Relationship between bone mineral density and bone stiffness in bone fracture

Objectives Using cancellous bone blocks of racehorses, the relationship between bone mineral density (BMD), which indicates bone strength, and stiffness in bone fracture occurrences was studied.Methods Two groups of cancellous bone blocks were prepared: a fractured group, using the first phalangeal bones of seven racehorses with sagittal fractures; and a nonfractured group, using the first phalangeal bones of nine autopsied racehorses without any fractures. By a peripheral quantitative computed tomography scan, the BMD values were shown as color images and evaluated. In addition, the BMD values obtained from the fractured and nonfractured groups were compared with the stiffness values obtained from a compression test.Results The difference between the average BMD values of the fractured and nonfractured groups was easily observed on the BMD color-conversion display image. The average BMD of the fractured group (472.1 mg/cm³) was significantly higher than that of the nonfractured group (284.5 mg/cm³, P = 0.005). Moreover, the average stiffness of the fractured group (5564.5 N/cm) was significantly higher than that of the nonfractured group (3808.6 N/cm, P = 0.008).Conclusion These results suggest that the occurrence of a fracture does not depend on the BMD or the bone stiffness value.     

胞元结构形式、材料性质对松质骨力学性能的影响

将均匀化理论与有限元方法相结合 ,讨论了骨小梁的弹性模量、泊松比和构成松质骨微结构的形式对松质骨力学性质的影响。结果表明微结构的形式和固体体分比确定时 ,松质骨的弹性模量与骨小梁弹性模量之间存在着确定的数量关系 ;当微结构的固体体分比较小时 ,骨小梁的泊松比对松质骨的弹性模量几乎没有影响。讨论了微结构形式对松质骨弹性模量的影响。     

Effect of slow-release sodium fluoride on cancellous bone histology and connectivity in osteoporosis

We have previously demonstrated that a treatment regimen of slow-release sodium fluoride (SRNaF) and continuous calcium citrate increases lumbar bone mass, improves cancellous bone material quality, and significantly reduces vertebral fracture rate in osteoporotic patients. In order to assess whether such treatment also improves trabecular structure, we quantitated cancellous bone connectivity before and following 2 years of therapy with SRNaF in 23 patients with osteoporosis and vertebral fractures. In addition, we performed bone histomorphometry on the same sections used for connectivity measurements. There was a significant increase in L2-L4 bone mineral density during therapy (0.827 ± 0.176 g/cm² SD to 0.872 ± 0.166, p = 0.0004). Significant histomorphometric changes were represented by increases in mineral apposition rate (0.6 ± 0.4μm/d to 1.1 ± 0.7, p = 0.0078) and adjusted apposition rate (0.4 ± 0.3 μm/d to 0.6 ± 0.4, p = 0.016). On the other hand, trabecular spacing significantly declined (from 1375 ± 878 μm to 1052 ± 541, p = 0.05). Two-dimensional quantitation of trabecular struts on iliac crest histological sections disclosed significant increases in mean node number per mm² of cancellous tissue area (0.22 ± 0.12 vs. 0.39 ± 0.27, p = 0.0077), the mean node to free-end ratio (0.23 ± 0.21 vs. 0.41 ± 0.46, p < 0.05), and in the mean node to node strut length per mm² of cancellous area (0.098 ± 0.101 vs. 0.212 ± 0.183, p < 0.01). There were no significant changes in any of the measurements associated with free-end number or free-end to free-end strut length. When patients were divided into those with severe and mild-modest spinal bone loss (based upon initial lumbar bone density) the significant changes in connectivity occurred in patients with mild-moderate bone loss, but not in those with severe bone loss, suggesting that fluoride's effect is in part dependent on the presence of a certain critical amount of bone. This finding in combination with the previously reported increases in bone mass and bone material quality may explain the significant reduction in vertebral fracture rate observed with this particular fluoride regimen.     

Saw tooth cardiomyopathy : comment mieux faire le diagnostic ?

With the increasing use of cardiac MRI, several cases were described as “sawtooth cardiomyopathy” or “tiger heart”. The pathological aspects of these rare forms of myocardial dysplasia, frequently assimilated to non-compaction of the left ventricle, and its prognostic implications remain unclear. We present a case of “sawtooth cardiomyopathy” in a patient with a transient ischemic attack. This article aims to determine, with the other clinical cases in the literature, the MRI and echocardiography criteria for the diagnosis of this cardiomyopathy. Sawtooth cardiomyopathy is probably under diagnosed and deserves to be better known.     

