title: Biomechanical effects of autonomous augmentation on the adjacent unaugmented vertebral bodies: influence of the number of functional spinal units in a finite element model.
abstract: The results of finite element analysis (FEA) studies on the effect of augmentation of one vertebral body (VB), using vertebroplasty (VP) or balloon kyphoplasty (BKP), on the biomechanics of the adjacent and nonadjacent VBs are contradictory. One reason for this record is that different levels of the spine, numbers of structures, and numbers of functional spinal units (FSUs) (X) were included in the models used in different studies. The purpose of the present study was to clarify this effect as far as X is concerned.
  
  
  
  A validated three-dimensional solid model of the lumbar spine was constructed from computed tomography scans and prophylactic augmentation of L2 was simulated. In the FEA, the model was subjected to a uniformly distributed compressive load (total load = 1300 N) on the superior endplate of L1. The extent to which a change in X affects the values of the mean von Mises stress (sigmaVM) and the mean elastic strain energy density (ESED) in all structures adjacent to L2 was determined. (These changes were with respect to the case where all the VBs in the model are intact.)
  
  
  
  As X increased (from 1 to 2, from 2 to 3, and from 3 to 4), there were clear variations in the number of stable changes in both sigmaVM and ESED in each structure. The largest number of these changes occurred when X changed from 2 to 3.
  
  
  
  The results suggest that three is the number of FSUs that should be included in models of the lumbar spine to be used in FEA studies of VP and BKP.
authors.affiliation: Department of Mechanical Engineering, The University of Memphis, Memphis, Tennessee - USA.
authors.forename: G
authors.initials: G
authors.lastname: Lewis
authors.forename: J
authors.initials: J
authors.lastname: Xu