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1.
Due to remodeling of bone architecture, an optimal structure is created that minimizes bone mass and maximizes strength. In the case of osteoporotic vertebral bodies, however, this process can create over-adaptation, making them vulnerable for non-habitual loads. In a recent study, micro-finite element models of a healthy and an osteoporotic human proximal femur were analyzed for the stance phase of gait. In the present study, tissue stresses and strains were calculated with the same proximal femur micro-finite element models for a simulated fall to the side onto the greater trochanter. Our specific objectives were to determine the contribution of trabecular bone to the strength of the proximal femurs for this non-habitual load. Further, we tested the hypothesis that the trabecular structure of osteoporotic bone is over-adapted to habitual loads. For that purpose, we calculated the load distributions and estimated the apparent yield and ultimate loads from linear analyses. Two different methods were used for this purpose, which resulted in very similar values, all in a realistic range. Distributions of maximal principal strain and effective strain in the entire model suggest that the contributions to bone strength of the trabecular and cortical structures are similar. However, a thick cortical shell is preferred over a dense trabecular core in the femoral neck. When the load applied to the osteoporotic femur was reduced to approximately 61% of the original value, strain distributions were created similar in value to those obtained for the healthy femur. Since a comparable reduction factor was found for habitual load cases, it was concluded that the osteoporotic femur was not 'over-adapted'.  相似文献   

2.
The increased hip fragility in osteoporosis has been attributed mainly to a thinning of the cortex. In contrast, hip arthritis (OA) is not associated with increased risk of hip fracture. The purpose of this study was to assess cortical and trabecular bone structures and their possible regional variability in the femoral neck taken from patients who sustained an osteoporotic hip fracture (OP) compared with patients with OA. We compared the distribution of bone in the ultradistal femoral neck in 21 postmenopausal women with OA (mean age: 66+/-7.8 years) and 20 postmenopausal women with an osteoporotic hip fracture (OP) (mean age: 79.5+/-1.9 years). Controlateral hip osteoporosis or osteopenia was confirmed in OP by DEXA (T-score: -2.5+/-0.8 in OP; -0.9+/-1.3 in OA). Histomorphometric parameters of bone structure, architecture and connectivity were measured on sections from the ultradistal part of the femoral neck, divided in 4 quadrants. When compared to OA, cortical thickness was significantly decreased in OP (p<0.0005) but was the highest in the inferior part in both groups. Cortical porosity was higher in OA (13.48+/-1.02 and 8.4+/-1.07% in OA and OP respectively). Compared to OA, the trabecular bone volume was decreased by 50% in OP (p<0.0001) with a diminution of the trabecular number (p<0.01) and thickness (p<0.0001). In parallel, OP group was characterized by a poor connectivity evaluated by the decreased number of nodes (p<0.0001), higher trabecular bone pattern factor (p<0.0001) and greater marrow star volume (p<0.0001). The connectivity was the lowest in the inferior quadrant in OP but not in OA. Our data suggest that in addition to the cortical thinning, the loss of the trabecular bone mass and connectivity plays a role in the skeletal fragility associated with hip fracture. Furthermore, the spatial distribution of the trabeculae differs between OP and OA whereas cortical thinning is homogenous.  相似文献   

3.
The purpose of the present study was to evaluate a noninvasive method that utilizes optical processing to analyze the trabecular pattern on bone radiographs. The trabecular network on proximal femur radiographs of 17 intact cadaveric femora was analyzed by optical Fourier transform, yielding a trabecular bone index (TBI) at several locations. The bone mineral density (BMD) of the proximal femur was measured by dual X-ray absorptiometry. Dimensions of the proximal femur were obtained from the radiograph. The bones were fractured in a "fall configuration" to yield the fracture load. A multiple regression model, combining only radiograph- derived parameters-bone dimensions and the TBI at the intertrochanteric region and at the greater trochanter-yielded a correlation of 0.938 with the fracture load. A model combining the BMD at the greater trochanter and at the neck yielded a correlation of 0.928 with the fracture load. When all the variables were introduced into a combined analysis, the correlation with the fracture load was 0.973. The TBI obtained by optical processing of the trabecular bone pattern on femoral radiographs together with bone dimensions derived from these radiographs may serve as an effective estimate for hip fracture risk.  相似文献   

