No abstract

In this study, we characterize bone microstructure, specifically sex differences, at multiple skeletal sites in 165 subjects >52 yr of age, using µCT technology in vitro. Significant sex differences are observed at the distal radius, femoral neck, and femoral trochanter, but not at the iliac crest, calcaneus, and lumbar vertebral body. Correlations in BV/TV between sites ranged from r = 0.13 to 0.56. Introduction:The goals of this study were (1) to assess potential sex differences of bone microstructure and their difference between skeletal sites and (2) to explore the relationship of trabecular microstructural properties between relevant skeletal sites. Materials and Methods: Trabecular bone microstructural properties were measured in vitro in 165 subjects 52-99 yr of age using CT. Defined volumes of interest (cylinders with 6 mm diameter and 6 mm length) were scanned at a resolution of 26 m (isotropic) in six different anatomical sites: distal radius, femoral neck and trochanter, iliac crest, calcaneus, and second lumbar vertebral body. Results: At the radius and femoral neck, trabecular bone displayed a more plate-like structure, thicker trabeculae, smaller separation/higher trabecular number, higher connectivity, and a higher degree of anisotropy in men than in women (p < 0.05). At the trochanter, men displayed more plate-like structure and thicker trabeculae (p < 0.05), but no differences in trabecular separation or other parameters compared with the women. At the calcaneus, iliac crest, and second lumbar vertebra none of the bone parameters displayed significant differences between sexes. The BV/TV at one site explained a range of only 2-32% of the variability at other sites. Conclusions: These results suggest that trabecular bone microstructural properties are remarkably heterogeneous throughout the skeleton. Significant differences between men and women are observed at some, but not at all, sites. The magnitude of sex differences in trabecular microstructure coincides with that of fracture incidence observed for some of the sites in epidemiological studies.

Osteoporosis leads to an increased risk of bone fracture. While bone density and architecture can be assessed in vivo with increasing accuracy using CT and MRI, their relationship with the critical mechanical properties at various anatomical sites remain unclear. The objective of this study was to quantify the quasi-static compressive mechanical properties of human trabecular bone among different skeletal sites and compare their relationships with bone volume fraction and a measure of microstructural anisotropy called fabric. Over 600 trabecular bone samples from six skeletal sites were assessed by microCT and tested in uniaxial compression. Bone volume fraction correlated positively with elastic modulus, yield stress, ultimate stress, and the relationships depended strongly on skeletal site. The account of fabric improved these correlations substantially, especially when the data of all sites were pooled together, but the fabric-mechanical property relationships remained somewhat distinct among the anatomical sites. The study confirms that, beyond volume fraction, fabric plays an important role in determining the mechanical properties of trabecular bone and should be exploited in mechanical analysis of clinically relevant sites of the human skeleton.

MR imaging at 3.0 T provided a better measure of the trabecular bone structure than did MR imaging at 1.5 T. There was a trend for better differentiation of donors with from those without osteoporotic vertebral fractures at 3.0 T than at 1.5 T.

Low-carbohydrate, high-fat (LC-HF) diets are popular for inducing weight loss in adults and are also used as part of a treatment for children with epilepsy. However, potential risks and side effects remain controversial. We investigated effects of LC-HF diets on growth, bone mineral density (BMD), and turnover in growing rats fed for 4 weeks either normal chow (CH, 9% fat, 33% protein, and 58% carbohydrates), LC-HF-1 (66% fat, 33% protein, and 1% carbohydrates), or LC-HF-2 (94.5% fat, 4.2% protein, and 1.3% carbohydrates). Rats fed LC-HF diets accumulated significantly more visceral and bone marrow fat and showed increased leptin but decreased insulin-like growth-factor 1 (IGF-1). Both LC-HF diets significantly decreased body length (nose to rump), but lengths of humerus, tibia, and femur were significantly reduced with LC-HF-2 only. Peripheral quantitative computed tomography (pQCT) and micro-CT (mCT) independently revealed significant reductions in BMD of tibiae in both LC-HF groups, and tibial maximum load was impaired. Bone-formation marker N-terminal propeptide of type I procollagen was reduced in sera of LC-HF groups, whereas bone resorption marker CrossLaps remained unchanged. Real-time PCR analysis revealed significant reductions by 70% to 80% of transcription factors influencing osteoblastogenesis (Runx2, osterix, and C/EBPb) in bone marrow of rats fed LC-HF diets. In conclusion, both LC-HF diets impaired longitudinal growth, BMD, and mechanical properties, possibly mediated by reductions in circulating IGF-1. Serum bone-formation markers as well as expression of transcription factors influencing osteoblastogenesis were reduced. This might indicate a lower rate of mesenchymal stem cells differentiating into osteoblasts, thus explaining reduced bone formation with LC-HF diets. ß