title: Posterior distraction forces of the posterior longitudinal ligament stratified according to vertebral level.
abstract: BACKGROUND
  Although considered significant in resisting midline intervertebral disc herniation, the posterior longitudinal ligament (PLL) has had relatively few studies performed regarding its morphology and function. We performed the present experiment to discern the amount of posterior tensile force necessary to disrupt the PLL at each vertebral level.
  
  
  METHODS
  Twenty-five adult cadavers underwent laminectomies of vertebrae C1 to S1. After removal of the spinal cord, nerve roots, and dura mater, the PLL was identified for each vertebral level and a steel wire placed around its waist in the midline and a tensile gauge attached and posterior tension applied perpendicular to the spine. Forces necessary to failure of the PLL were noted for each vertebral level.
  
  
  RESULTS
  The PLL was found to be stronger in the thoracic spine compared to the cervical and lumbar vertebrae (P < 0.05). Dividing the vertebral levels in this manner, we found an average posterior distraction force to failure of 48.3 N in the cervical region, 61.3 N in the thoracic region, and 48.8 N in the lumbar region.
  
  
  CONCLUSIONS
  These findings support clinical observations that thoracic disc herniation is rare. We hypothesize that this clinical observation is partially due to a stronger PLL in the thoracic spine.
authors.affiliation: Department of Cell Biology, Section Pediatric Neurosurgery, University of Alabama at Birmingham, Birmingham, AL 35233, USA. rstubbs@uab.edu
authors.forename: R Shane
authors.initials: RS
authors.lastname: Tubbs
authors.forename: Marios
authors.initials: M
authors.lastname: Loukas
authors.forename: April
authors.initials: A
authors.lastname: Phantana-Angkool
authors.forename: Mohammadali M
authors.initials: MM
authors.lastname: Shoja
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Ardalan
authors.forename: Ghaffar
authors.initials: G
authors.lastname: Shokouhi
authors.forename: W Jerry
authors.initials: WJ
authors.lastname: Oakes
mesh_terms: D000368:Aged; D002102:Cadaver; D005260:Female; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000503:physiopathology; D017846:Longitudinal Ligaments / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D013718:Tensile Strength