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. 2023 Oct 1;93(4):910-917.
doi: 10.1227/neu.0000000000002492. Epub 2023 Apr 14.

Biomechanical Comparison of Facet Versus Laminar C2 Screws

Alexandre Meynard  1   2 , Bertrand Fréchède  2 , Benjamin Pommier  1 , David Mitton  2 , Cédric Barrey  1   3
Affiliations

Biomechanical Comparison of Facet Versus Laminar C2 Screws

Alexandre Meynard et al. Neurosurgery. .

Abstract

Background: Transpedicular or transisthmic screws for C2 instrumentation represent the gold standard; however, the anatomy is not always compatible (hypoplastic pedicles, procidentia of the vertebral artery). Laminar screws (LS) have been proposed as a rescue technique and recently, bicortical facet screws (FS). To date, the biomechanical property of FS remains unknown.

Objective: To compare the pull-out resistance of bicortical facet (FS) vs laminar (LS) C2 screws.

Methods: Thirty-two human cadaveric C2 vertebrae were screened by CT scan imaging and dual x-ray absorptiometry before receiving both techniques and were randomized according to side and sequence (FS or LS first). Screw positioning was validated using 2-dimensional x-rays. Sixty-four mechanical tests were performed using pure tensile loading along the axis of the screws until pull-out. Mean pull-out strengths were compared using paired tests, multivariate and survival analysis (Kaplan-Meier curves).

Results: The morphometric data were consistent with previous studies. Over 64 tests, the mean pull-out strength of LS (707 ± 467 N) was significantly higher than that of FS (390 ± 230 N) ( P = .0004). Bone mineral density was weakly correlated with pull-out strength (r = 0.42 for FS and r = 0.3 for LS). Both techniques were mechanically equivalent for vertebrae in which intralaminar cortical grip was not achievable for LS. The mean pull-out strength for LS with laminar cortical grip (1071 ± 395 N) was significantly higher than that of LS without (423 ± 291 N) ( P < .0001).

Conclusion: Our results suggest that bicortical FS of C2 offer less mechanical resistance than LS.

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