title: Pelvic incidence-lumbar lordosis mismatch predisposes to adjacent segment disease after lumbar spinal fusion.
abstract: OBJECTIVE
  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 49 months (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 84 months (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 <10°) and a type B (∆PILL ≥10°) alignment according to pelvic incidence-lumbar lordosis mismatch. In type A spino-pelvic alignment, 25.5 % of patients underwent revision surgery for adjacent segment disease, whereas 78.3 % of patients classified as type B alignment had revision surgery. Classification of patients into type A and B alignments yields a sensitivity for predicting adjacent segment disease of 71 %, a specificity of 81 % and an odds ratio of 10.6.
  
  
  CONCLUSIONS
  In degenerative disease of the lumbar spine a high pelvic incidence with diminished lumbar lordosis seems to predispose to adjacent segment disease. Patients with such pelvic incidence-lumbar lordosis mismatch exhibit a 10-times higher risk for undergoing revision surgery than controls if sagittal malalignment is maintained after lumbar fusion surgery.
authors.affiliation: Department of Orthopaedics, Uniklinik Balgrist, University of Zurich, Zurich, Switzerland, dominique.rothenfluh@mac.com.
authors.forename: Dominique A
authors.initials: DA
authors.lastname: Rothenfluh
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Mueller
authors.forename: Esin
authors.initials: E
authors.lastname: Rothenfluh
authors.forename: Kan
authors.initials: K
authors.lastname: Min
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008141:Lordosis / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010384:Pelvic Bones / Q000000981:diagnostic imaging / Q000473:pathology*; D011859:Radiography; D012086:Reoperation / Q000379:methods; D012189:Retrospective Studies; D012307:Risk Factors; D012447:Sacrum / Q000000981:diagnostic imaging / Q000473:pathology; D013122:Spinal Diseases / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D013123:Spinal Fusion / Q000009:adverse effects*