title: Posterior arch C-1 screw technique: a cadaveric comparison study.
abstract: OBJECTIVE Posterior atlantoaxial stabilization and fusion using C-1 lateral mass screw fixation has become commonly used in the treatment of instability and for reconstructive indications since its introduction by Goel and Laheri in 1994 and modification by Harms in 2001. Placement of such lateral mass screws can be challenging because of the proximity to the spinal cord, vertebral artery, an extensive venous plexus, and the C-2 nerve root, which overlies the designated starting point on the posterior center of the lateral mass. An alternative posterior access point starting on the posterior arch of C-1 could provide a C-2 nerve root-sparing starting point for screw placement, with the potential benefit of greater directional control and simpler trajectory. The authors present a cadaveric study comparing an alternative strategy (i.e., a C-1 screw with a posterior arch starting point) to the conventional strategy (i.e., using the lower lateral mass entry site), specifically assessing the safety of screw placement to preserve the C-2 nerve root. METHODS Five US-trained spine fellows instrumented 17 fresh human cadaveric heads using the Goel/Harms C-1 lateral mass (GHLM) technique on the left and the posterior arch lateral mass (PALM) technique on the right, under fluoroscopic guidance. After screw placement, a CT scan was obtained on each specimen to assess for radiographic screw placement accuracy. Four faculty spine surgeons, blinded to the surgeon who instrumented the cadaver, independently graded the quality of screw placement using a modified Upendra classification. RESULTS Of the 17 specimens, the C-2 nerve root was anatomically impinged in 13 (76.5%) of the specimens. The GHLM technique was graded Type 1 or 2, which is considered "acceptable," in 12 specimens (70.6%), and graded Type 3 or 4 ("unacceptable") in 5 specimens (29.4%). In contrast, the PALM technique had 17 (100%) of 17 graded Type 1 or 2 (p = 0.015). There were no vertebral artery injuries found in either technique. All screw violations occurred in the medial direction. CONCLUSIONS The PALM technique showed statistically fewer medial penetrations than the GHLM technique in this study. The reason for this is not clear, but may stem from a more angulated "up-and-in" screw direction necessary with a lower starting point.
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.|Seattle Science Foundation, Seattle, Washington.
authors.forename: Marc
authors.initials: M
authors.lastname: Moisi
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.|Department of General and Trauma Surgery, BG University Hospital, Bergmannsheil Bochum, Germany ; and.
authors.forename: Christian
authors.initials: C
authors.lastname: Fisahn
authors.affiliation: Seattle Science Foundation, Seattle, Washington.
authors.forename: Lara
authors.initials: L
authors.lastname: Tkachenko
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Shiveindra
authors.initials: S
authors.lastname: Jeyamohan
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Stephen
authors.initials: S
authors.lastname: Reintjes
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Peter
authors.initials: P
authors.lastname: Grunert
authors.affiliation: Spectrum Research, Inc., Tacoma, Washington.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Norvell
authors.affiliation: Seattle Science Foundation, Seattle, Washington.
authors.forename: R Shane
authors.initials: RS
authors.lastname: Tubbs
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Jeni
authors.initials: J
authors.lastname: Page
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: David W
authors.initials: DW
authors.lastname: Newell
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Peter
authors.initials: P
authors.lastname: Nora
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Rod J
authors.initials: RJ
authors.lastname: Oskouian
authors.affiliation: Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Jens
authors.initials: J
authors.lastname: Chapman
mesh_terms: D000368:Aged; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging / Q000601:surgery; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D011183:Postoperative Complications / Q000517:prevention & control; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D013126:Spinal Nerve Roots / Q000000981:diagnostic imaging / Q000293:injuries; D014057:Tomography, X-Ray Computed
keywords: C-1; GHLM = Goel/Harms C-1 lateral mass; PALM = posterior arch lateral mass; cervical; lateral mass screw; posterior arch lateral mass