Objective To analyze the degeneration parameters of the multifidus muscle at the disjunc-tion in patients with isthmus spondylolisthesis and its correlation with the degree of spondylolisthesis.Meth-ods A retrospective analysis was conducted on the medical records and MRI imaging data of 59 patients with isthmus spondylolisthesis who visited this hospital from January 2022 to July 2024.The degeneration parame-ters of multifidus muscle were selected and assessed as cross-sectional area(CSA)and percentage of fat infil-tration area(FIA%).CSA and FIA%of the multifidus muscle at the disjunction and the previous non-sliding disconnection segment were measured and compared using Image J software.The degree of spondylolisthesis was evaluated referring to the Meyerding standard,and the correlation was analyzed between CSA,FIA%of the multifidus muscle at the disjunction and the degree of spondylolisthesis.Results Among the 59 patients,there were 2 cases of L3 spondylolisthesis,27 cases of L4 spondylolisthesis and 30 cases of L5 spondylolisthe-sis.CSA of the multifidus muscle at the disjunction and the previous non-sliding disconnection segment were(882.22±236.01)mm2 and(845.59±263.37)mm2 respectively,the difference was not statistically significant(t=0.796,P=0.428).FIA%were 37.16%(25.56%,50.78%)and 33.26%(18.65%,43.04%)respective-ly,the difference was statistically significant(Z=-2.008,P=0.045).Among the 59 patients,50 cases(84.75%)had grade Ⅰ spondylolisthesis,9 cases(15.25%)had grade Ⅱ spondylolisthesis,there were no pa-tients with grade Ⅲ or Ⅳ spondylolisthesis.The degree of spondylolisthesis was correlated with FIA%(r=0.443,P<0.001),but not correlated with CSA(r=-0.188,P=0.153).Conclusion In patients with isth-mus spondylolisthesis,FIA%of the multifidus muscle at the disjunction is significantly higher than that in the previous non-sliding disconnection segment,and it is related to the degree of spondylolisthesis.However,CSA of the multifidus muscle at the disjunction showed no significant difference from that in the previous non-slid-ing disconnection segment and was not correlated with the degree of spondylolisthesis.FIA%is more accurate in assessing the severity of multifidus muscle degeneration than CSA.