Structural and material mechanical properties of human vertebral cancellous bone

The structural Young's modulus (i.e. that of the cancellous framework) was determined by non-destructive compressive mechanical testing in the three orthogonal axes of 48 vertebral bone cubes. In addition, the material Young's modulus (i.e. of the trabeculae themselves) was estimated using an ultrasonic technique. Apparent and true density were determined by direct physical measurements. Significant mechanical anisotropy was observed: mean structural Young's modulus varied from 165 MPa in the supero-inferior direction to 43 MPa in the lateral direction. Structural Young's modulus correlated with apparent density, with power-law regression models giving the best correlations (r2 = 0.52-0.88). Mechanical anisotropy increased as a function of decreasing apparent density (p < 0.001). Material Young's modulus was 10.0 +/- 1.3 GPa, and was negatively correlated with apparent density (p < 0.001). In multiple regression models, material Young's modulus was a significant independent predictor of structural Young's modulus only in the supero-inferior direction. The data suggest the presence of two effects in vertebral bone associated with decreasing apparent density and, by implication, bone loss in general: (a) increased mechanical anisotropy, such that there is relative conservation of stiffness in the axial direction compared with the transverse directions; and (b) increased stiffness of the trabeculae themselves.     

Structural changes with aging in cortical bone of the human tibia

Structural modifications are considered to play a significant role in the age-related alterations of bone quality and strength. Senescent compact bone is characterized by an increasing heterogeneity of aspects, including high numbers of lowly mineralized osteons as well as the presence of osteons with hypermineralized lamellae or with a notched haversian canal wall, and of double-zone osteons. These latter three types of osteons are different from the structures involved in the haversian remodeling. In the present study, blocks of midshaft tibia from 7 young men (18-39 years), 14 aged men (50-92 years) and 15 aged women (57-96 years) were embedded in methyl methacrylate in order to perform microradiographic and histomorphometric analysis of undecalcified sections. The intracortical porosity was higher in the aged men than in the young ones, as were the numbers of haversian structures and, to a lesser extent, the diameters of the haversian canals. The aged women showed the same tendency, with cortical porosity still higher than in the men. The osteons with hypermineralized lamellae, those with a notched canal and the double-zone osteons appear to constitute large subgroups of the total haversian population, even in the early adult life. Among them, only the osteons with a notched canal wall increased in frequency with age. The 3 types are much more numerous than the structures involved in the typical haversian remodeling. The correlations between their frequencies as well as their significant topographic association corroborates the hypothesis that the hypermineralized lamellae may crumble down because of their excessive brittleness, giving rise to the haversian canals with notched walls. These enlarged canals could be refilled by bone apposition and result in the double-zone osteons. The 3 types of osteons could constitute different steps of one mechanism of bone desintegration and repair occurring very progressively, which might contribute to modify the bone quality and to increase the intracortical porosity.     

Conformational and electronic properties of the two cis (5S,6R) and (5R,6S) diastereoisomers of 5,6-dihydroxy-5,6-dihydrothymidine: X-ray and theoretical studies

For the first time, raloxifene or alendronate was administered to rats immediately after ovariectomy for 10 months and compared with estrogen to elucidate mechanisms behind the raloxifene effects observed in nonreproductive and reproductive tissues. Specifically, 75-day-old rats were randomly selected as sham controls (Sham), ovariectomized controls (Ovx) or ovariectomized rats treated with fully efficacious doses of raloxifene (RA), 17 alpha-ethynyl estradiol (EE2) or alendronate (ABP). Lumbar vertebrae and proximal tibiae were examined by computed tomography (QCT) and by histomorphometry. Histomorphometry showed differences in bone architecture between groups when QCT densities were similar, but tibial trabecular bone analysis by QCT correlated with histomorphometry with r = .86 to .93, depending on the parameter. Both techniques confirmed that Ovx had substantially less bone than Sham, with greater loss of trabecular bone in the proximal tibia than vertebrae. Both techniques showed that RA had effects similar to but not identical with EE2 in preventing bone loss in vertebrae and tibiae. ABP partially prevented loss of bone in L-5, but was not significantly different from Ovx in the proximal tibia. This may be caused by ABP suppression of bone apposition, beyond effects observed for EE2 or RA. RA appeared to be more similar to EE2 because ABP significantly depressed bone formation (bone formation rate, mineral apposition rate) to below RA or EE2 levels, especially in L-5. Mechanical loading to failure of L-6 vertebrae showed a rank order of vertebral strength of Sham > RA > EE2 > Ovx > ABP, although significant differences were not observed between treatment groups. These data show that ABP suppression of bone formation can affect bone quality with long-term treatment. In other tissues, RA had minimal uterine effects, while significantly lowering serum cholesterol to below EE2-treated levels. Both EE2 and RA rats had significantly lower body weights than the other groups. ABP had no effect on serum lipids, uterine weight or body weight. Therefore, RA appears to have a broader range of desirable effects on bone, body weight, uteri and cholesterol than ABP or EE2 in ovariectomized rats.     

