Osteon Population Research Articles

Diversity in intracortical remodeling in the human femoral bone: A novel view point with the morphological analysis of secondary osteons

IntroductionIn humans, intracortical bone remodeling is performed by a basic multicellular unit (BMU) composed of osteoclasts and osteoblasts penetrating through cortical bones. As a result, secondary osteons and their boundaries, cement lines, can be observed on the transverse section. There have been few reports mention whether there is diversity within a single individual and on the relevance to bone remodeling. The purpose of this study is to investigate the morphological diversity of secondary osteons in human femoral bone and to examine the relationship with bone remodeling. Material and methodsFirst of all, we developed an original method to get the cross-sectional images of the cortical bones around the whole circumference for the purpose of evaluating the morphology of the secondary osteon exhaustively. Then, a total of ten cross-sectional slices from one right human femoral bone of male were prepared and stained with this method. The osteon population density and complexity of cement lines in osteons were evaluated in detail. ResultsWithin this femoral bone, the osteon population density was significantly higher in the periosteal side and in the posterior area. Conversely, the cement line density and the osteon complexity were higher in the endosteal side; the proportion of complexed osteon significantly increased from the periosteal side toward the endosteal side. DiscussionThe results suggested that there were diversities in osteon population densities and osteon morphological pattern within one human femoral bone. It seemed that the BMUs ran to avoid the existing regions of osteon in the periosteal sides and to overlap the existing osteon in the endosteal sides. This seemed to be one of the novel viewpoints in the morphological analysis of secondary osteons. It might be better for the orthopedic surgeons to be aware that the osteon distribution in the cortical bone is not uniform.

Sex-specific patterns in cortical and trabecular bone microstructure in the Kirsten Skeletal Collection, South Africa.

The purpose of this study was to provide bone histomorphometric reference data for South Africans of the Western Cape who likely dealt with health issues under the apartheid regime. The 206 adult individuals (n female = 75, n male = 131, mean = 47.9 ± 15.8 years) from the Kirsten Skeletal Collection, U. Stellenbosch, lived in the Cape Town metropole from the late 1960s to the mid-1990s. To study age-related changes in cortical and trabecular bone microstructure, photomontages of mid-thoracic rib cross-sections were quantitatively examined. Variables include relative cortical area (Rt.Ct.Ar), osteon population density (OPD), osteon area (On.Ar), bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular spacing (Tb.Sp). All cortical variables demonstrated significant relationships with age in both sexes, with women showing stronger overall age associations. Peak bone mass was compromised in some men, possibly reflecting poor nutritional quality and/or substance abuse issues throughout adolescence and early adulthood. In women, greater predicted decrements in On.Ar and Rt.Ct.Ar suggest a structural disadvantage with age, consistent with postmenopausal bone loss. Age-related patterns in trabecular bone microarchitecture are variable and difficult to explain. Except for Tb.Th, there are no statistically significant relationships with age in women. Men demonstrate significant negative correlations between BV/TV, Tb.N, and age, and a significant positive correlation between Tb.Sp and age. This research highlights sex-specific differences in patterns of age-related bone loss, and provides context for discussion of contemporary South African bone health. While the study sample demonstrates indicators of poor bone quality, osteoporosis research continues to be under-prioritized in South Africa.

Bone deep: Variation in stable isotope ratios and histomorphometric measurements of bone remodelling within adult humans

Stable carbon (δ13C) and nitrogen (δ15N) isotope studies of ancient human diet increasingly sample several skeletal elements within an individual. Such studies draw upon differences in bone turnover rates to reconstruct diet during different periods of time within an individual's lifetime. Rib and femoral bone, with their respectively fast and slow remodelling rates, are the bones most often sampled to reconstruct shorter and longer term signals of diet prior to death. It is poorly understood if δ13C and δ15N vary between bone types within a single individual, or if this variation corresponds with bone turnover rate (BTR). Here, we determined δ13C and δ15N for ten different bones from ten adult human skeletons (n = 5 males; n = 5 females). Isotope values were compared to the rate that each bone remodeled, calculated from osteon population (OPD) density. Results reveal that isotope ratios varied within each skeleton (δ13C: max = −1.58‰; δ15N: max = 3.05‰). Humeri, metacarpals, and ribs had the highest rate of bone remodelling; the occipital bone had the lowest. A regression analyses revealed that higher rates of bone remodelling are significantly and negatively correlated with lower δ15N. Our results suggest that the occipital bone, with its slow rate of bone renewal, may prove useful for isotopic studies that reconstruct diet over longer periods of time within an individual's lifetime. Isotope studies that compare individual skeletal elements between populations should standardize their methodology to bones with either a slow or fast turnover rate.

Utility of osteon circularity for determining species and interpreting load history in primates and nonprimates.

Histomorphological analyses of bones are used to estimate an individual's chronological age, interpret a bone's load history, and differentiate species. Among various histomorphological characteristics that can influence mechanical properties of cortical bone, secondary osteon (Haversian system) population density and predominant collagen fiber orientation are particularly important. Cross-sectional shape characteristics of secondary osteons (On.Cr = osteon circularity, On.El = osteon ellipticality) are considered helpful in these contexts, but more robust proof is needed. We sought to determine if variations in osteon shape characteristics are sufficient for accurately differentiating species, load-complexity categories, and regional habitual strain-mode distributions (e.g., tension vs. compression regions). Circularly polarized light images were obtained from 100-micron transverse sections from diaphyses of adult deer calcanei; sheep calcanei, radii, and tibiae; equine calcanei, radii, and third metacarpals (MC3s); chimpanzee femora; and human femora and fibulae. Osteon cross-sectional area (On.Ar), On.Cr, and On.El were quantified indiscriminately and in the contexts of load-complexity and regional strain-mode distributions. On.Cr and On.El, when examined independently in terms of all data, or mean (nested) data, for each bone, exceeded 80% accuracy in the inter-species comparisons only with respect to distinguishing humans from nonhumans. Correct classification among the nonhuman species was <70%. When On.Cr and On.El were coupled together and with On.Ar in discriminant function analyses (nested and unnested data) there were high misclassifications in all but human vs. nonhuman comparisons. Frequent misclassifications in nonhuman comparisons might reflect influences of habitual load complexity and/or strain-mode distributions, or other factors not accounted for by these two considerations.

Cortical bone histomorphology of known-age skeletons from the Kirsten collection, Stellenbosch university, South Africa.

ABSTRACTObjectivesNormal human bone tissue changes predictably as adults get older, but substantial variability in pattern and pace remains unexplained. Information is needed regarding the characteristics of histological variables across diverse human populations.MethodsUndecalcified thin sections from mid‐thoracic ribs of 213 skeletons (138 M, 75 F, 17–82 years, mean age 48 years), are used to explore the efficacy of an established age‐at‐death estimation method and methodological approach (Cho et al.: J Forensic Sci 47 (2002) 12‐18) and expand on it. The ribs are an age‐balanced sample taken from skeletonized cadavers collected from 1967 to 1999 in South Africa, each with recorded sex, age, cause of death and government‐defined population group (129 “Colored,” 49 “Black,” 35 “White”).ResultsThe Ethnicity Unknown equation performs better than those developed for European‐Americans and African‐Americans, in terms of accuracy and bias. A new equation based solely on the study sample does not improve accuracy. Osteon population densities (OPD) show predicted values, yet secondary osteon areas (On.Ar) are smaller than expected for non‐Black subgroups. Relative cortical area (Ct.Ar/Tt.Ar) is low among non‐Whites.ConclusionsResults from this highly diverse sample show that population‐specific equations do not increase estimate precision. While within the published range of error for the method (±24.44 years), results demonstrate a systematic under‐aging of young adults and over‐aging of older adults. The regression approach is inappropriate. The field needs fresh approaches to statistical treatment and to factors behind cortical bone remodeling. Am J Phys Anthropol 160:137–147, 2016. © 2016 The Authors American Journal of Physical Anthropology Published by Wiley Periodicals, Inc.

Spatial variation in osteon population density at the human femoral midshaft: histomorphometric adaptations to habitual load environment.

Intracortical remodeling, and the osteons it produces, is one aspect of the bone microstructure that is influenced by and, in turn, can influence its mechanical properties. Previous research examining the spatial distribution of intracortical remodeling density across the femoral midshaft has been limited to either considering only small regions of the cortex or, when looking at the entirety of the cortex, considering only a single individual. This study examined the spatial distribution of all remodeling events (intact osteons, fragmentary osteons, and resorptive bays) across the entirety of the femoral midshaft in a sample of 30 modern cadaveric donors. The sample consisted of 15 males and 15 females, aged 21-97years at time of death. Using geographic information systems software, the femoral cortex was subdivided radially into thirds and circumferentially into octants, and the spatial location of all remodeling events was marked. Density maps and calculation of osteon population density in cortical regions of interest revealed that remodeling density is typically highest in the periosteal third of the bone, particularly in the lateral and anterolateral regions of the cortex. Due to modeling drift, this area of the midshaft femur has some of the youngest primary tissue, which consequently reveals that the lateral and anterolateral regions of the femoral midshaft have higher remodeling rates than elsewhere in the cortex. This is likely the result of tension/shear forces and/or greater strain magnitudes acting upon the anterolateral femur, which results in a greater amount of microdamage in need of repair than is seen in the medial and posterior regions of the femoral midshaft, which are more subject to compressive forces and/or lesser strain magnitudes.

Accuracy and sampling error of two age estimation techniques using rib histomorphometry on a modern sample

Most age estimation methods are proven problematic when applied in highly fragmented skeletal remains. Rib histomorphometry is advantageous in such cases; yet it is vital to test and revise existing techniques particularly when used in legal settings (Crowder and Rosella, 2007). This study tested Stout & Paine (1992) and Stout et al. (1994) histological age estimation methods on a Modern Greek sample using different sampling sites.Six left 4th ribs of known age and sex were selected from a modern skeletal collection. Each rib was cut into three equal segments. Two thin sections were acquired from each segment. A total of 36 thin sections were prepared and analysed. Four variables (cortical area, intact and fragmented osteon density and osteon population density) were calculated for each section and age was estimated according to Stout & Paine (1992) and Stout et al. (1994).The results showed that both methods produced a systemic underestimation of the individuals (to a maximum of 43 years) although a general improvement in accuracy levels was observed when applying the Stout et al. (1994) formula. There is an increase of error rates with increasing age with the oldest individual showing extreme differences between real age and estimated age.Comparison of the different sampling sites showed small differences between the estimated ages suggesting that any fragment of the rib could be used without introducing significant error. Yet, a larger sample should be used to confirm these results.

Ancient Human Bone Microstructure in MedievalEngland: Comparisons between Two Socio‐Economic Groups

Understanding the links between bone microstructure and human lifestyle is critical for clinical and anthropological research into skeletal growth and adaptation. The present study is the first to report correspondence between socio-economic status and variation in bone microstructure in ancient humans. Products of femoral cortical remodeling were assessed using histological methods in a large human medieval sample (N = 450) which represented two distinct socio-economic groups. Osteonal parameters were recorded in posterior midshaft femoral sections from adult males (N = 233) and females (N = 217). Using univariate and multivariate statistics, intact, fragmentary, and osteon population densities, Haversian canal area and diameter, and osteon area were compared between the two groups, accounting for sex, age, and estimated femoral robusticity. The size of osteons and their Haversian canals, as well as osteon density, varied significantly between the socio-economic groups, although minor inconsistencies were observed in females. Variation in microstructure was consistent with historical textual evidence that describes differences in mechanical loading and nutrition between the two groups. Results demonstrate that aspects of ancient human lifestyle can be inferred from bone microstructure.

