[Anatomical study of anterior approach screw fixation through C2 vertebral body into C1 lateral mass and its primary clinical application].

OBJECTIVE

To explore the anatomic basis for the anterior approach screw fixation through the C2 vertebral body into the C1 lateral mass and to investigate its primary clinical application.

METHODS

Twenty-one adult corpse specimens were anatomically measured. The minimum lateral angle a, the maximum lateral angle beta, and the maximum posterior angle gamma were calculated based on the data from the anatomic measurement. All the specimens were given an X-ray examination, the minimum lateral angle alpha, the maximum lateral angle beta, and the maximum posterior angle gamma were measured. The statistical analysis was made on the data obtained from the calculation in the specimens and the measurement in the X-ray films. The simulation of the approach was made on the specimen. From October 2004 to July 2006, the simulated approach was used in 5 patients (3 males, 2 females; age, 30-55 years; illness course, 3 months-2 years) with the old atlanto-axial joint dislocation . The Frankel grading system revealed the spinal cord injury degree as follows: 1 patient was in Grade B, 2 in Grade C, and 2 in Grade D. All the patients were treated with this surgical approach. The postoperative X-ray and CT examinations were performed.

RESULTS

Angle a was 14.0 +/- 1.6 degrees, beta was 30.0 +/- 2.3 degrees, gamma was 29.0 +/- 2.9 degrees. No significant difference existed between the angles calculated in the specimens and measured in the X-ray films (P > 0.05). The angles for the practical application during operation were as follows: a was 11.2 +/- 1.6 degrees, beta was 28.8 +/- 2.3 degrees, and gamma was 29.3 +/- 2.9 degrees. The follow-up for an average of 14 months revealed that 1 patient recovered to Grade C, 1 to Grade D2, and 3 to Grade D3 in the spinal cord function according the modified Frankel grading system.

CONCLUSION

The anterior approach screw fixation through the C2 vertebral body into the C1 lateral mass is feasible and safe in treatment of the old atlantoaxial joint dislocation if the screw insertion is exact in direction. This technique only makes the atlas temporarily stable, and so the posterior bone graft should be added into the atlanto-axial joint immediately in the one- or two-stage operation so as to achieve a long-lasting stability.