Atlantoaxial fusion: a biomechanical analysis of two C1–C2 fusion techniques

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.