4.
J Homminga  H Weinans  W Gowin  D Felsenberg  R Huiskes 《Spine》2001,26(14):1555-1561
STUDY DESIGN: A finite-element study to investigate the amount of trabecular bone at risk of fracture and the distribution of load between trabecular core and cortical shell, for healthy, osteopenic, and osteoporotic vertebrae. OBJECTIVES: To determine differences between healthy, osteopenic, and osteoporotic vertebrae with regard to the risk of fracture and the load distribution. SUMMARY OF BACKGROUND DATA: The literature contains no reports on the effects of osteopenia and osteoporosis on load distribution in vertebral bodies, nor any reports on the amount of trabecular bone at risk of fracture. METHODS: Computed tomography data of vertebral bodies were used to construct patient-specific finite-element models. These models were then used in finite-element analyses to determine the physiologic stresses and strains in the vertebrae. RESULTS: For all three classes of vertebrae the contribution of the trabecular core to the total load transfer decreased from about 70% near the endplates to about 50% in the midtransverse region. The amount of trabecular bone that is at risk of fracture was about 1% for healthy vertebrae, about 3% for osteopenic vertebrae, and about 16% for osteoporotic vertebrae. CONCLUSIONS: Our finite-element models indicated that neither osteopenia nor osteoporosis had any effect on the contribution of the trabecular core to the total load placed on the vertebra. The trabecular core carried about half the load. Our finite-element models indicated that osteoporosis had a significant effect on the amount of trabecular bone at risk of fracture, which increased from about 1% in healthy vertebrae to about 16% for osteoporotic vertebrae.  相似文献   

5.
Treatment of monkeys and humans with parathyroid hormone (PTH) 1-84 stimulates skeletal remodeling, which increases trabecular (Tb) bone mineral density (BMD) but decreases cortical (Ct) BMD at locations where these bone types predominate. We report the effects of daily PTH treatment (5, 10, or 25 μg/kg) of ovariectomized (OVX) rhesus monkeys for 16 months on bone structure and biomechanical properties at the proximal femur, a mixed trabecular and cortical bone site. PTH reversed the OVX-induced decrease in BMD measured by dual-energy X-ray absorptiometry at the proximal femur, femoral neck, and distal femur. Peripheral quantitative computed tomography confirmed a significant decrease in Ct.BMD and an increase in Tb.BMD at the total proximal femur and at the proximal and distal femoral metaphyses. The decrease in Ct.BMD resulted primarily from increased area because cortical bone mineral content was unaffected by PTH. Histomorphometry revealed that PTH significantly increased the trabecular bone formation rate (BFR) as well as trabecular bone volume and number. PTH did not affect periosteal or haversian BFR at the femoral neck, but cortical porosity was increased slightly. PTH had no effects on stiffness or peak load measured using a shear test, whereas work-to-failure, the energy required to fracture, was increased significantly. Thus, PTH treatment induced changes in trabecular and cortical bone at the proximal femur that were similar to those occurring at sites where these bone types predominate. Together, the changes had no effect on stiffness or peak load but increased the energy required to break the proximal femur, thereby making it more resistant to fracture.  相似文献   

6.
Hip fracture risk rises 100‐ to 1000‐fold over six decades of age, but only a minor part of this increase is explained by declining BMD. A potentially independent cause of fragility is cortical thinning predisposing to local crushing, in which bone tissue's material disintegrates at the microscopic level when compressed beyond its capacity to maintain integrity. Elastic instability or buckling of a much thinned cortex might alternatively occur under compression. In a buckle, the cortex moves approximately at right angles to the direction of load, thereby distorting its microstructure, eventually to the point of disintegration. By resisting buckling movement, trabecular buttressing would protect the femoral neck cortex against this type of failure but not against crushing. We quantified the effect of aging on trabecular BMD in the femoral neck and assessed its contribution to cortical elastic stability, which determines resistance to buckling. Using CT, we measured ex vivo the distribution of bone in the midfemoral necks of 35 female and 33 male proximal femurs from cases of sudden death in those 20–95 yr of age. We calculated the critical stress σcr, at which the cortex was predicted to buckle locally, from the geometric properties and density of the cortical zone most highly loaded in a sideways fall. Using long‐established engineering principles, we estimated the amount by which stability or buckling resistance was increased by the trabecular bone supporting the most stressed cortical sector in each femoral neck. We repeated these measurements and calculations in an age‐ and sex‐matched series of femoral necks donated by women who had suffered intracapsular hip fracture and controls, using histological measurements of cortical thickness to improve accuracy. With normal aging, trabecular BMD declined asymmetrically, fastest in the supero‐lateral one‐half (in antero‐posterior projection) of the trabecular compartment. When viewed axially with respect to the femoral neck, the most rapid loss of trabecular bone occurred in the posterior part of this region (supero‐posterior [S‐P]), amounting to a 42% reduction in women (34% in men) over five decades of adult age. Because local cortical bone thickness declined comparably, age had no significant effect on the relative contributions of cortical and trabecular bone to elastic stability, and trabecular bone was calculated to contribute 40% (in men) and 43% (in women) to the S‐P cortex of its overall elastic stability. Hip fracture cases had reduced elastic stability compared with age‐matched controls, with a median reduction of 49% or 37%, depending on whether thickness was measured histologically or by CT (pQCT; p < 0.002 for both). This effect was because of reduced cortical thickness and density. Trabecular BMD was similar in hip fracture cases and controls. The capacity of the femur to resist fracture in a sideways fall becomes compromised with normal aging because cortical thickness and trabecular BMD in the most compressed part of the femoral neck both decline substantially. This decline is relatively more rapid than that of femoral neck areal BMD. If elastic instability rather than cortical crushing initiates the fracture event, interventions that increase trabecular bone in the proximal femur have great potential to reduce fracture risk because the gradient defining the increase in elastic stability with increasing trabecular BMD is steep, and most hip fracture cases have sufficient trabecular bone for anabolic therapies to build on.  相似文献   

