Adjacent Segment Degeneration after Posterior Lumbar Interbody Fusion: Based on Cases with a Minimum of 10 years of Follow-Up
Authors: Nakashima Hiroaki , Kawakami Noriaki , Tsuji Taichi , Imagama Shiro 
Published: May 2015

Introduction Adjacent segment degeneration (ASD) is problematic sequelae after spinal fusion surgery. ASD is observed in 36 to 84% of patients followed-up for 5 years after lumbar fusion surgery. However, there are few reports of long-term follow-up studies after PLIF, although 75% of cases requiring reoperation for ASD were discovered > 4 years after the initial surgery. Moreover, there are limited reports describing changes related to disc degeneration and spinal stenosis on magnetic resonance imaging (MRI) after PLIF. The purpose of this study is to investigate the incidence of ASD and the associated risk factors over at least 10 years after PLIF. Material and Methods This study was a retrospective case-controlled study. A total of 167 patients who underwent PLIF were enrolled at a single spine center from April 1996 to May 2003. The inclusion criteria included age (> 21 years at the time of surgery), magnitude of scoliosis (Cobb angle < 15 degrees), and no additional decompression surgery at the level adjacent to the PLIF area. Overall, 66 patients were excluded in addition to those who did not meet these criteria, because they had not been followed up for at least 10 years. Finally, 101 patients (41 males, 60 females) with a mean age of 56.4 ± 15.3 years (range: 23–79 years) were included. The mean duration of follow-up was 11.6 ± 2.2 years (range: 10–17 years). Seventy patients had degenerative spondylolisthesis, 15 had spondylolytic spondylolisthesis, 11 had lumbar disc herniation, and 5 had spinal canal stenosis. Posterior lumbar interbody fusion was performed using pedicle screws, two carbon cages, and autologous iliac-crest bone graft. Preoperative and postoperative (2, 5, and 10 years after surgery) X-ray and MRI images were evaluated. Disc height, vertebral slip, and intervertebral angle were examined on X-ray images. Disc degeneration and spinal stenosis on MRI images were evaluated. Patients who developed severe spinal canal stenosis or exhibited listhesis (> 3 mm) within 5 years after surgery were defined as having early-onset radiographic ASD. Risk factors for developing early-onset radiographic ASD were evaluated using a multivariate logistic regression analysis. Results The degenerative changes in disc height, vertebral slip, and intervertebral angle on X-ray 10 years after surgery were 12, 35, and 17%, respectively, at the cranial-adjacent level and 4, 7, and 13%, respectively, at the caudal-adjacent level. The incidences of disc degeneration and spinal stenosis were 61 and 29%, respectively, at the cranial-adjacent level and 67 and 14%, respectively, at the caudal-adjacent level on MRI 10 years after surgery. Ten patients (9.9%) required reoperation, and 80% of revision surgeries were performed > 5 years after the initial surgery. High pelvic incidence was a risk factor for developing early-onset radiographic ASD. Conclusion The majority of the reoperation for ASD was performed > 5 years after the initial lumbar fusion surgery, although the progression of radiographic ASD began in the early postoperative period. A high pelvic incidence was a risk factor for developing early-onset radiographic ASD. Obtaining appropriate lumbar lordosis in PLIF is important for preventing ASD.