The histopathology of nonsteroidal anti-inflammatory drug-associated colitis

We combined three techniques--mechanical testing, three-dimensional imaging, and finite-element modeling--to distinguish between the contributions of architecture and tissue modulus to mechanical function in human trabecular bone. The objectives of this study were 2-fold. The first was to assess the accuracy of micromechanical modeling of trabecular bone using high-contrast x-ray images of the trabecular architecture. The second was to combine finite-element calculations with mechanical testing to infer an average tissue modulus for the specimen. Specimens from five human L1 vertebrae were mechanically tested along the three anatomic axes. The specimens were then imaged by synchrotron x-ray tomography, and the elastic moduli of each specimen were calculated from the tomographic image by finite-element modeling. We found that 23-microm tomographic images resolved sufficient structural detail such that the calculated anisotropy in the elastic modulus was within the uncertainties of the experimental measurements in all cases. The tissue modulus of each specimen was then estimated by comparing the calculated mean stiffness of the specimen, averaged over the three anatomical directions, with the experimental measurement. The absolute values of the experimental elastic constants could be fitted, again within the uncertainties of the experimental measurements, by a single tissue modulus of 6.6 GPa, which was the average tissue modulus of the five specimens. These observations suggest that a combination of mechanical testing, three-dimensional imaging, and finite-element modeling might enable the physiological variations in tissue moduli to be determined as a function of age and gender.     

Harmonic/noise ratio and spectrographic analysis in vocal abuse pathology

To evaluate the use of dual energy X-ray absorptiometry (DXA) in multiple myeloma (MM) we performed a prospective study of 34 patients with newly diagnosed MM. Most patients had advanced disease and all but two patients had osteolytic bone destructions and/or pathological fractures. Bone mineral content (BMC) and bone mineral density (BMD) of the lumbar spine (L1-L4) and hip were measured using a Hologic QDR-1000 scanner. Collapsed vertebrae were not excluded from analysis. Data from 289 healthy Danish volunteers aged 21-79 yr were used for calculation of Z-scores. Lumbar spine BMC (Z-score -0.46 +/- 0.23, p = 0.05) and lumbar spine BMD (Z-score -0.56 +/- 0.23, p = 0.02) were significantly reduced in MM patients, whereas no reduction was seen in hip BMC or BMD. Collapsed vertebrae had marked reduced BMD (Z-score -1.34 +/- 0.22, p < 0.001), as had non-fractured vertebrae in the same individuals (Z-score -1.42 +/- 0.25, p < 0.001). Lumbar spine BMD correlated with radiologically assessed bone morbidity (r -0.37, p = 0.03) and stronger with the incidence of vertebral fractures (r -0.64, p < 0.001). Thus, osteopenia of the back is common in multiple myeloma and correlates with an increased incidence of fractures. DXA may identify subjects with increased risk of vertebral fractures for more intensive chemotherapeutic or anti-resorptive treatment.     

Characterization of vertebral strength using digital radiographic analysis of bone structure

Bone mineral densitometry (BMD) is useful in predicting fracture risk, but, unfortunately, there is a significant degree of overlap in BMD measurements of patients who have a high risk of fracture and patients with a low risk of fracture. In this study, a method of characterizing trabecular bone structure in digitized radiographs of vertebrae is proposed and assessed. A significant correlation between bone "structure" and the compressive strength of vertebral bodies was found. The utility of the parameter for distinguishing between "weak" and "strong" bone samples was assessed using receiver operating characteristic (ROC) analysis. Using this analysis, the structural parameter produced an area under the ROC of 0.88 +/- 0.05, while a bone density measure produced an area of 0.79 +/- 0.07. The results suggest that the addition of a measure of bone structure to the conventional measures of bone density may prove useful in predicting the quality of bone when considering surgical or medical intervention for osteoporotic conditions.     

