title: Vertebral rotatory subluxation in degenerative scoliosis: facet joint tropism is related.
abstract: METHODS
  A cross-sectional study.
  
  
  OBJECTIVE
  To identify facet tropism as one of the possible risk factors leading to vertebral rotatory subluxation (VRS).
  
  
  BACKGROUND
  VRS has been considered as one of the prognostic factors for degenerative scoliosis. Although several risk factors of VRS, including age and Cobb angle, have been investigated, few studies exist that have evaluated the correlation between VRS and anatomical structures of the vertebral column.
  
  
  METHODS
  This retrospective study recruited 23 patients diagnosed with degenerative lumbar scoliosis with VRS and 20 patients with degenerative scoliosis without VRS. The lateral translation on coronal radiographs was measured and 5 mm was used as the cutoff value to define rotatory subluxation. Computed tomographic scans for facet joints were made for all lumbar levels. The difference between right and left facet angles was recorded as ΔFA. Facet tropism was defined as a difference between the bilateral facet angles of more than 10°.
  
  
  RESULTS
  In this study, VRS was most commonly found at the L3-L4 level (49%) and, with decreasing frequency at L2-L3 (24%), L4-L5 (20%), and L1-L2 (7%). On the convex side of the main curve, face joints at levels with VRS were more coronally oriented compared with those at levels without VRS (41.64° ± 11.65° vs. 36.30° ± 10.99°, P = 0.034). ΔFA was also significantly different between levels with and without VRS (P = 0.005). A strong correlation was found between ΔFA and lateral translation, with a coefficient of 0.33 (P < 0.001). In addition, ΔFA and a larger Cobb angle were found to be significantly associated with VRS based on binary regression analysis, with an odds ratio of 4.68 and 2.14, respectively.
  
  
  CONCLUSIONS
  Facet tropism was more significantly observed at levels with VRS. On the convex side of the main curve, facet joints at levels with VRS were more coronally oriented. A larger Cobb angle and severe facet tropism in degenerative scoliosis should be considered to be related to VRS.
authors.affiliation: *Department of Spine Surgery, the Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, China; and †Sir Charles Gairdner Hospital, Nedlands, Perth, Western Australia, Australia.
authors.forename: Hongda
authors.initials: H
authors.lastname: Bao
authors.forename: Feng
authors.initials: F
authors.lastname: Zhu
authors.forename: Zhen
authors.initials: Z
authors.lastname: Liu
authors.forename: Mark
authors.initials: M
authors.lastname: Bentley
authors.forename: Saihu
authors.initials: S
authors.lastname: Mao
authors.forename: Zezhang
authors.initials: Z
authors.lastname: Zhu
authors.forename: Yitao
authors.initials: Y
authors.lastname: Ding
authors.forename: Yong
authors.initials: Y
authors.lastname: Qiu
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D012600:Scoliosis / Q000150:complications / Q000601:surgery*; D013131:Spine / Q000503:physiopathology; D018523:Tropism / Q000502:physiology*; D021801:Zygapophyseal Joint / Q000473:pathology / Q000601:surgery*