Investigating histomorphometric relationships at the human femoral midshaft in a biomechanical context.

Cortical bone histomorphometry utilised in human and animal bone biology studies has demonstrated that osteon densities and their geometric properties may be in a relationship with biomechanical load application. Further research is required to investigate mutual links between bone histological variables to elucidate their usefulness in future biomechanical studies. Here, a series of correlations exploring bone biology relationships at the human midshaft femur were performed using a large sample. Mean intact, fragmentary and total osteon population densities, Haversian canal diameter and area, osteon area, as well as osteocyte lacunae density were measured along the sub-periosteal cortex in sections removed from the posterior midshaft aspect of modern human male (n=233) and female (n=217) femora (total n=450). Parametric and non-parametric correlations between the histology variables were sought in the entire sample, as well as within age and sex sub-groups. Several significant positive and negative correlations explaining a large proportion of data variation were found. Haversian canal area, diameter, and osteon area were positively correlated. As the density of osteocyte lacunae increased, Haversian canals and osteons became smaller. As osteons increased in density, so did osteocyte lacunae, but Haversian canal and osteon area became smaller. Results were consistent across age and sex groups. Findings suggest that an increased rate of bone remodelling is associated with a decrease in geometrical properties of osteons. An increased density of osteocyte lacunae and osteons indicates the involvement of bone maintenance cells in remodelling potentially induced by mechanical stimuli. Future histomorphometry studies will benefit from examining multiple bone histology variables due to many mutual bone biology relationships that exist at the human midshaft femur.

Morphology, Morphometry and Spatial Distribution of Secondary Osteons in Equine Femur.

A high number of differences exist in bone histological features depending on the species, breed, age and bone. Moreover, osteon distribution may vary in the different sides of a bone as a consequence of different biomechanical strains. The aim of this work was to study the distribution and morphology of osteons in different sides of the equine femoral diaphysis with the attempt to correlate them to the main strains operating on them. The following parameters of secondary osteons and Haversian canals were measured in the transverse sections of diaphyses: perimeter, area, minimum and maximum diameter, eccentricity and osteon population density. A typical Haversian tissue was observed with elliptic secondary osteons consisting in about 10 well-defined lamellae surrounding a circular Haversian canal. Quantitative analysis displays a different population density of secondary osteons depending on the side. The caudal and medial sides, where compression strains are higher, have more secondary osteons in comparison with the cranial and lateral sides, where tension strains are prevalent. These data suggest that secondary osteon population density may depend on the predominant strains. Even the elliptical shape of secondary osteons may be related to biomechanical strains, as their major axes are oriented cranio-caudally parallel to prevalent strains.

Anthropological Age Estimation with Bone Histomorphometry from the Human Clavicle

The purpose of present study was to apply histomorphometry to estimate the age at death using the clavicular osteonal remodeling rate and to develop an age-predicting equation. 46 clavicular samples consisting 28 males and 18 females were obtained from Korean cadavers. Two sequential 1-mm-thick sections, were prepared using a diamond wheel, and a 100 um-thick section was then made by manual grinding with polarizing filter optical microscopy. Three histomorphometric variables, including relative cortical area (RCA), osteon population density (OPD), and mean osteon area (OA), were measured. The mean values are indicated because no significant difference in any variable was noted by a paired t test between the two sequential sections. Analysis of covariance demonstrated that stratification of the statistical results of OPD and OA based on sex was unnecessary, except for RCA. Regression analysis indicated that the highest coefficient value was OPD (R2 = 0.583), which was selected as a significant value with RCA for an age-predicting equation (R2 = 0.628) by the multiple regression analysis stepwise method. In conclusion, a histomorphometric method using the clavicle is reliable for age estimation in physical and forensic anthropological fields.

