Richard M. Aspden

Composition and Mechanical Properties of Cancellous Bone from the Femoral Head of Patients with Osteoporosis or Osteoarthritis

The material properties of cancellous bone from patients with osteoporosis (OP) or osteoarthritis (OA) were determined and compared with normal controls. Samples were selected from defined sites in human femoral heads which are subjected to different loads in vivo. Overall, OP bone had the lowest stiffness and OA the highest, and this same order was reflected in the apparent densities of the bone, with OA being the most dense and OP the least. Normal and OP bone were found to have very similar stiffness–density relationships and composition. However, OA bone differed significantly from normal. The stiffness of OA bone increased more slowly with apparent density and its material density was significantly reduced. These findings were due to an altered composition of the bone in which the mass fraction of mineral is 12% less than normal. There was also greater site variation of both apparent and material density, suggesting an altered sensitivity to applied load. These results support the concept that osteoporosis is a loss of normal bone. They also provide evidence for the hypothesis that osteoarthritis is, at least partly, a bone disease in which proliferation of defective bone results in an increase in bone stiffness.

Mechanical and material properties of the subchondral bone plate from the femoral head of patients with osteoarthritis or osteoporosis

OBJECTIVE To determine the material properties of the subchondral bone plate in patients with osteoarthritis or osteoporosis. METHODS Femoral heads were obtained after surgical removal from age and sex matched groups of patients with either osteoporosis (OP), after a fractured neck of femur, or osteoarthritis (OA) and compared with a normal group. The mechanical stiffness, density, and composition of the subchondral bone plate from sites selected to represent areas of heavy, intermittent, and light loading were measured. RESULTS Overall, OP bone was the least stiff and dense, followed by OA bone; normal bone was stiffer and more dense (p < 0.05). Though OP bone contained less mineral, the organic and water contents were increased in proportion suggesting no change in the relative amount of organic matrix. OA bone was also hypomineralised (p < 0.05) but had different organic and water fractions suggesting a defect in the matrix. Site variation of most properties was small, though across all the groups the superior region was significantly stiffer than the inferior. CONCLUSION This study shows that subchondral bone plate is less stiff than normal in both OP and OA and so cannot, by itself, explain the preserving of the overlying cartilage in OP while aiding its destruction in OA. However, the subchondral bone plate is only one part of the bony structure of the femoral head and changes in the cancellous bone need to be considered. The generalised changes in bone composition found in patients with OA support the hypothesis that the disease could involve the bone in the primary pathogenesis.

Statistical methods in finite element analysis

Finite element analysis (FEA) is a commonly used tool within many areas of engineering and can provide useful information in structural analysis of mechanical systems. However, most analyses within the field of biomechanics usually take no account either of the wide variation in material properties and geometry that may occur in natural tissues or manufacturing imperfections in synthetic materials. This paper discusses two different methods of incorporating uncertainty in FE models. The first, Taguchis robust parameter design, uses orthogonal matrices to determine how to vary the parameters in a series of FE models, and provides information on the sensitivity of a model to input parameters. The second, probabilistic analysis, enables the distribution of a response variable to be determined from the distributions of the input variables. The methods are demonstrated using a simple example of an FE model of a beam that is assigned material properties and geometry over a range similar to an orthopaedic fixation plate. In addition to showing how each method may be used on its own, we also show how computational effort may be minimised by first identifying the most important input variables before determining the effects of imprecision.

Osteoarthritis as a systemic disorder including stromal cell differentiation and lipid metabolism

For many years articular cartilage has been the focus of research aimed at improving understanding of and treatment for osteoarthritis. Although much is known about the tissue, research has had little success in elucidating the pathogenesis of generalised osteoarthritis. A new hypothesis is required. Substantial changes in many tissues, including bone, muscle, ligaments, and joint capsule, as well as cartilage, are increasingly recognised in this disease, and not all these changes are localised to the affected joints. There is also a well established link with obesity. These observations, the common origins of the mesenchymal cells that maintain these tissues, and the possible role of neuroendocrine factors that can regulate bone mass, result in the hypothesis that systemic factors that include altered lipid metabolism could explain the diversity of physiological changes in generalised osteoarthritis. If proven, this hypothesis could have important implications for a new approach to pharmacological intervention in the early stages of the disease.

Effects of mechanical load on cartilage matrix biosynthesis in vitro

Cultured bovine articular cartilage full thickness explants were mechanically loaded, both statically and cyclically, at high frequency (2s of load with 2s intervals of no load) and low frequency (60s of load with 60s intervals of no load), at 1 MPa. Metabolic effects of the load were studied by radiolabeling and compared with non-loaded cartilage explants. High frequency load had a stimulatory effect on protein and proteoglycan synthesis while low frequency and static load showed decreased synthesis. Removing the load from the cultures restored synthesis to non-loaded control culture levels. No major differences in protein biosynthetic pattern were revealed, as determined by SDS-PAGE and fluorography, showing the generalized nature of the response.

Composition and properties of connective tissues

Abstract Connective tissues consist of a complex system of interacting macromolecules. The mechanical, and hence biological, properties of this system can be related to its chemical composition using ideas which have been developed to analyse the behaviour of fibre-reinforced composite materials.

Effect of the proportion of organic material in bone on thermal decomposition of bone mineral: an investigation of a variety of bones from different species using thermogravimetric analysis coupled to mass spectrometry, high-temperature X-ray diffraction, and Fourier transform infrared spectroscopy.

AbstractThermogravimetric analysis linked to mass spectrometry (TGA-MS) shows changes in mass and identifies gases evolved when a material is heated. Heating to 600°C enabled samples of bone to be classified as having a high (cod clythrum, deer antler, and whale periotic fin bone) or a low (porpoise ear bone, whale tympanic bulla, and whale ear bone) proportion of organic material. At higher temperatures, the mineral phase of the bone decomposed. High temperature X-ray diffraction (HTXRD) showed that the main solids produced by decomposition of mineral (in air or argon at 800°C to 1000°C) were β-tricalcium phosphate (TCP) and hydroxyapatite (HAP), in deer antler, and CaO and HAP, in whale tympanic bulla. In carbon dioxide, the decomposition was retarded, indicating that the changes observed in air and argon were a result of the loss of carbonate ions from the mineral. Fourier transform infrared (FTIR) spectroscopy of bones heated to different temperatures, showed that loss of carbon dioxide (as a result of decomposition of carbonate ions) was accompanied by the appearance of hydroxide ions. These results can be explained if the structure of bone mineral is represented by

Comparison of structure, mechanical properties, and functions of lumbar spinal ligaments

{\text{Ca}}_{{\text{10}} - {\text{x}}} {\text{V}}^{{\text{(Ca)}}} _{\text{x}} [({\text{PO}}_{\text{4}} )_{{\text{6}} - {\text{x}} - {\text{y}}} ({\text{HPO}}_{\text{4}} )_{\text{x}} ({\text{CO}}_{\text{3}} )_{\text{y}} ][({\text{OH}})_{{\text{2}} - {\text{x}} - {\text{y}}} ({\text{CO}}_{\text{3}} )_{\text{y}} {\text{V}}^{{\text{(OH)}}} _{\text{x}} ]