Mechanical Properties and Testing Methods of Bone
Yuehuei H. An, Richard J. Friedman in Animal Models in Orthopaedic Research, 2020
The density of a material is its mass per unit volume. The material density of cortical bone is the wet weight divided by the specimen volume. Cortical bone has a density of approximately 1.9 gm/cm . The common ways to measure the volume of a cortical bone specimen include the use of a gravity bottle based on Archimedes’ principle or directly measuring the dimensions of the specimen. The latter requires the specimen having a regular shape such as a cylinder. For cancellous bone there are different material characteristics arising from the two phase structure (trabeculae and marrow). Therefore, two mechanical properties are generally considered, the structural and material properties, which are based on their structural (apparent) density and material density, respectively. The measurement of structural (apparent) density (ρ) is achieved by weighing the cancellous structure without free water in its marrow cavities (wet weight, w) and dividing the wet weight by the structural volume (including both of trabeculae and marrow cavities):where d and h represent diameter and height of a cylindrical specimen. Other specimen shapes, such as cubic, can be used, but they are technically more demanding and have more sharp corners than cylinders, which may cause bone materials to fracture from the specimen during defatting or marrow removal. An accurate method for bone volume is using a gravity bottle based on Archimedes’ principle (before marrow removal). The compressive strength (σ in MPa) of cancellous bone is related to its apparent density (ρ in g/cm ) by a power law of the form:Similarly, the compressive modulus (E, in MPa) of cancellous bone is related to the apparent density (p, in g/cm ) by:Selected reports on apparent densities of human and animal bones are listed in Table 3. The apparent density of cancellous bone ranges from 0.14 to 1.10 gm/cm (average: 0.62 gm/cm , n=16). Material density of cancellous bone is measured using the weight of bone material (only trabeculae) divided by the volume of only trabeculae, which is a little smaller than that of cortical bone, being 1.6-1.9 gm/cm .
The locomotor system
C. Simon Herrington in Muir's Textbook of Pathology, 2020
Bone is found in two patterns, woven and lamellar (see Figure 13.1). Woven bone is formed where bone is laid down rapidly, as in fetal growth, during the healing of a fracture, and in bone-forming tumours. It contains numerous plump osteocytes. Collagen fibres are arranged randomly. Lamellar bone, in contrast, is laid down slowly, is structurally strong, and forms the adult skeleton. The collagen lies in parallel sheets, the fibres of which run in different directions, resulting in a laminated structure. The osteocytes are small and relatively sparse. Adult lamellar bone is arranged in two forms: compact and cancellous. Compact bone forms the cortex of bones. Its basic unit is the haversian system (osteon) (see Figure 13.1A), each consisting of a concentric array of bone surrounding a central artery and vein. Cancellous (spongy) bone is found between the cortices of bones and at the ends of long bones. It is composed of plates or trabeculae separated by marrow spaces. Compact bone accounts for about 80% of the adult skeleton and cancellous bone, about 20%.
Mechanical testing
C M Langton, C F Njeh in The Physical Measurement of Bone, 2016
Cancellous bone, as explained earlier, has the porous cells filled with marrow. Carter and Hayes [48] reported that the presence of marrow during testing did not generally alter the elastic properties of cancellous bone. While some researchers carry out their investigations on defatted specimens [97], others either work on specimens with fat in situ or do not bother to report on whether or not marrow is present [176]. It seems safe to assume that, provided very high strain rate testing is not anticipated, removal of bone marrow will not affect measured mechanical properties. Carter et al [63] compared two methods for marrow removal—warm water jetting and solvents (methanol and chloroform)—and found that the method of marrow extraction did not affect the elastic properties. They also showed that samples which were kept wet throughout the preparation procedure were generally more compliant than samples which were dried and rewetted. Sharp et al [177] showed that only immersion in trichloro-ethylene in an ultrasound bath for 4 h removed all the fat.
Bone density does not reflect mechanical properties in early-stage arthrosis
Published in Acta Orthopaedica Scandinavica, 2001
Ming Ding, Carl Christian Danielsen, Ivan Hvid
Subchondral cancellous bone specimens were removed from 10 human postmortem early-stage arthrotic proximal tibiae (mean age 73 (63-81) years) and 10 age- and gender-matched normal proximal tibiae. The early-stage arthrosis was confirmed histologically and the specimens were divided into 4 groups: medial arthrosis, lateral control, normal medial and normal lateral controls. The specimens were tested in compression to determine mechanical properties and then physical/compositional properties. Compared to the normal medial control, we found reductions in ultimate stress, Young's modulus, and failure energy, and an increase in ultimate strain of arthrotic cancellous bone. Bone volume fraction, apparent density, apparent ash density, and collagen density were higher in cancellous bone with arthrosis, but no differences were found in tissue density, mineral and collagen concentrations between arthrotic cancellous bone and the 3 controls. None of the mechanical properties of arthrotic cancellous bone could be predicted by the physical/compositional properties measured. The increase in bone tissue in early-stage arthrotic cancellous bone did not make up for the loss of mechanical properties, which suggests a deterioration in the quality of arthrotic cancellous bone.
Effect of 1α-Hydroxyvitamin D
Published in Acta Orthopaedica Scandinavica, 1981
T. Sam Lindholm, Olle S. Nilsson, Tom C. Lindholm
Two groups of adult male rats were treated perorally for 6 weeks with 0.1 μg and 1.0 μg of 1a-hydroxyvitamin D3 (la-OH-D3), respectively. The effect of the treatment on cancellous bone matrix was studied by chemical analysis and morphometric measurements. The effect of the 1.0 μg dose on the inorganic composition, and on the calcification of the cancellous bone matrix, was significantly more pronounced, decreasing the amount of glycosaminoglycans. The lower dose level, 0.1 μg of la-OH-D3, increased the collagen metabolism, whereas the higher dose level did not. The amount of cancellous bone determined morphometrically increased significantly during treatment with both dose levels. 1a-OH-D3, converted in the organism to the hormonal form 1.25 (OH)2D3, induces new bone formation, probably by direct influence on the cancellous bone tissue itself.
An approximate model for cancellous bone screw fixation
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2013
C. Brown, R. Sinclair, A. Day, B. Hess, P. Procter
This paper presents a finite element (FE) model to identify parameters that affect the performance of an improved cancellous bone screw fixation technique, and hence potentially improve fracture treatment. In cancellous bone of low apparent density, it can be difficult to achieve adequate screw fixation and hence provide stable fracture fixation that enables bone healing. Data from predictive FE models indicate that cements can have a significant potential to improve screw holding power in cancellous bone. These FE models are used to demonstrate the key parameters that determine pull-out strength in a variety of screw, bone and cement set-ups, and to compare the effectiveness of different configurations. The paper concludes that significant advantages, up to an order of magnitude, in screw pull-out strength in cancellous bone might be gained by the appropriate use of a currently approved calcium phosphate cement.
Related Knowledge Centers
- Bone Marrow
- Cortical Bone
- Vascular
- Haematopoiesis
- Surface Area
- Osseous Tissue