title: Pedicle Screw Safety: How Much Anterior Breach Is Safe?: A Cadaveric and CT-Based Study.
abstract: MINI: The objective of this study was to determine the safety limits of anterior/anterolateral pedicle screw breaches. Through clinical and cadaveric study, it appears that less than 4 mm of breach has a significantly lower likelihood of impingement on vital structures (P < 0.001).
  
  
  METHODS
  Clinical retrospective chart review and basic science study.
  
  
  OBJECTIVE
  To determine the safety limits of an anterior/anterorolateral misplaced pedicle screw on computed tomography (CT) scan in spinal deformity.
  
  
  BACKGROUND
  Although the limits of medial breaches (<4 mm) are known, the safe limits for anterior/anterolateral breaches in spine deformity are not yet defined.
  
  
  METHODS
  The present study had two parts. In part I, postoperative CT scans of 165 patients operated on for spine deformity were reviewed for screw misplacement (2800 screws). The amount of anterior/anterolateral breach was measured. Protrusions were also evaluated for proximity to vital structures. All scans were reviewed by musculoskeletal radiologist. In part II, eight cadavers were instrumented with 6 × 30 and 6 × 40 mm bilaterally from T1-S1. Screws were randomly inserted under navigation guidance either "IN" or "OUT-anterior/lateral." CT scan was performed, followed by gross dissection to determine screw position.
  
  
  RESULTS
  Part I: 116(4.2%) screws were misplaced anterior/anterolaterally. Thirty-one (26.7%) were adjacent to vital structures. Fisher exact test showed 4 mm or less breach has significantly lower likelihood of impingement (P < 0.001). Screws adjacent/impinging the aorta protruded an average 5.7 ± 0.6 mm, whereas screws not involving the aorta breached an average 3.9 ± 0.2 mm, (P < 0.001). Part II: 285 screws were inserted. On CT scan, 125 were misplaced anterior/anterolaterally. On gross dissection, 89 were visibly misplaced; 23 were covered entirely by soft tissue but were palpable; and 13 were contained in bone. All 23 screws did not endanger any structures and protruded less than 4 mm on CT scan.
  
  
  CONCLUSIONS
  Anterior/anterolateral breaches of 4 mm or less on CT poses no significant risk of impingement and therefore can be considered safe.
  
  
  METHODS
  3.
authors.affiliation: Department of Pediatric Orthopedics, Cohen Children's Medical Center, New Hyde Park, NY.
authors.forename: Vishal
authors.initials: V
authors.lastname: Sarwahi
authors.affiliation: Department of Orthopedic Surgery, Nicklaus Children's Hospital, Miami, FL.
authors.forename: Monica
authors.initials: M
authors.lastname: Payares
authors.affiliation: Department of Pediatric Orthopedics, Cohen Children's Medical Center, New Hyde Park, NY.
authors.forename: Stephen
authors.initials: S
authors.lastname: Wendolowski
authors.affiliation: Department of Pediatric Orthopedics, Cohen Children's Medical Center, New Hyde Park, NY.
authors.forename: Rachel
authors.initials: R
authors.lastname: Gecelter
authors.affiliation: Department of Orthopedic Surgery, Montefiore Medical Center, Bronx, NY.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Maguire
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY.
authors.forename: Dan
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Radiology, Montefiore Medical Center, Bronx, NY.
authors.forename: Beverly
authors.initials: B
authors.lastname: Thornhill
authors.affiliation: Department of Pediatric Orthopedics, Cohen Children's Medical Center, New Hyde Park, NY.
authors.forename: Terry
authors.initials: T
authors.lastname: Amaral
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D005260:Female; D006801:Humans; D008875:Middle Aged; D065289:Pedicle Screws / Q000009:adverse effects / Q000592:standards*; D012189:Retrospective Studies; D012447:Sacrum / Q000000981:diagnostic imaging* / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods / Q000592:standards; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed / Q000379:methods*