Biomechanical Comparison of Transpedicular Versus Intralaminar C2 Fixation in C2–C6 Subaxial Constructs

In Brief Study Design. Biomechanical study. Objective. To compare the relative rigidity of C2 transpedicular versus intralaminar fixation with and without offset connectors in C2–C6 subaxial constructs. Summary of Background Data. Insufficient biomechanical data exists on C2 laminar fixation in subaxial constructs, and no study has considered C2–C6 subaxial constructs or the use of offset connectors. Methods. Six fresh-frozen cadaveric cervical spines underwent rigidity testing in the intact condition and after a destabilizing C3–C6 laminectomy. Specimens were instrumented with 20 mm pedicle and 20 mm intralaminar screws at C2, and with 14 mm lateral mass screws from C3–C6. In random order, three conditions (C2 pedicle screws, C2 laminar screws, and C2 laminar screws with offset connectors) were tested in flexion-extension, axial rotation, and lateral bending. Results. Laminar screws in C2–C6 constructs were equivalent to transpedicular fixation in flexion-extension (P = 0.985), were significantly more rigid than pedicle screws in axial rotation (P = 0.002), and were significantly less rigid than pedicle screws in lateral bending (P = 0.002). Laminar screw constructs were more rigid than the intact condition in all planes. This biomechanical study compares the rigidity of C2 laminar and C2 pedicle screws in C2–C6 subaxial constructs. Laminar screws are more rigid in axial rotation, equivalent in flexion-extension, and less rigid in lateral bending when compared with pedicle screws. Offset connectors make laminar screw constructs less rigid in flexion-extension.