40 patients with L4/5 degenerative spondylolisthesis (LDS) underwent posterior lumbar interbody fusion (PLIF) of Harm's technique, based on our surgical strategy of LDS from 1995-2000. Patients in the advanced stage with / without lumbar instability or in the end stage with instability were candidates for PLIF. All patients were followed up with period of 6.8 years on average except two who are dead. The 34 patients without complication such as Parkinson's disease were evaluated. The JOA score was improved from 14.3 to 24.5 points on average. Solid bony union was observed in 32 of 34 patients. % slip decreased from 18.8 to 10.9 %. Slip angel was increade from 2.1 to 6.3 degrees. Two patients with symptom due to the adjacent disc (L3/4) degeneration required additional operation. PLIF for the patients in the advanced stage or in the end stage with instability in our surgical strategy affords acceptable results in middle term follow-up.
