Mechanical consequences of bone loss in cancellous bone

The skeleton is continuously being renewed in the bone remodeling process. This prevents accumulation of damage and adapts the architecture to externa l loads. A side effect is a gradual decrease of bone mass, strength, and st iffness with age. We investigated the effects of bone loss on the load dist ribution and mechanical properties of cancellous bone using three-dimension al (3D) computer models. Several bone loss scenarios were simulated. Bone m atrix was removed at locations of high strain, of low strain, and random th roughout the architecture. Furthermore, resorption cavities and thinning of trabeculae were simulated. Removal of 7% of the bone mass at highly strain ed locations had deleterious effects on the mechanical properties, while up to 50% of the bone volume could be removed at locations of low strain. Thu s, if remodeling would be initiated only at highly strained locations, wher e repair is likely needed, cancellous bone would be continuously at risk of fracture. Thinning of trabeculae resulted in relatively small decreases in stiffness; the same bone loss caused by resorption cavities caused large d ecreases in stiffness and high strain peaks at the bottom of the cavities, This explains that a reduction in the number and size of resorption cavitie s in antiresorptive drug treatment can result in large reductions in fractu re risk, with small increases in bone mass, Strains in trabeculae surroundi ng a cavity increased by up to 1000 microstrains, which could lead to bone apposition. These results give insight in the mechanical effects of bone re modeling and resorption at trabecular level.