Lumbar spinal instability can be evaluated as degenerative spondylolisthesis, degenerative instability of the adjacent spine, postdecompression instability, and postdiscectomy instability. Surgical treatment is indicated when persistent pain with nonoperative treatment, neural claudication and radiologicaly daignosed absolute instability. Fusion and instrumentation is stil controversial. The aim of this study is to determine the surgical and clinical results with Oswestry Disability Index and SRS-22 Questionarie of 24 patients that had persistent pain despite conservative treatment and surgically treated with posterolateral fusion and posterior instrumentation with minimum two years follow-up. Additionally relationship between pain, neurologic symptoms, functional status and fusion rates and surgical results evaluated. All of the patients had translation more than 4 mm (average 5.2 ± 1.4 mm) and angulation more than 10° (average 11.6° ± 1.1°) on flexion radiographies and had absolute lumbar instability. The instability was detected at L5-S1 level in 8 (33.3 %) patients, at L4-5 level in 14 (58.3 %) patients, at L3-4 level 2 (8.4 %) patients. In this study, it was stated that posterolateral instability was resolved after posterolateral fusion and posterior instrumentation, and according to Lenke et. al. classification solid fusion was obtained in 79.2 % of patients, inadequate fusion was seen in 12.5% of patients (Grade B and C), and in one patient (4.2 %) pseudoarthrosis developed. It was decided that neural claudication was resolved in all of the 10 patients that decompression was performed. When preoperative and postoperative ODI and SRS-22 questionaire were compared, postoperative and final results were improved to statistically significant values (p<0.05). At last follow-ups, minimal correction loss were observed. In 15 degenerative lumbar spondylolisthesis patients, sagittal contours were impaired to physiologic limits, and statistically significant postoperative reduction (average 70.9 ± 14.4 %) was obtained. Final correction rates did not changed also. It was seen that correction rate of sagittal contours and lystethic slip were correlated with ODI and SRS-22 questionarie results, and the translational improvement and the correction of sagittal contours to physiologic limits positively effect pain, functional capacity, mental and cosmetic status of patients and satisfaction rates of treatment. According to datas of this study, it was concluded that sagittal contours could be decreased to physiologic limits, high fusion rates and good clinical results can be obtained with posterolateral fusion and posterior segmental pedicular screw fixation in patients who had degenerative lumbar instability and not responded to conservative treatment methods. Additionally, it was stated that correction of sagittal contours, correction of instability and improvement of translational deformity positively effect pain, function, cosmetic-mental status and satisfaction from treatment

Keywords: Degenerative lumbar instability, degenerative spondylolisthesis, surgical treatment, posterolateral fusion, posterior instrumentation