3 Characteristics of bone

Apuntes

3 Characteristics of bone Bone is a scaffold that supports and protects soft structures and enables locomotion and mechanical functioning of the limbs. The most important mechanical characteristics of bone are its stiffness (bone deforms only a little under load) and strength (bone tolerates high load without failure). In considering a fracture and fracture healing, the brittleness of bone is of special interest. Bone is a strong material. However, it breaks under small deformation. This means that bone behaves more like glass than like rubber. Therefore, at the onset of natural fracture healing, bone cannot bridge a fracture gap that is repeatedly subject to excessive displacement. For an unstable or flexibly fixed fracture (relative stability), a sequence of biological events—mainly the formation of first a soft and then a hard callus—helps to reduce the strain and deformation of the repair tissues and thus increase stability (see section 4.3.3 in this chapter). Resorption at the fracture ends initially increases the fracture gap and this reduces the strain at the fracture site. The lowerstrain environment promotes formation of bridging callus, which then increases the mechanical...