title: Range of motion in reconstruction situations following corpectomy in the lumbar spine: a question of bone mineral density?
abstract: METHODS
  In vitro biomechanical study to evaluate the stability of different types of instrumentation in the lumbar spine following corpectomy in relation to bone mineral density (BMD).
  
  
  OBJECTIVE
  To investigate the relation between the stability of a spinal instrumentation and BMD. To determine a threshold value of BMD allowing a single ventral instrumentation following corpectomy in the lumbar spine.
  
  
  BACKGROUND
  Some in vitro studies determined the biomechanical properties of different spinal instrumentations in various spinal injury models. To the authors' knowledge, there are no published data available concerning stabilization in relation to BMD. A guideline for the treatment of a corpectomy depending on BMD would be helpful in order to choose the appropriate surgical method.
  
  
  METHODS
  Twenty-four fresh frozen human lumbar cadaveric spine specimens L1-L3 were used for testing of biomechanical properties. Plain radiographs were taken. BMD was determined using quantitative computed tomography (QCT). Testing in a 6 df loading device included native specimens and specimens after corpectomy of L2, restoration of the defect with a titanium cage, and two reconstruction situations: single ventral and additional dorsal instrumentation. Load-displacement curves and range of motion parameters were recorded and correlated with BMD.
  
  
  RESULTS
  A significant (P < 0.05) influence of BMD on range of motion was found. Single ventral instrumentation was critical concerning axial rotation. Combined dorsoventral instrumentation offered sufficient stability. The threshold value for use of single ventral instrumentation is a BMD > or = 0.22 g/cm.
  
  
  CONCLUSIONS
  Single ventral instrumentation can provide sufficient stability following corpectomy in the lumbar spine under the condition of a high BMD. Determination of BMD and the use of this guideline provides a valid tool for surgical planning.
authors.affiliation: Department of Orthopaedic Surgery, University of Freiburg, Freiburg, Germany. knoeller@ch11.ukl.uni-freiburg.de
authors.forename: Stefan M
authors.initials: SM
authors.lastname: Knöller
authors.forename: Georg
authors.initials: G
authors.lastname: Meyer
authors.forename: Christina
authors.initials: C
authors.lastname: Eckhardt
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Lill
authors.forename: Erich
authors.initials: E
authors.lastname: Schneider
authors.forename: Berend
authors.initials: B
authors.lastname: Linke
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D001863:Bone Screws; D005260:Female; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000378:metabolism / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D019651:Plastic Surgery Procedures / Q000295:instrumentation / Q000379:methods*; D012399:Rotation; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing