title: The effect of sacral decortication on lumbosacral fixation in a calf spine model.
abstract: METHODS
  Animal cadaveric biomechanical study.
  
  
  OBJECTIVE
  We hypothesized that increasing bony destabilization of a bovine cadaveric sacrum by anterior pedicle screw penetration and bilateral alar decortication would decrease the amount of load necessary for failure of the construct and result in failure through the decortication sites.
  
  
  BACKGROUND
  Fusion to the sacrum has become commonly used for treatment of neuromuscular scoliosis and fusions in osteoporotic patients. Fixation failure after attempted fusion to the sacrum may be attributed to iatrogenic causes such as S1 screw penetration and sacral ala decortication.
  
  
  METHODS
  Sixteen fresh-frozen 6- to 8-week-old calf spines were tested after instrumentation with pedicle screws and bilateral rods from L2 to S1 using four constructs: (1) S1 screws with posterior-only purchase; (2) S1 screws with bicortical purchase; (3) S1 screws with bicortical purchase and sacral alar decortication; and (4) S1 screws with bicortical purchase, decortication, and iliac fixation. A destructive flexural bending load was applied at L2 to each construct. Ultimate failure moment (Nm) was compared among the four groups, using a one-way analysis of variance combined with Holm-Sidak post hoc test.
  
  
  RESULTS
  No significant difference in failure moment was found among groups 1, 2, and 3. The addition of iliac fixation (group 4) significantly increased bending load to failure (P < 0.01), and iliac screw dislodgement was the dominant mechanism of failure. All specimens in group 3 failed with fractures extending through the decortication site. Groups 1 and 2 specimens failed by fracturing through the S1 body.
  
  
  CONCLUSIONS
  Sacral alar decortication and anterior pedicle screw purchase did not decrease the failure moment in long instrumentation to the sacrum. Pattern of failure was affected, with alar decortication being the site of fracture in each construct in which it was performed. Iliac fixation increased the failure moment under catastrophic loading conditions even when combined with sacral alar decortication and bicortical pedicle screw purchase.
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY, USA.
authors.forename: Adrian
authors.initials: A
authors.lastname: Thomas
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Kepler
authors.forename: Katherine
authors.initials: K
authors.lastname: Meyers
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Green
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Wright
authors.forename: Bernard A
authors.initials: BA
authors.lastname: Rawlins
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001863:Bone Screws; D002417:Cattle; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D023421:Models, Animal; D009984:Orthopedic Fixation Devices; D015203:Reproducibility of Results; D012447:Sacrum / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D013131:Spine / Q000601:surgery*