What is the difference between primary and secondary osteon

Slide 74 Bone, ground preparation. Observe the Haversian sytems or osteons of compact bone in this slide. The lamellae are concentrically located around a central canal haversian canal which contained blood vessels, nerves, and loose connective tissue.

Volkmann's canals may be seen connecting haversian canals. The other lamellae of compact bone are organized into inner circumferential, outer circumferential, and interstitial lamellae. Only interstitial lamellae are seen in this slide. Also in this section, note the empty lacunae and canaliculi that housed the osteocyte and its cell processes, respectively. Slide 11 Nasal mucosa.

Intramembranous ossification is visible in the nasal conchae on this slide. Bone arises directly within mesenchymal condensations. This process can be identified by the appearance of bone spicules islands of bone among mesenchymal cells. For example, cortical bone properties are often determined by machining a tensile specimen from the cortical diaphysis. This specimen may have a gauge area of 5x5mm and a length of 5 mm. A schematic is shown below:. Stress in this gauge section is computed simply as the force from the load cell in tension divided by the cross sectional area of the gauge.

Deformation is measured as the change in length of the gauge section divided by the original length of the gauge section. The gauge section, however, may contain many osteons. It is obvious that the experimental stress and strain are average over many osteons. This indicates that the stress we measure in the testing set-up above cannot represent the stress in a single osteon.

We can relate the average stress the 0th level structure in the cortical bone organizational chart to the first level stress at the osteonal level using the following equation:. We can also write the same relationship for the average strain:. Even though we can write strain and stress for a given macroscopic level as he average over the next microscopic level, we generally cannot do the same for the constitutive equations.

This is because the constitutive properties vary over distinct phases of material at the microscopic level. For example, with cortical bone, the microstructure contains stiffness properties for the osteons and the blood vessel space, in addition to the interstitial bone. If we assume that there are n phases of microstructure, then when can write the constitutive equation for the effective or macroscopic level as:. We can rewrite the above equations condensed in matrix form as:. The form of M can vary depending on the assumed model if we are doing computational or analytical models or on the experimental measures used to quantify structure.

What the above equations represents is what we know intuitively, namely that the effective properties at a macroscopic level depend on the microscopic properties [C], the the spatial arrangement or architecture of those microscopic properties [M]. It is important to note that the above equation governs the relationship between any structural level defined in the cortical and trabecular bone organization chart.

That is, the effective properties of osteons may be related to the distribution of lacunae, the collagen organization, degree of mineralization, etc. For trabecular bone, mechanical properties at the 0th level, most commonly referred to as "effective" or "continuum" level trabecular bone properties, are determined experimentally most often by testing cubes of trabecular bone between 8mm and 1 cm on a side in compression, underneath a loading platen:.

Again, as with cortical bone, It is assumed in these tests that one average stress measure can be computed as the force divided by the area of a face of the cube.

Strain is computed by divided the change in length of the cube by the original length of the cube. It is important to note that by computing the stress this way we are computing an average or effective stress.

In other words, the stress we compute is the same as if we average the stress over all the individual trabeculae and the available pore space.

This can be written mathematically as:. The average strain is defined in the same manner as:. The constitutive matrix at the effective level is related to the microscopic level properties using the same rule for the constitutive equation we used for cortical bone. Mechanical stiffness values have been measured most often for secondary haversian bone human and cow bovine bone as well as bovine plexiform bone. Stiffness has been measured using both standard mechanical testing techniques as well as ultrasonic measurements where the velocity of waves propagating through a material is measured.

This wave velocity is related to the stiffness and the density of the material. Reilly et al. Haversian Bovine Haversian Bovine Primary Note that bone stiffness is greater in the I-S direction along the osteonal length than in the transverse direction across the osteons.

Also note that secondary osteons haversian bone with more lamellae tend to reduce both the stiffness and strength of cortical bone.

Katz et al. C C 8. C 7. C 6. Notice that the plexiform bone with the brick like structure has orthotropic symmetry while the secondary haversian canal is nearly transversely isotropic. The type of material symmetry present results from the different types of 1 st level structures. Osteons are tube structures which exhibit a transversely isotropic symmetry while the brick like structures of plexiform bone exhibit an orthotropic symmetry depending on the aspect ratios of the brick.