Intracortical Bone Remodeling Variation Shows Strong Genetic Effects

Intracortical microstructure influences crack propagation and arrest within bone cortex. Genetic variation in intracortical remodeling may contribute to mechanical integrity and, therefore, fracture risk. Our aim was to determine the degree to which normal population-level variation in intracortical microstructure is due to genetic variation. We examined right femurs from 101 baboons (74 females, 27 males; aged 7–33 years) from a single, extended pedigree to determine osteon number, osteon area (On.Ar), haversian canal area, osteon population density, percent osteonal bone (%On.B), wall thickness (W.Th), and cortical porosity (Ct.Po). Through evaluation of the covariance in intracortical properties between pairs of relatives, we quantified the contribution of additive genetic effects (heritability [h 2]) to variation in these traits using a variance decomposition approach. Significant age and sex effects account for 9 % (Ct.Po) to 21 % (W.Th) of intracortical microstructural variation. After accounting for age and sex, significant genetic effects are evident for On.Ar (h 2 = 0.79, p = 0.002), %On.B (h 2 = 0.82, p = 0.003), and W.Th (h 2 = 0.61, p = 0.013), indicating that 61–82 % of the residual variation (after accounting for age and sex effects) is due to additive genetic effects. This corresponds to 48–75 % of the total phenotypic variance. Our results demonstrate that normal, population-level variation in cortical microstructure is significantly influenced by genes. As a critical mediator of crack behavior in bone cortex, intracortical microstructural variation provides another mechanism through which genetic variation may affect fracture risk.

Black Bears With Longer Disuse (Hibernation) Periods Have Lower Femoral Osteon Population Density and Greater Mineralization and Intracortical Porosity

Intracortical bone remodeling is persistent throughout life, leading to age related increases in osteon population density (OPD). Intracortical porosity also increases with age in many mammals including humans, contributing to bone fragility and fracture risk. Unbalanced bone resorption and formation during disuse (e.g., physical inactivity) also increases intracortical porosity. In contrast, hibernating bears are a naturally occurring model for the prevention of both age-related and disuse osteoporoses. Intracortical bone remodeling is decreased during hibernation, but resorption and formation remain balanced. Black bears spend 0.25-7 months in hibernation annually depending on climate and food availability. We found longer hibernating bears demonstrate lower OPD and higher cortical bone mineralization than bears with shorter hibernation durations, but we surprisingly found longer hibernating bears had higher intracortical porosity. However, bears from three different latitudes showed age-related decreases in intracortical porosity, indicating that regardless of hibernation duration, black bears do not show the disuse- or age-related increases in intracortical porosity which is typical of other animals. This ability to prevent increases in intracortical porosity likely contributes to their ability to maintain bone strength during prolonged periods of physical inactivity and throughout life. Improving our understanding of the unique bone metabolism in hibernating bears will potentially increase our ability to develop treatments for age- and disuse-related osteoporoses in humans.

The cast imaging of the osteon lacunar‐canalicular system and the implications with functional models of intracanalicular flow

