Amount and quality of trabecular bone in osteoporotic vertebral fractures

Abstract

The goal of the present study was to determine whether or not the amount of trabecular bone of vertebral bodies is related in a causal fashion to spontaneous vertebral fractures, biconcavity or wedging in osteoporosis. A secondary goal was to determine if the quality of the vertebral trabecular bone to withstand fracturing (brittleness) is normal or increased in the osteoporotic state. The system in which the study was undertaken was the measured trabecular bone concentration and vertebral body dimensions in about 800 routine postmortem examinations. Osteoporosis is generally defined as a state where there is a decrease in the quantity of bone tissue that is normal in character. Scveral questions immediately come to mind about this definition. First, how much of a decrease constitutes a disease state? Secondly, what are the criteria of normal bone tissue ? As pointed out by Nordin, MacGregor and Smith (1966) and Arnold (1970), the quantity of bone required to be considered normal must be equal to or greater than that associated with pathologic fractures. The criteria of normal bone generally referred to are its histologic appearance and its chemical composition. Perhaps we should think of the character or quality of bone in a more functional sense than its appearance and composition. The primary mechanical function of bone is to withstand applied forces without distortion. Bone of normal character can withstand a given maximal force without failing (fracturing) while abnormal bone breaks under the same conditions. Mechanical compression testing of vertebrae has indeed been attempted and the results have shown that equal masses of vertebral trabecular bone of osteoporotic and normals have comparable strength (Bartley et al, 1966; Rockoff, Zetner and Albright, 1967; Weaver and Chalmers, 1966). These studies reveal the ability to withstand slow compression. Since fractures generally are caused by a sharp blow, there is some question as to whether these tests are relevant to any change in quality that may be associated with clinical fracturing. In the present studies we have attempted to examine the fracture resistance quality of trabecular bone tissue as well as its quantity. Instead of directly