Bone Mechanical Function and the Gut Microbiota.

The primary function of bone in the body is to resist mechanical forces. Impairment of the mechanical performance of bone is therefore the primary clinical challenge presented by bone disease. Failure to resist forces associated with activities of daily living leads to fragility fracture. In this chapter we review the characteristics of bone that influence mechanical performance and fracture risk, how bone remodeling and modeling alter mechanically relevant characteristics of bone, and the potential for the gut microbiome to alter bone mechanical performance and risk of fragility fracture. The ability of bone to resist fragility fracture is determined by characteristics of bone tissue at scales ranging from nanometers to centimeters. Bone remodeling and modeling can influence whole bone shape and density, but the effects of bone remodeling on bone tissue mechanical properties are not as well understood. The gut microbiome may influence bone by altering nutrient absorption, stimulating the immune system or through translocation of microbes and microbial products across the gut endothelium. Although there is evidence that the microbiome can alter bone density and bone remodeling, the ability of the microbiome to cause changes in tissue material properties, whole bone strength, and fragility fracture remains to be determined.