title: Increased pelvic incidence may lead to arthritis and sagittal orientation of the facet joints at the lower lumbar spine.
abstract: BACKGROUND
  Correct sagittal alignment with a balanced pelvis and spine is crucial in the management of spinal disorders. The pelvic incidence (PI) describes the sagittal pelvic alignment and is position-independent. It has barely been investigated on CT scans. Furthermore, no studies have focused on the association between PI and facet joint (FJ) arthritis and orientation. Therefore, our goal was to clarify the remaining issues about PI in regard to (1) physiologic values, (2) age, (3) gender, (4) lumbar lordosis (LL) and (5) FJ arthritis and orientation using CT scans.
  
  
  METHODS
  We retrospectively analyzed CT scans of 620 individuals, with a mean age of 43 years, who presented to our traumatology department and underwent a whole body CT scan, between 2008 and 2010. The PI was determined on sagittal CT planes of the pelvis by measuring the angle between the hip axis to an orthogonal line originating at the center of the superior end plate axis of the first sacral vertebra. We also evaluated LL, FJ arthritis and orientation of the lumbar spine.
  
  
  RESULTS
  596 individuals yielded results for (1) PI with a mean of 50.8°. There was no significant difference for PI and (2) age, nor (3) gender. PI was significantly and linearly correlated with (4) LL (p = < 0.0001). Interestingly, PI and (5) FJ arthritis displayed a significant and linear correlation (p = 0.0062) with a cut-off point at 50°. An increased PI was also significantly associated with more sagitally oriented FJs at L5/S1 (p = 0.01).
  
  
  CONCLUSIONS
  PI is not correlated with age nor gender. However, this is the first report showing that PI is significantly and linearly associated with LL, FJ arthritis and more sagittal FJ orientation at the lower lumbar spine. This may be caused by a higher contact force on the lower lumbar FJs by an increased PI. Once symptomatic or in the event of spinal trauma, patients with increased PI and LL could benefit from corrective surgery and spondylodesis.
authors.affiliation: Division of Trauma Surgery, Department of Surgery, University Hospital Zuerich, Zuerich, Switzerland. thorsten.jentzsch@usz.ch.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Jentzsch
authors.forename: James
authors.initials: J
authors.lastname: Geiger
authors.forename: Samy
authors.initials: S
authors.lastname: Bouaicha
authors.forename: Ksenija
authors.initials: K
authors.lastname: Slankamenac
authors.forename: Thi Dan Linh
authors.initials: TD
authors.lastname: Nguyen-Kim
authors.forename: Clément M L
authors.initials: CM
authors.lastname: Werner
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001168:Arthritis / Q000000981:diagnostic imaging*; D002648:Child; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D013131:Spine / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D021801:Zygapophyseal Joint / Q000000981:diagnostic imaging*