Risk factors for predicting symptomatic adjacent segment degeneration requiring surgery in patients after posterior lumbar fusion

BACKGROUND Although measures to reduce and treat degenerative changes after fusion are discussed, these are still controversial. METHODS A retrospective study was conducted on a consecutive series of 3,799 patients who underwent posterior lumbar fusion for degenerative lumbar disease between January 1999 and January 2009. A total of 28 patients with symptomatic adjacent segment degeneration surgery were identified. Another group of 56 matched patients with degenerative lumbar disease without symptomatic adjacent segment degeneration after spinal fusion were marked as the control group. These two groups were compared for demographic distribution and clinical and radiographic data to investigate the predictive factors of symptomatic adjacent segment degeneration surgery by logistic regression. RESULTS The overall incidence rate of symptomatic adjacent segment degeneration surgery was 0.74%. Strong risk factors for the development of a symptomatic adjacent segment degeneration requiring surgery were preoperative distance from L1 to S1 sagittal plumb line (p = 0.031), preoperative lumbar lordosis (p = 0.005), and preoperative adjacent disc height (p = 0.003). Mean postoperative lumbar lordosis was smaller (p = 0.000) in symptomatic adjacent segment degeneration surgery (SASDS) group compared with in the control group (33.3° vs. 39.8°). Postoperative adjacent disc height was also significantly lower in the former group compared with the latter group (p = 0.002). Logistic regression analysis showed that body mass index (BMI) (OR: 1.75; p = 0.006), preoperative adjacent disc degeneration (ADD) on MRI (OR: 13.52; p = 0.027), and disc bulge in preoperative CT examination (OR: 390.4; p = 0.000) maintained their significance in predicting likelihood of symptomatic adjacent segment degeneration surgery. CONCLUSIONS The occurrence of a symptomatic adjacent segment degeneration surgery is most likely multifactorial and is related to BMI, preoperative ADD on MRI, and disc bulge in preoperative CT examination.