title: Unplanned reoperation after lumbopelvic fixation with S-2 alar-iliac screws or iliac bolts.
abstract: OBJECTIVE
  S-2 alar-iliac (S2AI) screws are an attractive alternative to conventional fixation with iliac bolts because they are lower profile, require less muscle dissection, and have greater pullout strength. Few studies, however, compare outcomes between these techniques.
  
  
  METHODS
  The authors conducted a retrospective cohort study of consecutive adult patients at a single institution from December 2009 to March 2012 who underwent lumbopelvic fixation using S2AI screws or iliac bolts. Medical records were reviewed for patients with clinical failure, defined as an unplanned reoperation because of instrumentation failure and/or wound-related complications. Univariate, multivariate, and survival analyses were used to compare patients who required reoperation with those who did not. Method of pelvic fixation was the main predictor variable of interest, and the authors adjusted for potential confounding risk factors.
  
  
  RESULTS
  Of the 60 patients included, 23 received S2AI screws. Seventeen patients (28%) underwent an osteotomy. The mean follow-up was 22 months. A Kaplan-Meier survival model was used to evaluate the time to reoperation from the initial placement of lumbopelvic instrumentation. The failure-free rate was 96.6% at 6 months, 87.0% at 1 year, and 73.5% at 2 years. Reoperation was more common in patients with iliac bolts than in those with S2AI screws (13 vs 2; p = 0.031). Univariate analysis identified potential risk factors for unplanned reoperation, including use of iliac bolts (p = 0.031), absence of L5-S1 interbody graft (p = 0.048), previous lumbar fusion (p = 0.034), and pathology other than degenerative disease or scoliosis (p = 0.034). After adjusting for other risk factors, multivariate analysis revealed that the use of S2AI screws (OR 8.1 [1.5-73.5]; p = 0.030) was the only independent predictor for preventing unplanned reoperation.
  
  
  CONCLUSIONS
  Both S2AI screws and iliac bolts were effective at improving fusion rates at the lumbosacral junction. The use of S2AI screws, however, was independently associated with fewer unplanned reoperations for wound-related complications and instrumentation failures than the use of iliac bolts.
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Marcus D
authors.initials: MD
authors.lastname: Mazur
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Vijay M
authors.initials: VM
authors.lastname: Ravindra
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Meic H
authors.initials: MH
authors.lastname: Schmidt
authors.affiliation: Orthopaedics, Clinical Neurosciences Center, University of Utah, Salt Lake City, Utah.
authors.forename: Darrel S
authors.initials: DS
authors.lastname: Brodke
authors.affiliation: Orthopaedics, Clinical Neurosciences Center, University of Utah, Salt Lake City, Utah.
authors.forename: Brandon D
authors.initials: BD
authors.lastname: Lawrence
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Jay
authors.initials: J
authors.lastname: Riva-Cambrin
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Dailey
mesh_terms: D000328:Adult; D000368:Aged; D001863:Bone Screws; D005260:Female; D006801:Humans; D007085:Ilium / Q000000981:diagnostic imaging / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010027:Osteotomy; D011859:Radiography; D012086:Reoperation; D012189:Retrospective Studies; D012307:Risk Factors; D013123:Spinal Fusion / Q000295:instrumentation*; D015996:Survival Rate; D017211:Treatment Failure
keywords: BMP = bone morphogenetic protein; ODI = Oswestry Disability Index; S-2 alar-iliac screws; S2AI = S-2 alar-iliac screw; iliac bolts; pelvic fixation; reoperation; sacral