Anatomical feasibility of C-2 pedicle screw fixation: the effect of variable angle interpolation of axial CT scans.

Object: Anatomical variability of the C-2 pedicle poses a challenge for C-2 fixation. The use of multidimensional CT scanning is not widely used but might be an asset to preoperative planning. Careful preoperative planning is imperative for instrumentation at C-2. Fine-cut, noncontrast CT scanning is a useful tool for delineating anatomy; however, the axis of the images is not always along the anatomical axis of the vertebra in question. The authors evaluated the suitability of C-2 pedicles for screw placement by using OsiriX (Pixmeo) software to change the gantry angle of CT angiograms to measure the anatomical dimensions of the C-2 pedicle.

Methods: The authors conducted a retrospective review of CT angiograms of the head and neck from 47 trauma patients seen consecutively at George Washington University Hospital. For each patient, 3 independent observers determined length and width of each C-2 pedicle (94 samples) by using OsiriX. OsiriX is a DICOM viewer that enables navigation and visualization in multidimensional imaging, such as 3D imaging, which was used for this study. Sex-specific measurements were also determined. Vertebral anatomy was studied to determine whether aberrant anatomy would preclude pedicle fixation. Statistical analyses were performed.

Results: Of the 47 patients, 27 were male. Overall mean C-2 pedicle widths and lengths were 8.272 ± 1.364 mm and 27.052 ± 3.471 mm, respectively. The average widths and lengths of the pedicle in female patients were 8.040 ± 1.262 mm and 27.241 ± 2.731 mm, respectively, and those in male patients were 8.444 ± 1.414 mm and 26.913 ± 3.933 mm, respectively. The sex difference was statistically significant for width (p = 0.012) but not for length (p = 0.41). On the basis of width, the percentages of pedicles that could tolerate a 3.5-mm and 4.0-mm screw were 98% and 97%, respectively. Vertebral anatomy precluded screw length greater than 14 mm for only 3 patients.

Conclusions: Using multidimensional CT or 3D imaging, the authors found that C-2 pedicles in over 90% of patients could tolerate 3.5-mm and 4.0-mm pedicle screws. Vertebral anatomy precluded use of screw lengths greater than 14 mm for only 3 (6%) of 47 patients. Therefore, the C-2 pedicle might be more tolerant of fixation than previously reported.