• Roderick Claybrooks, Mark Kayanja, Ryan Milks, and Edward Benzel.
• Spine Institute, The Cleveland Clinic Foundation, Cleveland, OH 44195, USA.
• Spine J. 2007 Nov 1;7(6):682-8.

Background ContextDifferent atlantoaxial fusion techniques are used for instability. Transarticular screws are biomechanically superior to wiring techniques and equivalent to C1 lateral mass to C2 pedicle (C1LM-C2P) fixation. Recently, C1 lateral mass to C2 laminar (C1LM-C2L) fixation has been shown to have flexibility similar to C1LM-C2P fixation in flexion, extension, lateral bending, and axial rotation.PurposeCompare the stiffness of C1LM-C2P with C1LM-C2L screw rod fixation.Study DesignIn vitro biomechanical study.Outcome MeasuresStiffness in flexion/extension, lateral bending, axial rotation, and anterior-posterior (AP) translation.MethodsEight fresh-frozen human cadaveric cervical spines (C1-C3) were tested intact and, after a type II odontoid fracture, were instrumented and tested with two fixation constructs: C1LM-C2P screws and C1LM-C2L screws. The testing involved flexion, extension, lateral bending, AP translation, and axial rotation. Stiffness was measured and compared with a repeated-measures analysis.ResultsC1LM-C2P was significantly stiffer than the intact in AP translation (p<.001), lateral bending (p=.001), and axial rotation (p=.002) and equivalent in flexion/extension (p=.09). C1LM-C2L was significantly stiffer than the intact in AP translation (p<.01) and axial rotation (p<.004) and equivalent in lateral bending (p<.71) and flexion/extension (p=.22). C1LM-C2P was stiffer than C1LM-C2L in right/left lateral bending (p<.001) and axial rotation (p=.009) and equivalent in AP translation (p=.06) and flexion/extension (p=.74).ConclusionC1LM-C2P fixation is equivalent to C1LM-C2L fixation in flexion/extension and AP translation and superior in lateral bending and axial rotation.

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