ObjectiveTo compare the effectiveness of treatment of isthmic spondylolisthesis between two different fusion surgeries combined with pedicle screw fixation system. MethodsA retrospectively analysis was made on the clinical data of 98 patients with lumbar isthmic spondylolisthesis treated between February 2009 and May 2012. Of 98 cases, 53 underwent posterior lumbar interbody fusion (PLIF) combined with internal fixation (group A), and 45 underwent posterolateral fusion (PLF) with internal fixation (group B). There was no significant difference in gender, age, disease duration, segmental lesions, and degree of spondylolisthesis between 2 groups (P>0.05). The operation time, intraoperative blood loss, reduction rate of spondylolisthesis, reduction loss rate, fusion rate, intervertebral space height, Japanese Orthopedic Association (JOA) score, and the recovery rate of JOA score were compared between 2 groups. ResultsThe operation time and intraoperative blood loss of group A were significantly higher than those of group B (P<0.05). Dural tear occured in 4 cases of group A and 1 case of group B during operation; 6 cases had radicular symptoms after operation in group A; incision infection was found in 1 case of 2 groups respectively. The follow-up time was 24-36 months in group A and was 26-40 months in group B. No significant difference was found in the JOA score at preoperation and 2 weeks after operation between 2 groups (P>0.05). The JOA score and the recovery rate of JOA score of group A were significantly better than those of group B at 2 years after operation (P<0.05). X-ray film showed that the reduction rate of group A was significantly higher than that of group B after 2 weeks of operation (P<0.05); the reduction loss rate of group A was significantly lower than that of group B after 2 years after operation (P<0.05). The intervertebral space height of group A was significantly higher than that of group B at 2 weeks and 2 years after operation (P<0.05). The fusion rate of group A was significantly better than that of group B at 2 years after operation (P<0.05). ConclusionPLIF can achieve a greater degree of reduction, better restore disc height, and lumbar curvature than PLF. PLIF is superior to PLF in maintaining intervertebral height after operation. And PLIF has higher fusion rate, restores the stability of the spine in a greater extent, and it also can achieve a better long-term outcome.