title: A biomechanical evaluation of graded posterior element removal for treatment of lumbar stenosis: comparison of a minimally invasive approach with two standard laminectomy techniques.
abstract: METHODS
  A validated finite element model of the intact lumbar spine (L1-S1) was modified to study the biomechanical changes as a result of surgical alteration for treatment of stenosis at L3-L4 and L4-L5 using 2 established techniques and 1 new minimally invasive technique.
  
  
  OBJECTIVE
  To investigate the impact of graded posterior element removal associated with new surgical techniques on postoperative segmental motion and loading in the annulus.
  
  
  BACKGROUND
  Several studies have shown that laminectomy increases and produces segmental instability unless fusion is performed. However, no data exist comparing the biomechanical impact of completely preserving the contralateral anatomy and what effect this has compared to traditional approaches.
  
  
  METHODS
  The effect of graded removal of posterior elements because of iatrogenic change associated with the 3 approaches was investigated using an 800 N compressive preload using the follower load technique and application of 8 Nm flexion, 6 Nm extension, 4 Nm torsion, and 6 Nm lateral bending moments.
  
  
  RESULTS
  This study shows that removal of posterior elements for treatment of stenosis at L3-L4 and L4-L5 results in increased flexion-extension and axial rotation at the surgical site. This study also shows that the segmental motion following a traditional laminectomy is greater than the minimally invasive approach in flexion, extension, left and right axial rotation. Moderate preservation of the posterior elements which occurs in the intralaminar approach generates greater segmental motion that the minimally invasive approach in extension, left and right axial rotation.
  
  
  CONCLUSIONS
  Minimization of bone and ligament removal associated with minimally invasive procedures results in greater preservation of the normal motion of the lumbar spine after surgery. This study suggests that preservation of the posterior spinal elements associated with minimally invasive surgery could minimize the risk of developing de novo postoperative changes in spinal alignment and/or acceleration of facet and disc degeneration.
authors.affiliation: Department of Neurological Surgery, Northwestern University, 676 North St. Clair, Chicago, IL 60611-2922, USA. lbresnah@nmff.org
authors.forename: Lacey
authors.initials: L
authors.lastname: Bresnahan
authors.forename: Alfred T
authors.initials: AT
authors.lastname: Ogden
authors.forename: Raghu N
authors.initials: RN
authors.lastname: Natarajan
authors.forename: Richard G
authors.initials: RG
authors.lastname: Fessler
mesh_terms: D001696:Biomechanical Phenomena; D020342:Finite Element Analysis; D006801:Humans; D007796:Laminectomy / Q000379:methods*; D008159:Lumbar Vertebrae / Q000601:surgery*; D019060:Minimally Invasive Surgical Procedures / Q000379:methods*; D008953:Models, Anatomic; D016059:Range of Motion, Articular; D013130:Spinal Stenosis / Q000601:surgery*