A mechanobiological model of epiphysis structures formation

Developing bone consists of epiphysis, metaphysis and diaphysis. The secondary ossification centre (SOC) appears and grows within the epiphysis, involving two histological stages. Firstly, cartilage canals appear; they carry hypertrophy factors towards the central area of the epiphysis. Canal growth and expansion is modulated by stress on the epiphysis. Secondly, the diffusion of hypertrophy factors causes SOC growth. Hypertrophy is regulated by biological and mechanical factors present within the epiphysis. The finite element method has been used for solving a coupled system of differential equations for modelling these histological stages of epiphyseal development. Cartilage canal spatial-temporal growth patterns were obtained as well as the SOC formation pattern. This model qualitatively agreed with experimental results reported by other authors.

► We model cartilage canal growth and SOC formation.
► Cartilage canal growth towards the epiphysis centre is modulated by octahedral stress.
► High stress levels cause release of hypertrophic factors from cartilage canal ends.
► Hypertrophy is the main cause of SOC growth.
► Low shear stress, high hydrostatic pressure and high PTHrP expression inhibit hypertrophy phase.