An overview or representative average of cortical bone properties for human and bovine cow were presented by Martin et al. Strain 2. It is important to note what the quantities of yield and ultimate stress represent. Although bone is not an elastic-plastic material in the classic sense like metals, bone will yield. This means that under high enough loads, permanent deformation will occur in bone. The ultimate strength is the stress at which the bone undergoes catastrophic failure.

The elastic modulus is the bone stiffness. We illustrate these concepts on a schematic stress strain curve below:. We saw that cortical bone properties are significantly affect be the microstructural differences between osteonal and plexiform bone.

However, these bone structure function relationships were qualitative, due to difficulties in quantifying these types of microstructures. One microstructural variable that has a significant influence on bone mechanical properties is porosity.

Porosity is difficult to classify however, because it occurs across multiple scales. In cortical bone, although porosity measurements take all these voids into account, it is believed that the larger scale voids, the haversian canals, have a large affect on mechanical properties.

Both Schaffler and Burr and Currey measured tensile elastic modulus of cortical bone and compared the results to measures of porosity. Both found statistically significant relationships and derived empirical relationships between porosity p and Young's modulus E:. Note that Young's modulus is given in GPa and that the exponent on porosity is very large and nonlinear.

This means that the moment one introduces porosity into bone, there is a large decrease in stiffness. The effect of ultimate stress on porosity is similar. Martin et al. A significant component of bone that differentiates it from soft tissues is the presence of the HA like ceramic mineral. It is postulated that the mineral component gives bone its high stiffness compared to soft tissues while the type I collagen contributes to the post-yield behavior of bone.

Specific mineralization is defined as the volume of mineral per volume of bone matrix exclusive of voids. Schaffler and Burr found that mineral did explain some variance in cortical bone stiffness, but not a significant amount due to the fact that there was little variability in specific mineralization between specimens.

They derived an equation relating mineral to elastic modulus:. Note that the exponent for mineralization is not as high for porosity, indicating that porosity has a large affect on bone stiffness than mineralization. This of course is only true if the variation in mineralization is small.

Very little mechanical data is available on 2nd level cortical bone mechanics. Ascenzi and colleagues see Martin and Burr, have performed the most mechanical testing of individual osteons.

The procedure by which Ascenzi and co-workers have tested osteons is illustrated below:. The results from Ascenzi's testing indicate that secondary osteon stiffness is less than that of large cortical bone specimens. This would indicate that some other structures in cortical bone, perhaps interstitial bone, contribute more to the overall stiffness of cortical bone. Longitudinal Compression 6. Transverse Compression 9. Alternating Compression 7. Longitudinal Tension Alternating Tension 5.

Longitudinal Shear 3. Transverse Shear 4. Alternating Shear 4. The terms longitudinal and alternating refer to how the collagen fiber bundles are oriented with respect to the plane of the osteon section.

Notice that collagen fiber bundles oriented with the direction of testing produce a higher normal stiffness while collagen fiber bundles oriented out of the plane of testing produce a lower normal stiffness but a higher shear stiffness.

Ascenzi also reported the affect of mineralization on the properties of these different types of osteons. The effect is illustrated in the stress strain diagram below:.

Another important aspect of how 2 nd level structure affects cortical bone mechanics is crack propagation and fatigue life. Since it seems that both primary and plexiform bone have higher strength and stiffness than secondary osteonal bone, the question arises as to why humans and other active mammals have secondary bone rather than plexiform or primary bone. Although there may be many metabolic reasons, one mechanical reason has to do with crack initiation and arrest.

Since humans and other smaller mammals are much more active than cows and sheep, their bones are subject to many cycles of loading. This would make human bone much more subject to fatigue failure. Once mechanical advantage of secondary bone is that it has many compliant interfaces such as cement lines. These weak interfaces provide many opportunities for crack arrest , thus making secondary osteonal bone perhaps more fatigue resistant. The main features of trabecular bone structure at the 1st level are the high porosity and the intricate architecture and orientation of the complicated rod and plate structure of trabeculae.

We can expect therefore that these features along with mineralization to be the major factors contributing to the effective stiffness of trabecular bone. This is similar to the determinants of cortical bone effective stiffness, which were osteons versus plexiform structure, the amount of porosity and the degree of mineralization.

