and tibia. After the approval of Ethics and Research Committees of Attikon University Hospital and K.A.T. General Hospital, 15 postmenopausal women and 5 healthy, which formed the control group, participated in our study. All the participants performed the pQCT tibia and lumbar spine bone mineral density examinations, at the same pQCT and DXA systems of K.A.T. General Hospital. Then, for the magnetic resonance imaging examination conduct of lumbar spine – tibia, the 15 postmenopausal women were divided into two groups. The group A, consisting of 9 postmenopausal women, conducted the MRI examinations at the MRI scanner of Eugenedion Hospital and respectively, the group B, consisting of 6 postmenopausal women performed the MRI scans at the MRI scanner of Attikon University Hospital. The group of the 5 healthy subjects performed the examination in both magnetic resonance imaging scanners in order to investigate whether the magnetic field affects the parameters that were to be calculated. To calculate the BMD of the lumbar spine, anteroposterior views of the lumbar spine and more specifically of the lumbar vertebrae L1 - L4 were obtained. The mean BMD of L1 - L4 and the BMD for each vertebra separately, were calculated. Additionally, for each patient, the data resulting from the study of the section 4% of the tibia length from the lower articular surface were taken into account. The section 4% provides information on the trabecular bone and the proposed parameters which were collected were the volumetric density of the trabecular bone (trabecular density) and the total bone density (total density, vBMD). In magnetic resonance imaging, multiple echoes (multi echo) and multiple slices (multi slice) sequences were received for measuring the transverse relaxation time Τ2*, without fat suppression in transverse and coronal plane. Thereafter, for assessing the transverse relaxation time Τ2, Τ2 - weighted anatomical sequences were received, without fat suppression in transverse and coronal plane. In the central section corresponding to 4% of the tibia length from the lower articular surface and in the central sections of lumbar vertebrae L1 - L4, were designed regions of interest (ROI) in all different TE images. Then, using the IDL software, Levenberg - Marquadt analysis algorithm was held, in which Τ2* and Τ2 times were calculated. The results in this study show a significant positive correlation between the parameters of lumbar spine and tibia bone density, (r = 0.76 - 0.86, p <0.05). Additionally, there was correlation of all parameters of bone mineral density with the age of the examined women, where there were sufficient negative correlations, (r = -0.66 - -0.73, p <0.05). Still, there has been good correlation between the transverse relaxation time Τ2*, especially for the region of the tibia, with the age of the examined women (r = 0.59 - 0.67, p <0.05). For the system of 3T, the Τ2* time, in the lumbar spine, was lower in the control group (4,9 ± 0,4 ms) compared to the group B of postmenopausal women (5,5 ± 0,8 ms). For the Τ2 time, the differentiation seemed to be clearer, as for the control group, the Τ2 was 65,7 ± 2,4 ms, while for group B 84,7 ± 2,7 ms. For the tibia measurements, Τ2* times which were recorded, were 7,8 ± 0,6 ms for the control group and 9,4 ± 0,4 ms for group B and the mFFE sequence. Respectively, for the shortest sequence, relaxation times were 9,0 ± 0,5 ms and 10,8 ± 0,4 ms. However, the Τ2 time difference for the two groups, did not allow safe separation, based on this time. For the system of 1.5 T, the Τ2* time, in the lumbar spine, was lower in the control group (14,0 ± 1,5 ms) compared to the group C of postmenopausal women (20,4 ± 1,2 ms). In contrast, the Τ2 time results, did not offer a clear conclusion. Regarding the tibia measurements, there were seen satisfactory differences between the Τ2* times of the two groups, for both sequences (mFFE and mFFE shortest). The recorded times were 16,7 ± 1,2 ms for the control group and 20,9 ± 1,7 ms for group C, for the mFFE sequence. Respectively, for the shortest sequence the relaxation times was 16,5 ± 1,2 ms and 20,6 ± 1,6 ms. Also, the Τ2 time difference between the two groups was satisfactory, (91,6 ± 2,4 ms for group A and 99,0 ± 2,8 ms for group C). In conclusion, this study demonstrated that, through the phenomenon of magnetic resonance recovery and hence the measurement of the transverse recovery (relaxation) times Τ2* and Τ2, can assess changes in bone status related to age and bone mineral density, between healthy and postmenopausal women.

L’ostéoporose ménopausique par une accélération du remodelage osseux, conduit à une masse osseuse basse et à des altérations de la microarchitecture, augmentant ainsi le risque de fracture. Les bisphosphonates diminuent l’activité du remodelage osseux en inhibant la résorption osseuse qui conduit à un maintien de la densité minérale osseuse et à une diminution du risque fracturaire. Ce traitement étant la plupart du temps chronique, l’étude de ses effets sur les différents niveaux d’organisation de l’os, du cristal à sa macrostructure, est primordiale. A travers deux études portant sur l’ibandronate et l’alendronate, nous avons montré que leur utilisation préservait la minéralisation osseuse tissulaire. Cependant, une utilisation prolongée (6,4 ans) de l’alendronate, nous a permis de mettre en évidence un mécanisme d’action impliquant des modifications de la structure des cristaux avec un effet sur les propriétés mécaniques locales. Si l’efficacité anti fracturaire de l’alendronate est démontrée après dix ans de traitement, nos résultats suggèrent des altérations de la qualité osseuse à une échelle plus locale / Postmenopausal osteoporosis is characterized by an increase in remodelling activity leading to a low bone mass and alterations in microarchitecture, increasing the risk of fracture. Bisphosphonates slowdown remodeling inhibiting bone resorption, thus bone mineral density is preserved with a decrease in the risk of fracture. Such a treatment is often chronic, making the study of their long-term effects on multiscale bone quality (from the crystal to the macrostructure) of clinical relevance. Thank to two different studies on ibandronate and alendronate, we showed that these treatments preserved the mineralization of bone tissue. However, we firstly described that a long-term treatment with alendronate alter the structure of bone mineral crystals with a direct effect on micromechanical properties. Even if, the reduction in the risk of fracture under alendronate has been established after a ten year treatment, our results suggest alterations in bone quality at tissular and sub-tissular levels of organization