title: Variation in reported safety of lumbar interbody fusion: influence of industrial sponsorship and other study characteristics.
abstract: METHODS
  Systematic review.
  
  
  OBJECTIVE
  To quantify variability in undesirable outcomes among studies of lumbar interbody fusion using stand-alone cage devices, and to determine whether author conflicts of interest contribute to variability.
  
  
  BACKGROUND
  Promising early studies of lumbar fusion with stand-alone cage devices led to rapid uptake of the technique, but some surgeons later expressed reservations regarding efficacy and safety.
  
  
  METHODS
  We systematically identified studies of lumbar interbody fusion with stand-alone cage devices that reported at least one undesirable outcome among 10 or more adult subjects. We performed meta-analyses of rates of 7 prespecified outcomes (nonunion, reoperation, major vessel injury, retrograde ejaculation, neurologic injury, dural injury, and infection). Heterogeneity in outcome rates was quantified as I2 (the proportion of variance due to differences among studies rather than random variation). Random-effects meta-regression identified sources of observed heterogeneity, including potential conflicts of interest.
  
  
  RESULTS
  We identified 30 eligible studies, including a total of 3228 subjects. A potential conflict of interest was identified in 18 (60%). We observed marked heterogeneity in rates of nonunion, reoperation, and neurologic injury (I2 > 85%; P < 0.001), and substantial heterogeneity in rates of dural injury (I2 = 63%; P < 0.01) and major vessel injury (I2 = 38%; P = 0.09). Among 24 studies reporting fusion status after 6 months of follow-up, nonunion rates ranged from 2.3% to 83.3% (median, 8.3%) and exceeded 45% in 4 studies. Potential author conflict of interest was associated with significantly lower rates of nonunion (P = 0.001). Heterogeneity in rates of other undesirable outcomes was not significantly associated with author conflicts of interest or other study characteristics.
  
  
  CONCLUSIONS
  We quantified substantial unexplained variation in reported complication rates of undesirable outcomes of lumbar interbody fusion with stand-alone cage devices. Authors with potential conflicts of interest, however, reported significantly lower rates of nonunion.
authors.affiliation: Department of Family and Community Medicine, University of California, Davis, Sacramento, CA 95817, USA. jjfenton@ucdavis.edu
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Fenton
authors.forename: Sohail K
authors.initials: SK
authors.lastname: Mirza
authors.forename: Amnon
authors.initials: A
authors.lastname: Lahad
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Stern
authors.forename: Richard A
authors.initials: RA
authors.lastname: Deyo
mesh_terms: D000328:Adult; D016265:Conflict of Interest; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D015588:Observer Variation; D011643:Publishing / Q000941:ethics; D012109:Research Support as Topic / Q000941:ethics*; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome