title: The spondylolytic vertebra and its adjacent segment. Mobility measured before and after posterolateral fusion.
abstract: METHODS
  By using roentgen stereophotogrammetric analysis in six patients having tantalum indicators implanted at a preoperative external fixation test, the mobility in the spondylolytic lumbosacral level and its adjacent segment could be studied before fusion and during the course of postoperative fusion consolidation.
  
  
  OBJECTIVE
  To study the mobility effects on the segment adjacent to a lumbar fusion over time from the preoperative situation until fusion healing as defined by roentgen stereophotogrammetric analysis.
  
  
  BACKGROUND
  In vitro studies indicate that the altered biomechanical situation after lumbar fusion increases the intradiscal pressure and changes the kinematics in the juxtafused segment.
  
  
  METHODS
  Six patients with low grade spondylolysisolisthesis were scheduled for fusion of the spondylolytic lumbosacral segment after a preoperative external fixation test. The latter procedure also included implantation of tantalum markers for spinal roentgen stereophotogrammetric analysis. Each patient was examined by roentgen stereophotogrammetric analysis at four separate occasions: before fusion (2 months after removal of the external frame) and 3, 6, and 12 months after surgery. The translatory movements of the L5 vertebra in relation to sacrum and of the L4 vertebra in relation to the L5 vertebra were calculated at each examination.
  
  
  RESULTS
  For the juxtafused L4-L5 level, increased and decreased mobility patterns could be identified. Transformation of the preoperative mobility in the lumbosacral segment to the adjacent segment during fusion consolidation was verified in two patients but was not a general phenomenon.
  
  
  CONCLUSIONS
  Fusion of the lumbosacral segment can alter the kinematics of the adjacent segment, redistributing the mobility toward relative hypermobility in the juxtafused segment.
authors.affiliation: Department of Orthopedics, Lund University Hospital, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Axelsson
authors.forename: R
authors.initials: R
authors.lastname: Johnsson
authors.forename: B
authors.initials: B
authors.lastname: Strömqvist
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011859:Radiography; D016059:Range of Motion, Articular; D013123:Spinal Fusion; D013169:Spondylolysis / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*