Correlation between computed tomography measurements and direct anatomic measurements of the axis for consideration of C2 laminar screw placement

Abstract Background C2 laminar screws are becoming an increasingly used method of fixation. They allow for avoidance of fixation through the C2 pedicle, eliminating the risk of vertebral artery injury. Recent studies have described the anatomic considerations of this technique in a large cadaveric population. In clinical practice, however, direct measurement is impractical and preoperative imaging must be relied upon to determine whether or not this technique can be safely used. Purpose To evaluate the ability of computed tomography (CT) to accurately assess critical dimensions of the C2 vertebrae with regard to intralaminar screw placement. Study design/setting Cadaveric analysis. Methods The C2 vertebrae of 84 adult spines were randomly selected from a large cadaveric collection. Direct measurements were performed to determine laminar thickness, estimated screw length, and spinolaminar angle. Fine cut axial CT scans were then performed on all specimens and all measurements were repeated from these images. Correlation coefficients were calculated to determine the ability of CT scan to accurately determine these measurements. Results CT scan measurements were found to be highly correlated with direct measurements for both left and right mean laminar thickness (0.975 and 0.947, respectively). Screw lengths using CT scan were found to be significantly longer than previously reported direct measurements (24.8 vs. 28.8 mm; p