The purpose of this study is to determine if Ixmyelocel-T grafting with demineralized bone matrix bound in autologous plasma after core decompression surgery is superior to core decompression with demineralized bone matrix bound in autologous plasma in preventing progression of osteonecrosis to a more severe disease stage (Stage II to III or higher) from the time of surgery until 24 months later, in patients with University of Pennsylvania (UPenn) Stage IIB or C disease at diagnosis.