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

  • 1Department of Orthopedic Surgery, Rush University Medical Center, Chicago, IL, USA. jatagi15@gmail.com
  • 2Department of Neurosurgery, The Catholic University of Korea, St. Vincent's Hospital, Suwon, Korea.
  • 3Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA.


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.
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.
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.
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.


Cervical spine; Intralaminar screw; Finite element method; Biomechanics
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