Neurospine.  2019 Jun;16(2):347-353. 10.14245/ns.1836156.078.

Biomechanical and Anatomical Validity of the Short Posterior Arch Screw

Affiliations
  • 1Department of Orthopaedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan. mjun@med.nagoya-cu.ac.jp
  • 2Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL, USA.

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.

Keyword

Cervical atlas; Pedicle screws; Vertebral artery; Internal carotid artery; Osteoporosis

MeSH Terms

Aged
Bone Density
Cadaver
Carotid Artery, Internal
Cervical Atlas
Humans
Osteoporosis
Pedicle Screws
Prevalence
Vertebral Artery
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