Bone Surface Density Research Articles

Age variations in the properties of human tibial trabecular bone and cartilage.

Initiated and motivated by clinical and scientific problems such as age-related bone fracture, prosthetic loosening, bone remodeling, and degenerative bone diseases, much significant research on the properties of trabecular bone has been carried out over the last two decades. This work has mainly focused on the central vertebral trabecular bone, while little is known about age-related changes in the properties of human peripheral (tibial) trabecular bone. Knowledge of the properties of peripheral (tibial) trabecular bone is of major importance for the understanding of degenerative diseases such as osteoarthrosis and osteoporosis, and for the design, fixation and durability of total joint prosthesis. The specific aims of the present studies were: 1) to investigate normal age-related variations in the mechanical, physical/compositional, and structural properties of human tibial trabecular bone; and 2) to investigate the age-related and osteoarthrosis-related changes in the mechanical properties of the human tibial cartilage-bone complex; and 3) to evaluate mutual associations among various properties. Normal specimens from human autopsy proximal tibiae were used for investigation of age variations in the properties of trabecular bone and the cartilage-bone complex, and osteoarthrotic specimens were used for the investigation of changes in the mechanical properties of the cartilage-bone complex induced by this disease process. The mechanical properties and physical/compositional properties of trabecular bone were quantified by means of standard techniques, and trabecular bone structure was quantified by means of unbiased three-dimensional methods. The present study demonstrated that the mechanical properties, such as Young's modulus, ultimate stress, ultimate strain and failure energy, and the densities, such as apparent, apparent ash and collagen densities of human tibial trabecular bone have significant relationships with age. Tissue density and mineral concentration remain constant throughout life. Trabecular bone is tougher in the younger age, i.e. fracture requires more energy. Collagen density was the single best predictor of failure energy, and collagen concentration was the only predictor of ultimate strain. The decrease in mechanical properties of trabecular bone mainly is a consequence of the loss of trabecular bone substance. This study showed that the degree of anisotropy (preferential orientation of trabeculae), mean marrow space volume, and bone surface-to-volume ratio increased significantly with age. Bone volume fraction, mean trabecular volume, and bone surface density decreased significantly with age. Connectivity did not have a general relationship with age, yet a trend exists. Age-related changes in the microstructural properties had the same trends for both medial and lateral condyles of the tibia. The observed increase of anisotropy may be interpreted as the consequence of structural adaptation secondary to age-induced bone loss. The aging trabeculae align more strongly to the primary direction, which is parallel to the longitudinal loading axis of the tibia. The mechanical properties of the normal cartilage and bone vary with age and respond simultaneously to mechanical loading. Both cartilage and bone in early-stage OA are mechanically inferior to normal, and OA cartilage and bone have lost their unit function to mechanical loading.

Analysis of trabecular microarchitecture of human iliac bone using microcomputed tomography in patients with hip arthrosis with or without vertebral fracture

Iliac bone samples were obtained from 50 women with osteoarthrosis of the hip (50–80 years of age) during hip surgery for total hip joint replacement. After determining the resolution and threshold for the binary image, the two-dimensional (2D) and three-dimensional (3D) data of the trabecular structure were obtained in these iliac bone samples using microcomputed tomography (micro-CT). Conventional histomorphometry was then performed. Both 2D and 3D parameters of the trabecular structure were significantly correlated with the parameters of conventional histomorphometry ( r = 0.63–0.86 in 2D analysis, and r = 0.60–0.77 in 3D analysis). The patients were classified into the non-spinal-fracture group (n = 36) and the spinal fracture group (n = 14). There was no significant difference in patient age between the two groups. The parameter values of bone mass, such as 2D fractional trabecular bone area and 3D fractional bone volume, and the values of trabecular number (Tb.N) in terms of both 2D and 3D analyses were significantly smaller, and those of trabecular separation (Tb.Sp) were significantly higher in the spinal fracture group than in the non-spinal-fracture group. Trabecular thickness (Tb.Th) values did not significantly differ between the two groups. There was no significant difference between 2D and 3D parameters in discriminating the spinal fracture group from the non-spinal-fracture group. However, 3D analysis demonstrated that the value of the bone surface to bone volume (BS/BV) ratio could discriminate between these two groups. These data demonstrated that micro-CT can evaluate the 3D structure of the human iliac bone, and that decreases in the parameters of the 3D-structure-related bone surface density as well as decreases in trabecular bone volume are related to osteoporotic fracture.

Morphometric Analysis of Human Bone Biopsies: A Quantitative Structural Comparison of Histological Sections and Micro-Computed Tomography

As a part of the European Union BIOMED I study “Assessment of Bone Quality in Osteoporosis,” the trabecular structure of transiliac bone biopsies was assessed by conventional histomorphometry and by three-dimensional microcomputed tomography (μCT). Sixty-three cylindrical human transiliac bone specimens were obtained post mortem from 27 women and 36 men (age 23–92 years) and evaluated morphometrically in this study. For the conventional histomorphometric analysis, a pair of four undecalcified sections were prepared from two regions in the mediolateral plane of the bone cores. The sections were stained with the von Kossa technique to obtain high-contrast two-dimensional images. Prior to the histologic sectioning the samples were measured with a desktop μCT, providing a 14 μm nominal resolution. The morphometric parameters computed by both methods in two or three dimensions, respectively, were bone volume density (BV/TV), bone surface density (BS/TV), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp). Results showed highly significant ( p < 0.0001) correlations between conventional histology and μCT for BV/TV ( r = 0.93), BS/TV ( r = 0.91), Tb.Th ( r = 0.84), and Tb.Sp ( r = 0.91). The mean percentage differences between histology and μCT ranged from 2.5% (BV/TV) to 6.1% (Tb.Th). The high correlations and the low differences in terms of absolute numbers between conventional histomorphometric and micro-tomographic analysis are very promising for the use of micro-tomographic imaging. μCT is a nondestructive, fast, and very precise procedure that allows the measurement of cancellous and compact bone in unprocessed biopsies or small bones, as well as a fully automatic determination of three-dimensional morphometric indices.

Marked changes in iliac crest bone structure in postmenopausal osteoporotic patients without any signs of disturbed bone remodeling or balance

Successful iliac crest bone biopsies were obtained from 63 women with postmenopausal vertebral crush fracture osteoporosis. Structural and static histomorphometric parameters were compared with 25 age-matched normal females, who had suffered an unexpected and sudden death. The control group for dynamic parameters comprised 13 younger normal females. Marked structural changes were observed in the osteoporotic patients in cortical as well as cancellous bone. Cortical width, trabecular volume, trabecular bone surface density and trabecular number were all reduced, whereas trabecular separation and star volume were increased. On the other hand trabecular thickness was normal in the patients. These structural changes in cancellous bone indicate that extensive perforations of trabecular plates have occurred or that whole trabecular elements have been removed. The remodeling cycles of cancellous bone surface and the frequency by which they were repeated (activation frequency) did not differ significantly between osteoporotic patients and normal younger women. The bone balance per remodeling cycle in osteoporotic patients and controls was not significantly different. No subset of individuals in the group of osteoporotic patients could be identified regarding extent of resorptive and formative surfaces, bone formation rate or activation frequency. In the present osteoporotic patients nothing in the ongoing remodeling process could explain the marked changes in bone structure. The pathophysiological changes leading to osteoporosis may therefore occur earlier in life, maybe long before the manifestation of the disease.