However, a significant difference between cortical bone 1st level structure and trabecular bone 1st level structure is the substantial variation in 1st level trabecular bone structure compared to cortical bone structure.

Osteons by and large have fairly consistent orientation in cortical bone but rods and plates in trabecular bone have a much greater variation in orientation. Therefore in addition to quantifying porosity in trabecular bone, we must also come up with a way to quantify orientation of rods and plates in trabecular bone.

We quantify trabecular structure using the techniques of stereology. These methods use points and lines laid across a structure and count the number of points that fall in each phase of the structure and the number of intersections between structural boundaries of phases. Initially, this was done using a microscope using 2D sections, but now with 3D imaging these approaches have been automated in computer algorithms.

The basic idea of making stereology measurements on trabecular bone or any tissue structure for that matter is shown below:. In the above picture, trabeculae are shown in cross hatch and void or marrow space is shown in white. A square grid is laid across this 2D section of bone. The dark circles within the bone are denoted as Pp.

This is one measurement made on trabecular architecture. Pp is basically a ratio of how many grids intersections fall within the bone divided by the total number of grid intersections. This is a measure of the volume fraction of bone, or equivalently the inverse of the porosity.

A second measurement, Pl, is made by counting the number of intersections between bone and the surrounding marrow space. This measure is actually a function of orientation, since the grids are rotated from 0 to degrees and intersect counts are made on the structure. Using CT voxel data, this anisotropy measurement is made using a sphere. We thus have Pl as a function of orientation, ie Pl q.

This measurement gives us and indication of the distances between bone marrow intersections, thus giving us some indication of the width of a trabecuale. Because of this, Pl is often called a mean intercept length. When one plots the number of intersects versus theta in polar plot for trabecular bone, the result is an ellipse. In 3D, the result is an ellipsoid. The general equation for an ellipsoid is neglecting terms that reflect orientation of the ellipsoid :.

Harrigan and Mann recognized that the above equation is essentially the inner product of a second order tensor with two vectors and that the above equation could be rewritten as:. Article :. DOI: Need Help? Akkus, O.

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R: A language and environment for statistical computing. R Foundation for Statistical Computing ,. Download references. The authors would like to thank JP Roux for his help during the polarized images acquisition. We are grateful to the patients and their legual guardians who consented us to use their samples for investigation. Aix-Marseille Univ. You can also search for this author in PubMed Google Scholar. Study design: E. Study conduct: E. Reprints and Permissions.

Compositional and mechanical properties of growing cortical bone tissue: a study of the human fibula. Sci Rep 9, Download citation. Received : 26 April Accepted : 08 October Published : 26 November Anyone you share the following link with will be able to read this content:.

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Advanced search. Skip to main content Thank you for visiting nature. Download PDF. Subjects Ageing Bone Bone quality and biomechanics. Abstract Human cortical bone contains two types of tissue: osteonal and interstitial tissue. Introduction From a clinical point of view, juvenile bone is of interest since various congenital, acquired diseases or trauma influence bone development in childhood and adolescence.

Results We analyzed the effect of gender using a multiple regression on adult and juvenile bone, and no influence of sex was found. Evolution of parameters with chronological age in juveniles and adults osteonal and interstitial tissue properties Figure 1 shows the evolution of the fibula with age in transverse DMB sections. Figure 1. Full size image.

Figure 2. Figure 3. Figure 4. Figure 5. Full size table. Figure 6. Discussion The aim of this study was to challenge our hypothesis that intrinsic properties would change with age in juveniles but not in adults.

Comparison of osteonal and interstitial tissue properties in juveniles and adults Material composition of bone tissue was studied at the level of osteons and interstitial tissue using microradiography and FTIRM Fig.

Correlations between compositional and indentation tissue properties in juveniles and adults within all areas Results were different when groups were separated or pooled only Table 2. Material and Methods Specimens Bone samples were collected at the same location from the distal third of the fibula of 13 children 10 male and 3 female 4 to 18 years old mean age of 9.

Microindentation tests Flat and parallel surfaces on the residual blocks of infiltrated samples were produced with an ultra-miller Polycut E, Reichert-Jung, Germany. References 1. Article Google Scholar 6. Article Google Scholar 8. Article Google Scholar Google Scholar CAS Google Scholar Author information Affiliations Aix-Marseille Univ.