Biomechanics of Bone and Fracture

Summary

• The strength of vertebral bone and of the femoral neck is determined by several factors, including cortical thickness, trabecular bone density, architecture, and bone size. All these factors change with age as a result of the remodeling process.

• When the changes become pronounced, osteoporotic fractures occur. Although there are differences in the aging patterns between men and women, the general pattern for both sexes is identical and leads to an extreme loss of bone strength (70–80%). In osteoporosis, this loss of bone strength might well amount to 90% of peak bone strength.

• Loading plays an important role in the maintenance of trabecular connectivity (through the remodeling process) and in the periosteal apposition (through the modeling process). Loading is therefore important for the maintenance of bone strength during normal aging, and exercise plays an important role in the prevention of osteoporotic fractures.

The incidence of vertebral fractures has increased three- to fourfold for women and more than fourfold for men during the last 30 years. In the UK and Scandinavia, fractures of the femoral neck have shown the same pattern, with a two- to threefold increase in incidence for both men and women. The data are age-adjusted and therefore highlight the decrease in bone mass or bone quality from generation to generation. To arrest or reverse these increases in osteoporotic fractures, effective preventive regimens must be established. However, in order to do this, a basic understanding of age-related changes in the quality and strength of vertebral bone and of the femoral neck is crucial.