title: Facet tropism and interfacet shape in the thoracolumbar vertebrae: characterization and biomechanical interpretation.
abstract: METHODS
  Thoracolumbar facet and interfacet linear dimensions were measured and analyzed.
  
  
  OBJECTIVE
  To characterize and analyze the thoracolumbar facet and interfacet size and shape in relation to gender, ethnic group, and age and to detect the extent of normal facet tropism along the thoracolumbar spine.
  
  
  BACKGROUND
  Knowledge on facet tropism and interfacet shape is limited in the literature as most data are based on 2-dimensional measurements, small samples, or isolated vertebrae.
  
  
  METHODS
  Facet shape as represented by width, length, width/length ratio and interfacet distances was obtained directly from dry vertebrae of 240 adult human spines. The specimen's osteologic material is part of the Hamann-Todd Osteological Collection housed at the Cleveland Museum of Natural History, Cleveland, OH. A total of 4080 vertebrae (T1-L5) from the vertebral columns of individuals 20 to 80 years of age were measured, using a Microscribe 3-dimensional apparatus (Immersion Co., San Jose, CA). Data were recorded directly on computer software. Statistical analysis included paired t tests and ANOVA.
  
  
  RESULTS
  A significant correlation was found between all thoracolumbar facet dimensions and an individual's height and weight. Facet tropism is a major characteristic of the thoracolumbar spine, the left being longer in the thorax while the right is longer in the lumbar. In general, facet size is age-independent and greater in males compared with females with a significant ethnic component. Facet length is similar for all thoracic vertebrae, whereas it sharply and continuously increases in the lumbar vertebrae. Facet dimension manifests a bipolar distribution along the thoracolumbar vertebrae. Width/length ratio indicates that facets are longer than wider for most verte-brae. The interarticular area manifests a marked inverted trapezoidal shape at T1-T2, a rectangular shape at T3-L3, and an ordinary trapezoidal shape at L4-L5.
  
  
  CONCLUSIONS
  Facet tropism is a normal characteristic in humans, yet it varies along the thoracolumbar spine.
authors.affiliation: Tel-Aviv University, Sackler Faculty of Medicine, Department of Physical Therapy, Ramat-Aviv, Tel-Aviv, Israel. yossefm@post.tau.ac.il
authors.forename: Youssef
authors.initials: Y
authors.lastname: Masharawi
authors.forename: Bruce
authors.initials: B
authors.lastname: Rothschild
authors.forename: Khalil
authors.initials: K
authors.lastname: Salame
authors.forename: Gali
authors.initials: G
authors.lastname: Dar
authors.forename: Smadar
authors.initials: S
authors.lastname: Peleg
authors.forename: Israel
authors.initials: I
authors.lastname: Hershkovitz
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000886:Anthropometry; D001696:Biomechanical Phenomena; D044383:Black People / Q000208:ethnology; D005006:Ethnicity; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009820:Ohio / Q000208:ethnology; D015203:Reproducibility of Results; D013904:Thoracic Vertebrae / Q000033:anatomy & histology*; D044465:White People / Q000208:ethnology; D021801:Zygapophyseal Joint / Q000033:anatomy & histology*; D001741:Black or African American