SummaryAging decreases the human femur's fatigue resistance, impact energy absorption, and the ability to withstand load. Changes in the osteocyte distribution and in their elemental composition might be involved in age-related bone impairment. To address this question, we carried out a histomorphometric assessment of the osteocyte lacunar distribution in the periosteal and endosteal human femoral cortexes of 16 female and 16 male donors with regard to age-and sex-related bone remodeling. Measurements of the bone mineral density distribution by quantitative backscattered electron imaging and energy dispersive X-ray analysis were taken to evaluate the osteocyte lacunar mineral composition and characteristics. Age-dependent decreases in the total osteocyte lacunar number were measured in all of the cases. This change signifies a risk for the bone's safety. Cortical subdivision into periosteal and endosteal regions of interest emphasized that, in both sexes, primarily the endosteal cortex is affected by age-dependent reduction in number of osteocyte lacunae, whereas the periosteal compartment showed a less pronounced osteocyte lacunar deficiency. In aged bone, osteocyte lacunae showed an increased amount of hypermineralized calcium phosphate occlusions in comparison with younger cases. With respect to Frost's early delineation of micropetrosis, our microanalyses revealed that the osteocyte lacunae are subject to hypermineralization. Intralacunar hypermineralization accompanied by a decrease in total osteocyte lacunar density may contribute to failure or delayed bone repair in aging bone. A decreased osteocyte lacunar density may cause deteriorations in the canalicular fluid flow and reduce the detection of microdamage, which counteracts the bone's structural integrity, while hypermineralized osteocyte lacunae may increase bone brittleness and render the bone fragile.

Osteocytes are ramified bone cells distributed throughout the bone matrix within a network of micrometer-scale cavities (lacunae) and numerous nanometer-thick tunnels (canaliculi). The integrity of the canalicular network might influence bone quality and reflect its mechanosensory potential. In this study, we applied an acid etching technique to embedded bone specimens that allows 3D observation of the canalicular network across a 2D plane to quantitatively assess the canalicular connections in cortical bone specimens from young and aged individuals. Our results showed a nearly 30% reduction in the number of canaliculi per osteocyte lacuna in aged individuals (N.Ot.Ca/Ot.Lc: 15.92 ± 1.5 in aged vs 22.10 ± 2.82 in young; p < 0.001); moreover, canalicular number was found to be inversely related to the osteonal tissue age represented by Ca/P ratio (p < 0.001). We frequently observed the phenomenon that canaliculi of osteocytes located near the osteon's periphery did not end at the osteon's cement line boundary but penetrated through the cement line and spread into the surrounding bone matrix, thus establishing an "external rooting" or "connection", which might have significant relevance to bone quality. Our findings showed that not only does the aging process diminish the canalicular network within osteons, but it also significantly reduces the probability of external osteonal rooting and connections with the surrounding bone tissue. Deterioration in the canalicular network with age reduces the connectivity between osteocytes and between osteons/interstitial tissue, which affects the supply of nutrients to osteocytes, degrades their mechanosensitivity, and contributes to increased bone fragility in the elderly.

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The combined finite element method and the maximum principal stress analysis gave insight into the fracture mechanisms of teeth with two-surface composite restorations followed by root canal preparation. Removal of tooth tissue, despite its subsequent restoration with dental materials, weakened the tooth by changing the stress intensity and distribution through tooth structures. Access cavity preparation had the greatest influence on tooth strength whilst canal enlargement did not contribute to this process substantially.

Bone fractures were analyzed from skeletal remains of 861 adult individuals from six cemeteries dating to the Late Medieval period in Serbia. Results of the study were compared to other cemetery populations (635 individual skeletons) of the same date and region in an attempt to understand fracture patterns. The association of types of fractures and their prevalence with sex, age at death, cemetery site, and information deriving from historical sources are discussed. Results showed that the long bone fracture frequency was 0.7%, and the majority of the fractures were the result of direct force. This rate is similar to some studies of contemporary British skeletal samples. However, it is much lower than for some other Old World sites. Cranial vault fractures had a rate of 6.7%, and of the facial skeleton, 1.3%; the frontal bone was the most affected of bones of the cranial vault. Injuries were more common on the upper extremities (0.8%) compared to the lower (0.6%). However, the fibula was the most fractured bone (2.8%), followed by the ulna (2.4%). This pattern is similar to three of six Late Medieval urban sites in Britain. These findings suggest that this rural community was exposed to a low risk of trauma, probably related mostly to accidents sustained during farming, and rarely to interpersonal violence.

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Despite evident interest in age-related bone changes, data on regional differences within the proximal femur are scarce. To date, there has been no comprehensive study on site-specific age-related changes in the trabecular architecture of three biomechanically important femoral subregions (medial neck, lateral neck, and intertrochanteric region) for both genders. In this study we investigated age-related deterioration in the trabecular architecture of those three subregions of the femoral neck for both genders. The research sample included 52 proximal femora (26 males, 26 females; age range, 26-96 years) from Forensic Department at University of Belgrade. Bone sections from the three regions of interest were scanned by micro-CT at University of Hamburg. The study revealed that proximal femoral microarchitecture cannot be perceived as homogeneous and, more importantly, that the aging process is not uniform. Besides the initial intersite differences, microarchitecture changed differently with increasing age, maintaining significant differences between the regions. In addition, we observed a different aging pattern between genders: deterioration was most significant in the intertrochanteric region in women, while the lateral neck was most affected in men. This finding supports epidemiological data about the differential occurrence of cervical vs. trochanteric fractures in aging males and females. In conclusion, the aging process in the proximal femur cannot be regarded as a simple function of quantitative bone loss but, rather, as an alteration of specific architecture that may degrade bone strength.

The data derived from osteons (as the basic structural units of the cortical bone) in different skeletal conditions can be employed to highlight structural factors contributing to the fracture susceptibility of various groups of individuals.