methods of identifying the ability of a stem cell to differentiate a cell into a chondrocyte, to differentiate ce = cell into a chondrocyte and to stem cell into a lesion tissue cell, to decrease chondrocyte death, to increase expression of at least a protein selected from the group consisting of tsp-2 and hb-egf from stem cell, sorting material that regulates stem cell activity and increasing expression of at least one selected from the group consisting of tsp -2 and hb-egf from stem cell and compositions for stimulating a cell to differentiate into a chondrocyte and to decrease chondrocyte d