The　range　of　the　bone　defect　and　the　filling　material　are　among　the　most　important　causes　of　prosthetic　instability　and　consequent　failure　of　the　artificial　knee　joint.　The　purpose　of　this　study　is　to　investigate　the　effect　of　bone　defects　on　the　stability　of　unicondylar　prostheses.　Different　lengths　of　medullary　cavity　extension　rods,　filling　gaps　(simulating　different　ranges　of　bone　defects)　and　filling　materials　are　selected　as　influencing　factors　for　the　orthogonal　test.　Compare　the　influence　of　various　factors　on　the　maximum　equivalent　stress　distribution　of　cortical　bone　through　finite　element　analysis,　and　the　optimal　combination　to　achieve　the　best　effect　on　the　stability　of　the　prosthesis　was　determined　to　be　an　extension　rod　length　of　18.5　mm,　a　filling　gap　of　6　mm,　and　a　filling　material　of　titanium　alloy.　It　is　concluded　that　the　use　of　metal　materials　to　fill　the　medial　femoral　condyle　defect　can　improve　the　stability　of　the　UKA　prosthesis,　and　that　the　stability　will　not　be　affected　by　expanding　the　filling　range　of　the　medial　femoral　condylar　bone　defect　within　an　appropriate　range,　while　changing　the　length　of　the　prosthesis　extension　rod　has　little　effect　on　the　stability　of　the　UKA　femoral　prosthesis.　©　(2021)　Society　for　Biomaterials　&　Artificial　Organs　#20046821