Cortical Bone Distribution Research Articles

Biomechanical scaling of the hominoid mandibular symphysis.

Experimental investigation of mandibular bone strain in cercopithecine primates has established that the mandible is bent in the transverse plane during the power stroke of mastication. Additional comparative work also supports the assumption that the morphology of the mandibular symphysis is functionally linked to the biomechanics of lateral transverse bending, or "wishboning" of the mandibular corpus. There are currently no experimental data to verify that lateral transverse bending constitutes an important loading regime among hominoid primates. There are, however, allometric models from cercopithecoid primates that allow prediction of scaling patterns in hominoid mandibular dimensions that would be consistent with a mechanical environment that includes wishboning as a significant component. This study uses computed tomography (CT) scans to visualize cortical bone distribution in the anterior corpus of a sample of four genera of extant hominoids. From the cortical bone contours, area properties of the mandibular symphysis are calculated, and these variables are subjected to an allometric analysis to detect whether scaling of jaw dimensions are consistent with a wishboning loading regime. Scaling of the hominoid symphysis recalls patterns observed in cercopithecoid monkeys, which lends indirect support for the hypothesis that wishboning is an integral part of the masticatory loading environment in living apes. Inclination of the symphysis, rather than changes in cross-sectional shape or development of the superior transverse torus, represents a morphological solution for minimizing the potentially harmful effects of wishboning in the jaws of these primates.

Linking structural variability in long bone diaphyses to habitual behaviors: foragers from the southern African Later Stone Age and the Andaman Islands.

The cross-sectional distribution of cortical bone in long bone diaphyses is highly responsive to mechanical loading during life, yet the relationship between systemic and localized influences on skeletal structure remains unclear. This study investigates postcranial robustness throughout the body among adults from two groups of foragers with different patterns and modes of mobility, to determine whether there is evidence for upper vs. lower body localization of skeletal robustness. The samples used for this comparison are from the southern African Later Stone Age (LSA; n = 65, male = 33, female = 28) dating from ca. 10,000 to 2,000 B.P., and 19th century indigenous Andaman Islanders (AI; n = 36, male = 17, female = 16). The LSA were highly mobile foragers who did not exploit offshore marine resources. In contrast, the AI had tightly constrained terrestrial, but significant marine, mobility. Geometric properties of cortical bone distribution in the diaphyses of the clavicle, humerus, femur, tibia, and first metatarsal are compared between the samples, providing a representation of skeletal robustness throughout the body. Multivariate ANOVA shows the AI to have significantly stronger clavicles and humeri, while the LSA femora, tibiae, and first metatarsals are stronger than those of the AI. These patterns, in which upper and lower limbs show biomechanical properties that are consistent with habitual behaviors, suggest localized osteogenic response. Although postcranial robustness appears to be correlated with overall limb function, the results suggest that more proximal elements within the limb may be more responsive to mechanical loading.

Cortical bone distribution in the femoral neck of strepsirhine primates

The thickness of the inferior and superior cortices of the femoral neck was measured on X-rays of 181 strepsirhine primate femora representing 24 species. Neck length, neck depth and neck-shaft angle were also measured. The strength of the femoral neck in frontal bending was estimated by modeling the neck as a hollow cylinder, with neck depth as the outer diameter and cortical thickness representing the superior and inferior shell dimensions. Results indicate that the inferior cortex is always thicker than the superior cortex. The ratio of superior to inferior cortical thickness is highly variable but distinguishes two of the three locomotor groups in the sample. Vertical clingers and leapers have higher ratios (i.e., a more even distribution of cortical bone) than quadrupeds. The slow climbers tend to have the lowest ratios, although they do not differ significantly from the leapers and quadrupeds. These results do not confirm prior theoretical expectations and reported data for anthropoid primates that link greater asymmetry of the cortical shell to more stereotypical hip excursions. The ratio of superior to inferior cortical thickness is unrelated to body mass, femoral neck length, and neck-shaft angle, calling into question whether the short neck of strepsirhine primates acts as a cantilever beam in bending. On the other hand, the estimated section moduli are highly correlated with body mass and neck length, a correlation that is driven primarily by body mass. In conclusion, we believe that an alternative interpretation to the cantilever beam model is needed to explain the asymmetry in bone distribution in the femoral neck, at least in strepsirhine primates (e.g., a thicker inferior cortex is required to reinforce the strongly curved inferior surface). As in prior studies of cross-sectional geometry of long bones, we found slightly positive allometry of cortical dimensions with body mass.

