Early Siberians from Lake Baikal and Alaskan population affinities

Among the materials excavated by the 1975 joint USSR–USA team in Siberia are two burials from Shaman's Cape, Olkhon Island, Lake Baikal. One is a middle-aged male of the Serovo culture, 6,000 B.C. , and the other is a young male of the Glaskovo culture of 2,000 B.C. This later burial displays an unusual pathology affecting the nose and post-cranial regions of the pelvic girdle and lower limbs. Osteon analysis confirms the determination of age at death and illustrates the difference between normal and pathological bone. Numerous cultural materials were associated with these burials, including harpoon heads, knives, a compound fishhook and a pestle with the Serovo man, and nephrite ornaments with the Glaskovo man. The skulls, though far apart in time, are pronouncedly Mongoloid and alike in their low cranial vaults. A low, broad and inclined ascending ramus resembles Chukchi, Eskimos and Aleuts. These two specimens document the Mongoloid character of the early inhabitants of Lake Baikal.     

Shear stress inhibits while disuse promotes osteocyte apoptosis

Cell apoptosis operates as an organizing mechanism in biology in addition to removing effete cells. We have recently proposed that during bone remodeling, osteocyte apoptosis steers osteonal alignment in relation to mechanical loading of the whole bone [J. Biomech. 36 (2003) 1453]. Here we present evidence that osteocyte apoptosis in cell culture is modulated by shear stress. Under static culture conditions, serum starved osteocytes exposed phosphatidylserine (PS) on their cell membrane 6x more often than periosteal fibroblasts and 3x more often than osteoblasts. Treatment with shear stress reduced the number of osteocytes that exposed PS by 90%, but did not affect the other cell types. Fluid shear stress of increasing magnitude, dose-dependently stimulated Bcl-2 mRNA expression in human bone cells, while shear stress did not change Bax expression. These data suggest that disuse promotes osteocyte apoptosis, while mechanical stimulation by fluid shear stress promotes osteocyte survival, by modulating the Bcl-2/Bax expression ratio.     

Bone osteonal tissues by Raman spectral mapping: orientation-composition

Bone is a composite material with a hierarchical structure. Its strength depends on its structural and material properties. In the present study, Raman microspectroscopic and Imaging analyses were employed to study 12 osteons in tissue sections from the femoral midshaft of a healthy human female, with a spatial resolution of approximately 1mum. Spatial changes in amount of mineral and organic matrix, as well as the variation in the mineral content were determined, imaged, and plotted as a function of the polarization of incident light. The results showed that the prominent bands, such as nu(1) PO(4) and amide I, commonly used for the determination of mineral and organic compositions, are quite sensitive to the orientation and the polarization direction of the incident light. On the other hand, bands such as amide III, nu(2) PO(4) and nu(4) PO(4) are less susceptible to the orientational effects. As a result, exclusive consideration of the nu(1) PO(4) and amide I bands for the calculation of material properties might lead to erroneous conclusions. Amide III, nu(2) PO(4) and nu(4) PO(4) Raman bands should also be taken into consideration for compositional analysis of bone structures, especially ones with unknown orientational features. Moreover, the results of the present study demonstrate the versatility of the analytical technique, and provide insights into the organization of bone tissue at the ultrastructural level.     

Interstitial fluid flow in the osteon with spatial gradients of mechanical properties: a finite element study

Bone remodelling is the process that maintains bone structure and strength through adaptation of bone tissue mechanical properties to applied loads. Bone can be modelled as a porous deformable material whose pores are filled with cells, organic material and interstitial fluid. Fluid flow is believed to play a role in the mechanotransduction of signals for bone remodelling. In this work, an osteon, the elementary unit of cortical bone, is idealized as a hollow cylinder made of a deformable porous matrix saturated with an interstitial fluid. We use Biot’s poroelasticity theory to model the mechanical behaviour of bone tissue taking into account transverse isotropic mechanical properties. A finite element poroelastic model is developed in the COMSOL Multiphysics software. Elasticity equations and Darcy’s law are implemented in this software; they are coupled through the introduction of an interaction term to obtain poroelasticity equations. Using numerical simulations, the investigation of the effect of spatial gradients of permeability or Poisson’s ratio is performed. Results are discussed for their implication on fluid flow in osteons: (i) a permeability gradient affects more the fluid pressure than the velocity profile; (ii) focusing on the fluid flow, the key element of loading is the strain rate; (iii) a Poisson’s ratio gradient affects both fluid pressure and fluid velocity. The influence of textural and mechanical properties of bone on mechanotransduction signals for bone remodelling is also discussed.     

Femoral diaphyseal histomorphometric age determinations for the Shanidar 3, 4, 5, and 6 Neandertals and Neandertal longevity

Histomorphometric analysis of femoral diaphyseal fragments from the Shanidar 3, 4, 5, and 6 Neandertals provide age at death estimates of 41 (+/- 6.7), 36 (+/- 6.7), 40 (+/- 6.7), and 24 (+/- 6.7) years. These determinations are in agreement with previous macroscopic age assessments. Since the Shanidar 3, 4, and 5 (and slightly younger Shanidar 1) individuals are among the oldest known Neandertals, these age determinations suggest that significant postreproductive survival was rare among the Neandertals and a phenomenon primarily of anatomically modern humans.     

