Objective To observe the correlations of subchondral insufficiency fracture(SIF)of medial femoral condyle with medial meniscus injury pattern and medial meniscus extrusion(MME).Methods Data of 36 patients with clinically confirmed unilateral medial femoral condyle SIF were retrospectively analyzed.The patients were divided into low-grade and high-grade groups according to SIF grade.Cartilage injury,medial meniscus injury and MME were compared between groups,and the correlations of SIF grade with cartilage injury,osteonecrosis volume(OV)and MME were analyzed.Cartilage injury grade,OV and MME were compared between groups,and the correlations were explored.Results There were 18 cases in each group.The percentage of cartilage injury grade Ⅲ-Ⅳ,OV and MME value(the distance between the vertical line of medial meniscus and the vertical line of tibial plateau cartilage)in high-grade group were greater than those in low-grade group(all P＜0.05).Significant difference of injury grades of meniscus posterior horn was found between groups(P=0.007).SIF grade was positively correlated with cartilage injury grade,OV and MME value(rs=0.710,0.765,0.540,all P≤0.01).MME value was positively correlated with meniscal injury degree and tear range(rs=0.502,0.520,both P＜0.01).There were 4,19 and 13 cases with 0,1 and 2 grade MME,respectively,and significant differences of cartilage injury grades,OV and MME values were found among different MME grades(all P＜0.05).MME value was positively correlated with cartilage injury grade and OV(rs=0.451,0.579,both P＜0.01).Conclusion In SIF patients,OV and cartilage injury were both correlated with medial meniscus injury pattern and MME.