炉料弹性模量对高炉内炉料运动行为与应力分布的影响

采用三维离散元法对不同弹性模量条件下,5000m3高炉内的炉料的运动行为进行了研究.发现,当弹性模量取0.06GPa时,炉料颗粒的变形量超过了自身半径的1/2,炉身处发生严重的混料现象,炉缸内焦炭颗粒发生堆积,无焦空间减小,而且计算在100步以后自动终止.而当弹性模量在10～0.6GPa范围内变化时,炉身段料层倾角随弹...     

Determining Hardness and Elastic Modulus of Asphalt by Nanoindentation

Nanoindentation is a relatively new technique which has been used to measure nanomechanical properties of surface layers of bulk materials and of thin films. In this study, micromechanical properties such as hardness and Young’s modulus of asphalt binders and asphalt concrete are determined by nanoindentation experiments. Indentation tests are conducted on a base binder and two polymer-modified performance grade (PG) binders such as PG-70-22 and PG76-28. In addition, two Superpave asphalt mixes such as SP-B and SP-III are designed using these PG binders, and the corresponding mixes are compacted to prepare asphalt concrete. Aggregate, matrix (Materials Passing No. 4 sieve) and mastic (Materials Passing No. 200 sieve) phases of each asphalt concrete sample are indented using both Berkovich and Spherical indenters. In nanoindentation, an indenter penetrates into asphalt material and the load (milli-Newton) and the depth (nanometers) of indentation are recorded continuously. Indentation load versus displacement data are analyzed using Oliver and Pharr method to measure hardness and Young’s modulus. The unloading data of base binder is a straight line and therefore could not be analyzed using Oliver and Pharr’s method. However, the indentation data of the PG grade binders are successfully analyzed. Young’s modulus value is less than 3 GPa for mastic, 3 to 12 GPa for matrix, and greater than 12 GPa for aggregate studied herein. Based on the hardness data, mastic is 2 to 15 times softer than matrix materials, and matrix is 10 times softer than aggregate materials. The fact that the properties of the mastic can be measured while in the mixture, this study has great potential for realistic characterization of asphalt mixture components. In this study, spherical indenter is found to be suitable for asphalt binders based on the fact that the spherical indenter produces higher indentation depths than the Berkovich indenter. The study contributes significantly to the use of nanoindentation for transportation material characterization.     

冷却介质对退火态Cu50Zr42Al8块体非晶合金力学性能的影响

考察在过冷液相区内790K+30min保温后炉冷和液氮冷却对Cu50Zr42Al8压缩断裂行为的影响。5mm铸态非晶复合棒的屈服强度、断裂强度和杨氏模量分别为1670MPa,1849MPa和104.4GPa,塑性应变为1.9%。经炉冷和液氮冷却试样的压缩断裂强度和杨氏模量下降,分别为912,678MPa和38,56.5GPa。液氮冷却试样为部分非晶结构,炉冷试样完全晶化。晶化相均为正交晶相Cu10Zr7,四角晶相CuZr2和DO3结构的AlCu2Zr三种脆化相。     

Failure characteristics of osteoporotic vertebral bodies monitored by acoustic emission

The third lumbar vertebrae of nine elderly subjects (average age, 81.4 +/- 6.7 years) graded osteoporotic and the second to fifth lumbar vertebrae of a 37-year-old man graded as normal were used to investigate microdamage accumulation during quasi-static compression loading with an acoustic emission detection system. Mechanical parameters (apparent elastic modulus, stress, and strain) and acoustic emission event count rates were measured simultaneously. The normalized mean value of any mechanical parameters of normal group was significantly high with respect to that of osteoporotic group. The normalized mean value of cumulative acoustic emission event counts to maximum stress of the normal vertebrae was substantially small with respect to that of the osteoporotic vertebrae (p < 0.0005, z-test). Postloading microradiographs displayed fracture lines adjacent to the end plates in six vertebrae of osteoporotic group. These results are consistent with the hypotheses that microdamages of osteoporotic vertebral bodies are generated and accumulate at lower strains than those of normal vertebrae at a specific site.     

