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A large proportion of overexertion injuries in sport and work related activities occur during high strain rate loading. The disc is known to have time dependent material properties (1). The joint load and stiffness may increase and the mode of failure may change from a location to another when higher loading rates are sustained (2). In order to quantify the response of the spine to dynamic loads, we need to account for the rate dependencies of the intervertebral disc in tension as well as other loading conditions. Bending tasks stretch the annulus fibrosus in the vertical direction and render the disc vulnerable to prolapse if the hydrostatic pressure in the nucleus pulposus is raised at the same time. Thus, the ability of the annulus to resist repeated vertical stretching may have a decisive influence on a disc’s susceptibility to prolapse. Tensile properties of the annulus fibrosus have been reported in the literature (3). However, to what extent loading rate can affect annulus tensile properties still needs to be clarified. The objective of this study was to investigate the loading rate sensitivity and regional variations in tensile mechanical properties of the annulus fibrosus, using disc annulus specimens from sheep.

This paper reviews the clinical and experimental findings on the effects of sodium fluoride (NaF) on human and animal bone. NaF has been shown to cause a significant increase in axial skeletal bone mass. However, there is concern that the new bone may not provide the desired increase in bone strength. Yet, NaF remains the most commonly used agent capable of stimulating bone formation in most patients (30% non-responders). But whether NaF reduces vertebral fracture rate (VFR) remains controversial. For a given treatment duration, the effect of F on bone quality appears to depend on dose: there is a marked detrimental effect on bone strength at high dose but there tends to be a beneficial effect at low dose. This biphasic NaF effect on bone strength has also been observed in fluoridated rat femurs. Unlike a study on young female rats which shows a linear dependence of cancellous bone volume (Cn-BV /TV) on NaF dose, a short-term study on young male rats, together with studies on chicks and dogs show biphasic NaF effects. Biphasic character is also observed in the effect of NaF on the packing of canine cortical bone mineral. When taken together, the animal models that show biphasic NaF effects seem to suggest that NaF at low dose improves Cn-BV/TV and bone strength and at high dose undermines them. These findings are in agreement with the clinical observations that high NaF dose does not help reduce VFR but low dose seems to help.

This paper reviews the changes in the quality of bone mineral with age and in disease. After a brief review of morphological changes with aging in mammalian bones, microradiography is compared to backscattered electron imaging and their use in bringing out subtle changes in bone mineralization outlined. Changes in the quality of bone with disease is described using osteoporosis as an example. Chemical changes in the skeleton are then discussed and related to morphological changes. Finally, some examples of localized and generalized changes in bone mineral are given. This paper emphasizes that understanding the nature of the mineral phase in bone as well as its heterogeneity and its changes with age and in disease is essential to the elucidation of skeletal physiology and pathology.

As crystals are important etiologic agents for disease, their accurate identification in tissues and body fluids is of utmost importance. This paper surveys the roles of crystals in disease process and outlines current analytical techniques for crystal detection and identification in bone tissues. The value of multiple correlated techniques is demonstrated including scanning electron microscopy, x-ray energy spectroscopy and powder diffraction analysis. The current feasibility of utilizing intermediate voltage scanning transmission analytical electron microscopy to integrate these analytical techniques on the same tissue sample is emphasized.