7.
We measured bone density in various parts of the femur by using single energy quantitative computed tomography. In the cadaver studies we found significant correlations between the trabecular and cortical bone density and the structural strength of the femur in bending and rotational loading. This was observed in parts of the femur distant from the fracture site in the femoral neck. Good reproducibility of the density measurements was obtained at the condylar level, a site easily accessible for clinical measurements. In a clinical study, we could record post-traumatic osteoporotic changes at 5% precision level.  相似文献   

8.
Cheng X  Li J  Lu Y  Keyak J  Lang T 《BONE》2007,40(1):169-174
INTRODUCTION: Bone mineral density and geometry measurements by volumetric quantitative computed tomography (vQCT) have been utilized in clinical research studies of aging, pharmacologic intervention and mechanical unloading, but there is relatively little information about the association of these measures with hip fracture. To address this issue, we have carried out a study comparing vQCT parameters in elderly Chinese women with hip fractures with measurements in age-matched controls. MATERIALS AND METHODS: Forty-five women (mean age 74.71+/-5.94) with hip fractures were compared to 66 age-matched control subjects (mean age 70.70+/-4.66). vQCT was employed to characterize the volumetric bone mineral density in cortical, trabecular, and integral volumes of interest in the proximal femur. In addition to the volume of interest measurements, we computed the cross-sectional areas of the femoral neck and intertrochanteric planes, the femoral neck axis length, indices of femoral neck bending and compressive strength, and measures of femoral neck cortical geometry. To determine if cortical geometry measures were associated with hip fracture independently of trabecular vBMD, we carried out multi-variate analyses including these parameters in a logistic regression model. RESULTS AND CONCLUSIONS: All vQCT measurements discriminated between fractured subjects and age-matched controls. There was no significant difference in predictive strength between volumetric and areal representations of BMD and trabecular and integral vBMD showed comparable discriminatory power, although both of these measures were more correlated to fracture status than cortical vBMD. We found that fractured subjects had larger femoral neck cross-sectional areas, consistent with adaptation to lower BMD in these osteoporotic subjects. The larger neck cross-sectional areas resulted in bending strength indices in the fractured subjects that were comparable or larger than those of the control subjects. In multi-variate analyses, reduced femoral neck cortical thickness and buckling ratio indices were associated with fracture status independently of trabecular vBMD.  相似文献   

9.
Background and purpose The micro-architecture of bone has been increasingly recognized as an important determinant of bone strength. Successful operative stabilization of fractures depends on bone strength. We evaluated the osseous micro-architecture and strength of the osteoporotic human femoral head.

Material and methods 6 femoral heads, obtained during arthroplasty surgery for femoral neck fracture, underwent micro-computed tomography (microCT) scanning at 30 μm, and bone volume ratio (BV/TV), trabecular thickness, structural model index, connection density, and degree of anisotropy for volumes of interest throughout the head were derived. A further 15 femoral heads underwent mechanical testing of compressive failure stress of cubes of trabecular bone from different regions of the head.

Results The greatest density and trabecular thickness was found in the central core that extended from the medial calcar to the physeal scar. This region also correlated with the greatest degree of anisotropy and proportion of plate-like trabeculae. In the epiphyseal region, the trabeculae were organized radially from the physeal scar. The weakest area was found at the apex and peripheral areas of the head. The strongest region was at the center of the head.

Interpretation The center of the femoral head contained the strongest trabecular bone, with the thickest, most dense trabeculae. The apical region was weaker. From an anatomical and mechanical point of view, implants that achieve fixation in or below this central core may achieve the most stable fixation during fracture healing.  相似文献   

10.
To elucidate the pathology of osteoporosis, we used a computer, to investigate three-dimensional tissue morphometry in biopsied iliac bone specimens from 20 female patients with femoral neck fractures. The 20 fracture patients were divided into two groups according to age: group I, patients below 70 years of age (n=10) and group II, patient 70 years of age or more (n=10). Five patients who also underwent iliac bone biopsy but who did not have fractures served as the control group. We found that the ilium in group I patients was composed of many small thin trabecular structures, while the ilium in group II was composed of only a few broad trabecular structures. The three-dimensional Euler number was small in osteoporosis, suggesting that trabecular connectivity was also diminished and the fractal dimension decreased. This indicated that the trabecular structure had become irregular. These findings indicate that the number of trabeculae appeared to decrease with trabecular blocking due to osteoporotic changes, and, simultaneously with this phenomenon, the which of the individual trabeculae seemed to become thicker in accordance with bone adaptation to mechanical stress.A summary of this paper was reported at the 9th Annual Orthopaedic Research Meeting of the Japanese Orthopaedics Association (October, 1994), and the 3rd Study Meeting of the Japanese Society of Osteoporosis (October, 1994).  相似文献   

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