A casting technique with methyl-methacrylate (MMA) was applied to the study of the osteon lacunar-canalicular network of human and rabbit cortical bone. The MMA monomer infiltration inside the vascular canals and from these into the lacunar-canalicular system was driven by capillarity, helped by evaporation and the resulting negative pressure in a system of small pipes. There was uniform, centrifugal penetration of the resin inside some osteons, but this was limited to a depth of four to five layers of lacunae. Moreover, not all of the osteon population was infiltrated. This failure can be the result of one of two factors: the incomplete removal of organic debris from the canal and canalicular systems, and lack of drainage at the osteon external border. These data suggest that each secondary osteon is a closed system with a peripheral barrier (represented by the reversal line). As the resin advances into the osteon, the air contained inside the canalicula is compressed and its pressure increases until infiltration is stopped. The casts gave a reliable visualization of the lacunar shape, position and connections between the lacunae without the need for manipulations such as cutting or sawing. Two systems of canalicula could be distinguished, the equatorial, which connected the lacunae (therefore the osteocytes) lying on the same concentric level, and the radial, which established connections between different levels. The equatorial canalicula radiated from the lacunar border forming ramifications on a planar surface around the lacuna, whereas the radial canalicula had a predominantly straight direction perpendicular to the equatorial plane. The mean length of the radial canalicula was 40.12 ± 10.26 μm in rabbits and 38.4 ± 7.35 μm in human osteons; their mean diameter was 174.4 ± 71.12 nm and 195.7 ± 79.58 nm, respectively. The mean equatorial canalicula diameter was 237 ± 66.04 nm in rabbit and 249.7 ± 73.78 nm in human bones, both significantly larger (P < 0.001) than the radial. There were no significant differences between the two species. The lacunar surface measured on the equatorial plane was higher in rabbit than in man, but the difference was not statistically significant. The cast of the lacunar-canalicular network obtained with the reported technique allows a direct, 3-D representation of the system architecture and illustrates how the connections between osteocytes are organized. The comparison with models derived by the assumption of the role of hydraulic conductance and other mechanistic functions provides descriptive, morphological data to the ongoing discussion on the Haversian system biology.

Residual stress distribution in rabbit limb bones

The presence of the residual stresses in bone tissue has been noted and the authors have reported that there are residual stresses in bone tissue. The aim of our study is to measure the residual stress distribution in the cortical bone of the extremities of vertebrates and to describe the relationships with the osteon population density. The study used the rabbit limb bones (femur, tibia/fibula, humerus, and radius/ulna) and measured the residual stresses in the bone axial direction at anterior and posterior positions on the cortical surface. The osteons at the sections at the measurement positions were observed by microscopy. As a result, the average stresses at the hindlimb bones and the forelimb bones were 210 and 149 MPa, respectively. In the femur, humerus, and radius/ulna, the residual stresses at the anterior position were larger than those at the posterior position, while in the tibia, the stress at the posterior position was larger than that at the anterior position. Further, in the femur and humerus, the osteon population densities in the anterior positions were larger than those in the posterior positions. In the tibia, the osteon population density in the posterior position was larger than that in the anterior position. Therefore, tensile residual stresses were observed at every measurement position in the rabbit limb bones and the value of residual stress correlated with the osteon population density ( r=0.55, P<0.01).

Histomorphometric estimation of age in paraffin-embedded ribs: a feasibility study

Estimation of age at death from human bones in legal medicine or in anthropology and archaeology is hampered by controversial results from the various macroscopic and histological techniques. This study attempted an estimation of age at death by histomorphometric analysis, from the fourth left rib adjacent to the costochondral joint in 80 forensic cases. Use of the picrosirius dye provided a reliable staining of the decalcified paraffin-embedded ribs. The total bone cortical area, the major and minor diameter as well as the area of the Haversian canals, the osteon areas of intact and remodelled secondary osteons, the area of non-Haversian canals were evaluated by means of image analysis, and derived parameters were calculated on both the internal and external sides of the rib. Most of the variables exhibited consistency between three different observers. Noteworthy, morphometric measurements in the internal cortex of the rib showed less variability than in the external cortex. Finally, discriminant statistical analysis from the 80 cases in this study indicated that the osteon population density was virtually sufficient to significantly discriminate between three groups of age: 20-39 (adulthood), 40-59 (middle age) and a group superior to 60. A subsequent blind evaluation of ten new subjects satisfactorily classified seven subjects out of ten within the three age groups. These results make feasible a larger study aimed at characterization of the practical relationships between bone tissue histomorphometry in ribs and chronological age in forensic cases.

