Background: Craniovertebral arthrodesis in the upper cervical spine
is challenging because of the high degree of mobility afforded by this region.
A novel method for achieving atlantoaxial fixation with use of polyaxial
screws inserted bilaterally into the lateral masses of C1 and transpedicularly
into C2 with longitudinal rod connection has recently been introduced. The
question remains as to whether this technique provides adequate stability when
extended cephalad to include the occiput. The purpose of this study was to
determine the primary stability afforded by this novel construct and compare
its stability with the current standard of bilateral longitudinal plates
combined with C1-C2 transarticular screws.
Methods: We used ten fresh-frozen human cadaveric cervical spines
(C0-C4). Pure moment loads were applied to the occiput, and C4 was constrained
during the testing protocol. We evaluated four conditions: (1) intact, (2)
destabilized by means of complete odontoidectomy, (3) stabilization with
longitudinal plates with C1-C2 transarticular screw fixation, and (4)
stabilization with a posterior rod system with C1 lateral mass screws and C2
pedicle screws. Rigid-body three-dimensional rotations were detected by
stereophotogrammetry by means of a three-camera system with use of marker
triads. The range of motion data (C0-C2) for each fixation scenario was
calculated, and a statistical analysis was performed.
Results: Destabilization of the specimen significantly increased
C0-C2 motion in both flexion-extension and lateral bending (p < 0.05). Both
fixation constructs significantly reduced motion in the destabilized spine by
over 90% for all motions tested (p < 0.05). No significant differences were
detected between the two constructs in any of the three rotational planes.
Conclusions: Both hardware systems provide equivalent construct
stability in the immediate postoperative period when it is critical for the
eventual success of a craniovertebral arthrodesis. On the basis of this work,
we believe that the decision to use either construct should be determined by
clinical rather than biomechanical concerns.