Mechanical Adaptability of the Skeleton

Abstract

In Chapter 4 we learned that the mechanical properties of bone are strongly affected by porosity, mineralization, collagen fiber orientation, and other aspects of histologic structure. We also saw evidence that the variations in structure from region to region within a bone are correlated with mechanical factors—for example, greater mineral content and more transversely oriented collagen fibers on the more compressed side of the human femur. Then, in Chapter 5, we learned that the histologic structure of bone is also important in providing bone’s exceptional capacity for resisting catastrophic crack propagation and fatigue failure. Furthermore, we saw that in addition to providing the structures (e.g., cement lines) that control crack formation, remodeling also rids the bone of microdamage by replacing old bone with new. Finally, there is strong evidence that microdamage itself initiates remodeling. In reading about these features of bone, it is difficult to avoid the impression that local mechanical factors are influencing the bone cells as each portion of the skeleton is formed and remodeled. If this thought captured your imagination, you are not alone. Many others have had similar notions. Indeed, this idea that bone structure is somehow controlled locally to suit its current mechanical function has become a central tenet of orthopaedic medicine and science.

Every change in the form and function of... bone[s] or of their function alone is followed by certain definite changes in their internal architecture, and equally definite secondary alterations in their external conformation, in accordance with mathematical laws.

J. Wolff as quoted by Keith (1918).