Anatomical and functional aspects of the thoracic and lumbar spine

The vertebral bodies and vertebral arches show a characteristic distribution of cortical and cancellous bone. The pedicles are loaded by uniplanar bending that is reflected by the arrangement of the Corticalis. The ligaments of the vertebral column consist of longitudinal and (with exception of the lig. longitudinal anterius) horizontal/oblique segmental ligament bundles. In combination with the anulus fibrosus, the ligaments work as a kind of gear system. They regulate the process of movements of adjacent vertebral bodies in a very precise manner and control the final phase of motion. Besides maintaining the necessary amount of pretension the intervertebral disc distributes the loads uniformly onto the adjacent vertebral bodies. The intervertebral joints are important for guided motion, by restricting the extent in specific planes and directions. Because of their position, they are able to take up the shear forces and to simultaneously restrict them in different planes. The integrity of the fascia thoracolumbalis warrants the protective function of the autochthonuos muscles.

Structural design of the femoral neck in primates.

This study investigates the structural design of the femoral neck with respect to phylogeny, locomotor behavior, and body size in a large comparative sample of primates. Since a bone's strength is determined by the amount and arrangement of its constituent material, the amount and distribution of bone in the femoral neck are the focus of the present study. Two types of data were collected. First, the total distribution of bone across the femoral neck (perpendicular to the femoral neck axis) was examined using image analysis techniques. The distribution of both cortical and trabecular bone are included in this analysis. Secondly, the external dimensions of the femoral neck and the thickness of the superior and inferior cortices, measured from radiographs, were used to calculate femoral neck cross-sectional properties (cortical area and second moment of area). These data were input into a simplified cantilevered beam model that incorporates femoral neck-shaft angle and femoral neck length and is used to predict stress under one unit body mass of loading on the femoral head. The patterns of bone distribution in the femoral neck between taxa are broadly similar for the analysis that includes both trabecular and cortical bone and that which includes only cortical bone. In all cases, there tends to be more bone on the inferior aspect of the femoral neck compared to the superior aspect. However, the non-human hominoids and New World monkeys (e.g., Ateles and Alouatta) have a more even distribution of bone across the femoral neck and have thicker superior cortices relative to inferior cortices compared to the rest of the comparative sample, including humans. It is proposed that the more equal distributional pattern in the non-human hominoids and atelines reflects less stereotypical, more generalized loading orientations. Differences between species in overall strength of the femoral neck are a function of both body size and locomotor mode.

Distribution of trabecular and cortical bone related to geometry. A quantitative computed tomography study of the femoral neck.

The relation between geometry and the distribution of trabecular and cortical bone mass and density in the human femoral neck was evaluated with quantitative computed tomography (QCT). Quantitative computed tomography data were obtained from 2-mm thick computed tomography slices of 20 human femur necks in vitro. A standardized scan position in each femur was used with the smallest cross-section as reference point. When trabecular bone mass (TrBM) and cortical bone mass were presented as percentage of total bone mass (ToBM), it was found that, starting at the cranial (head) side, ToBM consists of 78% TrBM. About 21% of ToBM can be found as TrBM at the caudal (trochanter) side. At the smallest cross-sectional volume TrBM is 33% of ToBM. For every 2-mm slice, an average decrease of 5% TrBM can be seen. These data show that geometry and bone mass distribution are related. Whereas total bone mass remains relatively stable, the cortical and trabecular bone mass changes extensively. This implies that QCT measurements in the femoral neck depend highly on midneck positioning.

Cross-sectional geometric properties of the Otavipithecus mandible.

