Bone fragility: conceptual framework, therapeutic implications, and COVID-19-related issues

Abstract

Bone fragility is the susceptibility to fracture even for common loads because of structural, architectural, or material alterations of bone tissue that result in poor bone strength. In osteoporosis, quantitative and qualitative changes in density, geometry, and micro-architecture modify the internal stress state predisposing to fragility fractures. Bone fragility substantially depends on the structural behavior related to the size and shape of the bone characterized by different responses in the load-deformation curve and on the material behavior that reflects the intrinsic material properties of the bone itself, such as yield and fatigue. From a clinical perspective, the measurement of bone density by DXA remains the gold standard for defining the risk of fragility fracture in all population groups. However, non-quantitative parameters, such as macro-architecture, geometry, tissue material properties, and microcracks accumulation can modify the bone's mechanical strength. This review provides an overview of the role of different contributors to bone fragility and how these factors might be influenced by the use of anti-osteoporotic drugs and by the COVID-19 pandemic.

Keywords: COVID-19; DXA; bone density; bone fragility; bone geometry; fragility fractures; osteoporosis; stress fracture.

Figure 1.

Load–deformation concept.

Figure 2.

Determinants of bone strength and possible mechanism-based treatment for bone fragility. BPs, bisphosphonates; Dmab, denosumab; Romo, romosozumab; TPTD, teriparatide. *Dmab partly favors bone modeling (deposition of limited amount of new crystals).