Objective:To compare the clinical outcomes of three methods of posterior lumbar interbody fusion (PLIF) using one cage and one mass of autogenus bone grafting fusion with pedicle screw fixation,two cages fusion with pedicle screw fixation and simple cage fusion with pedicle screw fixation for broken isthmic spondylolisthesisMethods:From Desember 2001 to Octuber 2005,56 cases of broken isthmic spondylolisthesis were treated surgically and divided in three groups.In group A,22 cases were treated with pedical screw system and intervertebral fusion using one cage and one mass of autogenous bone grafting.There were 12 males and 10 mamales,aging 35-52 years.Isthmic defects were located at L4 in 12 cases,L5 In 8 cases and L3 in 2 cases.The disc space height was 4.9mm preoperatively and 9mm postoperatively.In group B,16 cases were treated with pedical screw system and intervertebral fusion using two cages.There were 10 males and 6 females,aging 32-49 years.Isthmic defects were located at L4 in 7 cases,L5 In 9 cases.The disc space height was 5.1mm preoperatively and 9mm postoperatively In group C,18 cases were treated with pedical screw system and intervertebral fusion only using one cage.There were 10 males and 8 females,aging 28-50 years.Isthmic defects were located at L4 in 10 cases,L5 In 8 cases.The disc space height was 5.3mm preoperatively and 9mm postoperatively The amount of blood loss,duration of hospitalization,the height of disc space,fusion rate,and clinical evaluations were analysed in three groups.