Cross-sectional geometric properties of the postcanine mandibular corpus are determined for the only known specimen of Otavipithecus namibiensis, a middle Miocene hominoid from southern Africa. It is shown that Otavipithecus is unique in that several important mechanical properties of its mandible, including maximum and minimum moments of inertia and distribution of cortical bone, differ from patterns seen in both extant hominoids and the early hominids Australopithecus africanus and Australopithecus (Paranthropus) robustus. This is particularly apparent in the mechanical design of the posterior portion of the mandibular corpus for resisting increased torsional and transverse bending moments. Cortical index values at the level of M2 also reveal that both Otavipithecus and A. africanus are similarly designed to resist increased masticatory loads with relatively less cortical bone area, a highly efficient mechanical design.

Femoral ontogeny and locomotor biomechanics of Dryosaurus lettowvorbecki (Dinosauria, Iguanodontia)

Abstract Femoral ontogeny in the iguanodontian dinosaur Dryosaurus lettowvorbecki (Late Jurassic, Tanzania) is analysed biomechanically using principles of beam theory. Statistically significant differences in cross-sectional properties are found between animals of differing size, reflecting alterations to both the relative amount and distribution of cortical bone during growth. Two explanations are suggested to account for these modifications in bone architecture: (1) increasing mechanical loads related to increasing body size, and (2) changes in the orientation of these loadings associated with a caudal shift of the centre of gravity. It is argued that D. lettowvorbecki hatchlings were not bipedal as generally presumed but obligate quadrupeds. Based on avian growth rates, the transition from quadrupedality to habitual bipedalism is estimated to have occurred within several months of hatching. The biomechanical approach employed here contributes new insight into ontogeny of locomotion in D. lettowvorbecki and provides additional ways of analysing ontogenetic processes among extinct and living species.

Femoral ontogeny and locomotor biomechanics of Dryosaurus lettowvorbecki (Dinosauria, Iguanodontia)

Femoral ontogeny in the iguanodontian dinosaur Dryosaurus lettowvorbecki (Late Jurassic, Tanzania) is analysed biomechanically using principles of beam theory. Statistically significant differences in cross-sectional properties are found between animals of differing size, reflecting alterations to both the relative amount and distribution of cortical bone during growth. Two explanations are suggested to account for these modifications in bone architecture: (1) increasing mechanical loads related to increasing body size, and (2) changes in the orientation of these loadings associated with a caudal shift of the centre of gravity. It is argued that D. lettowvorbecki hatchlings were not bipedal as generally presumed but obligate quadrupeds. Based on avian growth rates, the transition from quadrupedality to habitual bipedalism is estimated to have occurred within several months of hatching. The biomechanical approach employed here contributes new insight into ontogeny of locomotion in D. lettowvorbecki and provides additional ways of analysing ontogenetic processes among extinct and living species.

Mandibular morphology and diet in the genusCebus

The influence of hard-object feeding on the size and shape of the mandibular corpus was investigated through a comparative biomechanical analysis of the jaws of adult femaleCebus apella andCebus capucinus. Computed tomography (CT) was used to discern the amount and distribution of cortical bone at M2 and symphyseal cross sections. From these data, the biomechanical properties of the mandibular corpus were determined to assess the structural rigidity of the jaw with respect to the bending, torsional, and shear stresses that occur during mastication and incision. The mandibles ofC. apella are demonstrably more robust than those ofC. capucinus in terms of biomechanical rigidity; differences in corporeal size rather than shape largely account for the enhanced robusticity in the sample ofC. apella. The differences that separate the two taxa probably represent a structural response to the mechanical demands of durophagy inC. apella. These observations suggest that specialization on a diet of hard objects may be expected to result in an overall hypertrophy of bony contours throughout the mandibular corpus.

Use of biplanar radiographs for estimating cross-sectional geometric properties of mandibles.

Several radiographic techniques for estimating bone cross-sectional geometric properties of mandibular corpora are compared. A hollow asymmetrical model significantly improves estimates compared to solid or hollow symmetrical models that have been used in previous studies. Using this model, biplanar radiographs can give sufficiently accurate information of the amount and distribution of cortical bone in a section given relatively regular subperiosteal and endosteal perimeters.

