  Fibrous dysplasia (FD) is a mosaic non-inheritable genetic disorder of the
skeleton in which normal bone is replaced by structurally unsound fibro-osseous
tissue. There is no curative treatment for FD, partly because its
pathophysiology is not yet fully known. We present a simple mathematical model
of the disease incorporating its basic known biology, to gain insight on the
dynamics of the involved bone-cell populations, and shed light on its
pathophysiology. Our mathematical models account for the dynamic evolution over
time of several interacting populations of bone cells averaged over a volume of
bone of sufficient size in order to obtain consistent results. We develop an
analytical study of the model and study its basic properties. The existence and
stability of steady states are studied, an analysis of sensitivity on the model
parameters is done, and different numerical simulations provide findings in
agreement with the analytical results. We discuss the model dynamics match with
known facts on the disease, and how some open questions could be addressed
using the model.