Trabecular bone mineral and calculated structure of human bone specimens scanned by peripheral quantitative computed tomography: relation to biomechanical properties

The relationship of cortical bone mineral density (BMD), and geometry to bone strength has been well documented. In this study, we used peripheral quantitative computerized tomography (pQCT) to acquire trabecular BMD and high-resolution images of trabeculae from specimens to determine their relationship with biomechanical properties. Fifty-eight human cubic trabecular bone specimens, including 26 from the vertebral bodies, were scanned in water and air. Trabecular structure was quantitated using software developed with Advanced Visual Systems interfaced on a Sun/Sparc Workstation. BMD was also obtained using a whole-body computerized tomography scanner (QCT). Nondestructive testing of the specimens was performed to assess their elastic modulus. QCT and pQCT measurements of BMD of specimens in water were strongly correlated (r2 = 0.95, p < 0.0001), with a slope (0.96) statistically not significantly different from 1. Strong correlations were found between pQCT measurements of specimens in water and in air, for BMD (r2 = 0.96, p < 0.0001), and for apparent trabecular structural parameters (r2 = 0.89-0.93, p < 0.0001). Correlations were moderate between BMD and apparent trabecular structural parameters (r2 = 0.37-0.64, p < 0.0001). Precision as coefficient of variation (CV) and standardized coefficient of variation (SCV) for these measurements was < 5%. For the vertebral specimens, the correlation was higher between elastic modulus and BMD (r2 = 0.76,p < 0.0001) than between elastic modulus and apparent trabecular structural parameters (r2 = 0.58-0.72, p < 0.0001), while the addition of apparent trabecular nodes and branches to BMD in a multivariate regression model significantly increased the correlation with the elastic modulus (r2 = 0.86, p < 0.01). Thus, pQCT can comparably and reproducibly measure trabecular bone mineral in water or air, and trabecular structure can be quantitated from pQCT images. The combination of volumetric BMD with trabecular structural parameters rather than either alone improves the prediction of biomechanical properties. Such a noninvasive approach may be useful for the preclinical study of osteoporosis.     

Relationship between ultrastructure and "pin test" in osteons

In the 3 types commonly recognizable under the polarizing microscope (longitudinally, alternately and transversally structured osteons), the lamellar appearance of osteons in electron micrographs (EM) is due to the presence of layers of paralleloriented collagen bundles, with the orientation of the bundles changing abruptly through about 90 degrees in successive layers. On the EM scale, lamellae appear as completely independent entities. All 3 osteon types can be considered as consisting of a series of complete or incomplete lamellae. The quantities of collagen bundles in each of the 2 types of lamella--those with longitudinally or concentrically oriented bundles--is a distinctive feature determining the specific appearance of each type of osteon. This view has interesting implications as regards the nature of the factors which instruct and regulate osteoblasts in determining the cross-parallel arrangement of lamellar bone, and the specific characteristics of the various types of osteon. The mechanical properties of osteons are closely related to their structure. The highest values for ultimate dilating strength were obtained with transversally and alternately structured osteons, and the lowest values with longitudinally structured ones.     

Yield strain behavior of trabecular bone

If bone adapts to maintain constant strains and if on-axis yield strains in trabecular bone are independent of apparent density, adaptive remodeling in trabecular bone should maintain a constant safety factor (yield strain/functional strain) during habitual loading. To test the hypothesis that yield strains are indeed independent of density, compressive (n = 22) and tensile (n = 22) yield strains were measured without end-artifacts for low density (0.18 +/- 0.04 g cm(-3)) human vertebral trabecular bone specimens. Loads were applied in the superior-inferior direction along the principal trabecular orientation. These 'on-axis' yield strains were compared to those measured previously for high-density (0.51 +/- 0.06 g cm(-3)) bovine tibial trabecular bone (n = 44). Mean (+/- S.D.) yield strains for the human bone were 0.78 +/- 0.04% in tension and 0.84 +/- 0.06% in compression; corresponding values for the bovine bone were 0.78 +/- 0.04 and 1.09 +/- 0.12%, respectively. Tensile yield strains were independent of the apparent density across the entire density range (human p = 0.40, bovine p = 0.64, pooled p = 0.97). By contrast, compressive yield strains were linearly correlated with apparent density for the human bone (p < 0.001) and the pooled data (p < 0.001), and a suggestive trend existed for the bovine data (p = 0.06). These results refute the hypothesis that on-axis yield strains for trabecular bone are independent of density for compressive loading, although values may appear constant over a narrow density range. On-axis tensile yield strains appear to be independent of both apparent density and anatomic site.     

