title: Harms C1-C2 instrumentation technique: anatomo-surgical guide.
abstract: METHODS
  Anatomic study.
  
  
  OBJECTIVE
  To measure C1 and C2 critical areas related to the screws trajectory, according to Harms technique, in Latin specimens. To investigate vertebral's artery course in cadavers.
  
  
  BACKGROUND
  To our knowledge there are no studies addressing vertebral surface measurements for screw placement, according to Harms C1-C2 instrumentation technique, nor cadaveric measurements of the trajectory of the vertebral artery in Latin specimens.
  
  
  METHODS
  C1 and C2 specimens were measured. C1 measurements: height, width, anteroposterior diameter (intraosseus screw length) and convergence in the axial plane of the lateral mass; length from the posterior border of the posterior C1 arch to the anterior cortex of the articular mass (total screw length). C2 measurements: width, height, convergence and sagittal inclination of the pars interarticularis. Direction of the trajectory of the vertebral artery in the suboccipital region in fresh cadavers.
  
  
  RESULTS
  C1: left mass width 14.20 mm, right: 14.32 mm; left intraosseus screw length: 17.17 mm, right 16.9 mm; left total length of the screw: 27.14 mm, right: 26.72 mm; left mass height: 10.22 mm, right: 10.29 mm. Right mass convergence: 24.68°, left: 22.44°. C2: width: left 8.75 mm, right: 8.53 mm; height: left 10 mm, right 9.81 mm; convergence: left 42.15°, right: 38.98°; sagittal inclination: left 35.50°, right 33.07°. Vertebral artery's medial border is between 13 and 22 mm from the middle line of C1 posterior arch.
  
  
  CONCLUSIONS
  Convergence and inclination of the pars are slightly greater than the suggested by Harms. Individual and/or racial variations must be considered. There is enough space for safe placement of a 3.5 mm screw in the lateral masses of C1 and through the pars of C2. Dissecting the superior face of the posterior arch of C1 laterally more than 10 mm from the posterior tubercule could injure the vertebral artery.
authors.affiliation: Spine Unit, Department of Orthopaedics and Traumatology, Hospital Clínico Universidad de Chile, Chile. schulzibaceta@gmail.com
authors.forename: Ronald
authors.initials: R
authors.lastname: Schulz
authors.forename: Nicolás
authors.initials: N
authors.lastname: Macchiavello
authors.forename: Elias
authors.initials: E
authors.lastname: Fernández
authors.forename: Xabier
authors.initials: X
authors.lastname: Carredano
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Garrido
authors.forename: Jorge
authors.initials: J
authors.lastname: Diaz
authors.forename: Robert P
authors.initials: RP
authors.lastname: Melcher
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000033:anatomy & histology* / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017410:Practice Guidelines as Topic / Q000592:standards*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*