title: Short-segment fixation of lumbar burst fractures using pedicle fixation at the level of the fracture.
abstract: METHODS
  Cadaveric biomechanical study and retrospective chart review.
  
  
  OBJECTIVE
  Biomechanical comparison of segmental versus nonsegmental fixation of lumbar burst fractures and clinical analysis of short-term radiographic outcomes.
  
  
  BACKGROUND
  Traditional short nonsegmental posterior fixation of thoracolumbar burst fractures suffers from high rates of failure. Construct stability may be improved by inserting additional screws at the fracture level.
  
  
  METHODS
  Six intact human spines (L1-L3) were biomechanically tested in flexion-extension, lateral bending, and axial torsion. The inferior half of the L2 vertebral bodies and L2-L3 discs were resected to mimic an unstable L2 burst fracture with loss of anterior column support. Pedicle screws were inserted in L1 and L3 for the control group (nonsegmental fixation). Screws were inserted at all levels for the experimental group (segmental fixation). Construct stiffness and L1-L2 disc pressure were analyzed. Twelve patients with thoracolumbar burst fractures treated with this type of segmental fixation were reviewed.
  
  
  RESULTS
  Construct stiffness during axial torsion was significantly higher for segmental constructs compared with nonsegmental constructs (P < 0.02) with no differences between flexion-extension and lateral bending. Disc pressure fluctuations during flexion-extension were significantly higher for segmental compared with nonsegmental constructs (P < 0.02), with no differences in lateral bending and torsion. Mean preoperative kyphotic deformity was 9 degrees and improved by 15 degrees after surgery. Follow-up films on 9 patients showed 5 degrees of kyphosis correction loss. Mean anterior vertebral body height was 58% of normal before surgery. After surgery height was 89% of normal and at final follow-up, 78%.
  
  
  CONCLUSIONS
  Segmental fixation of burst fractures with screws at the level of the fracture offers improved biomechanical stability. Theoretically, segmental fixation provides for additional fixation points that may aid in fracture reduction and kyphosis correction. This specific parameter is not evaluated in this study but will be an important outcome measure for a planned randomized controlled trial.
authors.affiliation: Department of Orthopedic Surgery, University of California-San Diego, San Diego, CA, USA. amahar@chsd.org
authors.forename: Andrew
authors.initials: A
authors.lastname: Mahar
authors.forename: Choll
authors.initials: C
authors.lastname: Kim
authors.forename: Michelle
authors.initials: M
authors.lastname: Wedemeyer
authors.forename: Lance
authors.initials: L
authors.lastname: Mitsunaga
authors.forename: Tim
authors.initials: T
authors.lastname: Odell
authors.forename: Bryce
authors.initials: B
authors.lastname: Johnson
authors.forename: Steven
authors.initials: S
authors.lastname: Garfin
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D011859:Radiography; D016103:Spinal Fractures / Q000000981:diagnostic imaging / Q000601:surgery*; D013314:Stress, Mechanical; D016896:Treatment Outcome