Vertebral artery location in relation to the vertebral body as determined by two-dimensional computed tomography evaluation

STUDY DESIGN: This study analyzed the precise two-dimensional location of the vertebral artery within cervical vertebrae as determined by measurements obtained from axial computed tomographic images of the cervical spine. OBJECTIVE: To determine the margin of safety necessary to avoid vertebral artery laceration during central decompression and lateral nerve root decompression for cervical spinal stenosis. SUMMARY OF BACKGROUND DATA: Laceration of the vertebral artery is a rare but potentially catastrophic complication of anterior decompressive surgery of the cervical spine. METHODS: The mean, standard deviation, and 95% confidence interval of the mean of measurements localizing the vertebral artery within the vertebral body were calculated from 50 transaxial computed tomography images of each of the second through sixth cervical vertebrae. RESULTS: Both the mean interforaminal distance (from 25.90 +/- 1.89 mm at C3 to 29.30 +/- 2.70 mm at C6) and the average distance of the posterior border of the foramen transversarium from the ventral border of the spinal canal (from 2.16 +/- 1.18 mm at C3 to 3.53 +/- 1.56 mm at C6) increased from C3 to C6. CONCLUSIONS: According to our measurements, the risk of vertebral artery laceration is greater at more cephalad vertebrae during lateral extension of central decompressive procedures and lateral nerve root decompression. Because of the variability of these parameters between individuals, accurate individual preoperative localization of the vertebral arteries is recommended.     

Differential effect of gender on the sizes of the bones in the axial and appendicular skeletons

Recent observations suggest that throughout life the size of the vertebral bodies in females is smaller than that in males even after accounting for differences in body size. To confirm these reports and to determine whether similar differences exist in the appendicular skeleton, detailed measurements of the sizes of the vertebrae and the femur were obtained using computed tomography in 30 pairs of prepubertal boys and girls matched for age, height, and weight. Anthropometric parameters as well as gender influenced the cross-sectional area of the vertebrae. Heavier children had greater vertebral cross-sectional area than slender children regardless of gender, and the vertebral bodies were found to be significantly smaller in girls than in matched boys (approximately 11%), both using Student's t test (P < 0.0001) and its multivariate analog, the Hotelling's T2 test (P < 0.0001). In contrast to these findings in the axial skeleton, gender status did not influence the size of the bones in the appendicular skeleton, and neither the cross-sectional area (3.28 +/- 0.84 vs. 3.10 +/- 0.56 cm2) nor the cortical bone area (1.80 +/- 0.37 vs. 1.85 +/- 0.36 cm2) at the midshaft of the femur differed between boys and girls. These values, however, correlated strongly with all anthropometric indexes, and multiple regression analyses indicated that both measurements were primarily related to weight. The results suggest that although increases in mechanical loading associated with growth are the main determinant of the cross-sectional properties of the appendicular skeleton in children, factors other than body mass and related to gender have a significant role in the regulation of the sizes of the bones in the axial skeleton.     

Morphometric texture analysis of spinal trabecular bone structure assessed using orthogonal radiographic projections

The measurement of bone microstructure as well as bone mineral density may improve the estimation of bone strength. Cubic specimens (N = 26, 12 mm X 12 mm X 12 mm) of human cadaver vertebrae were cut along three orthogonal anatomic orientations, i.e., superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP). Contact radiographs of the bone cubes along all three orientations were obtained and then digitized by a laser scanner with pixel size of 50 microns x 50 microns. The specimens were tested in compression along the 3 orthogonal orientations and the Young's modulus (YM) was calculated for each direction. Quantitative computed tomography (QCT) was used to obtain a measure of trabecular bone mineral density (BMD). Global gray level thresholding and local thresholding algorithms were used to extract the trabecular bone network. Apparent trabecular bone fraction (ABV/TV), mean intercept length (I.TH), mean intercept separation (I.SP), and number of nodes (N.ND) were measured from the extracted trabecular network. Fractal dimension (Fr.D) of the trabecular bone texture was also measured. Paired t-tests showed that the mean values of each texture parameter (except ABV/TV) and of YM along the SI direction were significantly different (p < 0.05) from those along the ML and AP direction. However, the mean values along the ML and AP directions were not significantly different. Multivariate regression of YM as a function of the texture parameters and BMD showed that without adjusting for the effect of BMD, YM was significantly explained by all the texture parameters (R2 = 0.2-0.6). When BMD was included in the regression, although the variations in YM of ML, AP, and SI orientations could be explained by BMD alone, some of the texture parameters did improve the overall prediction of the biomechanical properties, while, some parameters such as ABV/TV and Fr.D in the ML orientation showed a more significant overall effect in explaining mechanical strength than did BMD. In conclusion, trabecular texture parameters correlated significantly with BMD and YM. Trabecular texture parameters from projectional radiographs reflect the anisotropy of trabecular structure. Quantitative radiographic assessment of trabecular structure using fine-detail radiography can potentially improve the estimation of bone strength.     

