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. 2019 Jun;16(2):347-353.
doi: 10.14245/ns.1836156.078. Epub 2018 Oct 14.

Biomechanical and Anatomical Validity of the Short Posterior Arch Screw

Jun Mizutani  1 , Nozomu Inoue  2 , Yoshihisa Otsuka  1 , Aiharu Furuya  1 , Alejandro A Espinoza Orias  2 , Takanobu Otsuka  1
Affiliations

Biomechanical and Anatomical Validity of the Short Posterior Arch Screw

Jun Mizutani et al. Neurospine. 2019 Jun.

Abstract

Objective: This study was conducted to clarify the validity of the short posterior arch screw (S-PAS). The S-PAS is inserted only in the pedicle-analogue portion of the posterior arch. The S-PAS screw length is almost half that conventional C1 lateral mass screws inserted via the posterior arch (via-PAS). S-PAS reduces the risk of vertebral artery injury (VAI) because it never reaches the transverse foramen. Although the biomechanical validity of various C1 lateral mass screws (C1LMS) analyzed in young specimens have been published, that of unicortically inserted C1LMS such as the unicortical Harms screw, S-PAS, and via-PAS for elderly patients is concerning because of the high prevalence of osteoporosis in the elderly.

Methods: Nine fresh frozen cadavers (average age at death, 72.1 years) were used for pullout testing. The bone mineral density of each specimen was evaluated using quantitative computed tomography.

Results: The pullout strength of via-PAS (1,048.5 N) was significantly greater than that of the unicortical Harms screw (257.9 N) (p<0.05). The pullout strength of S-PAS was 720.3 N, which was also significantly greater than that of the unicortical Harms screw (p<0.05).

Conclusion: The via-PAS and S-PAS are valid surgical options, even in elderly patients. Along with sufficient biomechanical strength, the S-PAS screw prevents VAI.

Keywords: Cervical atlas; Internal carotid artery; Osteoporosis; Pedicle screws; Vertebral artery.

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Conflict of interest statement

The authors have nothing to disclose.

Figures

Fig. 1.
Fig. 1.
Potential risk of vertebral artery injury at transverse foramen. Although this patient did not occur vertebral artery injury, the left screw (arrows) violated medial wall of the transverse foramen.
Fig. 2.
Fig. 2.
Schematic flowchart of the experimental design. via-PAS, via the posterior arch-inserted C1 lateral mass screw; S-PAS, short posterior arch screw; uni-Harms, unicortical inserted Harms screw.
Fig. 3.
Fig. 3.
Concept of the S-PAS. Right side: Via the posterior arch-inserted C1 lateral mass screw (via PAS). Left side: Short posterior arch screw (S-PAS); inserted a half purchase length via the PAS. The S-PAS is inserted at the same entry point and trajectory of via posterior arch technique. Using this S-PAS, the screw never reaches the transverse foramen.
Fig. 4.
Fig. 4.
Pullout testing. Left: S-PAS. Right: via-PAS. S-PAS, short posterior arch screw; via-PAS, via the posterior arch-inserted C1 lateral mass screw.
Fig. 5.
Fig. 5.
Results of pullout strength in each group. The pullout strengths (mean±standard deviation) for via-PAS, S-PAS, and uni-Harms groups were 1,048.5±193.7 N, 720.3±279.6 N, and 257.9±131.5 N, respectively. via-PAS, via the posterior arch-inserted C1 lateral mass screw; S-PAS, short posterior arch screw; uni-Harms, unicortically inserted Harms screw. *Compared uni-Harms, (p<0.0001). †Compared with S-Tan, (p<0.0471). ‡Compared with uni-Harms, (p<0.0471).
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References

    1. Goel A, Laheri V. Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien) 1994;129:47–53. - PubMed
    1. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976) 2001;26:2467–71. - PubMed
    1. Tan M, Wang H, Wang Y, et al. Morphometric evaluation of screw fixation in atlas via posterior arch and lateral mass. Spine (Phila Pa 1976) 2003;28:888–95. - PubMed
    1. Lee MJ, Cassinelli E, Riew KD. The feasibility of inserting atlas lateral mass screws via the posterior arch. Spine (Phila Pa 1976) 2006;31:2798–801. - PubMed
    1. Ma XY, Yin QS, Wu ZH, et al. Anatomic considerations for the pedicle screw placement in the first cervical vertebra. Spine (Phila Pa 1976) 2005;30:1519–23. - PubMed

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