title: C1 lateral mass anatomy: Proper placement of lateral mass screws.
abstract: METHODS
  Cadaveric specimens were measured to determine appropriate placement for C1 lateral mass screws. Instrumentation guidelines were developed and used to instrument a series of cadaveric specimens. Clinical experience with C1 lateral mass fixation was reviewed to evaluate results. Postoperative computed tomographic (CT) scans were reviewed to evaluate screw placement.
  
  
  OBJECTIVE
  The cadaveric study measured the dimensions of the atlas and determined ideal trajectory for screw placement. This technique was applied clinically, and 50 cases were retrospectively reviewed for fixation difficulties, neurologic or vascular injuries, and perioperative complications. Postoperative CT scans were reviewed when available.
  
  
  BACKGROUND
  Halo application, posterior wiring, and C1 to C2 transarticular screws have been used to stabilize the upper cervical spine. Each technique has disadvantages, and C1 lateral mass fixation recently has gained popularity as a potential alternative. Recent anatomic studies have documented the dimensions of the C1 lateral mass and its ability to accommodate screw fixation. Small clinical series have documented early success with this technique.
  
  
  METHODS
  Fifteen specimens were stripped of soft tissue and measured by using calipers and CT scans. Guidelines were formulated for C1 lateral mass screw fixation. Additional specimens with intact soft tissue were instrumented without difficulty. A clinical series was reviewed to evaluate for complications related to this technique. Postoperative CT scans were reviewed to evaluate screw placement.
  
  
  RESULTS
  The C1 lateral mass safely accommodated screw fixation. Trajectory of 10 degrees medial and 22 degrees cephalad was preferred. The technique was safely applied in a series of 50 patients. Postoperative CT scans showed the ability of the surgeon to achieve the intended goals for starting point and safe trajectory.
  
  
  CONCLUSIONS
  C1 lateral mass fixation is a safe alternative for upper cervical fixation with several potential advantages versus other techniques, but further clinical evaluation is warranted.
authors.affiliation: Department of Orthopaedics, University of Maryland, Baltimore, MD 21201, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Seal
authors.forename: Christopher
authors.initials: C
authors.lastname: Zarro
authors.forename: Daniel
authors.initials: D
authors.lastname: Gelb
authors.forename: Steven
authors.initials: S
authors.lastname: Ludwig
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001268:Atlanto-Axial Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery; D001269:Atlanto-Occipital Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery; D001863:Bone Screws / Q000592:standards*; D002102:Cadaver; D001270:Cervical Atlas / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods; D011183:Postoperative Complications / Q000517:prevention & control; D012189:Retrospective Studies; D013119:Spinal Cord Injuries / Q000517:prevention & control; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D055815:Young Adult; D021801:Zygapophyseal Joint / Q000033:anatomy & histology* / Q000601:surgery*