ABSTRACT
Compact bone is replaced and repaired through remodelling processes carried out by so-called Basic Mineralisation Units (BMUs). The method of operation of BMUs has been often described but is poorly understood. This paper takes as a starting point the physical shape of the BMU, which includes a resorption cavity and an apposition region. A simple hypothesis is proposed to explain the shape, based on signals emitted from a single growth point. It is shown that a BMU with the appropriate shape and properties can arise if cellular activity is controlled from this point. The point is then identified with a fatigue crack, the signal being diffusable substances emitted during its growth. A computer simulation is used to show that the solution obtained analytically is stable and capable of demonstrating BMU initiation, growth and movement. A number of other features can be explained, such as bifurcation. This hypothesis is attractive because it provides a natural link between the processes of damage and repair in bone.
