Objective To explore the anatomic basis for theanterior approach screw fixation through the C2 vertebral body into the C1 lateral mass and toinvestigate its primary clinical application. Methods Twenty-one adult corpse specimens were anatomically measured. The minimum lateral angle α, the maximum lateral angle β, and the maximum posterior angle γ were calculated based on the data from the anatomic measurement. All the specimens were given an X-ray examination, the minimum lateral angle α, the maximum lateral angle β, and the maximum posterior angle γ 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 onthe 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 patientwas 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 α was 14.0±1.6°, β was 30.0±2.3°, γ was 29.0±2.9°. No significant difference existed between the angles calculated in the specimens and measured in the X-ray films (Pgt;0.05). The angles for the practical application during operation were as follows: α was 11.2±1.6°, β was 28.8±2.3°, and γ was 29.3±2.9°. 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 massis feasible and safe in treatment of the old atlantoaxial joint dislocation ifthe 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 atlantoaxial joint immediately in the one- or two-stage operation so as to achieve a long-lasting stability.