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Computed Tomographic Evaluation of the Normal Adult Odontoid: Implications for Internal Fixation

Nucci, Robert C., MD*; Seigal, Stacey, MD*; Merola, Andrew A., MD*; Gorup, John, MD*; Mroczek, Kenneth J., MD*; Dryer, Joseph, MD*; Zipnick, Richard I., MD*; Haher, Thomas R., MD

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Study Design Compute tomography scans of the dens were performed on patients who had no atlantoaxial pathology.

Objectives To determine whether one or two screws is optimal for fracture fixation and whether two screws can always negotiate the intramedullary odontoid cavity.

Summary of Background Data. Fixation of Type Ii dens fractures traditionally has used C1-C2 posterior wiring and fusion. Two screws placed across an odontoid fracture as a method of rigid internal fixation also has been described. However, it is not known whether two screws can always negotiate the odontoid canal.

Methods Ninety-two consecutive computerized tomography scans of the dens were performed on adults who had no atiantoaxial pathology. Measurements were taken from the scan and compared with the cross-sectional diameter of two odontoid screws.

Results The critical diameter for the placement of two 3.5-mm cortical screws with tapping was 9.0 mm. This dimension was present in 95% of the patients studied.

Conclusions Correct orientation of the computerized tomography scanner is critical for accurate measurements. Two 3.5-mm screws can be used in internal fixation of Type II dens fractures in 95% of the patients if the inner cortex is tapped.

* From the Departments of Orthopaedic Surgery, S.U.N.Y. Downstate Medical Center, Brooklyn, New York.

© Lippincott-Raven Publishers.