Indications for OATS The ideal chondral defect would be relatively small, full thickness defect in the range of 10-20mm. Unfortunately, very large, deep defects are not suitable to OATS due to to technical limitations including the inability to reconsruct subchondral bone and limited availability of donor graft.   Step-by Step Guide Two excellent guides are available online: Dr. V. Bobic step by step guide is at http://www.isakos.com/innovations/oats2.aspx