title: Relationship of facet tropism with degeneration and stability of functional spinal unit.
abstract: OBJECTIVE
  The authors investigated the effect of lumbar facet tropism (FT) on intervertebral disc degeneration (DD), facet joint degeneration (FJD), and segmental translational motion.
  
  
  METHODS
  Using kinetic MRI (KMRI), lumbar FT, which was defined as a difference in symmetry of more than 7 degrees between the orientations of the facet joints, was investigated in 900 functional spinal units (300 subjects) in flexion, neutral, and extension postures. Each segment at L3-L4, L4-L5, and L5-S1 was assessed based on the extent of DD (grade I-V) and FJD (grade 1-4). According to the presence of FT, they were classified into two groups; one with FT and one with facet symmetry. For each group, demographics, DD, FJD and translational segmental motion were compared.
  
  
  RESULTS
  The incidence of FT was 34.5% at L3-L4, 35.1% at L4-L5, and 35.2% at L5-S1. Age and gender did not show any significant relationship with FT. Additionally, no correlation was observed between DD and FT. FT, however, was found to be associated with a higher incidence of highly degenerated facet joints at L4-L5 when compared to patients without FT (p < 0.01). Finally, FT was not observed to have any effects upon translational segmental motion.
  
  
  CONCLUSIONS
  No significant correlation was observed between lumbar FT and DD or translational segmental motion. However, FT was shown to be associated significantly with the presence of high grades of FJD at L4-L5. This suggests that at active sites of segmental motion, FT may predispose to the development of facet joint degeneration.
authors.affiliation: Department of Neurosurgery, Seoul Medical Center, Seoul, Korea. davidmhkong@gmail.com
authors.forename: Min Ho
authors.initials: MH
authors.lastname: Kong
authors.forename: Wubing
authors.initials: W
authors.lastname: He
authors.forename: Yu-Duan
authors.initials: YD
authors.lastname: Tsai
authors.forename: Nan-Fu
authors.initials: NF
authors.lastname: Chen
authors.forename: Gun
authors.initials: G
authors.lastname: Keorochana
authors.forename: Duc H
authors.initials: DH
authors.lastname: Do
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000209:etiology* / Q000473:pathology; D007592:Joint Diseases / Q000150:complications* / Q000473:pathology; D008159:Lumbar Vertebrae / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D021801:Zygapophyseal Joint / Q000473:pathology* / Q000503:physiopathology