Biomechanical competence of vertebral trabecular bone in relation to ash density and age in normal individuals

Abstract

Cylindrical trabecular bone samples from the central part of the first lumbar vertebral body were obtained from 42 normal people (27 females and 15 males) aged 15–87 years and analyzed by a compression test in either vertical or horizontal direction. Maximum stress, maximum stiffness, energy absorption capacity, and strain at maximum stress (compressibility) were calculated from the load-deformation curves. The ash density of the samples was measured after incineration. From age 20 to 80 years, the decline ( P < 0.01) in ash density was 48–50% compared to a 75–80% decrease ( P < 0.001) in vertical stress, stiffness, and energy absorption capacity. Qualitatively similar age-related changes ( P < 0.01) were observed by horizontal compression, but the absolute values were smaller. In both directions, highly significant positive correlations ( P < 0.01) were observed between the biomechanical properties and ash density. However, after normalization for ash density stress, stiffness and energy absorption capacity still showed significant decreases with age ( P < 0.01). The vertical maximum strain values, which increased ( P < 0.05) with age, were inversely related to the other biomechanical variables ( P < 0.05) and to the ash density ( P < 0.05). It is concluded from the study that the biomechanical competence of vertebral trabecular bone depends not only on bone mass (ash density) but also on the continuity of the trabecular lattice, which changes with increasing age.