可注射硫酸钙修复骨质疏松大鼠股骨近端骨小梁的实验研究*

目的探讨可注射硫酸钙植入对骨质疏松大鼠股骨近端骨小梁的影响。方法复制去卵巢大鼠骨质疏松模型,采用穿刺注射技术将可注射硫酸钙植入骨质疏松实验大鼠股骨近端,对侧做自身对照,于术后2、4、8、12周取材,对双侧股骨近端行影像学、组织学观察,骨组织形态计量学及双能x线骨密度测定。结果影像学显示：术后4、8、12周实验侧股骨近端密度明显高于对照侧。骨组织学检查显示：术后4周实验侧硫酸钙降解,出现成骨效应;8周股骨近端穿刺注射区域已为致密、分化不成熟的骨小梁所填充;12周股骨近端骨小梁得到较好修复,为成熟的骨小梁组织所填充;对照侧为典型骨质疏松病理改变。骨组织形态计量学测定显示：术后8和12周实验侧骨小梁面积百分数、骨小梁宽度和骨小梁数量显著高于对照侧,实验侧骨小梁分离度显著小于对照侧。术后2、4、8、12周实验侧股骨近端骨密度较对照侧明显增加。结论可注射硫酸钙能快速有效的修复骨质疏松大鼠股骨近端骨小梁。     

Clinical L-Type CaChannel Blockade Prevents Ischemic Preconditioning of Human Myocardium

B. S. Cain, D. R. Meldrum, J. C. Cleveland, Jr, X. Meng, A. Banerjee and A. H. Harken. Clinical L-Type Ca²⁺Channel Blockade Prevents Ischemic Preconditioning of Human Myocardium. Journal of Molecular and Cellular Cardiology (1999) 31, 2191–2197. Although Ca²⁺channel blockers are commonly used to control both blood pressure and angina in patients with coronary artery disease, clinical trials have associated the use of -type Ca²⁺channel blockers with increased cardiovascular mortality. Recent evidence has implicated Ca²⁺entry through the -type Ca²⁺channel during transient ischemia as a proximal stimulus for ischemic preconditioning (IPC) in experimental animals. We therefore hypothesized that clinical -type Ca²⁺channel blockade prevents IPC in human myocardium. Human atrial trabeculae were suspended in organ baths, field simulated at 1 Hz, and force development was recorded. Following 90 min equilibration, trabeculae from control patients and patients taking -type Ca²⁺channel blockers were subjected to simulated ischemia/reperfusion (I/R: 45/120 min) with or without 5 min of simulated ischemia (IPC stimulus) prior to I/R. IPC increased post-ischemic developed force in control patients from 14.6±2.6 to 43.1±3.5% baseline developed force (%BDFP <0.05 I/R vs IPC). Whereas IPC failed to increase post-ischemic developed force in myocardium from patients taking -type Ca²⁺channel blockers (15.1±1.9 vs 16.6±1.7 %BDF,P >0.05 -type I/R v -type IPC). We conclude that: (1) atrial muscle can be preconditioned by transient ischemia; (2) atrial muscle from patients taking -type Ca²⁺channel blockers cannot be preconditioned by transient ischemia; and (3) the increased cardiovascular mortality historically associated with the use of Ca²channel blockers in patients with coronary artery disease may be, in part, due to the pharmacological inhibition of ischemic preconditioning.     

The concentration of calcium and phosphorus in trabecular bone from the iliac crest

Summary The concentrations of calcium and phosphorus were determined in central parts of bone trabeculae in the human iliac crest by means of an energy dispersive microanalysis technique. Two age groups, each consisting of six suddenly diseased male subjects, were investigated. It was found that the concentrations of calcium and phosphorus did not differ between young and old men. The obtained mean values were fairly alike and determined to 40 and 17 weight %, respectively.     

Trabecular bone is more deteriorated in spinal cord injured versus estrogen-free postmenopausal women

The prevalence of osteoporosis is high among postmenopausal women and individuals sustaining a spinal cord injury (SCI). We assessed the effects of estrogen loss and unloading on the trabecular bone of the knee in women. Pre- and postmenopausal ambulatory women (n=17) were compared to pre- and postmenopausal women with SCI (n=20). High-resolution magnetic resonance imaging was used to compare groups on apparent measures of trabecular bone volume, trabecular number, trabecular spacing, and trabecular thickness in the distal femur and proximal tibia, regions with a high proportion of trabecular bone and the most common fracture site for SCI patients. Trabecular bone was deteriorated in women with SCI compared to ambulatory women. SCI groups had fewer, (–19 and –26% less) and thinner trabeculae (–6%) that were spaced further apart (40% and 62% more space between structures) resulting in less trabecular bone volume (–22% and –33%) compared to the ambulatory groups (tibia and femur, respectively). Postmenopausal women with SCI also had 34% greater trabecular spacing in the tibia compared to the 40-year-old premenopausal women with SCI, showing an interaction between unloading and estrogen loss. Middle-aged postmenopausal, ambulatory women, not taking estrogen or medications that affect bone, did not show the deteriorated trabeculae that were evident in women with SCI, nor did they show differences in distal femur and proximal tibia trabeculae compared to a premenopausal group. We conclude that the effect of unloading on bone architecture is greater than that of estrogen loss in middle-aged women.     

