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Computed tomographic evaluation of the normal adult odontoid. Implications for internal fixation
R C Nucci1, S Seigal, A A Merola
1Department of Orthopaedic Surgery, S.U.N.Y. Downstate Medical Center, Brooklyn, USA.
Study Design:
Computed 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 atlantoaxial 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.