J Korean Neurosurg Soc.  2013 Jun;53(6):331-336. 10.3340/jkns.2013.53.6.331.

A Biomechanical Comparison of Intralaminar C7 Screw Constructs with and without Offset Connector Used for C6-7 Cervical Spine Immobilization : A Finite Element Study

• Qasim M
• Hong JT
• Natarajan
• An HS

• KMID: 2190819
• DOI: http://doi.org/10.3340/jkns.2013.53.6.331

Abstract

OBJECTIVE
The offset connector can allow medial and lateral variability and facilitate intralaminar screw incorporation into the construct. The aim of this study was to compare the biomechanical characteristics of C7 intralaminar screw constructs with and without offset connector using a three dimensional finite element model of a C6-7 cervical spine segment.
METHODS
Finite element models representing C7 intralaminar screw constructs with and without the offset connector were developed. Range of motion (ROM) and maximum von Mises stresses in the vertebra for the two techniques were compared under pure moments in flexion, extension, lateral bending and axial rotation.
RESULTS
ROM for intralaminar screw construct with offset connector was less than the construct without the offset connector in the three principal directions. The maximum von Misses stress was observed in the C7 vertebra around the pedicle in both constructs. Maximum von Mises stress in the construct without offset connector was found to be 12-30% higher than the corresponding stresses in the construct with offset connector in the three principal directions.
CONCLUSION
This study demonstrated that the intralaminar screw fixation with offset connector is better than the construct without offset connector in terms of biomechanical stability. Construct with the offset connector reduces the ROM of C6-7 segment more significantly compared to the construct without the offset connector and causes lower stresses around the C7 pedicle-vertebral body complex.

Keyword

Cervical spine; Intralaminar screw; Finite element method; Biomechanics

MeSH Terms

Biomechanics
Immobilization
Range of Motion, Articular
Spine

Figure

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  Fig. 1 Finite element models of C6C7 motion segment representing. A : Intralaminar screw construct with offset connector. B : Intralaminar screw construct without offset connector.

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  Fig. 2 ROM for intact C6C7 motion segment from cadaver study and FEA model in the three principal directions. ROM : range of motion, FEA : finite element analysis.

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  Fig. 3 Percentage ROM for C6C7 intralaminar screw construct with and without offset connector. ROM : range of motion.

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  Fig. 4 Maximum von Misses stress was observed at the C7 vertebra level in the pedicles (white circular areas) under all loading modes.

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  Fig. 5 Maximum von Misses stresses in the intralaminar screw constructs with and without the offset connector under flexion, extension, axial rotation and lateral bending.

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