title: Classification of high-grade spondylolistheses based on pelvic version and spine balance: possible rationale for reduction.
abstract: METHODS
  Retrospective review of a radiographic database of high-grade spondylolisthesis patients in comparison with asymptomatic controls.
  
  
  OBJECTIVE
  To analyze the sagittal spinopelvic alignment in high-grade spondylolisthesis patients and identify subgroups that may require reduction to restore sagittal balance.
  
  
  BACKGROUND
  High-grade spondylolisthesis is associated with an abnormally high pelvic incidence (PI); however, the spatial orientation of the pelvis, determined by sacral slope (SS) and pelvic tilt (PT), is not known. We hypothesized that sagittal spinal alignment would vary with the pelvic orientation.
  
  
  METHODS
  Digitized sagittal radiographs of 133 high-grade spondylolisthesis patients (mean age, 17 years) were measured to determined sagittal alignment. K-means cluster analysis identified 2 groups based on the PT and SS, which were compared by paired t test. Comparisons were made to asymptomatic controls matched for PI.
  
  
  RESULTS
  High-grade spondylolisthesis patients had a mean PI of 78.9 degrees +/- 12.1 degrees . Cluster analysis identified a retroverted, unbalanced pelvis group with high PT (36.5 degrees +/- 8.0 degrees )/low SS (40.3 degrees +/- 9.0 degrees ) and a balanced pelvic group with low PT (mean 21.3 degrees +/- 8.2 degrees )/high SS (59.9 degrees +/- 11.2 degrees ). The retroverted pelvis group had significantly greater L5 incidence and lumbosacral angle with less thoracic kyphosis than the balanced pelvic group. A total of 83% of controls had a "balanced pelvis" based on the categorization by SS and PT.
  
  
  CONCLUSIONS
  Analysis of sagittal alignment of high-grade spondylolisthesis patients revealed distinct groups termed "balanced" and "unbalanced" pelvis. The PT and SS were similar in controls and balanced pelvis patients. Unbalanced pelvis patients had a sagittal spinal alignment that differed from the balanced pelvis and control groups. Treatment strategies for high-grade spondylolisthesis should reflect the different mechanical strain on the spinopelvic junction in each group; reduction techniques might be considered in patients with an unbalanced pelvis high-grade spondylolisthesis.
authors.affiliation: Department of Orthopaedic Surgery, Children Hospital Boston, Harvard Medical School, Boston, MA 02115, USA. timothy.hresko@childrens.Harvard.edu
authors.forename: Michael T
authors.initials: MT
authors.lastname: Hresko
authors.forename: Hubert
authors.initials: H
authors.lastname: Labelle
authors.forename: Pierre
authors.initials: P
authors.lastname: Roussouly
authors.forename: Eric
authors.initials: E
authors.lastname: Berthonnaud
mesh_terms: D000293:Adolescent; D001900:Boston; D016022:Case-Control Studies; D016000:Cluster Analysis; D005602:France; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D008141:Lordosis / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology; D018579:Patient Selection; D010388:Pelvis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D004856:Postural Balance; D011792:Quebec; D011859:Radiography; D012189:Retrospective Studies; D012447:Sacrum / Q000000981:diagnostic imaging / Q000503:physiopathology; D012720:Severity of Illness Index; D013131:Spine / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013168:Spondylolisthesis / Q000145:classification / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000628:therapy; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology