A critical damping approach for assessing the role of marrow fat on the mechanical strength of trabecular bone.

Several clinical findings revealed that post-menopausal osteoporosis and age-related osteopenia are accompanied by trabecular bone marrow fat (BMF) increase. To help understand this phenomenon, a vibrating string model is proposed, based on the hypothesis that, when bone marrow properties change, the trabecular bone structure remodels itself to preserve its critical damping state. It is found that an inverse relationship holds between trabecular average length and marrow damping coefficient. Such a result leads us to hypothesize the following bone-weakening mechanism. Since fat-rich bone marrow is a worse damper, a BMF increment causes an increase of trabecular average length, which is accomplished by the absorption of horizontal trabeculae (structurally less important than vertical trabeculae). The resulting bone patterns are in excellent agreement with clinical observations of osteoporotic bone. A definitive confirmation of the proposed mechanism will support a therapeutical approach to widespread osteopenic diseases aimed at avoiding, or limiting, BMF increase.