Cartilage defects that penetrate the subchondral bone can undergo spontaneous repair through the formation of a fibrous or cartilaginous tissue mediated primarily by mesenchymal stem cells from the bone marrow. This tissue is biomechanically inferior to normal articular cartilage, and is often observed to degrade over time. The factors that control the type and quality of the repair tissue, and its subsequent degradation, have yet to be elucidated. In this paper, we hypothesise a relationship between the mechanical environment of mesenchymal stem cells and their subsequent dispersal, proliferation, differentiation and death. The mechano-regulation stimulus is hypothesised to be a function of strain and fluid flow; these quantities are calculated using a finite element model of the tissue. A finite element model of an osteochondral defect in the knee was created, and used to simulate the spontaneous repair process.