Pelvic incidence-lumbar lordosis mismatch predisposes to adjacent segment disease after lumbar spinal fusion

Purpose: Several risk factors and causes of adjacent segment disease have been debated; however, no quantitative relationship to spino-pelvic parameters has been established so far. A retrospective case-control study was carried out to investigate spino-pelvic alignment in patients with adjacent segment disease compared to a control group. Methods: 45 patients (ASDis) were identified that underwent revision surgery for adjacent segment disease after on average 49months (7-125), 39 patients were selected as control group (CTRL) similar in the distribution of the matching variables, such as age, gender, preoperative degenerative changes, and numbers of segments fused with a mean follow-up of 84months (61-142) (total n=84). Several radiographic parameters were measured on pre- and postoperative radiographs, including lumbar lordosis measured (LL), sacral slope, pelvic incidence (PI), and tilt. Results: Significant differences between ASDis and CTRL groups on preoperative radiographs were seen for PI (60.9±10.0° vs. 51.7±10.4°, p=0.001) and LL (48.1±12.5° vs. 53.8±10.8°, p=0.012). Pelvic incidence was put into relation to lumbar lordosis by calculating the difference between pelvic incidence and lumbar lordosis (∆PILL=PI−LL, ASDis 12.5±16.7° vs. CTRL 3.4±12.1°, p=0.001). A cutoff value of 9.8° was determined by logistic regression and ROC analysis and patients classified into a type A (∆PILL