Effects of the basic multicellular unit and lamellar thickness on osteonal fatigue life

A remodeling cycle sets the size of the osteon and associated lamellae in the basic multicellular unit. Treatments and aging affect these micro-structural features. We previously demonstrated decreased fatigue life with an unexplained mechanism and decreased osteon size in cortical bone treated with high-dose bisphosphonate. Here, three finite element models were examined: type-1: a single osteon, as a homogeneous unit and with heterogeneous lamellae and interlamellae, type-2: a control, interstitial-only tissue and type-3: the osteon with cement line, set within the interstitial tissue. Models were loaded in simulated, sinusoidal bending fatigue. As osteon size was decreased, lamellar number and lamellar thickness were incrementally adjusted for each model. As hypothesized, lamellae within the larger type-1 models attained greater cycles to failure and the addition of an osteon to type-2 models (generating a type-3 model set) yielded increased fatigue life. However, as the osteon size was decreased, the potential for compressive damage nucleation was increased within the lamellae of the osteons versus the interstitium. Also, osteons with fewer, thicker lamellae displayed increased fatigue life. Osteonal microstructure plays a role in damage initiation location, especially when BMU size is smaller. Previous findings by us and others could partially be explained by this further understanding of increased probability for damage nucleation in smaller osteons.     

Orientation of collagen at the osteocyte lacunae in human secondary osteons

This work characterizes an aspect of human bone micro-structure, pertinent to fracture initiation and arrest. It addresses how the orientation of elementary components proximate to osteocyte lacunae influences secondary osteon micro-biomechanics. New data at the perilacunar region concerning orientation of collagen-apatite, and prior data on collagen orientation outside the perilacunar region, are incorporated in a novel simulation of osteons to investigate how orientation relates to strains and stresses during mechanical testing. The perilacunar region was observed by confocal microscopy within single lamellar specimens, isolated from osteons. The specimens were separated by extinct or bright appearance in transverse section under circularly polarizing light. This is because synchrotron diffraction and confocal microscopy had established that each type, away from the perilacunar region, corresponds to specific dominant collagen orientation (extinct lamellae's dominant collagen forming small angles with the original osteon axis, while the bright lamellae's forms larger angles). Morphometry of serial confocal images of each perilacunar region showed collagen orientation generally following the orientation of canaliculi, circumambiently-perpendicular to the lacuna. The lacunae tilted relative to the lamellar walls were more numerous in extinct than in bright lamella. Their apices were less likely in extinct than bright lamella to show collagen following the canalicular orientation. The simulation of osteocyte lacunae in osteons, under tension or compression loading, supports the hypothesis that collagen orientation affects strains and stresses at the equatorial perilacunar region in conjunction with the presence of the lacuna. We further conjecture that collagen orientation diverts propagation of micro-cracks initiating from apices.     

The effect of hydration on mechanical anisotropy,topography and fibril organization of the osteonal lamellae

The effect of hydration on the mechanical properties of osteonal bone, in directions parallel and perpendicular to the bone axis, was studied on three length scales: (i) the mineralized fibril level (~100 nm), (ii) the lamellar level (~6 µm); and (iii) the osteon level (up to ~30 µm).We used a number of techniques, namely atomic force microscopy (AFM), nanoindentation and microindentation. The mechanical properties (stiffness, modulus and/or hardness) have been studied under dry and wet conditions. On all three length scales the mechanical properties under dry conditions were found to be higher by 30–50% compared to wet conditions. Also the mechanical anisotropy, represented by the ratio between the properties in directions parallel and perpendicular to the osteon axis (anisotropy ratio, designated here by AnR), surprisingly decreased somewhat upon hydration. AFM imaging of osteonal lamellae revealed a disappearance of the distinctive lamellar structure under wet conditions. Altogether, these results suggest that a change in mineralized fibril orientation takes place upon hydration.     

含液体骨单元的力学模型

基于骨单元的生理结构特性,将骨单元作为厚壁圆筒春内部合弗氏管内充满组织液。并考虑屯液体在筒壁内的扩散,从而得取了骨单元沿轴向的等效本方程。该本构方程表明,含液体骨单元具有粘生力学性质;若筒壁的轴向治松经为１／２,则哈弗氏管内的液体将不影响骨单元的力学行为,骨单元的孔隙率越大,液体艰骨单元的影响也越大。     

Effects of field size when using Kerley's histological method for determination of age at death

The field size at which a bone is read affects the results obtained when using Kerley's histological method for age estimation, even after applying the recommended correction factor. Whereas there is no tendency for any one of three field sizes tested to consistently underestimate or overestimate age, a field size closest to that used by Kerley in his original study had significantly lower variances for its age estimates, and thus provides greater reliability. This particular field size yields more precise estimates because it is sampling a pattern and number of structures more similar to that of Kerley. Correction factors cannot equalize the counts of osteons and osteon fragments because of spatial variations in the distributions of these histological structures. A field size similar to that used by Kerley in gathering the data from which he developed his regression equations must be used to assure that the same pattern and number of structures is being sampled. For this reason, we suggest a field size as close to 2.06 mm² as possible be used when employing Kerley's method.