Browsing by Author "Rolvien, Tim (56671307900)"

Background. Age- and sex-specific 3D bone structure patterns in human radii and tibiae were investigated with respect to individuals' osteodensitometric status to unravel associations with site-specific fracture occurrences and underlying loading patterns. Methods. A sample of 385 patients (121 men and 264 women, age range: 23-91 years) were investigated. The patients were classified according to dual X-ray absorptiometry T-scores in three groups: control (n = 60), osteopenia (n = 160), and osteoporosis (n = 165). Bone architecture and geometry were assessed by high-resolution peripheral quantitative computed tomography of the cortical and trabecular compartments in distal radii and tibiae. Results. We found site-dependent age- and sex-related trends regarding bone architecture and geometry. Females displayed more pronounced age-related changes than males. Specifically, female radii showed both cortical and trabecular structural deterioration with aging, whereas the tibiae demonstrated exclusively cortical deterioration. The mean cortical perimeter revealed a significant age-related increase for both sexes even after adjusting for body height and weight, which suggests that periosteal expansion can be observed in both the tibia and also in the radius. Osteopenia and osteoporosis cases did not reveal higher cortical perimeters in comparison to controls. Conclusions. The tomographic assessment of bone structure further clarifies the architectural basis for increased bone fragility at distal radii and tibiae with advanced age leading to fracture predilection in females. Our findings may represent a morphological link to epidemiological data on age-dependent fracture incidences. Our data support the presence of periosteal apposition at both skeletal sites despite different loading magnitudes, and challenges the view on periosteal expansion just as a compensatory mechanism to counterbalance bone loss. © 2015 The Author.

Background: The osteocytic lacunar network is considered to be an integral player in the regulation of bone homeostasis, and reduction in osteocytes is associated with reduced bone strength. Here, we analyzed site-specific patterns in osteocyte characteristics and matrix composition in the cortical compartment of the femoral neck to reveal the structural basis of its fragility. Methods: Cross-sections of the human femoral neck - one of the most common fracture sites - were acquired from 12 female cadavers (age 34–86 years) and analyzed with backscattered scanning electron microscopy and high-resolution micro-computed tomography (μ-CT). The 2D/3D density and size of the osteocyte lacunae as well as bone mineral density distribution (BMDD) were measured in two regions subject to different biomechanical loads in vivo: the inferomedial (medial) region (habitually highly loaded in compression) and the superolateral (lateral) region (lower habitual loading intensity). Using quantitative polarized light microscopy, collagen fiber orientation was quantified in these two regions, accordingly. Results: In 2D measurements, the inferomedial region displayed lower mineralization heterogeneity, 19% higher osteocyte lacunar density (p = 0.005), but equal lacunar size compared to the superolateral region. 3D measurements confirmed a significantly higher osteocyte lacunar density in the inferomedial region (p = 0.015). Osteocyte lacunar density decreased in aged individuals, and inter-site differences were reduced. Site-specific osteocyte characteristics were not accompanied by changes in collagen fiber orientation. Conclusions: Since osteocyte characteristics may provide valuable insights into bone mechanical competence, the variations in osteocyte properties might reflect the increased fracture susceptibility of the superolateral neck. © 2018

Background: The osteocytic lacunar network is considered to be an integral player in the regulation of bone homeostasis, and reduction in osteocytes is associated with reduced bone strength. Here, we analyzed site-specific patterns in osteocyte characteristics and matrix composition in the cortical compartment of the femoral neck to reveal the structural basis of its fragility. Methods: Cross-sections of the human femoral neck - one of the most common fracture sites - were acquired from 12 female cadavers (age 34–86 years) and analyzed with backscattered scanning electron microscopy and high-resolution micro-computed tomography (μ-CT). The 2D/3D density and size of the osteocyte lacunae as well as bone mineral density distribution (BMDD) were measured in two regions subject to different biomechanical loads in vivo: the inferomedial (medial) region (habitually highly loaded in compression) and the superolateral (lateral) region (lower habitual loading intensity). Using quantitative polarized light microscopy, collagen fiber orientation was quantified in these two regions, accordingly. Results: In 2D measurements, the inferomedial region displayed lower mineralization heterogeneity, 19% higher osteocyte lacunar density (p = 0.005), but equal lacunar size compared to the superolateral region. 3D measurements confirmed a significantly higher osteocyte lacunar density in the inferomedial region (p = 0.015). Osteocyte lacunar density decreased in aged individuals, and inter-site differences were reduced. Site-specific osteocyte characteristics were not accompanied by changes in collagen fiber orientation. Conclusions: Since osteocyte characteristics may provide valuable insights into bone mechanical competence, the variations in osteocyte properties might reflect the increased fracture susceptibility of the superolateral neck. © 2018

Immobilization as a result of long-term bed rest can lead to gradual bone loss. Because of their distribution throughout the bone matrix and remarkable interconnectivity, osteocytes represent the major mechanosensors in bone and translate mechanical into biochemical signals controlling bone remodeling. To test whether immobilization affects the characteristics of the osteocyte network in human cortical bone, femoral diaphyseal bone specimens were analyzed in immobilized female individuals and compared with age-matched postmenopausal individuals with primary osteoporosis. Premenopausal and postmenopausal healthy individuals served as control groups. Cortical porosity, osteocyte number and lacunar area, the frequency of hypermineralized lacunae, as well as cortical bone calcium content (CaMean) were assessed using bone histomorphometry and quantitative backscattered electron imaging (qBEI). Bone matrix properties were further analyzed by Fourier transform infrared spectroscopy (FTIR). In the immobilization group, cortical porosity was significantly higher, and qBEI revealed a trend toward higher matrix mineralization compared with osteoporotic individuals. Osteocyte density and canalicular density showed a declining rate from premenopausal toward healthy postmenopausal and osteoporotic individuals with peculiar reductions in the immobilization group, whereas the number of hypermineralized lacunae accumulated inversely. In conclusion, reduced osteocyte density and impaired connectivity during immobilization are associated with a specific bone loss pattern, reflecting a phenotype clearly distinguishable from postmenopausal osteoporosis. Immobilization periods may lead to a loss of survival signals for osteocytes, provoking bone loss that is even higher than in osteoporosis states, whereas osteocytic osteolysis remains absent. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research