title: The value of intraoperative Gram stain in revision spine surgery.
abstract: BACKGROUND
  Intraoperative cultures and Gram stains are often obtained in cases of revision spine surgery even when clinical signs of infection are not present. The clinical utility and cost-effectiveness of this behavior remain unproven.
  
  
  OBJECTIVE
  The aim was to evaluate the clinical utility and cost-effectiveness of routine intraoperative Gram stains in revision spine surgery.
  
  
  METHODS
  This was a retrospective clinical review performed at an academic center in an urban setting.
  
  
  METHODS
  One hundred twenty-nine consecutive adult revision spine surgeries were performed.
  
  
  METHODS
  The outcome measures included intraoperative Gram stains.
  
  
  METHODS
  We retrospectively reviewed the records of 594 consecutive revision spine surgeries performed by four senior surgeons between 2008 and 2013 to identify patients who had operative cultures and Gram stains performed. All revision cases including cervical, thoracic, and lumbar fusion and non-fusion, with and without instrumentation were reviewed. One hundred twenty-nine (21.7%) patients had operative cultures obtained and were included in the study.
  
  
  RESULTS
  The most common primary diagnosis code at the time of revision surgery was pseudarthrosis, which was present in 41.9% of cases (54 of 129). Infection was the primary diagnosis in 10.1% (13 of 129) of cases. Operative cultures were obtained in 129 of 595 (21.7%) cases, and 47.3% (61 of 129) were positive. Gram stains were performed in 98 of 129 (76.0%) cases and were positive in 5 of 98 (5.1%) cases. Overall, there was no correlation between revision diagnosis and whether or not a Gram stain was obtained (p=.697). Patients with a history of prior instrumentation were more likely to have a positive Gram stain (p<.0444). Intraoperative Gram staining was found to have a sensitivity of 10.9% (confidence interval [CI] 3.9%-23.6%) and specificity of 100% (CI 93.1%-100%). The positive and negative predictive values were 100% (CI 48.0%-100%) and 57.3% (CI 45.2%-66.2%), respectively. Kappa coefficient was calculated to be 0.1172 (CI 0.0194-0.2151). The cost per discrepant diagnosis (total cost/number discrepant) was $172.10.
  
  
  CONCLUSIONS
  This study demonstrates that while very specific for infection, the sensitivity of intraoperative Gram staining is low, and agreement between positive cultures and Gram stains is very poor. Gram staining demonstrated limited cost-effectiveness because of the low prevalence of findings that altered patient management.
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA. Electronic address: shifflettg@hss.edu.
authors.forename: Grant D
authors.initials: GD
authors.lastname: Shifflett
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Benedict U
authors.initials: BU
authors.lastname: Nwachukwu
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Bjerke-Kroll
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Janina
authors.initials: J
authors.lastname: Kueper
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Jayme B
authors.initials: JB
authors.lastname: Koltsov
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Sama
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Federico P
authors.initials: FP
authors.lastname: Girardi
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Frank P
authors.initials: FP
authors.lastname: Cammisa
authors.affiliation: Spine and Scoliosis Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th St, New York, NY 10021, USA.
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Hughes
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005840:Gentian Violet / Q000191:economics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000009:adverse effects* / Q000379:methods / Q000706:statistics & numerical data; D010619:Phenazines / Q000191:economics*; D016459:Prosthesis-Related Infections / Q000175:diagnosis* / Q000517:prevention & control; D013124:Spinal Injuries / Q000601:surgery*; D013530:Surgical Wound Infection / Q000175:diagnosis* / Q000517:prevention & control
chemical_list: C035863:Gram's stain; D010619:Phenazines; D005840:Gentian Violet
keywords: Cost-effectiveness; Gram stain; Infection; Operative culture; Revision spine surgery; Value