Constructs Incorporating Intralaminar C2 Screws Provide Rigid Stability for Atlantoaxial Fixation

In Brief Study Design. An in vitro biomechanical study of C1–C2 posterior fusion techniques using a cadaveric model. Objectives. To investigate the acute stability afforded across the atlantoaxial segment by a novel technique that uses intralaminar screws in C2, and to compare these results to the stability obtained using a C2 pedicle fixation technique. Summary of Background Data. There are numerous techniques available for rigidly coupling C1 and C2. It has been shown that screw techniques provide higher acute stability than wiring practices. However, many of these methods that use screw fixation in C2 can be technically difficult, especially in cases in which there is an aberrant vertebral artery course or if the C2 pedicle is not large enough to accommodate the instrumentation. A novel technique that uses intralaminar screws in C2 with C1 pedicle screws and bilateral longitudinal rods has been recently developed in an effort to overcome many of these issues. To date, there are no published reports as to whether this new technique provides equivalent (or better) fixation to the currently accepted methods. Methods. Six fresh-frozen human cadaveric cervical spines (C0–C4) were used in this study. Specimens were tested in their intact condition after destabilization via odontoidectomy, and after implantation of 3 different fixation constructs: (1) the Harms technique, 2 pedicle screws in C2, (2) a single C2 pedicle screw and a single C2 intralaminar screw, and (3) a construct having bilateral intralaminar C2 screws. Pure moment loading in flexion/extension, lateral bending, and axial rotation was applied to the occiput. Subsequent relative intervertebral rotations were determined using a 3 camera system. Range of motion for the intact, destabilized, and 3 fixation scenarios was determined, and statistical analysis was performed using one-way analysis of variance Fisher least-significant-difference post hoc test for multiple comparisons. Results. The data indicate that odontoidectomy significantly increased C1–C2 motion in flexion/extension and lateral bending. All 3 fixation techniques significantly reduced motion compared to the intact and destabilized cases. There were no statistically significant differences between the C2 intralaminar and pedicle screw techniques. Conclusions. The results clearly indicate the potential of the intralaminar screw technique to provide stability that is equivalent to methods currently used. Given the serious complications that can follow vertebral artery injury and the decreased likelihood of injury by avoiding placement of C2 pedicle screw(s) and C1–C2 transarticular screw(s), strong consideration should be given to using a construct that incorporates C2 intralaminar screw(s). A cadaveric model was used to investigate the acute stability afforded across the atlantoaxial segment by a novel technique that uses intralaminar screws in C2. These techniques were compared to the more commonly used C2 pedicle screw (Harms) technique. All techniques reduced motion in a highly destabilized upper cervical model, and there were no significant differences between groups.