Shear Modulus of Standard Pultruded Fiber Reinforced Plastic Material

Research to determine the shear modulus of standard pultruded fiber reinforced plastic (FRP) material is reviewed and appraised. It is found that different test methods have given shear moduli data in the range from 1.3 to 5.1 GPa, with varying degrees of scatter. Pultruded material is comprised of alternate layers of two distinct glass reinforcement types. By applying micromechanical modeling, it is shown that the in-plane shear modulus of the continuous unidirectional rovings layer is similar to that of the continuous filament (or strand) mat layer, and that these layer moduli, generally, lie in the range 3.5 to 4.8 GPa (depending on fiber volume fraction). This finding indicates that the significant difference (>1.3 times) between the in-plane (3 GPa or less) and the St. Venant torsion (always >4 GPa) shear moduli is likely to be due to the experimental test procedures and the physical interpretation of shearing, rather than the layer construction of the material. For structural profiles, it is seen that the shear modulus of 3 GPa in company design manuals is often less than measured. Researchers require correlated elastic constant data if elastic deflections and instability loads for structural members can be accurately predicted using elastic theory. Further work is, therefore, recommended to establish standard test and analytical methods for the determination of shear moduli of pultruded FRP material.     

Porcine aortic wall flexibility. Fresh vs Denacol fixed vs glutaraldehyde fixed

It has been postulated that, in theory, stentless bioprosthetic heart valves provide improved hemodynamics and durability over their stented counterparts. A number of glutaraldehyde modified porcine stentless valves are currently either on the market or in clinical trials. Polyepoxy compound as an alternative cross-linking reagent to glutaraldehyde for bioprostheses has been reported to mitigate calcification. The present study was to investigate the effect of the fixation methods on porcine aortic wall flexibility. Ring specimens were selected from three groups of porcine roots: fresh, low pressure glutaraldehyde fixed, and low pressure Denacol (polyepoxy compound) fixed. Pulled between two rods on a tensile tester, a ring specimen's load-deformation relationship was recorded and analyzed to numerically compute the tissue modulus at low strains. The results showed that the Young's moduli were 0.113 +/- 0.036, 0.494 +/- 0.113, and 1.320 +/- 0.292 MPa (mean +/- SD, n = 10) for the fresh, Denacol fixed, and glutaraldehyde fixed aortic walls, respectively. The Denacol fixed aortic wall was more flexible than the glutaraldehyde fixed one. It was also found that the Denacol fixed aortic wall maintained most of the natural residual strains, while the glutaraldehyde fixed aortic wall did not.     

轻质钢的研究进展(二)——铁素体—奥氏体双相轻质钢和奥氏体轻质钢

首先主要阐述了富Al铁素体—奥氏体双相轻质钢和奥氏体轻质钢的微观组织特征、力学性能和强韧化机制。尽管添加Al可以降低钢的密度和提高比强度,但是它会使钢的弹性模量显著降低。针对这一不利属性,介绍了一种切实可行的提高轻质钢(以及碳钢)弹性模量的措施,即利用凝固过程中原位自生高弹性模量的硬质颗粒(如Ti C和Ti B2等)来增强钢的基体。所形成的颗粒增强钢基复合材料可以具有较常规碳钢和富Al轻质钢更高的弹性模量和比弹性模量。     

Rapid-staged strategy for concomitant critical carotid and left main coronary disease with left ventricular dysfunction: IABP use

Fascicle length, pennation angle, and tendon elongation of the human tibialis anterior were measured in vivo by ultrasonography. Subjects (n = 9) were requested to develop isometric dorsiflexion torque gradually up to maximal at the ankle joint angle of 20 degrees plantarflexion from the anatomic position. Fascicle length shortened from 90 +/- 7 to 76 +/- 7 (SE) mm, pennation angle increased from 10 +/- 1 to 12 +/- 1 degrees, and tendon elongation increased up to 15 +/- 2 mm with graded force development up to maximum. The tendon stiffness increased with increasing tendon force from 10 N/mm at 0-20 N to 32 N/mm at 240-260 N. Young's modulus increased from 157 MPa at 0-20 N to 530 MPa at 240-260 N. It can be concluded that, in isometric contractions of a human muscle, mechanical work, some of which is absorbed by the tendinous tissue, is generated by the shortening of muscle fibers and that ultrasonography can be used to determine the stiffness and Young's modulus for human tendons.