Technical note: A stereological analysis of the cross‐sectional variability of the femoral osteon population

Unbiased selection of regions of interest (ROIs) and unbiased definition of histological structures are needed to improve the repeatability of microscopic methods for age at death determination and to reduce operator subjectivity. We present results obtained by selecting ROIs according to stereological principles on a sample of 28 femoral cross sections of Caucasoid males aged 20-89 years. A regular grid was overlaid on the cross section, and the ROIs were selected as close as possible to the periosteum in the anterior, lateral, and medial regions. The areas consisting of all intact secondary osteons plus fragments were outlined and osteon population density, percent osteon population, area, and perimeter were calculated using stereological methods and software. Overall, the analyses of intra- and inter-section variability showed no significant difference between the ROIs, i.e., the location within the cross section of the ROIs does not affect the outcome of the analyses. The individual variability was found to be higher in adults aged 30-55 years than in other age ranges. ranges.

New Formulas to Estimate Age at Death in Maya Populations Using Histomorphological Changes in the Fourth Human Rib*

This study develops new histomorphological algorithms for Maya populations' human ribs and tests the applicability of published algorithms. Thin sections from the fourth rib of 36 individuals of known age were analyzed under polarized light microscopy. Osteon population density (OPD, the concentration of intact and fragmented osteons per mm(2)), cortical area (CA), and osteon size (OS) were recorded. Seven algorithms were calculated, using all combinations of variables, and compared to the performance of published formulas. The OPD-based formulas deviate from the known age 8.7 years on average, while those from OS and CA deviate between 10.7 and 12.8 years. In comparison, our OPD-based algorithms perform better than the one by Stout and Paine and much better than Cho et al. In conclusion, algorithms should be developed using OPD for different ethnic groups; although Stout and Paine's can be used for Maya and maybe Mesoamerican individuals.

Patterns of Femoral Bone Remodeling: Comparison of the Tongariki Native Easter Islanders with European Population

The relationship between sex, age and histomorphometry in femoral cortical bone was examined in a 19 th cen- tury skeletal population from the XIX-XX Century Northern Italy, and compared with the femoral sections belonging to the Tongariki Easter Islanders (XVII-XVIII Century A.D.). Femoral cross sections were examined using an image analy- sis system. Several histological variables were calculated to assess differences between sexes and among age groups. The results indicate significant differences between the two populations in osteon remodeling. OPD (Osteon Population Den- sity) increased especially in the female sample in both populations, but In the Easter Island female sample OA (Osteon Area) was lower than in the European female population. In the Easter Island female sample, %Or (percent Osteon refill- ing) decreased after 49 years of age. The phenomenon was also evident in both sexes of European population, although the involution process was not so marked as age advanced.

Bone microstructure in juvenile chimpanzees

The growth, development, and maintenance of bone are influenced by genetic and environmental variables. Understanding variability in bone microstructure among primates may help illuminate the factors influencing the number and size of secondary osteons. The purpose of this study is to assess the bone microstructure in 8 humeral and 12 femoral sections of 12 juvenile chimpanzees, aged 2-15.3 years, and one adult chimp. Secondary osteons were counted and measured for 16 fields per section. Results indicate that the femur exhibits a mean osteon population density (OPD) of 4.46 +/- 2.34/mm(2), mean Haversian canal area of 0.0016 +/- 0.0007 mm(2), and mean osteon area of 0.033 +/- 0.006 mm(2). The humerus has a mean OPD of 4.72 +/- 1.57/mm(2), mean Haversian canal area of 0.0013 +/- 0.0003 mm(2), and mean osteon area of 0.033 +/- 0.005 mm(2). Differences are not significant between the humerus and femur, possibly indicating similar mechanical demands during locomotion. Osteon population density exhibits a moderate correlation with age (r = 0.498) in the femur of the juvenile chimps, but the adult chimp has an OPD of 10.28/mm(2), suggesting that osteons likely accumulate with age. Females exhibit higher osteon densities in the periosteal envelope compared to males in the humerus, indicating more remodeling during periosteal expansion. Overall similarities between chimpanzees and humans as well as previously published data on Late Pleistocene hominids (Abbott et al.: Am J Phys Anthropol 99 1996 585-601) suggest that bone microstructure has been stable throughout human evolution.