Changes in Activities with the Shift to Agriculture in the Southeastern United States

Changes in Activities with the Shift to Agriculture in the Southeastern United States

Assessment of cortical and trabecular bone distribution in the beagle skeleton by neutron activation analysis.

The distribution of bone calcium between morphologically identifiable cortical and trabecular bone obtained by dissection and quantitated by neutron activation analysis (NAA) is described. The skeleton of a female beagle dog was dissected into approximately 400 pieces and assayed for 49Ca produced in the University of California, Irvine TRIGA reactor. For each of the skeletal sections, we give the initial weight of the alcohol-fixed tissue, which includes cortical bone, trabecular bone, marrow, and cartilage, and a final tissue weight after the marrow and trabecular bone have been dissected away; total section and cortical section calcium weights are reported. The level of detail is represented, for example, by the vertebrae, which were divided into three parts (body, spine, and transverse processes) and by the long bones, which were divided into 10-12 parts such that characterization of the epiphysis, metaphysis, and diaphysis was accomplished. The median percentage cortical calcium values for cervical, thoracic, and lumbar vertebrae were 82%, 56%, and 66%, respectively; however, variation within these groups and among individual vertebral sections was about a factor of 2. For long bones, the median percentage cortical calcium varied from 90-100% in the midshaft to below 50% in the proximal and distal sections. The final calculated cortical tissue-to-calcium mass ratio (TCR) varied from about 4.5 for midshafts of the long bones to about 9 for thoracic vertebral bodies and indicated that the mineral fraction of cortical bone is not constant throughout the skeleton. The ratio of cortical to trabecular calcium in the skeleton was 79.6:20.4.

大腿骨骨体部横断面の断面特性値

This paper presents the geometrical data for the human femoral shaft. Geometrical properties of the cross section from 13 sites along the bone length (from 20-80% in 5% increments) on each of 31 femoral shafts were calculated by using a digitizing unit and on-line microcomputer. More than 400 cross sections were analyzed in terms of L (circumference), A (gross cortical area), IX (area moment of inertia about the medio-lateral axis), IY (area moment of inertia about the antero-posterior axis), I1 (major principal moment of inertia), I2 (minor principal moment of inertia), IP (polar moment of inertia), PA (orientation of the major principal axis), and SI (section index). SI is a newly defined index: [numerical formula], which represents the deviation of mass distribution of cortical bone in the cross section or the flatness. The results indicate some general tendencies of the change in geometrical properties as a function of the position along the shaft, although there can be found considerable variability in quantity. (1) IY tapers distally in the middle third of the shaft, while IX remains constant along the length of the shaft. Different patterns of the change in the area moments of inertia about the antero-posterior and medio-lateral axes as a function of the section level are expected to correspond to the "structure of uniform strength", if one accepts Pauwels' simplified equilibrium model of lower limb bones in the frontal and sagittal planes; change of IY and IX is similar to that of the bending moments in the two planes. As a result, however, the marginal bending stress inferred in the frontal plane by Pauwels turns out to be incorrect because of the "structure of uniform strength". (2) There exists torsion of the shaft in most of the femurs examined in this study. SI indicates strong flatness at the subtrochanteric region and distal end of the shaft. The variance of PA becomes mimimal at the same regions. These findings suggest local morphological directivities which may involve mechanical significances related to torsion of the femoral neck and rotation of the knee joint. (3) Sex and agerelated differences of the properties normalized by the whole length of the femur were also discussed.

Variations in the Amount and Distribution of Cortical Bone Across the Partes Interarticulares of L5

The possible role of the physical and mechanical properties of the neural arch as contributing factors in the etiology of spondylolysis was tested by comparing two groups of vertebral specimens obtained at necropsy. Group I specimens had been subjected to repetitive cyclic force which they withstood without fracturing. Group II specimens were randomly selected. The cross-sectional distribution of cortical and cancellous bone in the partes interarticulares were measured, and the two groups compared. The previously stressed group was found to have a greater percentage of cortical bone than the random group. The data are interpreted to suggest that thin partes interarticulares may predispose to spondylolysis through the mechanism of fatigue failure.