Electron microscopy of osteocytes and the pericellular matrix in rat trabecular bone

The fine structure of the osteocytes and of the immediately adjacent bone matrix has been studied in the jaws of young rats demineralized with EDTA. The events marking the life cycle of the cell and their effects on the pericellular bone substance have been grouped into 3 phases. 1. The formative period, where the osteocyte resembles an osteoblast but shows a gradual decrease in the amount of endoplasmic reticulum and in the size of the Golgi complex. 2. The beginning of resorption (osteocytic osteolysis) which is characterized by a further decrease of the secretory organelles and the jagged appearance of the perilacunar border. Later in this phase there is further development and activity of the lysosomes resulting in increased widening of the lacuna and accumulation in the lacuna of fibrillar and flocculent material. 3. The eventual degeneration and death of the cell. No evidence of regeneration (osteoplasia) has been observed.

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Zusammenfassung Die Feinstruktur der Osteozyten und der unmittelbar angelagerten Knochenmatrix wurde an den Kiefern junger mit EDTA demineralisierten Ratten untersucht. Die Ereignisse, welche den Lebenszyklus der Zelle und ihre Wirkung auf die pericelluläre Knochensubstanz markieren, wurden in 3 Phasen eingeteilt: 1. die bildende Periode, während welcher der Osteocyt dem Osteoblasten gleicht, jedoch eine stufenweise Abnahme der Menge von endoplasmatischem Reticulum und in der Größe des Golgi-Apparates zeigt; 2. der Resorptionsbeginn (Osteozyten-Osteolyse), welcher durch eine weitere Abnahme der sekretorischen Organellen und das zackige Aussehen der perilacunären Grenze charakterisiert ist; 3. schließlich die Degeneration und der Tod der Zelle. Der Nachweis einer Regeneration (Osteoplasie) konnte nicht erbracht werden.

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Résumé L'ultrastructure des ostéocytes et de la matrice osseuse adjacente a des été étudiée au niveau maxillaires de jeunes rats, après décalcification à l'E.D.T.A. Les événements caractéristiques du cycle d'évolution de la cellule et ses effets sur la substance osseuse péricellulaire, peuvent être groupés en 3 stades: 1. La période de formation, pendant laquelle l'ostéocyte, analogue à l'ostéoblaste, montre, cependant, une diminution progressive en ergastoplasme et une réduction de l'appareil de Golgi. 2. La phase de résorption (ostéolyse ostéocytaire) caractérisée par l'apparition des lysosomes et leur activité, provoquant un élargissement de la lacune, où s'accumule du matériel fibrillaire et floconneux. 3. La dégénérescence éventuelle et la mort de la cellule. Une régénérescence cellulaire (ostéoplasie) n'a pas été observée.

     

Abnormal myocardial contraction in alpha(1A)- and alpha(1B)-adrenoceptor double-knockout mice

We used double-knockout mice (ABKO) lacking both predominant myocardial alpha(1)-adrenergic receptor (AR) subtypes (alpha(1A) and alpha(1B)) to determine if alpha(1)-ARs are required for normal myocardial contraction. Langendorff-perfused ABKO hearts had higher developed pressure than wild type (WT) hearts (123 +/- 3 mmHg n = 22 vs. 103 +/- 3 mmHg, n = 38, P < 0.001). Acutely inhibiting alpha(1)-ARs in WT hearts with prazosin did not increase pressure, suggesting that the increased pressure of ABKO hearts was mediated by long-term trophic effects on contraction rather than direct regulatory effects of alpha(1)-AR removal. Similar to perfused hearts, ABKO ventricular trabeculae had higher submaximal force at 2 mM extracellular [Ca(2+)] than WT (11.4 +/- 1.7 vs. 6.9 +/- 0.6 mN/mm(2), n = 8, P < 0.05); however, the peaks of fura-2 Ca(2+) transients were not different (0.79 +/- 0.11 vs. 0.75 +/- 0.16 microM, n = 10-12, P > 0.05), suggesting ABKO myocardium had increased myofilament Ca(2+)-sensitivity. This conclusion was supported by measuring the Ca(2+)-force relationship using tetanization. Increased myofilament Ca(2+)-sensitivity was not explained by intracellular pH, which did not differ between ABKO and WT (7.41 +/- 0.01 vs. 7.39 +/- 0.02, n = 4-6, P > 0.05; from BCECF fluorescence). However, ABKO displayed impaired troponin I phosphorylation, which may have played a role. In contrast to increased submaximal force, ABKO trabeculae had lower maximal force than WT at high extracellular [Ca(2+)] (29.6 +/- 1.9 vs. 37.6 +/- 1.4 mN/mm(2), n = 7, P < 0.01). However, peak cytosolic [Ca(2+)] was not different (1.13 +/- 0.15 vs. 1.19 +/- 0.04 microM, n = 6-7, P > 0.05), suggesting ABKO myocardium had impaired myofilament function. Finally, ABKO myocardium had decreased responsiveness to beta-AR stimulation. We conclude: alpha(1)-ARs are required for normal myocardial contraction; alpha(1)-ARs mediate long-term trophic effects on contraction; loss of alpha(1)-AR function causes some of the functional abnormalities that are also found in heart failure.