Peak bone mass and peak bone strength

Abstract

The risk of fracture is determined by the load applied on bone and bone's mechanical strength. The balance of the two is established early in life. During growth, bone adapts its material composition and structural design - the way the cortical and trabecular mass is distributed in space - to accommodate the ever-increasing loads imposed by growth while minimally increasing its bulk (mass per unit volume) to facilitate mobility. Bone's structural strength reaches the highest level at the cessation of growth and then decays as abnormalities emerge in bone modelling and remodelling, the cellular machinery that assembled it during growth. The age-related changes determine structural decay include a decline in periosteal apposition, a negative bone multi-cellular unit (BMU) balance and accelerated remodelling. However, the severity of the structural decay also depends on the way bone is assembled by bone modelling and remodelling during growth. When bone is assembled with a thick and densely connected trabecular network and a thick cortex of little porosity, remodelling is less likely to perforate trabeculae and cavitate cortices.When bone is assembled with thin trabeculae and thin porous cortices, the same intensity of remodelling is likely to produce more severe structural decay and bone fragility. The peak bone structural strength reflects the modelling and remodelling that assembled it and determines the effect of abnormalities in that same machinery responsible for the emergence of bone fragility later in life.