title: Evaluation of anatomic landmarks and safe zones for screw placement in the atlas via the posterior arch.
abstract: Several studies have evaluated quantitative anatomic data for direct lateral mass screw fixation. To analyze anatomic landmarks and safe zones for optimal screw placement through the posterior arc of the human atlas, morphometric parameters of 41 adult native human atlas specimens were quantitatively measured. Internal dimensions of the atlas (lateral mass, maximum and minimum intraosseous screw length), minimum height and width of the posterior arc and optimal screw insertion angles were defined on pQCT scans. By this, an optimal posterior screw insertion point (OIP) and a preferable screw direction (PSD) through the posterior arch into the lateral mass of C1 were defined. External dimensions (transverse and sagittal diameter) as well as the width of the mid-portion of C1 lateral mass were significantly higher in male specimens. The mean height of the posterior arch at the vertebral artery groove was 4.1 +/- 0.8 mm in female and 4.6 +/- 0.9 mm in male specimens. The optimal screw insertion point was located 21.6 +/- 1.7 mm in female and 23.6 +/- 2.3 mm in male lateral from the posterior tubercle of C1 (P < 0.01). The preferable screw direction was a mean medial inclination of 7.9 +/- 1.9 degrees in female and 7.3 +/- 2.7 degrees in male specimens and a mean rostral direction of 2.4 +/- 1.8 degrees in female and 3.1 +/- 1.7 degrees in male specimens. In conclusion, the presented study provides information for the use and design of upper cervical spine instrumentation techniques, such as screw placement to C1 via the posterior arch. The characterization of working areas and safe zones (OIP, PSD) might contribute to a minimization of screw malposition in this highly demanding instrumentation technique.
authors.affiliation: Department of Trauma-, Hand-, and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. mgebauer@uke.uni-hamburg.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Gebauer
authors.forename: Florian
authors.initials: F
authors.lastname: Barvencik
authors.forename: Daniel
authors.initials: D
authors.lastname: Briem
authors.forename: Jan P
authors.initials: JP
authors.lastname: Kolb
authors.forename: Sebastian
authors.initials: S
authors.lastname: Seitz
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Rueger
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Michael
authors.initials: M
authors.lastname: Amling
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000886:Anthropometry; D001368:Axis, Cervical Vertebra / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D049628:Body Size / Q000502:physiology; D001863:Bone Screws / Q000592:standards*; D001270:Cervical Atlas / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012727:Sex Characteristics; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*; D014057:Tomography, X-Ray Computed; D055815:Young Adult